dynamic class loaders - Page 3

Creating a dynamic proxy generator with c# – Part 2 – Interceptor Design

- by SeanMcAlinden

Creating a dynamic proxy generator – Part 1 – Creating the Assembly builder, Module builder and caching mechanism For the latest code go to http://rapidioc.codeplex.com/ Before getting too involved in generating the proxy, I thought it would be worth while going through the intended design, this is important as the next step is to start creating the constructors for the proxy. Each proxy derives from a specified type The proxy has a corresponding constructor for each of the base type constructors The proxy has overrides for all methods and properties marked as Virtual on the base type For each overridden method, there is also a private method whose sole job is to call the base method. For each overridden method, a delegate is created whose sole job is to call the private method that calls the base method. The following class diagram shows the main classes and interfaces involved in the interception process. I’ll go through each of them to explain their place in the overall proxy. IProxy Interface The proxy implements the IProxy interface for the sole purpose of adding custom interceptors. This allows the created proxy interface to be cast as an IProxy and then simply add Interceptors by calling it’s AddInterceptor method. This is done internally within the proxy building process so the consumer of the API doesn’t need knowledge of this. IInterceptor Interface The IInterceptor interface has one method: Handle. The handle method accepts a IMethodInvocation parameter which contains methods and data for handling method interception. Multiple classes that implement this interface can be added to the proxy. Each method override in the proxy calls the handle method rather than simply calling the base method. How the proxy fully works will be explained in the next section MethodInvocation. IMethodInvocation Interface & MethodInvocation class The MethodInvocation will contain one main method and multiple helper properties. Continue Method The method Continue() has two functions hidden away from the consumer. When Continue is called, if there are multiple Interceptors, the next Interceptors Handle method is called. If all Interceptors Handle methods have been called, the Continue method then calls the base class method. Properties The MethodInvocation will contain multiple helper properties including at least the following: Method Name (Read Only) Method Arguments (Read and Write) Method Argument Types (Read Only) Method Result (Read and Write) – this property remains null if the method return type is void Target Object (Read Only) Return Type (Read Only) DefaultInterceptor class The DefaultInterceptor class is a simple class that implements the IInterceptor interface. Here is the code: DefaultInterceptor namespace Rapid.DynamicProxy.Interception { /// <summary> /// Default interceptor for the proxy. /// </summary> /// <typeparam name="TBase">The base type.</typeparam> public class DefaultInterceptor<TBase> : IInterceptor<TBase> where TBase : class { /// <summary> /// Handles the specified method invocation. /// </summary> /// <param name="methodInvocation">The method invocation.</param> public void Handle(IMethodInvocation<TBase> methodInvocation) { methodInvocation.Continue(); } } } This is automatically created in the proxy and is the first interceptor that each method override calls. It’s sole function is to ensure that if no interceptors have been added, the base method is still called. Custom Interceptor Example A consumer of the Rapid.DynamicProxy API could create an interceptor for logging when the FirstName property of the User class is set. Just for illustration, I have also wrapped a transaction around the methodInvocation.Coninue() method. This means that any overriden methods within the user class will run within a transaction scope. MyInterceptor public class MyInterceptor : IInterceptor<User<int, IRepository>> { public void Handle(IMethodInvocation<User<int, IRepository>> methodInvocation) { if (methodInvocation.Name == "set_FirstName") { Logger.Log("First name seting to: " + methodInvocation.Arguments[0]); } using (TransactionScope scope = new TransactionScope()) { methodInvocation.Continue(); } if (methodInvocation.Name == "set_FirstName") { Logger.Log("First name has been set to: " + methodInvocation.Arguments[0]); } } } Overridden Method Example To show a taster of what the overridden methods on the proxy would look like, the setter method for the property FirstName used in the above example would look something similar to the following (this is not real code but will look similar): set_FirstName public override void set_FirstName(string value) { set_FirstNameBaseMethodDelegate callBase = new set_FirstNameBaseMethodDelegate(this.set_FirstNameProxyGetBaseMethod); object[] arguments = new object[] { value }; IMethodInvocation<User<IRepository>> methodInvocation = new MethodInvocation<User<IRepository>>(this, callBase, "set_FirstName", arguments, interceptors); this.Interceptors[0].Handle(methodInvocation); } As you can see, a delegate instance is created which calls to a private method on the class, the private method calls the base method and would look like the following: calls base setter private void set_FirstNameProxyGetBaseMethod(string value) { base.set_FirstName(value); } The delegate is invoked when methodInvocation.Continue() is called within an interceptor. The set_FirstName parameters are loaded into an object array. The current instance, delegate, method name and method arguments are passed into the methodInvocation constructor (there will be more data not illustrated here passed in when created including method info, return types, argument types etc.) The DefaultInterceptor’s Handle method is called with the methodInvocation instance as it’s parameter. Obviously methods can have return values, ref and out parameters etc. in these cases the generated method override body will be slightly different from above. I’ll go into more detail on these aspects as we build them. Conclusion I hope this has been useful, I can’t guarantee that the proxy will look exactly like the above, but at the moment, this is pretty much what I intend to do. Always worth downloading the code at http://rapidioc.codeplex.com/ to see the latest. There will also be some tests that you can debug through to help see what’s going on. Cheers, Sean.

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dynamic urls and links on one web page

- by John

I am trying to figure out how to create dynamic links and urls on a static webpage. What I want to do is the following: I have a single webpage for example: MYWEBPAGEdotCOM/INDEX.HTML that will always look the same, except for one link on the page. the link would be on the page for example: LINK TO AFFILIATE: affiliatedotCOM/my-affiliate_code_here_DYNAMIC_REFERER the only thing would change is the "DYNAMIC_REFERER" with every dynamic url on this page: MYWEBPAGEdotCOM/INDEX.PHP_id=test1 MYWEBPAGEdotCOM/INDEX.PHP_id=test2 MYWEBPAGEdotCOM/INDEX.PHP_id=test3 MYWEBPAGEdotCOM/INDEX.PHP_id=test4 which would only hange the dynamic link on the page to: affiliatedotCOM/my-affiliate_code_here_test1 affiliatedotCOM/my-affiliate_code_here_test2 affiliatedotCOM/my-affiliate_code_here_test3 affiliatedotCOM/my-affiliate_code_here_test4 Can someone tell me how I could go about doing this? I just dont want to have to make 100's of pages, as this would prevent me from having to do so.

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dynamic urls and links on one web page

- by John

I am trying to figure out how to create dynamic links and urls on a static webpage. What I want to do is the following: I have a single webpage for example: MYWEBPAGEdotCOM/INDEX.HTML that will always look the same, except for one link on the page. the link would be on the page for example: LINK TO AFFILIATE: affiliatedotCOM/my-affiliate_code_here_DYNAMIC_REFERER the only thing would change is the "DYNAMIC_REFERER" with every dynamic url on this page: MYWEBPAGEdotCOM/INDEX.PHP_id=test1 MYWEBPAGEdotCOM/INDEX.PHP_id=test2 MYWEBPAGEdotCOM/INDEX.PHP_id=test3 MYWEBPAGEdotCOM/INDEX.PHP_id=test4 which would only hange the dynamic link on the page to: affiliatedotCOM/my-affiliate_code_here_test1 affiliatedotCOM/my-affiliate_code_here_test2 affiliatedotCOM/my-affiliate_code_here_test3 affiliatedotCOM/my-affiliate_code_here_test4 Can someone tell me how I could go about doing this? I just dont want to have to make 100's of pages, as this would prevent me from having to do so.

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Linking a template class using another template class (error LNK2001)

- by Luís Guilherme

I implemented the "Strategy" design pattern using an Abstract template class, and two subclasses. Goes like this: template <class T> class Neighbourhood { public: virtual void alter(std::vector<T>& array, int i1, int i2) = 0; }; and template <class T> class Swap : public Neighbourhood<T> { public: virtual void alter(std::vector<T>& array, int i1, int i2); }; There's another subclass, just like this one, and alter is implemented in the cpp file. Ok, fine! Now I declare another method, in another class (including neighbourhood header file, of course), like this: void lSearch(/*parameters*/, Neighbourhood<LotSolutionInformation> nhood); It compiles fine and cleanly. When starting to link, I get the following error: 1>SolverFV.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall lsc::Neighbourhood<class LotSolutionInformation>::alter(class std::vector<class LotSolutionInformation,class std::allocator<class LotSolutionInformation> > &,int,int)" (?alter@?$Neighbourhood@VLotSolutionInformation@@@lsc@@UAEXAAV?$vector@VLotSolutionInformation@@V?$allocator@VLotSolutionInformation@@@std@@@std@@HH@Z)

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xen 4.1 host priodically dropping network packets of domU

- by Dyutiman Chakraborty

I have xen 4.1 Host running on a ubuntu 12.04 LTS Server with ip 153.x.x.54. I have setup 2 VMs on it, namely, "dev.mydomain.com" and "web.mydomain.com" with ips 195.X.X.2 and 195.x.x.3 respectively. For network the VMs connect through xendbr0 (xen-bridge), and can accces the network properly. I can also login to the VMs with ssh with no issue. However when I ping any of the VMs, there is a high amount of periodic packet drop. If I the ping the xen host (dom0) there is no packet drop. Following is a output of "tcpdump | grep ICMP" on dOM0 while I was pinging one of the domU tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 05:19:55.682493 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 30, length 64 05:19:56.691144 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 31, length 64 05:19:57.698776 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 32, length 64 05:19:58.706784 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 33, length 64 05:19:59.714751 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 34, length 64 05:20:00.723144 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 35, length 64 05:20:01.730349 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 36, length 64 05:20:02.739017 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 37, length 64 05:20:03.746806 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 38, length 64 05:20:06.770326 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 41, length 64 05:20:07.778801 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 42, length 64 05:20:08.786481 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 43, length 64 05:20:09.794720 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 44, length 64 05:20:10.802395 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 45, length 64 05:20:11.810770 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 46, length 64 05:20:12.818511 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 47, length 64 05:20:13.826817 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 48, length 64 05:20:14.835125 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 49, length 64 05:20:15.842138 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 50, length 64 05:20:18.274072 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 1, length 64 05:20:19.282347 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 2, length 64 05:20:20.290746 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 3, length 64 05:20:21.297910 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 4, length 64 05:20:22.305656 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 5, length 64 05:20:23.314369 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 6, length 64 05:20:24.322055 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 7, length 64 05:20:25.329782 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 8, length 64 05:20:26.338473 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 9, length 64 05:20:27.346411 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 10, length 64 05:20:28.354175 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 11, length 64 05:20:29.361640 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 12, length 64 05:20:30.370026 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 13, length 64 05:20:31.377696 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 14, length 64 05:20:32.386151 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 15, length 64 05:20:33.394118 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 16, length 64 05:20:34.402058 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 17, length 64 05:20:35.409002 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 18, length 64 05:20:36.417692 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 19, length 64 05:20:36.496916 IP6 fe80::3285:a9ff:feec:fc69 > ip6-allnodes: HBH ICMP6, multicast listener querymax resp delay: 1000 addr: ::, length 24 05:20:36.499112 IP6 fe80::21c:c0ff:fe6c:c091 > ff02::1:ff6c:c091: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff6c:c091, length 24 05:20:36.507041 IP6 fe80::227:eff:fe11:fa3f > ff02::1:ff00:2: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:2, length 24 05:20:36.523919 IP6 fe80::21c:c0ff:fe77:6257 > ff02::1:ff77:6257: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff77:6257, length 24 05:20:36.544785 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff12:ea9a: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff12:ea9a, length 24 05:20:36.581740 IP6 fe80::5604:a6ff:fef1:6da7 > ff02::1:fff1:6da7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:fff1:6da7, length 24 05:20:36.600103 IP6 fe80::8a8:8aa0:5e18:917a > ff02::1:ff18:917a: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff18:917a, length 24 05:20:36.601989 IP6 fe80::227:eff:fe11:fa3e > ff02::1:ff11:fa3e: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff11:fa3e, length 24 05:20:36.611090 IP6 fe80::dcad:56ff:fe57:3bbe > ff02::1:ff57:3bbe: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff57:3bbe, length 24 05:20:36.660521 IP6 fe80::54:ff:fe02:1d31 > ff02::1:ff00:6: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:6, length 24 05:20:36.698871 IP6 fe80::21e:8cff:feb4:9f89 > ff02::1:ffb4:9f89: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ffb4:9f89, length 24 05:20:36.776548 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff01:7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff01:7, length 24 05:20:36.781910 IP6 fe80::54:ff:fe8f:6dd > ff02::1:ff00:3: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:3, length 24 05:20:36.865475 IP6 fe80::21c:c0ff:fe4a:ae9f > ff02::1:ff4a:ae9f: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff4a:ae9f, length 24 05:20:36.908333 IP6 fe80::dcad:45ff:fe90:84db > ff02::1:ff90:84db: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff90:84db, length 24 05:20:36.919653 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff00:7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:7, length 24 05:20:36.924276 IP6 fe80::59a2:2a4a:2082:6dee > ff02::1:ff82:6dee: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff82:6dee, length 24 05:20:37.001905 IP6 fe80::54:ff:fe8f:6dd > ff02::1:ff8f:6dd: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff8f:6dd, length 24 05:20:37.042403 IP6 fe80::54:ff:fe95:54f2 > ff02::1:ff95:54f2: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff95:54f2, length 24 05:20:37.090992 IP6 fe80::21c:c0ff:fe77:62ac > ff02::1:ff77:62ac: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff77:62ac, length 24 05:20:37.098118 IP6 fe80::d63d:7eff:fe01:b67f > ff02::1:ff01:b67f: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff01:b67f, length 24 05:20:37.118784 IP6 fe80::54:ff:fe12:ea9a > ff02::202: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::202, length 24 05:20:37.168548 IP6 fe80::54:ff:fe02:1d31 > ff02::1:ff02:1d31: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff02:1d31, length 24 05:20:41.743286 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 1, length 64 05:20:41.743542 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 1, length 64 05:20:42.743859 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 2, length 64 05:20:42.743952 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 2, length 64 05:20:43.745689 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 3, length 64 05:20:43.745777 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 3, length 64 05:20:44.746706 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 4, length 64 05:20:44.746796 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 4, length 64 05:20:45.747986 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 5, length 64 05:20:45.748082 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 5, length 64 05:20:46.749834 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 6, length 64 05:20:46.749920 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 6, length 64 05:20:47.750838 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 7, length 64 05:20:47.751182 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 7, length 64 05:20:48.751909 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 8, length 64 05:20:48.751991 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 8, length 64 05:20:49.752542 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 9, length 64 05:20:49.752620 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 9, length 64 05:20:50.754246 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 10, length 64 05:20:51.753856 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 11, length 64 05:20:52.752868 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 12, length 64 05:20:53.754174 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 13, length 64 05:20:54.753972 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 14, length 64 05:20:55.753814 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 15, length 64 05:20:56.753391 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 16, length 64 05:20:57.753683 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 17, length 64 05:20:58.753487 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 18, length 64 05:20:59.754013 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 19, length 64 05:21:00.753169 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 20, length 64 05:21:01.753757 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 21, length 64 05:21:02.753307 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 22, length 64 05:21:03.753021 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 23, length 64 05:21:04.753628 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 24, length 64 ^C479 packets captured 718 packets received by filter 238 packets dropped by kernel 3 packets dropped by interface You see the ping request is not responed to initially, then for a moment it is replied back and then again no reply. I have tried everything (to the best of my knowledge) to fix this, but can't find any answer Any help will be greatly appreciated Thanks.

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Building a database class in PHP

- by Sprottenwels

I wonder if I should write a database class for my application, and if so, how to accomplish it? Over there on SO, a guy mentioned it should be written as an abstract class. However, I can't understand why this would be a benefit. Do I understand correctly, that if I would write an abstract class, every other class that methods will need a database connection, could simply extend this abstract class and have it's own database object? If so, how is this different from a "normal" class where I could instantiate an database object? Another method would be to completely forget about my own class and to instantiate a mysqli object on demand. What do you recommend?

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Class design for calling "the same method" on different classes from one place

- by betatester07

Let me introduce my situation: I have Java EE application and in one package, I want to have classes which will act primarily as cache for some data from database, for example: class that will hold all articles for our website class that will hold all categories etc. Every class should have some update() method, which will update data for that class from database and also some other methods for data manipulation specific for that data type. Now, I would like to call update() method for all class instances (there will be exactly one class instance for every class) from one place. What is the best design?

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Does Java support dynamic method invocation?

- by eSKay

class A { void F() { System.out.println("a"); }} class B extends A { void F() { System.out.println("b"); }} public class X { public static void main(String[] args) { A objA = new B(); objA.F(); } } Here, F() is being invoked dynamically, isn't it? This article says ... the Java bytecode doesn’t support dynamic method invocation. There are three supported invocations modes : invokestatic, invokespecial, invokeinterface or invokevirtual. These modes allows to call methods with known signature. We talk of strongly typed language. This allows to to make some checks directly at compile time. On the other side, the dynamic languages use dynamic types. So we can call a method unknown at the compile time, but that’s completely impossible with the Java bytecode. What am I missing?

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Debugging dynamic sql + dynamic tables in MS SQL Server 2008.

- by Hamish Grubijan

Hi, I have a messy stored procedure which uses dynamic sql. I can debug it in runtime by adding print @sql; where @sql; is the string containing the dynamic SQL, right before I call execute (@sql);. Now, the multi-page stored procedure also creates dynamic tables and uses them in a query. I want to print those tables to the console right before I do an execute, so that I know exactly what the query is trying to do. However, the SQL Server 08 does not like that. When I try: print #temp_table; and try to compile the S.P. I get this error: The name "#temp_table" is not permitted in this context. Valid expressions are constants, constant expressions, and (in some contexts) variables. Column names are not permitted. Please help.

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How to easily substitute a Base class

- by JTom

Hi, I have the following hierarchy of classes class classOne { virtual void abstractMethod() = 0; }; class classTwo : public classOne { }; class classThree : public classTwo { }; All classOne, classTwo and classThree are abstract classes, and I have another class that is defining the pure virtual methods class classNonAbstract : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; And right now I need it differently...I need it like class classNonAbstractOne : public classOne { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; class classNonAbstractTwo : public classTwo { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; and class classNonAbstractThree : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; But all the nonAbstract classes have the same new methods, with the same code...and I would like to avoid copying all the methods and it's code to every nonAbstract class. How could I accomplish that? Hopefully it's understandable...

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Using a class within a class?

- by Josh

I built myself a MySQL class which I use in all my projects. I'm about to start a project that is heavily based on user accounts and I plan on building my own class for this aswell. The thing is, a lot of the methods in the user class will be MySQL queries and methods from the MySQL class. For example, I have a method in my user class to update someone's password: class user() { function updatePassword($usrName, $newPass) { $con = mysql_connect('db_host', 'db_user', 'db_pass'); $sql = "UPDATE users SET password = '$newPass' WHERE username = '$userName'"; $res = mysql_query($sql, $con); if($res) return true; mysql_close($con); } } (I kind of rushed this so excuse any syntax errors :) ) As you can see that would use MySQL to update a users password, but without using my MySQL class, is this correct? I see no way in which I can use my MySQL class within my users class without it seeming dirty. Do I just use it the normal way like $DB = new DB();? That would mean including my mysql.class.php somewhere too... I'm quite confused about this, so any help would be appreciated, thanks.

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Identifying that a variable is a new-style class in Python?

- by Dave Johansen

I'm using Python 2.x and I'm wondering if there's a way to tell if a variable is a new-style class? I know that if it's an old-style class that I can do the following to find out. import types class oldclass: pass def test(): o = oldclass() if type(o) is types.InstanceType: print 'Is old-style' else: print 'Is NOT old-style' But I haven't been able to find anything that works for new-style classes. I found this question, but the proposed solutions don't seem to work as expected, because simple values as are identified as classes. import inspect def newclass(object): pass def test(): n = newclass() if inspect.isclass(n): print 'Is class' else: print 'Is NOT class' if inspect.isclass(type(n)): print 'Is class' else: print 'Is NOT class' if inspect.isclass(type(1)): print 'Is class' else: print 'Is NOT class' if isinstance(n, object): print 'Is class' else: print 'Is NOT class' if isinstance(1, object): print 'Is class' else: print 'Is NOT class' So is there anyway to do something like this? Or is everything in Python just a class and there's no way to get around that?

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How to get a Class literal from a generically specific Class

- by h2g2java

There are methods like these which require Class literals as argument. Collection<EmpInfo> emps = SomeSqlUtil.select( EmpInfo.class, "select * from emps"); or GWT.create(Razmataz.class); The problem presents itself when I need to supply generic specific classes like EmpInfo<String> Razmataz<Integer> The following would be wrong syntax Collection<EmpInfo<String>> emps = SomeSqlUtil.select( EmpInfo<String>.class, "select * from emps"); or GWT.create(Razmataz<Integer>.class); Because you cannot do syntax like Razmataz<Integer>.class So, how would I be able to squeeze a class literal out of EmpInfo<String> Razmataz<Integer> so that I could feed them as arguments to methods requiring Class literals? Further info Okay, I confess that I am asking this primarily for GWT. I have a pair of GWT RPC interface Razmataz. (FYI, GWT RPC interface has to be defined in server-client pairs). I plan to use the same interface pair for communicating whether it be String, Integer, Boolean, etc. GWT.create(Razmataz) for Razmataz<T> complains that, since I did not specify T, GWT compiler treated it as Object. Then GWT compiler would not accept Object class. It needs to be more specific than being an Object. So, it seems there is no way for me to tell GWT.create what T is because a Class literal is a runtime concept while generics is a compile time concept, Right?

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Getting the class of an n dimensional array of an runtime supplied class name

- by MeBigFatGuy

Given a fully qualified class name, and a number of dimensions, i would like to get the Class name for this class. I believe i can do this like such public Class<?> getArrayClass(String className, int dimensions) throws ClassNotFoundException { Class<?> elementType = Class.forName(className); return Array.newInstance(elementType, new int[dimensions]).getClass(); } However this requires me to create an unneeded instance of the class. Is there a way to do this without creating the instance? It does not appear that Class.forName("[[[[Ljava/lang/String;") (or a algorithmically generated version) works correctly in all instances from various blog posts i've seen.

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Returning and instance of a Class given its .class (MyClass.class)

- by jax

I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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dynamic, How to test if a property is available

- by Miau

Scenario is very simple somewhere in the code I have this dynamic myVariable = GetDataThatLooksVerySimilarButNotTheSame(); //how to do this? if (myVariable.MyProperty.Exists) //Do stuff So basically the question is how to check (avoiding exceptions) that a certain property is available in my dynamic variable. I could do GetType() but I d rather avoid that, I dont actually want to know the type of the object I want to know if a property (or method if that makes life easier) is available Any pointers? Cheers

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How to add class to selective <li> in a generated menu

- by Vikram

Hi I am looking for a solution to add a class to every list item <li> which has a child item with a class of and a different class to <li> with an anchor link. I use Joomla and the menu is being generated somewhat like this: <ul class="menu"> <li class="item1"><a href="">Home</a></li> <li class="parent item59">Demo</li> <li class="item62"><a href="">Article</a></li> <li id="current" class="parent active item27"><a href="">CMS</a> <ul> <li class="item50"><a href="">The News</a></li> <li class="item48"><a href="">Web Links</a></li> <li class="item65"></li> <li class="item49"><a href="">News Feeds</a></li> <li class="item66"></li> <li class="item67"></li> <li class="item68"></li> </ul> </li> <li class="item71">Help</li> </ul> What I want is to add class "anclink" or "seplink" to the <li> depending on their child item so that the final output looks like below. <ul class="menu"> <li class="item1 anclink"><a href="">Home</a></li> <li class="parent item59 seplink">Demo</li> <li class="item62 anclink"><a href="">Article</a></li> <li id="current" class="parent active item27" anclink><a href="">CMS</a> <ul> <li class="item50 anclink"><a href="">The News</a></li> <li class="item48 anclink"><a href="">Web Links</a></li> <li class="item65 seplink"></li> <li class="item49 anclink"><a href="">News Feeds</a></li> <li class="item66 seplink"></li> <li class="item67 seplink"></li> <li class="item68 seplink"></li> </ul> </li> <li class="item71 seplink">Help</li> </ul> How can I achieve this using PHP or even a jQuery solution will be fine. Kindly help.

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New insights I can learn from the Groovy language

- by Andrea

I realize that, for a programmer coming from the Java world, Groovy contains a lot of new ideas and cool tricks. My situation is different, as I am learning Groovy coming from a dynamic background, mainly Python and Javascript. When learning a new language, I find that it helps me if I know beforehand which features are more or less old acquaintances under a new syntax and which ones are really new, so that I can concentrate on the latter. So I would like to know which traits distinguish Groovy among the dynamic languages. What are the ideas and insights that a programmer well-versed in dynamic languages should pay attention to when learning Groovy?

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Dynamic class creation

- by Polaris

Is is possible in runtime create class from DataTable where ColumnName will be dynamic class properties?

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Subclassing to avoid line length

- by Super User

The standard line length of code is 80 characters per line. This is accepted and followed by the most of programmers. I working on a state machine of a character and is necessary for me follow this too. I have four classes who pass this limit. I can subclass each class in two more and then avoid the line length limit. class Stand class Walk class Punch class Crouch The new classes would be StandLeft, StandRight and so on. Stand, Walk, Punch and Crouch would be then abstract classes. The question if there is a limit for the long of the hierarchies tree or this is depends of the case.

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c++ defining a static member of a template class with type inner class pointer

- by Jack

I have a template class like here (in a header) with a inner class and a static member of type pointer to inner class template <class t> class outer { class inner { int a; }; static inner *m; }; template <class t> outer <t>::inner *outer <t>::m; when i want to define that static member i says "error: expected constructor, destructor, or type conversion before '*' token" on the last line (mingw32-g++ 3.4.5)

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Class.Class vs Namespace.Class for top level general use class libraries?

- by Joan Venge

Which one is more acceptable (best-practice)?: namespace NP public static class IO public static class Xml ... // extension methods using NP; IO.GetAvailableResources (); vs public static class NP public static class IO public static class Xml ... // extension methods NP.IO.GetAvailableResources (); Also for #2, the code size is managed by having partial classes so each nested class can be in a separate file, same for extension methods (except that there is no nested class for them) I prefer #2, for a couple of reasons like being able to use type names that are already commonly used, like IO, that I don't want to replace or collide. Which one do you prefer? Any pros and cons for each? What's the best practice for this case? EDIT: Also would there be a performance difference between the two?

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Some confusion with a class variable, but with a twist...

- by Omega

I have a class called MyPackage.WebServer and it has a property called DBEngine. I am also dynamically loading a module and class using load_module. Inside this class, it attempts to reference MyPackage.WebServer. When it does though, DBEngine is not set to the value given when WebServer is instantiated. It's the default (None). Would the fact that I'm using load_module cause a different object graph to be created and thus isolate my dynamically loaded class from the rest of my python app?

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"Class ref in pre-verified class resolved to unexpected implementation" when running android tests i

- by Mike

I have a module that builds an app called MyApp. I have another that builds some testcases for that app, called MyAppTests. They both build their own APKs, and they both work fine from within my IDE. I'd like to build them using ant so that I can take advantage of continuous integration. Building the app module works fine. I'm having difficulty getting the Test module to compile and run. Using Christopher's tip from a previous question, I used android create test-project -p MyAppTests -m ../MyApp -n MyAppTests to create the necessary build files to build and run my test project. This seems to work great (once I remove an unnecessary test case that it constructed for me and revert my AndroidManifest.xml to the one I was using before it got replaced by android create), but I have two problems. The first problem: The project doesn't compile because it's missing libraries. $ ant run-tests Buildfile: build.xml [setup] Project Target: Google APIs [setup] Vendor: Google Inc. [setup] Platform Version: 1.6 [setup] API level: 4 [setup] WARNING: No minSdkVersion value set. Application will install on all Android versions. -install-tested-project: [setup] Project Target: Google APIs [setup] Vendor: Google Inc. [setup] Platform Version: 1.6 [setup] API level: 4 [setup] WARNING: No minSdkVersion value set. Application will install on all Android versions. -compile-tested-if-test: -dirs: [echo] Creating output directories if needed... -resource-src: [echo] Generating R.java / Manifest.java from the resources... -aidl: [echo] Compiling aidl files into Java classes... compile: [javac] Compiling 1 source file to /Users/mike/Projects/myapp/android/MyApp/bin/classes -dex: [echo] Converting compiled files and external libraries into /Users/mike/Projects/myapp/android/MyApp/bin/classes.dex... [echo] -package-resources: [echo] Packaging resources [aaptexec] Creating full resource package... -package-debug-sign: [apkbuilder] Creating MyApp-debug-unaligned.apk and signing it with a debug key... [apkbuilder] Using keystore: /Users/mike/.android/debug.keystore debug: [echo] Running zip align on final apk... [echo] Debug Package: /Users/mike/Projects/myapp/android/MyApp/bin/MyApp-debug.apk install: [echo] Installing /Users/mike/Projects/myapp/android/MyApp/bin/MyApp-debug.apk onto default emulator or device... [exec] 1567 KB/s (288354 bytes in 0.179s) [exec] pkg: /data/local/tmp/MyApp-debug.apk [exec] Success -compile-tested-if-test: -dirs: [echo] Creating output directories if needed... [mkdir] Created dir: /Users/mike/Projects/myapp/android/MyAppTests/gen [mkdir] Created dir: /Users/mike/Projects/myapp/android/MyAppTests/bin [mkdir] Created dir: /Users/mike/Projects/myapp/android/MyAppTests/bin/classes -resource-src: [echo] Generating R.java / Manifest.java from the resources... -aidl: [echo] Compiling aidl files into Java classes... compile: [javac] Compiling 5 source files to /Users/mike/Projects/myapp/android/MyAppTests/bin/classes [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:4: package roboguice.test does not exist [javac] import roboguice.test.RoboUnitTestCase; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:8: package com.google.gson does not exist [javac] import com.google.gson.JsonElement; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:9: package com.google.gson does not exist [javac] import com.google.gson.JsonParser; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:11: cannot find symbol [javac] symbol: class RoboUnitTestCase [javac] public class GsonTest extends RoboUnitTestCase<MyApplication> { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:6: package roboguice.test does not exist [javac] import roboguice.test.RoboUnitTestCase; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:7: package roboguice.util does not exist [javac] import roboguice.util.RoboLooperThread; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:11: package com.google.gson does not exist [javac] import com.google.gson.JsonObject; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:15: cannot find symbol [javac] symbol: class RoboUnitTestCase [javac] public class HttpTest extends RoboUnitTestCase<MyApplication> { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/LinksTest.java:4: package roboguice.test does not exist [javac] import roboguice.test.RoboUnitTestCase; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/LinksTest.java:12: cannot find symbol [javac] symbol: class RoboUnitTestCase [javac] public class LinksTest extends RoboUnitTestCase<MyApplication> { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:4: package roboguice.test does not exist [javac] import roboguice.test.RoboUnitTestCase; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:5: package roboguice.util does not exist [javac] import roboguice.util.RoboAsyncTask; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:6: package roboguice.util does not exist [javac] import roboguice.util.RoboLooperThread; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:12: cannot find symbol [javac] symbol: class RoboUnitTestCase [javac] public class SafeAsyncTest extends RoboUnitTestCase<MyApplication> { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyApp/bin/classes/com/myapp/activity/Stories.class: warning: Cannot find annotation method 'value()' in type 'roboguice.inject.InjectResource': class file for roboguice.inject.InjectResource not found [javac] /Users/mike/Projects/myapp/android/MyApp/bin/classes/com/myapp/activity/Stories.class: warning: Cannot find annotation method 'value()' in type 'roboguice.inject.InjectResource' [javac] /Users/mike/Projects/myapp/android/MyApp/bin/classes/com/myapp/activity/Stories.class: warning: Cannot find annotation method 'value()' in type 'roboguice.inject.InjectView': class file for roboguice.inject.InjectView not found [javac] /Users/mike/Projects/myapp/android/MyApp/bin/classes/com/myapp/activity/Stories.class: warning: Cannot find annotation method 'value()' in type 'roboguice.inject.InjectView' [javac] /Users/mike/Projects/myapp/android/MyApp/bin/classes/com/myapp/activity/Stories.class: warning: Cannot find annotation method 'value()' in type 'roboguice.inject.InjectView' [javac] /Users/mike/Projects/myapp/android/MyApp/bin/classes/com/myapp/activity/Stories.class: warning: Cannot find annotation method 'value()' in type 'roboguice.inject.InjectView' [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:15: cannot find symbol [javac] symbol : class JsonParser [javac] location: class com.myapp.test.GsonTest [javac] final JsonParser parser = new JsonParser(); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:15: cannot find symbol [javac] symbol : class JsonParser [javac] location: class com.myapp.test.GsonTest [javac] final JsonParser parser = new JsonParser(); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:18: cannot find symbol [javac] symbol : class JsonElement [javac] location: class com.myapp.test.GsonTest [javac] final JsonElement e = parser.parse(s); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/GsonTest.java:20: cannot find symbol [javac] symbol : class JsonElement [javac] location: class com.myapp.test.GsonTest [javac] final JsonElement e2 = parser.parse(s2); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:19: cannot find symbol [javac] symbol : method getInstrumentation() [javac] location: class com.myapp.test.HttpTest [javac] assertEquals("MyApp", getInstrumentation().getTargetContext().getResources().getString(com.myapp.R.string.app_name)); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:62: cannot find symbol [javac] symbol : class RoboLooperThread [javac] location: class com.myapp.test.HttpTest [javac] new RoboLooperThread() { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:82: cannot find symbol [javac] symbol : method assertTrue(java.lang.String,boolean) [javac] location: class com.myapp.test.HttpTest [javac] assertTrue(result[0], result[0].contains("Search")); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:87: cannot find symbol [javac] symbol : class JsonObject [javac] location: class com.myapp.test.HttpTest [javac] final JsonObject[] result = {null}; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:90: cannot find symbol [javac] symbol : class RoboLooperThread [javac] location: class com.myapp.test.HttpTest [javac] new RoboLooperThread() { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:117: cannot find symbol [javac] symbol : class JsonObject [javac] location: class com.myapp.test.HttpTest [javac] final JsonObject[] result = {null}; [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/HttpTest.java:120: cannot find symbol [javac] symbol : class RoboLooperThread [javac] location: class com.myapp.test.HttpTest [javac] new RoboLooperThread() { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/LinksTest.java:27: cannot find symbol [javac] symbol : method assertTrue(boolean) [javac] location: class com.myapp.test.LinksTest [javac] assertTrue(m.matches()); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/LinksTest.java:28: cannot find symbol [javac] symbol : method assertEquals(java.lang.String,java.lang.String) [javac] location: class com.myapp.test.LinksTest [javac] assertEquals( map.get(url), m.group(1) ); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:19: cannot find symbol [javac] symbol : method getInstrumentation() [javac] location: class com.myapp.test.SafeAsyncTest [javac] assertEquals("MyApp", getInstrumentation().getTargetContext().getString(com.myapp.R.string.app_name)); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:27: cannot find symbol [javac] symbol : class RoboLooperThread [javac] location: class com.myapp.test.SafeAsyncTest [javac] new RoboLooperThread() { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:65: cannot find symbol [javac] symbol : method assertEquals(com.myapp.test.SafeAsyncTest.State,com.myapp.test.SafeAsyncTest.State) [javac] location: class com.myapp.test.SafeAsyncTest [javac] assertEquals(State.TEST_SUCCESS,state[0]); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:74: cannot find symbol [javac] symbol : class RoboLooperThread [javac] location: class com.myapp.test.SafeAsyncTest [javac] new RoboLooperThread() { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:105: cannot find symbol [javac] symbol : method assertEquals(com.myapp.test.SafeAsyncTest.State,com.myapp.test.SafeAsyncTest.State) [javac] location: class com.myapp.test.SafeAsyncTest [javac] assertEquals(State.TEST_SUCCESS,state[0]); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:113: cannot find symbol [javac] symbol : class RoboLooperThread [javac] location: class com.myapp.test.SafeAsyncTest [javac] new RoboLooperThread() { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:144: cannot find symbol [javac] symbol : method assertEquals(com.myapp.test.SafeAsyncTest.State,com.myapp.test.SafeAsyncTest.State) [javac] location: class com.myapp.test.SafeAsyncTest [javac] assertEquals(State.TEST_SUCCESS,state[0]); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:154: cannot find symbol [javac] symbol : class RoboLooperThread [javac] location: class com.myapp.test.SafeAsyncTest [javac] new RoboLooperThread() { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java:187: cannot find symbol [javac] symbol : method assertEquals(com.myapp.test.SafeAsyncTest.State,com.myapp.test.SafeAsyncTest.State) [javac] location: class com.myapp.test.SafeAsyncTest [javac] assertEquals(State.TEST_SUCCESS,state[0]); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/StoriesTest.java:11: cannot access roboguice.activity.GuiceListActivity [javac] class file for roboguice.activity.GuiceListActivity not found [javac] public class StoriesTest extends ActivityUnitTestCase<Stories> { [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/StoriesTest.java:21: cannot access roboguice.application.GuiceApplication [javac] class file for roboguice.application.GuiceApplication not found [javac] setApplication( new MyApplication( getInstrumentation().getTargetContext() ) ); [javac] ^ [javac] /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/StoriesTest.java:22: incompatible types [javac] found : com.myapp.activity.Stories [javac] required: android.app.Activity [javac] final Activity activity = startActivity(intent, null, null); [javac] ^ [javac] 39 errors [javac] 6 warnings BUILD FAILED /opt/local/android-sdk-mac/platforms/android-1.6/templates/android_rules.xml:248: Compile failed; see the compiler error output for details. Total time: 24 seconds That's not a hard problem to solve. I'm not sure it's the right thing to do, but I copied the missing libraries (roboguice and gson) from the MyApp/libs directory to the MyAppTests/libs directory and everything seems to compile fine. But that leads to the second problem, which I'm currently stuck on. The tests compile fine but they won't run: $ cp ../MyApp/libs/gson-r538.jar libs/ $ cp ../MyApp/libs/roboguice-1.1-SNAPSHOT.jar libs/ 0 10:23 /Users/mike/Projects/myapp/android/MyAppTests $ ant run-testsBuildfile: build.xml [setup] Project Target: Google APIs [setup] Vendor: Google Inc. [setup] Platform Version: 1.6 [setup] API level: 4 [setup] WARNING: No minSdkVersion value set. Application will install on all Android versions. -install-tested-project: [setup] Project Target: Google APIs [setup] Vendor: Google Inc. [setup] Platform Version: 1.6 [setup] API level: 4 [setup] WARNING: No minSdkVersion value set. Application will install on all Android versions. -compile-tested-if-test: -dirs: [echo] Creating output directories if needed... -resource-src: [echo] Generating R.java / Manifest.java from the resources... -aidl: [echo] Compiling aidl files into Java classes... compile: [javac] Compiling 1 source file to /Users/mike/Projects/myapp/android/MyApp/bin/classes -dex: [echo] Converting compiled files and external libraries into /Users/mike/Projects/myapp/android/MyApp/bin/classes.dex... [echo] -package-resources: [echo] Packaging resources [aaptexec] Creating full resource package... -package-debug-sign: [apkbuilder] Creating MyApp-debug-unaligned.apk and signing it with a debug key... [apkbuilder] Using keystore: /Users/mike/.android/debug.keystore debug: [echo] Running zip align on final apk... [echo] Debug Package: /Users/mike/Projects/myapp/android/MyApp/bin/MyApp-debug.apk install: [echo] Installing /Users/mike/Projects/myapp/android/MyApp/bin/MyApp-debug.apk onto default emulator or device... [exec] 1396 KB/s (288354 bytes in 0.201s) [exec] pkg: /data/local/tmp/MyApp-debug.apk [exec] Success -compile-tested-if-test: -dirs: [echo] Creating output directories if needed... -resource-src: [echo] Generating R.java / Manifest.java from the resources... -aidl: [echo] Compiling aidl files into Java classes... compile: [javac] Compiling 5 source files to /Users/mike/Projects/myapp/android/MyAppTests/bin/classes [javac] Note: /Users/mike/Projects/myapp/android/MyAppTests/src/com/myapp/test/SafeAsyncTest.java uses unchecked or unsafe operations. [javac] Note: Recompile with -Xlint:unchecked for details. -dex: [echo] Converting compiled files and external libraries into /Users/mike/Projects/myapp/android/MyAppTests/bin/classes.dex... [echo] -package-resources: [echo] Packaging resources [aaptexec] Creating full resource package... -package-debug-sign: [apkbuilder] Creating MyAppTests-debug-unaligned.apk and signing it with a debug key... [apkbuilder] Using keystore: /Users/mike/.android/debug.keystore debug: [echo] Running zip align on final apk... [echo] Debug Package: /Users/mike/Projects/myapp/android/MyAppTests/bin/MyAppTests-debug.apk install: [echo] Installing /Users/mike/Projects/myapp/android/MyAppTests/bin/MyAppTests-debug.apk onto default emulator or device... [exec] 1227 KB/s (94595 bytes in 0.075s) [exec] pkg: /data/local/tmp/MyAppTests-debug.apk [exec] Success run-tests: [echo] Running tests ... [exec] [exec] android.test.suitebuilder.TestSuiteBuilder$FailedToCreateTests:INSTRUMENTATION_RESULT: shortMsg=Class ref in pre-verified class resolved to unexpected implementation [exec] INSTRUMENTATION_RESULT: longMsg=java.lang.IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation [exec] INSTRUMENTATION_CODE: 0 BUILD SUCCESSFUL Total time: 38 seconds Any idea what's causing the "Class ref in pre-verified class resolved to unexpected implementation" error?

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Creating a dynamic proxy generator – Part 1 – Creating the Assembly builder, Module builder and cach

- by SeanMcAlinden

I’ve recently started a project with a few mates to learn the ins and outs of Dependency Injection, AOP and a number of other pretty crucial patterns of development as we’ve all been using these patterns for a while but have relied totally on third part solutions to do the magic. We thought it would be interesting to really get into the details by rolling our own IoC container and hopefully learn a lot on the way, and you never know, we might even create an excellent framework. The open source project is called Rapid IoC and is hosted at http://rapidioc.codeplex.com/ One of the most interesting tasks for me is creating the dynamic proxy generator for enabling Aspect Orientated Programming (AOP). In this series of articles, I’m going to track each step I take for creating the dynamic proxy generator and I’ll try my best to explain what everything means - mainly as I’ll be using Reflection.Emit to emit a fair amount of intermediate language code (IL) to create the proxy types at runtime which can be a little taxing to read. It’s worth noting that building the proxy is without a doubt going to be slightly painful so I imagine there will be plenty of areas I’ll need to change along the way. Anyway lets get started… Part 1 - Creating the Assembly builder, Module builder and caching mechanism Part 1 is going to be a really nice simple start, I’m just going to start by creating the assembly, module and type caches. The reason we need to create caches for the assembly, module and types is simply to save the overhead of recreating proxy types that have already been generated, this will be one of the important steps to ensure that the framework is fast… kind of important as we’re calling the IoC container ‘Rapid’ – will be a little bit embarrassing if we manage to create the slowest framework. The Assembly builder The assembly builder is what is used to create an assembly at runtime, we’re going to have two overloads, one will be for the actual use of the proxy generator, the other will be mainly for testing purposes as it will also save the assembly so we can use Reflector to examine the code that has been created. Here’s the code: DynamicAssemblyBuilder using System; using System.Reflection; using System.Reflection.Emit; namespace Rapid.DynamicProxy.Assembly { /// <summary> /// Class for creating an assembly builder. /// </summary> internal static class DynamicAssemblyBuilder { #region Create /// <summary> /// Creates an assembly builder. /// </summary> /// <param name="assemblyName">Name of the assembly.</param> public static AssemblyBuilder Create(string assemblyName) { AssemblyName name = new AssemblyName(assemblyName); AssemblyBuilder assembly = AppDomain.CurrentDomain.DefineDynamicAssembly( name, AssemblyBuilderAccess.Run); DynamicAssemblyCache.Add(assembly); return assembly; } /// <summary> /// Creates an assembly builder and saves the assembly to the passed in location. /// </summary> /// <param name="assemblyName">Name of the assembly.</param> /// <param name="filePath">The file path.</param> public static AssemblyBuilder Create(string assemblyName, string filePath) { AssemblyName name = new AssemblyName(assemblyName); AssemblyBuilder assembly = AppDomain.CurrentDomain.DefineDynamicAssembly( name, AssemblyBuilderAccess.RunAndSave, filePath); DynamicAssemblyCache.Add(assembly); return assembly; } #endregion } } So hopefully the above class is fairly explanatory, an AssemblyName is created using the passed in string for the actual name of the assembly. An AssemblyBuilder is then constructed with the current AppDomain and depending on the overload used, it is either just run in the current context or it is set up ready for saving. It is then added to the cache. DynamicAssemblyCache using System.Reflection.Emit; using Rapid.DynamicProxy.Exceptions; using Rapid.DynamicProxy.Resources.Exceptions; namespace Rapid.DynamicProxy.Assembly { /// <summary> /// Cache for storing the dynamic assembly builder. /// </summary> internal static class DynamicAssemblyCache { #region Declarations private static object syncRoot = new object(); internal static AssemblyBuilder Cache = null; #endregion #region Adds a dynamic assembly to the cache. /// <summary> /// Adds a dynamic assembly builder to the cache. /// </summary> /// <param name="assemblyBuilder">The assembly builder.</param> public static void Add(AssemblyBuilder assemblyBuilder) { lock (syncRoot) { Cache = assemblyBuilder; } } #endregion #region Gets the cached assembly /// <summary> /// Gets the cached assembly builder. /// </summary> /// <returns></returns> public static AssemblyBuilder Get { get { lock (syncRoot) { if (Cache != null) { return Cache; } } throw new RapidDynamicProxyAssertionException(AssertionResources.NoAssemblyInCache); } } #endregion } } The cache is simply a static property that will store the AssemblyBuilder (I know it’s a little weird that I’ve made it public, this is for testing purposes, I know that’s a bad excuse but hey…) There are two methods for using the cache – Add and Get, these just provide thread safe access to the cache. The Module Builder The module builder is required as the create proxy classes will need to live inside a module within the assembly. Here’s the code: DynamicModuleBuilder using System.Reflection.Emit; using Rapid.DynamicProxy.Assembly; namespace Rapid.DynamicProxy.Module { /// <summary> /// Class for creating a module builder. /// </summary> internal static class DynamicModuleBuilder { /// <summary> /// Creates a module builder using the cached assembly. /// </summary> public static ModuleBuilder Create() { string assemblyName = DynamicAssemblyCache.Get.GetName().Name; ModuleBuilder moduleBuilder = DynamicAssemblyCache.Get.DefineDynamicModule (assemblyName, string.Format("{0}.dll", assemblyName)); DynamicModuleCache.Add(moduleBuilder); return moduleBuilder; } } } As you can see, the module builder is created on the assembly that lives in the DynamicAssemblyCache, the module is given the assembly name and also a string representing the filename if the assembly is to be saved. It is then added to the DynamicModuleCache. DynamicModuleCache using System.Reflection.Emit; using Rapid.DynamicProxy.Exceptions; using Rapid.DynamicProxy.Resources.Exceptions; namespace Rapid.DynamicProxy.Module { /// <summary> /// Class for storing the module builder. /// </summary> internal static class DynamicModuleCache { #region Declarations private static object syncRoot = new object(); internal static ModuleBuilder Cache = null; #endregion #region Add /// <summary> /// Adds a dynamic module builder to the cache. /// </summary> /// <param name="moduleBuilder">The module builder.</param> public static void Add(ModuleBuilder moduleBuilder) { lock (syncRoot) { Cache = moduleBuilder; } } #endregion #region Get /// <summary> /// Gets the cached module builder. /// </summary> /// <returns></returns> public static ModuleBuilder Get { get { lock (syncRoot) { if (Cache != null) { return Cache; } } throw new RapidDynamicProxyAssertionException(AssertionResources.NoModuleInCache); } } #endregion } } The DynamicModuleCache is very similar to the assembly cache, it is simply a statically stored module with thread safe Add and Get methods. The DynamicTypeCache To end off this post, I’m going to create the cache for storing the generated proxy classes. I’ve spent a fair amount of time thinking about the type of collection I should use to store the types and have finally decided that for the time being I’m going to use a generic dictionary. This may change when I can actually performance test the proxy generator but the time being I think it makes good sense in theory, mainly as it pretty much maintains it’s performance with varying numbers of items – almost constant (0)1. Plus I won’t ever need to loop through the items which is not the dictionaries strong point. Here’s the code as it currently stands: DynamicTypeCache using System; using System.Collections.Generic; using System.Security.Cryptography; using System.Text; namespace Rapid.DynamicProxy.Types { /// <summary> /// Cache for storing proxy types. /// </summary> internal static class DynamicTypeCache { #region Declarations static object syncRoot = new object(); public static Dictionary<string, Type> Cache = new Dictionary<string, Type>(); #endregion /// <summary> /// Adds a proxy to the type cache. /// </summary> /// <param name="type">The type.</param> /// <param name="proxy">The proxy.</param> public static void AddProxyForType(Type type, Type proxy) { lock (syncRoot) { Cache.Add(GetHashCode(type.AssemblyQualifiedName), proxy); } } /// <summary> /// Tries the type of the get proxy for. /// </summary> /// <param name="type">The type.</param> /// <returns></returns> public static Type TryGetProxyForType(Type type) { lock (syncRoot) { Type proxyType; Cache.TryGetValue(GetHashCode(type.AssemblyQualifiedName), out proxyType); return proxyType; } } #region Private Methods private static string GetHashCode(string fullName) { SHA1CryptoServiceProvider provider = new SHA1CryptoServiceProvider(); Byte[] buffer = Encoding.UTF8.GetBytes(fullName); Byte[] hash = provider.ComputeHash(buffer, 0, buffer.Length); return Convert.ToBase64String(hash); } #endregion } } As you can see, there are two public methods, one for adding to the cache and one for getting from the cache. Hopefully they should be clear enough, the Get is a TryGet as I do not want the dictionary to throw an exception if a proxy doesn’t exist within the cache. Other than that I’ve decided to create a key using the SHA1CryptoServiceProvider, this may change but my initial though is the SHA1 algorithm is pretty fast to put together using the provider and it is also very unlikely to have any hashing collisions. (there are some maths behind how unlikely this is – here’s the wiki if you’re interested http://en.wikipedia.org/wiki/SHA_hash_functions) Anyway, that’s the end of part 1 – although I haven’t started any of the fun stuff (by fun I mean hairpulling, teeth grating Relfection.Emit style fun), I’ve got the basis of the DynamicProxy in place so all we have to worry about now is creating the types, interceptor classes, method invocation information classes and finally a really nice fluent interface that will abstract all of the hard-core craziness away and leave us with a lightning fast, easy to use AOP framework. Hope you find the series interesting. All of the source code can be viewed and/or downloaded at our codeplex site - http://rapidioc.codeplex.com/ Kind Regards, Sean.

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