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  • Pros & Cons of Google App Engine

    - by Rishi
    Pros & Cons of Google App Engine [An Updated List 21st Aug 09] Help me Compile a List of all the Advantages & Disadvantages of Building an Application on the Google App Engine Pros: 1) No Need to buy Servers or Server Space (no maintenance). 2) Makes solving the problem of scaling much easier. Cons: 1) Locked into Google App Engine ?? 2)Developers have read-only access to the filesystem on App Engine. 3)App Engine can only execute code called from an HTTP request (except for scheduled background tasks). 4)Users may upload arbitrary Python modules, but only if they are pure-Python; C and Pyrex modules are not supported. 5)App Engine limits the maximum rows returned from an entity get to 1000 rows per Datastore call. 6)Java applications may only use a subset (The JRE Class White List) of the classes from the JRE standard edition. 7)Java applications cannot create new threads. Known Issues!! http://code.google.com/p/googleappengine/issues/list Hard limits Apps per developer - 10 Time per request - 30 sec Files per app - 3,000 HTTP response size - 10 MB Datastore item size - 1 MB Application code size - 150 MB Pro or Con? App Engine's infrastructure removes many of the system administration and development challenges of building applications to scale to millions of hits. Google handles deploying code to a cluster, monitoring, failover, and launching application instances as necessary. While other services let users install and configure nearly any *NIX compatible software, App Engine requires developers to use Python or Java as the programming language and a limited set of APIs. Current APIs allow storing and retrieving data from a BigTable non-relational database; making HTTP requests; sending e-mail; manipulating images; and caching. Most existing Web applications can't run on App Engine without modification, because they require a relational database.

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  • Twitter4J throws exception in TwitterFactory

    - by Philipp Andre
    Hello Guys, i'm trying to access twitter via oauth. Therefore, i registered my app, downloaded Twitter4j, added the jars in my Eclipse-Project, and then tried to execute the following code: Twitter twitter = new TwitterFactory().getOAuthAuthorizedInstance("[key]","[secretKey]); RequestToken requestToken = twitter.getOAuthRequestToken(); System.out.println(requestToken.getAuthorizationURL()); But it raises the following exception: [Sat May 29 11:19:11 CEST 2010]Using class twitter4j.internal.logging.StdOutLoggerFactory as logging factory. [Sat May 29 11:19:11 CEST 2010]Use twitter4j.internal.http.alternative.HttpClientImpl as HttpClient implementation. Exception in thread "main" java.lang.AssertionError: java.lang.reflect.InvocationTargetException at twitter4j.internal.http.HttpClientFactory.getInstance(HttpClientFactory.java:71) at twitter4j.internal.http.HttpClientWrapper.<init>(HttpClientWrapper.java:59) at twitter4j.http.OAuthAuthorization.init(OAuthAuthorization.java:83) at twitter4j.http.OAuthAuthorization.<init>(OAuthAuthorization.java:74) at twitter4j.TwitterFactory.getOAuthAuthorizedInstance(TwitterFactory.java:112) at MainProgram.main(MainProgram.java:18) Caused by: java.lang.reflect.InvocationTargetException at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at twitter4j.internal.http.HttpClientFactory.getInstance(HttpClientFactory.java:65) ... 5 more Caused by: java.lang.NoClassDefFoundError: org/apache/http/impl/client/DefaultHttpClient at twitter4j.internal.http.alternative.HttpClientImpl.<init>(HttpClientImpl.java:63) ... 10 more I currently can't figure out why ... can you please give me some suggestions? Best regards Philipp

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  • How can I write classes that don't rely on "global" variables?

    - by Joel
    When I took my first programming course in university, we were taught that global variables were evil & should be avoided at all cost (since you can quickly develop confusing and unmaintainable code). The following year, we were taught object oriented programming, and how to create modular code using classes. I find that whenever I work with OOP, I use my classes' private variables as global variables, i.e., they can be (and are) read and modified by any function within the class. This isn't really sitting right with me, as it seems to introduce the same problems global variables had in languages like C. So I guess my question is, how do I stop writing classes with "global" variables? Would it make more sense to pretend I'm writing in a functional language? By this I mean having all functions take parameters & return values instead of directly modifying class variables. If I need to set any fields, I can just take the output of the function and assign it instead of having the function do it directly. This seems like it might make more maintainable code, at least for larger classes. What's common practice? Thanks!

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  • Can GWT image sprites using ImageBundle be made to work in IE7 and IE6?

    - by aem
    I'm trying to use a ClientBundle in my GWT application to make multiple images get sent as a single file. I declare the bundle like so: public interface MyResources extends ClientBundle { public static final MyResources INSTANCE = GWT.create(MyResources.class); @Source("icon1.png") ImageResource icon1(); @Source("icon2.png") ImageResource icon2(); } This works great in Firefox and IE8, but in IE7 (and earlier) the whole sprite shows up in place of one of my original images - that is, icon1 is next to icon2 next to icon3, and so on. In IE8's developer tools using IE8-as-IE7 mode or Compatibility View, I can see that it's showing an image with a file name like 26BEFD2399A92A5DDA54277BA550C75B.cache.png, which is what I'd expect. So is there any way to make GWT image sprites work in IE7 and lower? If not, is there any way to gracefully degrade so users of other browsers get the speedup of spriting and IE7 and IE6 users get something that looks right but is slower? Edit: The Client Bundle Developer's Guide has a discussion of using ClientBundle and @sprite, and says "Support for IE6 isn't feasible in this format, because structural changes to the DOM are necessary to implement a "windowing" effect. Once it's possible to distinguish ie6 and ie7 in user.agent, we could revisit support for ie6. In the current implementation, the ie6 code won't render correctly, although is a purely cosmetic issue." Is this what's going on in my case, and is there a way to work around it? Showing all the images is "purely a cosmetic issue", but it's a pretty severe one.

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  • FluentNHibernate SQLite configuration exception - after switching to .net4

    - by stiank81
    I get an exception thrown when trying to use Fluent to configure my NHibernate connection to SQLite. The code I use to configure is as follows: var cfg = Fluently.Configure(). Database(SQLiteConfiguration.Standard.ShowSql().UsingFile("MyDb.db")). Mappings(m => m.FluentMappings.AddFromAssemblyOf<MappingsPersistenceModel>()); _sessionFactory = cfg.BuildSessionFactory(); A HibernateException is thrown when BuildSessionFactory() is called, saying: Could not create the driver from NHibernate.Driver.SQLite20Driver, NHibernate, Version=2.1.2.4000, Culture=neutral, PublicKeyToken=aa95f207798dfdb4. It has an InnerException: Exception has been thrown by the target of an invocation. Which again has an InnerException: The IDbCommand and IDbConnection implementation in the assembly System.Data.SQLite could not be found. Ensure that the assembly System.Data.SQLite is located in the application directory or in the Global Assembly Cache. If the assembly is in the GAC, use element in the application configuration file to specify the full name of the assembly. Now - to me it sounds like it doesn't find System.Data.SQLite.dll, but I can't understand this. Everywhere this is referenced I have "Copy Local", and I have verified that it is in every build folder for projects using SQLite. I have also copied it manually to every Debug folder of the solution - without luck. What can be causing this? Any ideas? My suspicion is that it is related to .Net4 somehow. The reason is that it worked just fine when I used .Net3.5, and then I changed to .Net4, and the problem started. You can also check out this other question for a more general approach towards Fluent-.Net4 compatibility.

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  • Memory mapped files and "soft" page faults. Unavoidable?

    - by Robert Oschler
    I have two applications (processes) running under Windows XP that share data via a memory mapped file. Despite all my efforts to eliminate per iteration memory allocations, I still get about 10 soft page faults per data transfer. I've tried every flag there is in CreateFileMapping() and CreateFileView() and it still happens. I'm beginning to wonder if it's just the way memory mapped files work. If anyone there knows the O/S implementation details behind memory mapped files I would appreciate comments on the following theory: If two processes share a memory mapped file and one process writes to it while another reads it, then the O/S marks the pages written to as invalid. When the other process goes to read the memory areas that now belong to invalidated pages, this causes a soft page fault (by design) and the O/S knows to reload the invalidated page. Also, the number of soft page faults is therefore directly proportional to the size of the data write. My experiments seem to bear out the above theory. When I share data I write one contiguous block of data. In other words, the entire shared memory area is overwritten each time. If I make the block bigger the number of soft page faults goes up correspondingly. So, if my theory is true, there is nothing I can do to eliminate the soft page faults short of not using memory mapped files because that is how they work (using soft page faults to maintain page consistency). What is ironic is that I chose to use a memory mapped file instead of a TCP socket connection because I thought it would be more efficient. Note, if the soft page faults are harmless please note that. I've heard that at some point if the number is excessive, the system's performance can be marred. If soft page faults intrinsically are not significantly harmful then if anyone has any guidelines as to what number per second is "excessive" I'd like to hear that. Thanks.

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  • Big-O of PHP functions?

    - by Kendall Hopkins
    After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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  • Drag-n-Drop on contentEditable elements

    - by Raybiez
    There are numerous WYSIWYG editors available on the internet, but I'm yet to find one that implements some form of drag-n-drop implementation. It is easy to create one's own editor, but I want to the user to be able to drag elements (ie. tokens) from outside the editable area and have them drop it at a location of their choice inside the editable area. It is easy to inject html at a specific location of an editable element, but how do one determine where the caret should be when the user is dragging a DIV over some element in the editable area. To better illustrate what I'm trying to explain, see the following scenario. The editable area (either an IFRAME in edit mode or a DIV with its contentEditable attribute set to true) already contains the following text: "Dear , please take note of ...." The user now drags an element representing some token from a list of elements, over the editable area, moving the cursor over the text until the caret appear just before the comma (,) in the text as shown above. When the user releases the mouse button at that location, HTML will be injected which could result in something like this: "Dear {UserFirstName}, please take note of ...". I do not know if anyone has ever done anything similar to this, or at least know of how one would go about doing this using JavaScript. Any help will be greatly appreciated.

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  • Efficiently Determine if EF 4 POCO Already in ObjectSet

    - by Eric J.
    I'm trying EF 4 with POCO's on a small project for the first time. In my Repository implementation, I want to provide a method AddOrUpdate that will add a passed-in POCO to the repository if it's new, else do nothing (as the updated POCO will be saved when SaveChanges is called). My first thought was to do this: public void AddOrUpdate(Poco p) { if (!Ctx.Pocos.Contains<Poco>(p)) { Ctx.Pocos.AddObject(p); } } However that results in a NotSupportedException as documented under Referencing Non-Scalar Variables Not Supported (bonus question: why would that not be supported?) Just removing the Contains part and always calling AddObject results in an InvalidStateException: An object with the same key already exists in the ObjectStateManager. The existing object is in the Unchanged state. An object can only be added to the ObjectStateManager again if it is in the added state. So clearly EF 4 knows somewhere that this is a duplicate based on the key. What's a clean, efficient way for the Repository to update Pocos for either a new or pre-existing object when AddOrUpdate is called so that the subsequent call to SaveChanges() will do the right thing? I did consider carrying an isNew flag on the object itself, but I'm trying to take persistence ignorance as far as practical.

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  • JSF ISO-8859-2 charset

    - by Vladimir
    Hi! I have problem with setting proper charset on my jsf pages. I use MySql db with latin2 (ISO-8859-2 charset) and latin2_croatian_ci collation. But, I have problems with setting values on backing managed bean properties. Page directive on top of my page is: <%@ page language="java" pageEncoding="ISO-8859-2" contentType="text/html; charset=ISO-8859-2" %> In head I included: <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-2"> And my form tag is: <h:form id="entityDetails" acceptcharset="ISO-8859-2"> I've created and registered Filter in web.xml with following doFilter method implementation: public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { request.setCharacterEncoding("ISO-8859-2"); response.setCharacterEncoding("ISO-8859-2"); chain.doFilter(request, response); } But, i.e. when I set managed bean property through inputText, all special (unicode) characters are replaced with '?' character. I really don't have any other ideas how to set charset to pages to perform well. Any suggestions? Thanks in advance.

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  • Workflow engine BPMN, Drools, etc or ESB?

    - by Tom
    We currently have an application that is based on an in-house developed workflow engine with YAML based DSL. We are looking to move parts of it to Java. I have discovered a number of java solutions like Intalio, JBPM, Drools Expert, Drools Flow etc. They appear to be aimed at businesses where the business analyst creates the workflows using a graphical editor and submits them to the workflow engine. They seem geared towards ease of use for non-technical people rather than for developers with a focus on human interaction. The workflows tend to look like. Discover-a-file -\ -> join -> process-file -> move-file -> register-file Discover-some-metadata -/ If any step fails we need to retry it X times. We also need to be able to stop the system and be able to restart it and have it continue from where it was (durable). Some of our workflows can be defined by a set of goals we need to achieve so Jess's backwards rule chaining sounds interesting but it is not open source. It might be that what we are after is a Finite State Machine engine or just an Enterprise Service Bus and do everything as JMS queues. Is there a good open source workflow engine that is both standards-based but also geared towards developers. We don't particular want to use a graphical workflow designer or write reams of XML and it should ideally be in Java or language agnostic (makes REST/Soap calls to external services). Thanks, Tom

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  • Unable to call RESTful web services methods

    - by Alessandro
    Hello, I'm trying to dive into the RESTful web services world and have started with the following template: [ServiceContract] [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)] [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)] public class Test { // TODO: Implement the collection resource that will contain the SampleItem instances [WebGet(UriTemplate = ""), OperationContract] public List<SampleItem> GetCollection() { // TODO: Replace the current implementation to return a collection of SampleItem instances return new List<SampleItem>() {new SampleItem() {Id = 1, StringValue = "Hello"}}; } [WebInvoke(UriTemplate = "", Method = "POST"), OperationContract] public SampleItem Create(SampleItem instance) { // TODO: Add the new instance of SampleItem to the collection throw new NotImplementedException(); } [WebGet(UriTemplate = "{id}"), OperationContract] public SampleItem Get(string id) { // TODO: Return the instance of SampleItem with the given id throw new NotImplementedException(); } [WebInvoke(UriTemplate = "{id}", Method = "PUT"), OperationContract] public SampleItem Update(string id, SampleItem instance) { return new SampleItem { Id = 99, StringValue = "Done" }; } [WebInvoke(UriTemplate = "{id}", Method = "DELETE"), OperationContract] public void Delete(string id) { // TODO: Remove the instance of SampleItem with the given id from the collection throw new NotImplementedException(); } } I am able to perform the GET operation but I am unable to perform PUT, POST or DELETE requests. Can anyone explain me how to perform these operations and how to create the correct URLs? Best regards Alessandro

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  • InternetExplorer.Application object and cookie container

    - by Darin Dimitrov
    I have the following console application written in VB.NET: Sub Main() Dim ie As Object = CreateObject("InternetExplorer.Application") ie.Visible = True ie.Navigate2("http://localhost:4631/Default.aspx") End Sub This program uses the InternetExplorer.Application automation object to launch an IE window and navigate a given url. The problem that I encountered is that even if I launch multiple instances of my application, the IE windows that are created with this method all share the same cookie container. Is there any parameter I could use specifying that a different cookie container is created for every window? This is the web page I used to test cookies: <%@ Page Language="C#" AutoEventWireup="true" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script runat="server"> protected void Page_Load(object sender, EventArgs e) { // Store something into the session in order to create the cookie Session["foo"] "bar"; Response.Write(Session.SessionID); } </script> <html xmlns="http://www.w3.org/1999/xhtml" > <body> <form id="form1" runat="server"></form> </body> </html>

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  • Best approach for a multi-tab ASP.NET AJAX control?

    - by NovaJoe
    Looking for some implementation advice: I have a page that has a 3-tab ajaxToolkit:TabContainer. The purpose of the page is to expose a calculator that has two basic inputs: geo-location and date. The three tabs are labeled "City and State", "Postal Code", and "GPS Coordinates". The layout of each tab container is the same for each tab, with the exception of the location section; the location section changes because each type of location has different inputs. For example, to specify city/state, there will be three fields: city, country, and state (country and state will use cascading drop-down lists). But Postal code requires only one field (which will validate via regular expression for allowed countries). See the example design mockup: So, what I WOULD LIKE to do (in order to minimize duplicate code), is to have a common control that contains the layout and structure of the calculator without specifying anything about the location section. Then, I'd like to be able to pull in each of the unique location controls based on what tab is selected. The tab structure exists at the page level, not in a control. Any advice? I was looking at templated controls (see MSDN article here), but I'm not convinced that it's the right solution. If I HAVE to create three separate controls with similar layouts and common elements, then that's what I have to do. But REALLY, I'd prefer a more elegant, inheritance-based solution. Any advice would be greatly appreciated. Thanks.

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  • .NET Membership with Repository Pattern

    - by Zac
    My team is in the process of designing a domain model which will hide various different data sources behind a unified repository abstraction. One of the main drivers for this approach is the very high probability that these data sources will undergo significant change in the near future and we don't want to be re-writing business logic when this happens. One data source will be our membership database which was originally implemented using the default ASP.Net Membership Provider. The membership provider is tied to the System.Web.Security namespace but we have a design guideline requiring that our domain model layer is not dependent upon System.Web (or any other implementation/environment dependency) as it will be consumed in different environments - nor do we want our websites directly communicating with databases. I am considering what would be a good approach to reconciling the MembershipProvider approach with our abstracted n-tier architecture. My initial feeling is that we could create a "DomainMembershipProvider" which interacts with the domain model and then implement objects in the model which deal with the repository and handle validation/business logic. The repository would then implement data access using our (as-yet undecided) ORM/data access tool. Are there are any glaring holes in this approach - I haven't worked closely with the MembershipProvider class so may well be missing something. Alternatively, is there an approach that you think will better serve the requirements I described above? Thanks in advance for your thoughts and advice. Regards, Zac

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  • P6 Architecture - Register renaming aside, does the limited user registers result in more ops spent

    - by mrjoltcola
    I'm studying JIT design with regard to dynamic languages VM implementation. I haven't done much Assembly since the 8086/8088 days, just a little here or there, so be nice if I'm out of sorts. As I understand it, the x86 (IA-32) architecture still has the same basic limited register set today that it always did, but the internal register count has grown tremendously, but these internal registers are not generally available and are used with register renaming to achieve parallel pipelining of code that otherwise could not be parallelizable. I understand this optimization pretty well, but my feeling is, while these optimizations help in overall throughput and for parallel algorithms, the limited register set we are still stuck with results in more register spilling overhead such that if x86 had double, or quadruple the registers available to us, there may be significantly less push/pop opcodes in a typical instruction stream? Or are there other processor optmizations that also optimize this away that I am unaware of? Basically if I've a unit of code that has 4 registers to work with for integer work, but my unit has a dozen variables, I've got potentially a push/pop for every 2 or so instructions. Any references to studies, or better yet, personal experiences?

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  • TLS with SNI in Java clients

    - by ftrotter
    There is an ongoing discussion on the security and trust working group for NHIN Direct regarding the IP-to-domain mapping problem that is created with traditional SSL. If an HISP (as defined by NHIN Direct) wants to host thousands of NHIN Direct "Health Domains" for providers, then it will an "artificially inflated cost" to have to purchase an IP for each of those domains. Because Apache and OpenSSL have recently released TLS with support for the SNI extension, it is possible to use SNI as a solution to this problem on the server side. However, if we decide that we will allow server implementations of the NHINDirect transport layer to support TLS+SNI, then we must require that all clients support SNI too. OpenSSL based clients should do this by default and one could always us stunnel to implement an TLS+SNI aware client to proxy if your given programming language SSL implementation does not support SNI. It appears that native Java applications using OpenJDK do not yet support SNI, but I cannot get a straight answer out of that project. I know that there are OpenSSL Java libraries available but I have no idea if that would be considered viable. Can you give me a "state of the art" summary of where TLS+SNI support is for Java clients? I need a Java implementers perspective on this.

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  • Scrolling with two fingers with a UIScrollView

    - by Craig
    I have an app where my main view accepts both touchesBegan and touchesMoved, and therefore takes in single finger touches, and drags. I want to implement a UIScrollView, and I have it working, but it overrides the drags, and therefore my contentView never receives them. I'd like to implement a UIScrollview, where a two finger drag indicates a scroll, and a one finger drag event gets passed to my content view, so it performs normally. Do I need create my own subclass of UIScrollView? Here's my code from my appDelegate where I implement the UIScrollView. @implementation MusicGridAppDelegate @synthesize window; @synthesize viewController; @synthesize scrollView; - (void)applicationDidFinishLaunching:(UIApplication *)application { // Override point for customization after app launch //[application setStatusBarHidden:YES animated:NO]; //[window addSubview:viewController.view]; scrollView.contentSize = CGSizeMake(720, 480); scrollView.showsHorizontalScrollIndicator = YES; scrollView.showsVerticalScrollIndicator = YES; scrollView.delegate = self; [scrollView addSubview:viewController.view]; [window makeKeyAndVisible]; } - (void)dealloc { [viewController release]; [scrollView release]; [window release]; [super dealloc]; }

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  • Is there a good tutorial for figuring out what a website is doing so your program can do the same th

    - by brian d foy
    Is there a good guide or tutorial for people who need to programmatically interact with dynamic websites? There's been a rash of Perl questions about that lately, and I haven't found a good resource to point people toward. I'm asking not because I need one but because I don't want to waste my time writing it if it already exists. Although I'm most interested in Perl, the extra tools and techniques are mostly the same. Typically, I see see these problems in people's questions: Handling, setting, and saving cookies Finding and interacting with forms Handling JavaScript inside your user-agent especially things like onLoad, onSumbit, and Ajax Using HTTP sniffer tools Using Web developer plugins in interactive browsers Interacting with DOM, screen scraping, etc. If there's no good tutorial, I'll add it to my list of things to do (unless someone else wants to do it :). Along the way, if you don't have a suggestion for an existing tutorial, please suggest the things that you think should be in a new one, including links, your favorite tools, and your own user-agent development experiences. I don't care about the particular language you use.

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  • How to avoid using this in a contructor

    - by Paralife
    I have this situation: interface MessageListener { void onMessageReceipt(Message message); } class MessageReceiver { MessageListener listener; public MessageReceiver(MessageListener listener, other arguments...) { this.listener = listener; } loop() { Message message = nextMessage(); listener.onMessageReceipt(message); } } and I want to avoid the following pattern: (Using the this in the Client constructor) class Client implements MessageListener { MessageReceiver receiver; MessageSender sender; public Client(...) { receiver = new MessageReceiver(this, other arguments...); sender = new Sender(...); } . . . @Override public void onMessageReceipt(Message message) { if(Message.isGood()) sender.send("Congrtulations"); else sender.send("Boooooooo"); } } The reason why i need the above functionality is because i want to call the sender inside the onMessageReceipt() function, for example to send a reply. But I dont want to pass the sender into a listener, so the only way I can think of is containing the sender in a class that implements the listener, hence the above resulting Client implementation. Is there a way to achive this without the use of 'this' in the constructor? It feels bizare and i dont like it, since i am passing myself to an object(MessageReceiver) before I am fully constructed. On the other hand, the MessageReceiver is not passed from outside, it is constructed inside, but does this 'purifies' the bizarre pattern? I am seeking for an alternative or an assurance of some kind that this is safe, or situations on which it might backfire on me.

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  • Hibernate: order multiple one-to-many relations

    - by Markos Fragkakis
    I have a search screen, using JSF, JBoss Seam and Hibernate underneath. There are columns for A, B and C, where the relations are as follows: A (1< -- ) B (1< -- ) C A has a List< B and B has a List< C (both relations are one-to-many). The UI table supports ordering by any column (ASC or DESC), so I want the results of the query to be ordered. This is the reason I used Lists in the model. However, I got an exception that Hibernate cannot eagerly fetch multiple bags (it considers both lists to be bags). There is an interesting blog post here, and they identify the following solutions: Use @IndexColumn annotation (there is none in my DB, and what's more, I want the position of results to be determined by the ordering, not by an index column) Fetch lazily (for performance reasons, I need eager fetching) Change List to Set So, I changed the List to Set, which by the way is more correct, model-wise. First, if don't use @OrderBy, the PersistentSet returned by Hibernate wraps a HashSet, which has no ordering. Second, If I do use @OrderBy, the PersistentSet wraps a LinkedHashSet, which is what I would like, but the OrderBy property is hardcoded, so all other ordering I perform through the UI comes after it. I tried again with Sets, and used SortedSet (and its implementation, TreeSet), but I have some issues: I want ordering to take place in the DB, and not in-memory, which is what TreeSet does (either through a Comparator, or through the Comparable interface of the elements). Second, I found that there is the Hibernate annotation @Sort, which has a SortOrder.UNSORTED and you can also set a Comparator. I still haven't managed to make it compile, but I am still not convinced it is what I need. Any advice?

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  • Proof of library bug vs developer side application bug

    - by Paralife
    I have a problem with a specific java client library. I wont say here the problem or the name of the library because my question is a different one. Here is the situation: I have made a program that uses the library. The program is a class named 'WorkerThread' that extends Thread. To start it I have made a Main class that only contains a main() function that starts the thread and nothing else. The worker uses the library to perform comm with a server and get results. The problem appears when I want to run 2 WorkerThreads simultaneously. What I first did was to do this in the Main class: public class Main { public static void main(String args[]) { new WorkerThread().start(); // 1st thread. new WorkerThread().start(); // 2nd thread. } } When I run this, both threads produce irrational results and what is more , some results that should be received by 1st thread are received by the 2nd instead. If instead of the above, I just run 2 separate processes of one thread each, then everything works fine. Also: 1.There is no static class or method used inside WorkerThread that could cause the problem. My application consists of only the worker thread class and contains no static fields or methods 2.The library is supposed to be usable in a multithreaded environment. In my thread I just create a new instance of a library's class and then call methods on it. Nothing more. My question is this: Without knowing any details of my implementation, is the above situation and facts enough to prove that there is a bug in the library and not in my programm? Is it safe to assume that the library inside uses a static method or object that is indirectly shared by my 2 threads and this causes the problem? If no then in what hypothetical situation could the bug originate in the worker class code?

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  • How should I go about implementing a points-to analysis in Maude?

    - by reprogrammer
    I'm going to implement a points-to analysis algorithm. I'd like to implement this analysis mainly based on the algorithm by Whaley and Lam. Whaley and Lam use a BDD based implementation of Datalog to represent and compute the points-to analysis relations. The following lists some of the relations that are used in a typical points-to analysis. Note that D(w, z) :- A(w, x),B(x, y), C(y, z) means D(w, z) is true if A(w, x), B(x, y), and C(y, z) are all true. BDD is the data structure used to represent these relations. Relations input vP0 (variable : V, heap : H) input store (base : V, field : F, source : V) input load (base : V, field : F, dest : V) input assign (dest : V, source : V) output vP (variable : V, heap : H) output hP (base : H, field : F, target : H) Rules vP(v, h) :- vP0(v, h) vP(v1, h) :- assign(v1, v2), vP(v2, h) hP(h1, f,h2) :- store(v1, f, v2), vP(v1, h1), vP(v2, h2) vP(v2, h2) :- load(v1, f, v2), vP(v1, h1), hP(h1, f, h2) I need to understand if Maude is a good environment for implementing points-to analysis. I noticed that Maude uses a BDD library called BuDDy. But, it looks like that Maude uses BDDs for a different purpose, i.e. unification. So, I thought I might be able to use Maude instead of a Datalog engine to compute the relations of my points-to analysis. I assume Maude propagates independent information concurrently. And this concurrency could potentially make my points-to analysis faster than sequential processing of rules. But, I don't know the best way to represent my relations in Maude. Should I implement BDD in Maude myself, or Maude's internal unification based on BDD has the same effect?

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  • Implementing the ‘defer’ statement from Go in Objective-C?

    - by zoul
    Hello! Today I read about the defer statement in the Go language: A defer statement pushes a function call onto a list. The list of saved calls is executed after the surrounding function returns. Defer is commonly used to simplify functions that perform various clean-up actions. I thought it would be fun to implement something like this in Objective-C. Do you have some idea how to do it? I thought about dispatch finalizers, autoreleased objects and C++ destructors. Autoreleased objects: @interface Defer : NSObject {} + (id) withCode: (dispatch_block_t) block; @end @implementation Defer - (void) dealloc { block(); [super dealloc]; } @end #define defer(__x) [Defer withCode:^{__x}] - (void) function { defer(NSLog(@"Done")); … } Autoreleased objects seem like the only solution that would last at least to the end of the function, as the other solutions would trigger when the current scope ends. On the other hand they could stay in the memory much longer, which would be asking for trouble. Dispatch finalizers were my first thought, because blocks live on the stack and therefore I could easily make something execute when the stack unrolls. But after a peek in the documentation it doesn’t look like I can attach a simple “destructor” function to a block, can I? C++ destructors are about the same thing, I would create a stack-based object with a block to be executed when the destructor runs. This would have the ugly disadvantage of turning the plain .m files into Objective-C++? I don’t really think about using this stuff in production, I’m just interested in various solutions. Can you come up with something working, without obvious disadvantages? Both scope-based and function-based solutions would be interesting.

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  • MacBook Pro - Aquamacs - spell check

    - by peggy Li
    I have tried to use spell check for aquamac. I highlighted a region of the text. Then clicked Edit, then spell check region. I got the error message: Error : No word lists can be found for the language "en_US". Then I went to the website to download the following dictionaries: CocoAspell : I just clicked the download button. It was reported that the download was successful. However, when I tested it and highlighted a text region and clicked spell check. The same error message came out. Do I need to pull the downloaded .pkg to a certain place, such as the application folder, before I opened the .pkg? Or what else do I need to do make it work? I also downloaded the base package Aspell (for Intel) and the pre-built dictionaries as (as the instruction of the website), just the same way as point 1. I still got the same error message. Again, Do I need to pull the downloaded .pkg to a certain place, such as the application folder, before I opened the .pkg? Or what else do I need to do make it work? I would be greatly appreciated if someone could give me some help? Peggy Li

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