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• What is the best way to iterate over a large result set in JDBC/iBatis 3?

  - by paul_sns

  We're trying to iterate over a large number of rows from the database and convert those into objects. Behavior will be as follows: Result will be sorted by sequence id, a new object will be created when sequence id changes. The object created will be sent to an external service and will sometimes have to wait before sending another one (which means the next set of data will not be immediately used) We already have invested code in iBatis 3 so an iBatis solution will be the best approach for us (we've tried using RowBounds but haven't seen how it does the iteration under the hood). We'd like to balance minimizing memory usage and reducing number of DB trips. We're also open to pure JDBC approach but we'd like the solution to work on different databases. UPDATE: We need to make as few calls to DB as possible (1 call would be the ideal scenario) while also preventing the application to use too much memory. Are there any other solutions out there for this type of problem may it be pure JDBC or any other technology? Thanks and hope to hear your insights on this.

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• Debugging in VS 2008 locks a stored procedure

  - by larryq

  Hi everyone, I've got a strange one here. I have a .Net executable that, under the hood, calls a few stored procedures. For whatever reason, one of the stored procs hangs when I'm debugging. If I run the executable outside of visual studio things go fine, including this stored proc. It's when I'm debugging that this hangs, and it really hangs. If I stop the debugging session the IDE freezes and I have to kill it via taskmanager. I know which stored procedure has the trouble, as well as the actual statement within it that's the problem. It's calling an update statement that doesn't stand out as particularly special. I can run the identical statement (and the stored procedure itself) from SQL management studio wtih no problem. And, as I mentioned, the exe runs just fine outside the debugger. If I use the SQL activity monitor to see why things are hanging, the wait type says PREEMPTIVE_DEBUG. I'm not sure if that's helpful but if you need more info I'll try to get it to you. I've rebooted my machine (the SQL Server in question is on this box as well) and that didn't do anything, nor did rebuilding the executable. I'm scratching my head on this one and if you have any ideas what to check on next, I'm be happy to listen. Thanks!

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• Does git clone work through NTLM proxies?

  - by AndreaG

  I've tried both using export http_proxy=http://[username]:[pwd]@[proxy] and git config --global http.proxy http://[username]:[pwd]@[proxy]. I couldn't make it work. It looks like git uses Basic authentication: Initialized empty Git repository in /home/.../.git/ * Couldn't find host github.com in the .netrc file, using defaults * About to connect() to github.com port 8080 (#0) * Trying 10.... * Connected to github.com (10....) port 8080 (#0) * Proxy auth using Basic with user '...' > GET http://github.com/sunlightlabs/fiftystates.git/info/refs HTTP/1.1 Proxy-Authorization: Basic MD... User-Agent: git/1.6.1.2 Host: github.com Pragma: no-cache Accept: */* Proxy-Connection: Keep-Alive < HTTP/1.1 407 Proxy Authentication Required ( The ISA Server requires authorization to fulfill the request. Access to t he Web Proxy filter is denied. ) < Via: 1.1 ... < Proxy-Authenticate: Negotiate < Proxy-Authenticate: Kerberos < Proxy-Authenticate: NTLM < Connection: Keep-Alive < Proxy-Connection: Keep-Alive < Pragma: no-cache < Cache-Control: no-cache < Content-Type: text/html < Content-Length: 4118 * The requested URL returned error: 407 * Closing connection #0 fatal: http://github.com/sunlightlabs/fiftystates.git/info/refs download error - The requested URL returned error: 407 Google search returned mixed and probably not updated results. Somewhere it says that curl is (was?) used under the hood, but its options are (were?) hardwired into code. For example, curl --proxy-ntlm --proxy ...:8080 google.com works, and I'd like to use the same option with git. I need some more definite answers here: has anybody succeed using git through Windows proxies? Which version? Thanks.

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• What is actually happening to this cancelled HTTP request?

  - by Brian Schroth

  When a user takes a particular action on a page, an AJAX call is made to save their data. Unfortunately, this call is synchronous as they need to wait to see if the data is valid before being allowed to continue. Obviously, this eliminates a lot of the benefit of using Asynchronous Javascript And XML, but that's a subject for another post. That's the design I'm working with. The request is made using the dojo.xhrPost function, with a 60s timeout parameter, and the error handler redirects to an error page. What I am finding in testing is that in Firefox, if I initiate the ajax request and then press ESC, the page hangs waiting for a response, and then eventually after exactly 90s (not 60s, the function's timeout), the error handler will kick in and redirect to the error page. I expected this to happen, but either immediately as soon as the request was cancelled, or after 60s due to the timeout value being 60s. What I don't understand is why is it 90s? What is actually happening under the hood when the user cancels their request in Firefox, and how does it differ from IE, where everything works fine exactly the same as if the request had not been cancelled? Is the 90s related to any user-configurable browser settings?

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• Git as mercurial client? Why no git-hg?

  - by aapeli

  This is a question that's been bothering me for a while. I've done my homework and checked stackoverflow and found at least these two topics about my question: Git for Mercurial like git-svn and Git interoperability with a Mercurial repository I've done some serious googling to solve this issue, but so far with no luck. I've also read the Git Internals book, and the Mercurial Definitive Behind the Scenes to try to figure this out. I'm still a bit puzzled why I haven't been able to find any suitable git-hg type of a tool. From my perspective hg-svn is one of the main features, why I've chosen to use git over mercurial also at work. It allows me to use a workflow I like, and nobody else needs to bother, if they don't care. I just don't see the point in using the intermediate hg repo to convert back and forth, as suggested in one of the chains. So anyway, from what I've read hg and git seem very similar in conceptual design. There are differences under the hood, but none of those should prevent creating a git client for hg. As it seems to me, remote tracking branches and octopus merges make git even more powerful than hg is. So, the real question, is there any real reason why git-hg does not exist (or at least is very hard to find)? Is there some animosity from git users (and developers) towards their hg counterparts that has caused the lack of the git-hg tool? Do any of you have any plans to develop something like this, and go public with it? I could volunteer (although with very feeble C-skills) to participate to get this done. I just don't possess the full knowledge to start this up myself. Could this be the tool to end all DVCS wars for good?

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• How to Store State in Silverlight WCF RIA Services

  - by peter

  Hi All, I am developing a silverlight 3 application using WCF RIA services. I am using the AuthenticationBase class to handle my authentication. As I understand it under the hood this uses the ASP .NET authentication libraries. When I log into the site the authentication service handles login state so that if I close the site and open it straight away I am still logged in according to the server. When the webpage is refreshed or closed and reloaded I can call the method, WebContextBase.Current.Authentication.LoadUser() And it goes back to the authentication service (running on the server) and figures out whether I am still logged into the site. If a timeout has occured the answer will be no. If that is the case I can show a login dialog. The problem I want to solve is that the authentication service consumes the password, and there is no way I can ever retrieve that password again. If the user logs into the site I want to store the password on the server, and return a token to the client side to match up with that password. I have some other services on the server side that need that password. So where should I store that password on the server? How can that be done? How does the WCF authentication store state?

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• Rails: Multi-Step New User Signup Form (FSM?)

  - by neezer

  I've read the "Create Multi-Step Wizard" in Advanced Rails Recipes. I've also read and re-read the documentation for the updated FSM I'm using called Workflow, and looked here and here. The Advanced Rails Recipe focuses on records (quizzes) that already exist, and doesn't cover creating new ones. The Workflow docs don't cover any code for controllers or views, so I've no idea what to do with all this model magic, and the last two links barely touch on implementation either. From the aforementioned resources, I have a good understanding of what a FSM in Rails is and how to play with it in the console or IRB, but I've got very little direction or understanding how to implement one into my Rails app. What I would like is this: a simple, multi-step user signup process. Step 1: User enters in their critical details (with validations). Step 2: User enters in their search criteria, for their profile (with validations). Step 3: User agrees to the Terms of Service (with validations). Step 4: User is greeted by a confirmation page, including a link that takes them to their newly created account. I'd also like full navigation between the steps and full capture (saves to the database) with each transition. Can someone please give me a clear implementation of something similar to this? I would LOVE an example app that includes a multi-step signup process where I can look at the code (FULL source code--models AND controllers and views) under the hood, but I've been unable to find anything like that. Any guidance would be appreciated! EDIT: Please help make this a Railscast! Ryan B. (a.k.a. Superman), if you're reading this, we need you! http://feedback.railscasts.com/forums/77-episode-suggestions/suggestions/35553-multi-step-forms-and-wizards

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• Is my method for avoiding dynamic_cast<> faster than dynamic_cast<> itself ?

  - by ereOn

  Hi, I was answering a question a few minutes ago and it raised to me another one: In one of my projects, I do some network message parsing. The messages are in the form of: [1 byte message type][2 bytes payload length][x bytes payload] The format and content of the payload are determined by the message type. I have a class hierarchy, based on a common class Message. To instanciate my messages, i have a static parsing method which gives back a Message* depending on the message type byte. Something like: Message* parse(const char* frame) { // This is sample code, in real life I obviously check that the buffer // is not NULL, and the size, and so on. switch(frame[0]) { case 0x01: return new FooMessage(); case 0x02: return new BarMessage(); } // Throw an exception here because the mesage type is unknown. } I sometimes need to access the methods of the subclasses. Since my network message handling must be fast, I decived to avoid dynamic_cast<> and I added a method to the base Message class that gives back the message type. Depending on this return value, I use a static_cast<> to the right child type instead. I did this mainly because I was told once that dynamic_cast<> was slow. However, I don't know exactly what it really does and how slow it is, thus, my method might be as just as slow (or slower) but far more complicated. What do you guys think of this design ? Is it common ? Is it really faster than using dynamic_cast<> ? Any detailed explanation of what happen under the hood when one use dynamic_cast<> is welcome !

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• Which are the RDBMS that minimize the server roundtrips? Which RDBMS are better (in this area) than

  - by user193655

  When the latency is high ("when pinging the server takes time") the server roundtrips make the difference. Now I don't want to focus on the roundtrips created in programming, but the roundtrips that occur "under the hood" in the DB engine, so the roundtrips that are 100% dependant on how the RDBMS is written itself. I have been told that FireBird has more roundtrips than MySQL. But this is the only information I know. I am currently supporting MS SQL but I'd like to change RDBMS (because I use Express Editions and in my scenario they are quite limiting from the performance point of view), so to make a wise choice I would like to include also this point into "my RDBMS comparison feature matrix" to understand which is the best RDBMS to choose as an alternative to MS SQL. So the bold sentence above would make me prefer MySQL to Firebird (for the roundtrips concept, not in general), but can anyone add informations? And MS SQL where is it located? Is someone able to "rank" the roundtrip performance of the main RDBMS, or at least: MS SQL, MySql, Postegresql, Firebird (I am not interested in Oracle since it is not free, and if I have to change I would change to a free RDBMS). Anyway MySql (as mentioned several times on stackoverflow) has a not clear future and a not 100% free license. So my final choice will probably dall on PostgreSQL or Firebird. Additional info: somehow you can answer my question by making a simple list like: MSSQL:3; MySQL:1; Firebird:2; Postgresql:2 (where 1 is good, 2 average, 3 bad). Of course if you can post some links where the roundtrips per RDBMSs are compared it would be great

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• What can cause my code to run slower when the server JIT is activated?

  - by durandai

  I am doing some optimizations on an MPEG decoder. To ensure my optimizations aren't breaking anything I have a test suite that benchmarks the entire codebase (both optimized and original) as well as verifying that they both produce identical results (basically just feeding a couple of different streams through the decoder and crc32 the outputs). When using the "-server" option with the Sun 1.6.0_18, the test suite runs about 12% slower on the optimized version after warmup (in comparison to the default "-client" setting), while the original codebase gains a good boost running about twice as fast as in client mode. While at first this seemed to be simply a warmup issue to me, I added a loop to repeat the entire test suite multiple times. Then execution times become constant for each pass starting at the 3rd iteration of the test, still the optimized version stays 12% slower than in the client mode. I am also pretty sure its not a garbage collection issue, since the code involves absolutely no object allocations after startup. The code consists mainly of some bit manipulation operations (stream decoding) and lots of basic floating math (generating PCM audio). The only JDK classes involved are ByteArrayInputStream (feeds the stream to the test and excluding disk IO from the tests) and CRC32 (to verify the result). I also observed the same behaviour with Sun JDK 1.7.0_b98 (only that ist 15% instead of 12% there). Oh, and the tests were all done on the same machine (single core) with no other applications running (WinXP). While there is some inevitable variation on the measured execution times (using System.nanoTime btw), the variation between different test runs with the same settings never exceeded 2%, usually less than 1% (after warmup), so I conclude the effect is real and not purely induced by the measuring mechanism/machine. Are there any known coding patterns that perform worse on the server JIT? Failing that, what options are available to "peek" under the hood and observe what the JIT is doing there?

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• Is this a hole in dynamic binding in C# 4?

  - by Galilyou

  I've seen a very interesting post on Fabio Maulo's blog. Here's the code and the bug if you don't want to jump to the url. I defined a new generic class like so: public class TableStorageInitializer<TTableEntity> where TTableEntity : class, new() { public void Initialize() { InitializeInstance(new TTableEntity()); } public void InitializeInstance(dynamic entity) { entity.PartitionKey = Guid.NewGuid().ToString(); entity.RowKey = Guid.NewGuid().ToString(); } } Note that InitializeInstance accepts one parameter, which is of type dynamic. Now to test this class, I defined another class that is nested inside my main Program class like so: class Program { static void Main(string[] args) { TableStorageInitializer<MyClass> x = new TableStorageInitializer<MyClass>(); x.Initialize(); } private class MyClass { public string PartitionKey { get; set; } public string RowKey { get; set; } public DateTime Timestamp { get; set; } } } Note: the inner class "MyClass" is declared private. Now if i run this code I get a "Microsoft.CSharp.RuntimeBinder.RuntimeBinderException" on the line "entity.PartitionKey = Guide.NewGuid().ToString()". The interesting part, though is that the message of the exception says "Object doesn't contain a definition for PartitionKey". Also note that if you changed the modifier of the nested class to public, the code will execute with no problems. So what do you guys think is really happening under the hood? Please refer to any documentation -of course if this is documented anywhere- that you may find?

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• How do i write tasks? (parallel code)

  - by acidzombie24

  I am impressed with intel thread building blocks. I like how i should write task and not thread code and i like how it works under the hood with my limited understanding (task are in a pool, there wont be 100 threads on 4cores, a task is not guaranteed to run because it isnt on its own thread and may be far into the pool. But it may be run with another related task so you cant do bad things like typical thread unsafe code). I wanted to know more about writing task. I like the 'Task-based Multithreading - How to Program for 100 cores' video here http://www.gdcvault.com/sponsor.php?sponsor_id=1 (currently second last link. WARNING it isnt 'great'). My fav part was 'solving the maze is better done in parallel' which is around the 48min mark (you can click the link on the left side. That part is really all you need to watch if any). However i like to see more code examples and some API of how to write task. Does anyone have a good resource? I have no idea how a class or pieces of code may look after pushing it onto a pool or how weird code may look when you need to make a copy of everything and how much of everything is pushed onto a pool.

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• Is there a JSON library that can serialize Proxy objects?

  - by gmoore

  Using ActiveObjects as my ORM and Gson as my JSON processor. Ran into a problem going toJson from persisted objects. The problem is that my persisted class is actually an Interface and AO is proxying that object under the hood. Here's some sample code: Venue venue = manager.get(Venue.class, id); gson.toJson(venue); Comes up with this exception: java.lang.UnsupportedOperationException: Expecting parameterized type, got interface java.lang.reflect.InvocationHandler. Are you missing the use of TypeToken idiom? See http://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and... Because venue.getClass().getName() gives: $Proxy228 I've tried a few solutions in various combinations: gsonBuilder.registerTypeAdapter(Venue.class, newVenueSerializer()); Type listType = new TypeToken<Venue>() {}.getType(); Nothing has worked so far and I'm using a wonky field-by-field workaround. Any suggestions? I'm not married to Gson, so if there's an alternative library that can do this I'd be happy to use it.

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• ObjC internals. Why my duck typing attempt failed?

  - by Piotr Czapla

  I've tried to use id to create duck typing in objective-c. The concept looks fine in theory but failed in practice. I was unable to use any parameters in my methods. The methods were called but parameters were wrong. I was getting BAD_ACESS for objects and random values for primitives. I've attached a simple example below. The question: Does any one knows why the methods parameters are wrong? What is happening under the hood of the objective-c? Note: I'm interest in the details. I know how to make the example below work. An example: I've created a simple class Test that is passed to an other class using property id test. @implementation Test - (void) aSampleMethodWithFloat:(float) f andInt: (int) i { NSLog(@"Parameters: %f, %i\n", f, i); } @end Then in the class the following loop is executed: for (float f=0.0f; f < 100.0f ; f += 0.3f) { [self.test aSampleMethodWithOneFloatParameter: f]; // warning: no method found. } Here is the output that I'm getting. As you can see the method was called but the parameters were wrong. Parameters: 0.000000, 0 Parameters: -0.000000, 1069128089 Parameters: -0.000000, 1070176665 Parameters: 2.000000, 1070805811 Parameters: -0.000000, 1071225241 Parameters: 0.000000, 1071644672 Parameters: 2.000000, 1071854387 Parameters: 36893488147419103232.000000, 1072064102 Parameters: -0.000000, 1072273817 Parameters: -36893488147419103232.000000, 1072483532

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• How do i write task? (parallel code)

  - by acidzombie24

  I am impressed with intel thread building blocks. I like how i should write task and not thread code and i like how it works under the hood with my limited understanding (task are in a pool, there wont be 100 threads on 4cores, a task is not guaranteed to run because it isnt on its own thread and may be far into the pool. But it may be run with another related task so you cant do bad things like typical thread unsafe code). I wanted to know more about writing task. I like the 'Task-based Multithreading - How to Program for 100 cores' video here http://www.gdcvault.com/sponsor.php?sponsor_id=1 (currently second last link. WARNING it isnt 'great'). My fav part was 'solving the maze is better done in parallel' which is around the 48min mark (you can click the link on the left side). However i like to see more code examples and some API of how to write task. Does anyone have a good resource? I have no idea how a class or pieces of code may look after pushing it onto a pool or how weird code may look when you need to make a copy of everything and how much of everything is pushed onto a pool.

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• Why is BorderLayout calling setSize() and setBounds()?

  - by ags

  I'm trying to get my head around proper use of the different LayoutManagers to make my GUI design skills more efficient and effective. For me, that usually requires a detailed understanding of what is going on under the hood. I've found some good discussion of the interaction and consequences of a Container using BorderLayout containing a Container using FlowLayout. I understand it for the most part, but wanted to confirm my mental model and to do so I am looking at the code for BorderLayout. In the code snippet below taken from BorderLayout.layoutContainer(), note the calls to the child Component's setSize() method followed by setBounds(). Looking at the source for these methods of Component, setSize() actually calls setBounds() with the current values for Component.x and Component.y. Why is this done (and not entirely redudant?) Doesn't the setBounds() call completely overwrite the results of the setSize() call? if ((c=getChild(NORTH,ltr)) != null) { c.setSize(right - left, c.height); Dimension d = c.getPreferredSize(); c.setBounds(left, top, right - left, d.height); top += d.height + vgap; } I'm also tring to understand where/when the child Component's size is initially set (before the LayoutManager.layoutContainer() method is called). Finally, this post itself raises a "meta-question": in a situation like this, where the source is available elsewhere, is the accepteed protocol to include the entire method? Or some other way to make it easier for folks to participate in the thread? Thanks.

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• How to properly load HTML data from third party website using MVC+AJAX?

  - by Dmitry

  I'm building ASP.NET MVC2 website that lets users store and analyze data about goods found on various online trade sites. When user is filling a form to create or edit an item, he should have a button "Import data" that automatically fills some fields based on data from third party website. The question is: what should this button do under the hood? I see at least 2 possible solutions. First. Do the import on client side using AJAX+jQuery load method. I tried it in IE8 and received browser warning popup about insecure script actions. Of course, it is completely unacceptable. Second. Add method ImportData(string URL) to ItemController class. It is called via AJAX, does the import + data processing server-side and returns JSON-d result to client. I tried it and received server exception (503) Server unavailable when loading HTML data into XMLDocument. Also I have a feeling that dealing with not well-formed HTML (missing closing tags, etc.) will be a huge pain. Any ideas how to parse such HTML documents?

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• What happens when we say "listen to a port" ?

  - by smwikipedia

  Hi, When we start a server application, we always need to speicify the port number it listens to. But how is this "listening mechanism" implemented under the hood? My current imagination is like this: The operating system associate the port number with some buffer. The server application's responsibiligy is to monitor this buffer. If there's no data in this buffer, the server application's listen operation will just block the application. When some data arrives from the wire, the operating system will know that check the data and see if it is targed at this port number. And then it will fill the buffer. And then OS will notify the blocked server application and the server application will get the data and continue to run. Question is: If the above scenario is correct, how could the opearting system know there's data arriving from wire? It cannot be a busy pooling. Is it some kind of interrupt-based mechanism? If there's too much data arriving and the buffer is not big enough, will there be data loss? Is the "listen to a port" operation really a blocking operation? Many thanks.

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• I'm graduating with a Computer Science degree but I don't feel like I know how to program.

  - by Wendy Peters

  I'm graduating with a Computer Science degree but I see websites like Stackoverflow and search engines like Google and don't know where I'd even begin to write something like that. During one summer I worked as a iPhone developer, but I felt like I was mostly gluing together libraries that other people had written with little understanding of what's happening underneath the hood. I'm trying to improve my knowledge by studying algorithms, but it is a long and painful process. I find algorithms difficult and at the rate I am working through my book it will a decade will have passed before I will finish. Given my current situation, I've spent a month looking for work but my skills (C, Python, Objective-C) are not so desirable in the local market, where C#, Java, and web development are much higher in demand. My GPA is ok (3.0) but it's not high enough to apply to the large companies or return for graduate studies and I don't have a good network of friends. Basically I'm graduating with a Computer Science degree but I don't feel like I know how to program. I thought that joining a company and programming full-time would give me a chance to develop my skills and learn from those more experienced than myself, but I'm struggling to find work and am starting to get really frustrated. I am going to cast my net wider and look beyond the city I've grown up in, but what have other people in similar situation tried to do?

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• Javascript XMLHttpRequest Post method

  - by user535617

  Hey So I have a question about posting using an XMLHttpRequest. In theory, if I am to post a username and password to an https domain (which I have yet to get working, unfortunately) would the responseText then change to the next website, or should the text fields become filled in? What normally happens is you navigate to this page via browser, enter a username and password, and it uses a POST method when the submit button is clicked, doing some authentication under the hood and returning a different page. I feel like maybe the responseText should even stay exactly the same (which is what happens now), but I don't know as I have no experience with this kind of thing. this.requests[1].open("POST", "https://" + this.address, true); var query = "target=%2Fcgi-bin%2FStatusConfig.cgi%3FPage%3Dindex&userfile=&username=user&password=pass&log+in=Log+in"; this.requests[1].setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); this.requests[1].setRequestHeader("Content-length", query.length); this.requests[1].setRequestHeader("Keep-Alive", 115); this.requests[1].setRequestHeader("Connection", "keep-alive"); this.requests[1].setRequestHeader("Host", this.address); this.requests[1].send(query); this.requests[1].onreadystatechange = onReadyStateChange1; Then basically onReadyStateChange1 displays the responseText when ready. Any light that could be shed on what SHOULD be happening with the post and responseText would be very appreciated. As would any advice in getting the new, logged into page. For further clarification, what I'm trying to do is log in and then return the new page, because the login page displays only log in information/functionality and the page after logging in has a lot of relevant information. I'm not trying to check the credentials as much as I'm trying to get it (the script) to log in so it can access the next page. Granted, the credentials will have to be valid for that. Thanks all.

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• Best (Java) book for understanding 'under the bonnet' for programming?

  - by Ben

  What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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• JPA - Can an @JoinColumn be an @Id as well? SerializationException occurs.

  - by Shivago

  Hi everyone, I am trying to use an @JoinColumn as an @Id using JPA and I am getting SerializationExceptions, "Could not serialize." UserRole.java: @Entity @Table(name = "authorities") public class UserRole implements Serializable { @Column(name = "authority") private String role; @Id @ManyToOne @JoinColumn(name = "username") private User owner; ... } User.java: @Entity @Table(name = "users") public class User implements Serializable { @Id @GeneratedValue protected Long id; @Column(name = "username") protected String email; @OneToMany(mappedBy = "owner", fetch = FetchType.LAZY, cascade = CascadeType.ALL) protected Set<UserRole> roles = new HashSet<UserRole>(); .... } "username" is set up as a unique index in my Users table but not as the primary key. Is there any way to make "username" act as the ID for UserRole? I don't want to introduce a numeric key in UserRole. Have I totally lost the plot here? I am using MySQL and Hibernate under the hood.

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• How do software events work internally?

  - by Duddle

  Hello! I am a student of Computer Science and have learned many of the basic concepts of what is going on "under the hood" while a computer program is running. But recently I realized that I do not understand how software events work efficiently. In hardware, this is easy: instead of the processor "busy waiting" to see if something happened, the component sends an interrupt request. But how does this work in, for example, a mouse-over event? My guess is as follows: if the mouse sends a signal ("moved"), the operating system calculates its new position p, then checks what program is being drawn on the screen, tells that program position p, then the program itself checks what object is at p, checks if any event handlers are associated with said object and finally fires them. That sounds terribly inefficient to me, since a tiny mouse movement equates to a lot of cpu context switches (which I learned are relatively expensive). And then there are dozens of background applications that may want to do stuff of their own as well. Where is my intuition failing me? I realize that even "slow" 500MHz processors do 500 million operations per second, but still it seems too much work for such a simple event. Thanks in advance!

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• XSL(like) declarative language as MVC view over strongtyped model?

  - by Martin Kool

  As a huge XSL fan, I am very happy to use xsl as the view in our proprietary MVC framework on ASP.NET. Objects in the model are serialized under the hood using .NET's xml serializer, and we use quite atomic xsl templates to declare how each object or property should transform. For example: <xsl:template match="/Article"> <html> <body> <div class="article"> <xsl:apply-templates /> </div> </body> </html> </xsl:template> <xsl:template match="Article/Title"> <h1> <xsl:apply-templates /> </h1> </xsl:template> <xsl:template match="@*|text()"> <xsl:copy /> </xsl:template> This mechanism allows us to quickly override default matching templates, like having a template matching on the last item in a list, or the selected one, etc. Also, xsl extension objects in .NET allow us just the bit of extra grip that we need. Common shared templates can be split up and included. However Even though I can ignore the verbosity downside of xsl (because Visual Studio schema intellisense + snippets really is slick, praise to the VS-team), the downside of not having intellisense over strongtyped objects in the model is really something that's bugging me. I've seen ASP.NET MVC + user controls in action and really starting to love it, but I wonder; Is there a way of getting some sort of intellisense over XML that we're iterating over, or do you know of a language that offers the freedom and declarativeness of XSL but has the strongtype/intellisense benefits of say webforms/usercontrols/asp.net.mvc-view? (I probably know the answer: "no", and I'll find myself using Phil Haack's utterly cool mvc shizzle soon...)

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• How do I call C++/CLI (.NET) DLLs from standard, unmanaged non-.NET applications?

  - by tronjohnson

  In the unmanaged world, I was able to write a __declspec(dllexport) or, alternatively, use a .DEF file to expose a function to be able to call a DLL. (Because of name mangling in C++ for the __stdcall, I put aliases into the .DEF file so certain applications could re-use certain exported DLL functions.) Now, I am interested in being able to expose a single entry-point function from a .NET assembly, in unmanaged-fashion, but have it enter into .NET-style functions within the DLL. Is this possible, in a simple and straight-forward fashion? What I have is a third-party program that I have extended through DLLs (plugins) that implement some complex mathematics. However, the third-party program has no means for me to visualize the calculations. I want to somehow take these pre-written math functions, compile them into a separate DLL (but using C++/CLI in .NET), but then add hooks to the functions so I can render what's going on under the hood in a .NET user control. I'm not sure how to blend the .NET stuff with the unmanaged stuff, or what to Google to accomplish this task. Specific suggestions with regard to the managed/unmanaged bridge, or alternative methods to accomplish the rendering in the manner I have described would be helpful. Thank you.

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