If you cast to an HttpURLConnection, there is a [disconnect()][1] method. If the connection is idle, it will probably disconnect immediately. No guarantees.


  [1]: http://docs.oracle.com/javase/7/docs/api/java/net/HttpURLConnection.html#disconnect()

It depends on the specific protocol specified in the protocol. Some maintain persistent connections, other close their connections when your call close in the input or outputstream given by the connection. But other than remembering to closing the streams you opened from the URLConnection, there is nothing else you can do.

From the javadoc for java.net.URLConnection

&gt; Invoking the close() methods on the
&gt; InputStream or OutputStream of an
&gt; URLConnection after a request may free
&gt; network resources associated with this
&gt; instance, unless particular protocol
&gt; specifications specify different
&gt; behaviours for it.

I had to download several hunders of files at a time and meet the problem.

You may check your app&#39;s open descriptors with the following command:

    adb shell ps

Find your application PID in the list and use another command:

    adb shell run-as YOUR_PACKAGE_NAME ls -l  /proc/YOUR_PID/fd

I see about 150 open descriptors on a usual launch. And there are 700+ when files are downloading. Their number decreases only after some minutes, looks like Android frees them in the background, not when you can `close` on a stream.

So we can&#39;t be sure when the connection closes actually.

I&#39;ve got a bunch of properties which I am going to use read/write locks on. I can implement them either with a `try finally` or a `using` clause.

In the `try finally` I would acquire the lock before the `try`, and release in the `finally`. In the `using` clause, I would create a class which acquires the lock in its constructor, and releases in its Dispose method.

I&#39;m using read/write locks in a lot of places, so I&#39;ve been looking for ways that might be more concise than `try finally`. I&#39;m interested in hearing some ideas on why one way may not be recommended, or why one might be better than another.

Method 1 (`try finally`):

    static ReaderWriterLock rwlMyLock_m  = new ReaderWriterLock();
    private DateTime dtMyDateTime_m
    public DateTime MyDateTime
    {
        get
        {
            rwlMyLock_m .AcquireReaderLock(0);
            try
            {
                return dtMyDateTime_m
            }
            finally
            {
                rwlMyLock_m .ReleaseReaderLock();
            }
        }
        set
        {
            rwlMyLock_m .AcquireWriterLock(0);
            try
            {
                dtMyDateTime_m = value;
            }
            finally
            {
                rwlMyLock_m .ReleaseWriterLock();
            }
        }
    }

Method 2:

    static ReaderWriterLock rwlMyLock_m  = new ReaderWriterLock();
    private DateTime dtMyDateTime_m
    public DateTime MyDateTime
    {
        get
        {
            using (new ReadLock(rwlMyLock_m))
            {
                return dtMyDateTime_m;
            }
        }
        set
        {
            using (new WriteLock(rwlMyLock_m))
            {
                dtMyDateTime_m = value;
            }
        }
    }

    public class ReadLock : IDisposable
    {
        private ReaderWriterLock rwl;
        public ReadLock(ReaderWriterLock rwl)
        {
            this.rwl = rwl;
            rwl.AcquireReaderLock(0);
        }

        public void Dispose()
        {
            rwl.ReleaseReaderLock();
        }
    }

    public class WriteLock : IDisposable
    {
        private ReaderWriterLock rwl;
        public WriteLock(ReaderWriterLock rwl)
        {
            this.rwl = rwl;
            rwl.AcquireWriterLock(0);
        }

        public void Dispose()
        {
            rwl.ReleaseWriterLock();
        }
    }


&#39;using&#39; statement vs &#39;try finally&#39;

Trends data from Twitter Search API in JSON.

Grabbing the file using:

    $jsonurl = &quot;http://search.twitter.com/trends.json&quot;;
    $json = file_get_contents($jsonurl,0,null,null);
    $json_output = json_decode($json);

How do I work with data from this object. As an array? Only really need to extract data from the [name] values.

JSON object contains:

    stdClass Object
    (
        [trends] =&gt; Array
            (
                [0] =&gt; stdClass Object
                    (
                        [name] =&gt; Vote
                        [url] =&gt; http://search.twitter.com/search?q=Vote
                    )
    
                [1] =&gt; stdClass Object
                    (
                        [name] =&gt; Halloween
                        [url] =&gt; http://search.twitter.com/search?q=Halloween
                    )
    
                [2] =&gt; stdClass Object
                    (
                        [name] =&gt; Starbucks
                        [url] =&gt; http://search.twitter.com/search?q=Starbucks
                    )
    
                [3] =&gt; stdClass Object
                    (
                        [name] =&gt; #flylady
                        [url] =&gt; http://search.twitter.com/search?q=%23flylady
                    )
    
                [4] =&gt; stdClass Object
                    (
                        [name] =&gt; #votereport
                        [url] =&gt; http://search.twitter.com/search?q=%23votereport
                    )
    
                [5] =&gt; stdClass Object
                    (
                        [name] =&gt; Election Day
                        [url] =&gt; http://search.twitter.com/search?q=%22Election+Day%22
                    )
    
                [6] =&gt; stdClass Object
                    (
                        [name] =&gt; #PubCon
                        [url] =&gt; http://search.twitter.com/search?q=%23PubCon
                    )
    
                [7] =&gt; stdClass Object
                    (
                        [name] =&gt; #defrag08
                        [url] =&gt; http://search.twitter.com/search?q=%23defrag08
                    )
    
                [8] =&gt; stdClass Object
                    (
                        [name] =&gt; Melbourne Cup
                        [url] =&gt; http://search.twitter.com/search?q=%22Melbourne+Cup%22
                    )
    
                [9] =&gt; stdClass Object
                    (
                        [name] =&gt; Cheney
                        [url] =&gt; http://search.twitter.com/search?q=Cheney
                    )
    
            )
    
        [as_of] =&gt; Mon, 03 Nov 2008 21:49:36 +0000
    )

Handling data in a PHP JSON Object

When does java let go of a connections to a URL? I don&#39;t see a close() method on either URL or URLConnection so does it free up the connection as soon as the request finishes? I&#39;m mainly asking to see if I need to do any clean up in an exception handler.

    try {
      URL url = new URL(&quot;http://foo.bar&quot;);
      URLConnection conn = url.openConnection();
      // use the connection
    }
    catch (Exception e) {
      // any clean up here?
    }


In Java when does a URL connection close?

When does java let go of a connections to a URL? I don't see a close() method on either URL or URLConnection so does it free up the connection as soon as the request finishes? I'm mainly asking to see if I need to do any clean up in an exception handler.
<pre><code class="hljs language-java">try {
 URL url = new URL("http://foo.bar");
 URLConnection conn = url.openConnection();
 // use the connection
}
catch (Exception e) {
 // any clean up here?
}
</code></pre>

Seems likes it might be useful to have the assert display a message when an assertion fails.

Currently an `AssertionError` gets thrown, can you specify a custom message for it?

Can you show an example mechanism for doing this (other than creating your own exception type and throwing it)?

Can java&#39;s assert statement allow you to specify a message?

Is there a better way of getting this result? This function fails if num has more digits than digits, and I feel like it should be in the library somewhere (like Integer.toString(x,&quot;%3d&quot;) or something)

    static String intToString(int num, int digits) {
        StringBuffer s = new StringBuffer(digits);
        int zeroes = digits - (int) (Math.log(num) / Math.log(10)) - 1; 
        for (int i = 0; i &lt; zeroes; i++) {
            s.append(0);
        }
        return s.append(num).toString();
    }

Add leading zeroes to number in Java?

I have the string 

    a.b.c.d

I want to count the occurrences of &#39;.&#39; in an idiomatic way, preferably a one-liner.

(Previously I had expressed this constraint as &quot;without a loop&quot;, in case you&#39;re wondering why everyone&#39;s trying to answer without using a loop).

How do I count the number of occurrences of a char in a String?

How can I continuously capture images from a webcam?

I want to experiment with object recognition (by maybe using java media framework). 

I was thinking of creating two threads

one thread:

  - Node 1: capture live image
  - Node 2: save image as &quot;1.jpg&quot;
  - Node 3: wait 5 seconds
  - Node 4: repeat...

other thread:

  - Node 1: wait until image is captured
  - Node 2: using the &quot;1.jpg&quot; get colors
    from every pixle
  - Node 3: save data in arrays
  - Node 4: repeat...



Capturing image from webcam in java?

[bCrypt&#39;s javadoc][1] has this code for how to encrypt a password:

    String pw_hash = BCrypt.hashpw(plain_password, BCrypt.gensalt()); 

To check whether a plaintext password matches one that has been hashed previously, use the checkpw method:

    if (BCrypt.checkpw(candidate_password, stored_hash))
        System.out.println(&quot;It matches&quot;);
    else
        System.out.println(&quot;It does not match&quot;);

These code snippets imply to me that the randomly generated salt is thrown away. Is this the case, or is this just a misleading code snippet?


  [1]: http://www.mindrot.org/files/jBCrypt/jBCrypt-0.2-doc/

Do I need to store the salt with bcrypt?

What is the most elegant way to check if the directory a file is going to be written to exists, and if not, create the directory using Python? Here is what I tried:

    import os

    file_path = &quot;/my/directory/filename.txt&quot;
    directory = os.path.dirname(file_path)

    try:
        os.stat(directory)
    except:
        os.mkdir(directory)
    
    f = file(filename)

Somehow, I missed `os.path.exists` (thanks kanja, Blair, and Douglas). This is what I have now:

    def ensure_dir(file_path):
        directory = os.path.dirname(file_path)
        if not os.path.exists(directory):
            os.makedirs(directory)

Is there a flag for `open()`, that makes this happen automatically?


How can I safely create a nested directory?

Question:  Is exception handling in Java actually slow?

Conventional wisdom, as well as a lot of Google results, says that exceptional logic shouldn&#39;t be used for normal program flow in Java.  Two reasons are usually given,

1. it is really slow - even an order of magnitude slower than regular code (the reasons given vary),  

and 

2. it is messy because people expect only errors to be handled in exceptional code.  

This question is about #1.

As an example, [this page][1] describes Java exception handling as &quot;very slow&quot; and relates the slowness to the creation of the exception message string - &quot;this string is then used in creating the exception object that is thrown. This is not fast.&quot;  The article [Effective Exception Handling in Java][2] says that &quot;the reason for this is due to the object creation aspect of exception handling, which thereby makes throwing exceptions inherently slow&quot;.  Another reason out there is that the stack trace generation is what slows it down.

My testing (using Java 1.6.0_07, Java HotSpot 10.0, on 32 bit Linux), indicates that exception handling is no slower than regular code.  I tried running a method in a loop that executes some code.  At the end of the method, I use a boolean to indicate whether to *return* or *throw*.  This way the actual processing is the same. I tried running the methods in different orders and averaging my test times, thinking it may have been the JVM warming up.  In all my tests, the throw was at least as fast as the return, if not faster (up to 3.1% faster).  I am completely open to the possibility that my tests were wrong, but I haven&#39;t seen anything out there in the way of the code sample, test comparisons, or results in the last year or two that show exception handling in Java to actually be slow.

What leads me down this path was an API I needed to use that threw exceptions as part of normal control logic.  I wanted to correct them in their usage, but now I may not be able to.  Will I instead have to praise them on their forward thinking?

In the paper [Efficient Java exception handling in just-in-time compilation][3], the authors suggest that the presence of exception handlers alone, even if no exceptions are thrown, is enough to prevent the JIT compiler from optimizing the code properly, thus slowing it down.  I haven&#39;t tested this theory yet.


  [1]: http://leepoint.net/notes-java/flow/exceptions/03exceptions.html
  [2]: http://adtmag.com/articles/2000/08/22/effective-exception-handling-in-java.aspx
  [3]: http://portal.acm.org/citation.cfm?id=337453

What are the effects of exceptions on performance in Java?

I keep seeing people say that exceptions are slow, but I never see any proof. So, instead of asking if they are, I will ask how do exceptions work behind the scenes, so I can make decisions of when to use them and whether they are slow.

From what I know, exceptions are the same as doing a return bunch of times, except that it also checks after each return whether it needs to do another one or to stop. How does it check when to stop returning? I guess there is a second stack that holds the type of the exception and a stack location, it then does returns until it gets there. I am also guessing that the only time this second stack is touched is on a throw and on each try/catch. AFAICT implementing a similar behaviour with return codes would take the same amount of time. But this is all just a guess, so I want to know what really happens.

How do exceptions really work?

How do exceptions work (behind the scenes) in c++

Is there a c++ equivalent of Java&#39;s

    try {
    	...
    }
    catch (Throwable t) {
    	...
    }

I am trying to debug Java/jni code that calls native windows functions and the virtual machine keeps crashing.  The native code appears fine in unit testing and only seems to crash when called through jni.  A generic exception catching mechanism would prove extremely useful.

C++ catching all exceptions

I&#39;m using .NET 3.5, trying to recursively delete a directory using:

    Directory.Delete(myPath, true);

My understanding is that this should throw if files are in use or there is a permissions problem, but otherwise it should delete the directory and all of its contents.

However, I occasionally get this:

    System.IO.IOException: The directory is not empty.
        at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
        at System.IO.Directory.DeleteHelper(String fullPath, String userPath, Boolean recursive)
        at System.IO.Directory.Delete(String fullPath, String userPath, Boolean recursive)
        ...

I&#39;m not surprised that the method sometimes throws, but I&#39;m surprised to get this particular message when recursive is true.  (I *know* the directory is not empty.)

Is there a reason I&#39;d see this instead of AccessViolationException?

Cannot delete directory with Directory.Delete(path, true)

If for example you follow the link:

`data:application/octet-stream;base64,SGVsbG8=`

The browser will prompt you to download a file consisting of the data held as base64 in the hyperlink itself.  Is there any way of suggesting a default name in the markup?  If not, is there a JavaScript solution?


Is there any way to specify a suggested filename when using data: URI?

Getting the subdomain from a URL sounds easy at first.

    http://www.domain.example

Scan for the first period then return whatever came after the &quot;http://&quot; ...

Then you remember

    http://super.duper.domain.example

Oh. So then you think, okay, find the last period, go back a word and get everything before! 

Then you remember

    http://super.duper.domain.co.uk

And you&#39;re back to square one. Anyone have any great ideas besides storing a list of all TLDs?

Get the subdomain from a URL

What is a simple way of downloading a file from a URL path?

How to download a file from a URL in C#?

I know on client side (javascript) you can use windows.location.hash but could not find anyway to access from the server side. I&#39;m using asp.net.

How to get Url Hash (#) from server side

How do you safely encode a URL using JavaScript such that it can be put into a GET string?

    var myUrl = &quot;http://example.com/index.html?param=1&amp;anotherParam=2&quot;;
    var myOtherUrl = &quot;http://example.com/index.html?url=&quot; + myUrl;

I assume that you need to encode the `myUrl` variable on that second line?


Encode URL in JavaScript?

How can I detect that a client has disconnected from my server?

I have the following code in my `AcceptCallBack` method

    static Socket handler = null;
    public static void AcceptCallback(IAsyncResult ar)
    {
      //Accept incoming connection
      Socket listener = (Socket)ar.AsyncState;
      handler = listener.EndAccept(ar);
    }

I need to find a way to discover as soon as possible that the client has disconnected from the `handler` Socket.

I&#39;ve tried:

 1. `handler.Available;`
 2. `handler.Send(new byte[1], 0,
    SocketFlags.None);`
 3. `handler.Receive(new byte[1], 0,
    SocketFlags.None);`

The above approaches work when you are connecting to a server and want to detect when the server disconnects but they do not work *when you are the server and want to detect client disconnection.*

Any help will be appreciated.

Instantly detect client disconnection from server socket

When updating from subversion repository using tortoise svn client I get error looking like that:

    Could not read chunk size: An existing connection was forcibly closed by the remote host.

It doesn&#39;t prevent me from updating, just interrupts update process, so that I have to repeat update several times, before it is complete.

What can cause such behaviour and how to fix it?

Updating from svn repository returns &quot;Could not read chunk size&quot; error

In a Linux environment, I need to detect the physical connected or disconnected state of an RJ45 connector to its socket.  Preferably using BASH scripting only.

The following solutions which have been proposed on other sites do NOT work for this purpose:

 1. Using &#39;ifconfig&#39; - since a network cable may be connected but the network not properly configured or not currently up.
 2. Ping a host - since the product will be within a LAN using an unknown network configuration and unknown hosts.

Isn&#39;t there some state which can be used in the /proc file system (everything else is in there)?

How is the Linux world suppose to have their own version of the Windows bubble that pop up from the icon tray indicating that you&#39;ve just unplugged the network cable?

----------

&lt;b&gt;Kent Fredric&lt;/b&gt; and &lt;b&gt;lothar&lt;/b&gt;, both of your answers satisfy my need... thanks a lot!  Which one I&#39;ll use... I still don&#39;t know.

I guess I can&#39;t put you both down as the correct answer?  And its probably fair for you that I do choose one.  Flip a coin I guess?  Again, thanks!

How to detect the physical connected state of a network cable/connector?

Those &quot;fine&quot; RFCs mandate from every RFC-client that they beware of not using more than 2 connections per host...

Microsoft implemented this in WebClient. I know that it can be turned off with 

App.config:
   
    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot; ?&gt; 
    &lt;configuration&gt; 
     &lt;system.net&gt; 
      &lt;connectionManagement&gt; 
       &lt;add address=&quot;*&quot; maxconnection=&quot;100&quot; /&gt; 
      &lt;/connectionManagement&gt; 
     &lt;/system.net&gt; 
    &lt;/configuration&gt; 

(found on http://social.msdn.microsoft.com/forums/en-US/netfxnetcom/thread/1f863f20-09f9-49a5-8eee-17a89b591007 )

But how can I do it programmatically?

Accordin to
http://msdn.microsoft.com/en-us/library/system.net.servicepointmanager.defaultconnectionlimit.aspx

&quot;Changing the DefaultConnectionLimit property has no effect on existing 
ServicePoint objects; it affects only ServicePoint objects that are 
initialized after the change. If the value of this property has not been 
set either directly or through configuration, the value defaults to the 
constant DefaultPersistentConnectionLimit.&quot;


I&#39;d like best to configure the limit when I instanciate the WebClient, but just removing this sad limitation programmatically at the start of my programm would be fine, too.


The server I access is not a regular webserver in the internet, but under my control and in the local lan. I want to do API-calls, but I don&#39;t use webservices or remoting

How can I programmatically remove the 2 connection limit in WebClient

How can an internet connection be tested without pinging some website?
I mean, what if there is a connection but the site is down? Is there a check for a connection with the world?


Content Type	Original Author	Original Content on Stackoverflow
Question	timdisney	View Question on Stackoverflow
Solution 1 - Java	James Schek	View Answer on Stackoverflow
Solution 2 - Java	kasperjj	View Answer on Stackoverflow
Solution 3 - Java	Artem Mostyaev	View Answer on Stackoverflow

In Java when does a URL connection close?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Handling data in a PHP JSON Object

'using' statement vs 'try finally'

Attributions