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  • List All Active Sessions in Oracle 11g
    02/01/2012 12:26PM

    Here is a query with which you can see all of the active sessions on an Oracle database:

    SELECT SID, Serial#, UserName, Status, SchemaName, Logon_Time
    FROM V$Session
    WHERE
    Status='ACTIVE' AND
    UserName IS NOT NULL;

  • Adding MultipartConfig Configuration to web.xml in JBoss 6.x for a Servlet 3.0 File Upload Servlet
    01/12/2012 11:45AM

    If you do not want to hard-code your file upload servlet with the @MultipartConfig annotation but would rather add it to your <servlet> configuration element in web.xml, following is the syntax (add this as a child element of <servlet>):

    <multipart-config>
          <location>/tmp</location>
          <max-file-size>20848820</max-file-size>
          <max-request-size>418018841</max-request-size>
          <file-size-threshold>1048576</file-size-threshold>
    </multipart-config>

  • Invocation of request.getParts() in a Servlet 3.0 doPost Method Will Not Throw IllegalStateException
    01/12/2012 11:34AM

    This one requires a bit of explaination.

    When writing a Servlet that will enable users to upload files from a form you need to be able to limit both the size of the file(s) and the entire multipart/form-data request.  The Servlet 3.0 spec now includes a @MultipartConfig annotation (which can also be specified in web.xml, see other post in this blog).

    Based on the Servlet 3.0 spec here is what is supposed to happen.

    1. The user submits a multi-part form that exceeds any of upload limitation parameters in the @MultipartConfig annotation.
    2. An attempt in the doPost method of the Servlet to invoke a  Collection<Part> parts = request.getParts(); should throw an IllegalStateException enabling the Servlet to respond to the client and somehow communicate that the multi-part message was too large.

    However, if within the doPost method a request.getParameter([param_name]) is invoked on the request object BEFORE attempting to invoke request.getParts(), the Servlet will not throw an IllegalStateException if any of the parameters in the MultipartConfig have been exceeded.  Instead, .getParts() returns a Collection of 0 parts, and without the Exception you have no idea why the multipart POST failed.

     If request.getParameter([param_name]) is invoked on the request object AFTER the first attempt to invoke request.getParts(), .getParts() will throw an IllegalStateException with the details about why the POST failed if any any of the parameters in the MultipartConfig have been exceeded.

    This took me quite a while to track down.

    The long and the short of it is that if you want to be able to check to make sure that any of the @MultipartConfig limitations are exceeded on the server-side (which you should) you MUST invoke request.getParts()before attempting to read any query string values.

    Certainly, there will be those that will say 'why not just check all of this on the client-side in JavaScript?'.  To which I would say, that is absolutely what you should do.  However, you should always double-check on the server-side to prevent someone who has managed to circumvent your client-side form validation.  Furthermore, there are a number of very slick and easy JavaScript implementations to do this that do not work in various versions of IE.

    Attachment: multipartconfig_bug_1.zip 1389 bytes
  • Touching a File in Java
    01/10/2012 11:05AM

    The following is a tutorial on how to create a empty file on the filesystem:

    // Destination directory
    File destinationDir = new File("/some/path");

    // The 'touched' file
    File doneFile = new File(destinationDir, "some_file_name");

    // The JVM will only 'touch' the file if you instantiate a
    // FileOutputStream instance for the file in question.
    // You don't actually write any data to the file through
    // the FileOutputStream.  Just instantiate it and close it.
    FileOutputStream doneFOS = null;
    try {
        doneFOS = new FileOutputStream(doneFile);
    } catch (FileNotFoundException e) {
        // Handle error
    }

    try {
        doneFOS.close();
    } catch (IOException e) {
        // Handle error
    }

  • Fixing "Software installation has been disabled by your system administrator" Notice When Attempting to Install An Addon for Firefox
    01/05/2012 9:49AM

    When I attempted to install the Web Developer Add-on in Firefox I was presented with the error in the title of this post.

    After some searching it seems that the least intrusive way to go about fixing it is to update the Firefox configuration for your user profile.

    If you are on WinXP look in C:\Documents and Settings\UID\Application Data\Mozilla\Firefox\Profiles\fxlme5ka.default.  On my install the following preference was in prefs.js

    Change:

    user_pref("xpinstall.enabled", false);

    to:

    user_pref("xpinstall.enabled", true);

    Save the file and restart Firefox.

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