Versions Compared

Old Version 13

changes.mady.by.user ASF Infrabot

Saved on

compared with

New Version 14

changes.mady.by.user ASF Infrabot

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.
Comment: Add STDOUT/STDERR redirection

...

  • Use a ResourceBundle. See the Java docs for the specifics of how the ResourceBundle class works. Using this method, the properties file must go into the WEB-INF/classes directory or in a jar file contained in the WEB-INF/lib directory.
  • Another way is to use the method getResourceAsStream() from the ServletContext class. This allows you update the file without having to reload the webapp as required by the first method. Here is an example code snippet, without any error trapping:
    No Format
        // Assuming you are in a Servlet extending HttpServlet 
    // This will look for a file called "/more/cowbell.properties" relative 
    // to your servlet Root Context 
    InputStream is = getServletContext().getResourceAsStream("/more/cowbell.properties"); 
    Properties  p  = new Properties(); 
    p.load(is); 
    is.close();


How do I use log4j for all Tomcat log output?

...

Thus, if you have JNI code that follows the convention of including a static initilaizer like this:

No Format
  
class FooWrapper { 
    static { 
        System.loadLibrary("foo"); 
    } 

    native void doFoo(); 
  }

then both this class and the shared library should be placed in the $CATALINA_HOME/shared/lib directory.

...

No Format
    java.lang.UnsatisfiedLinkError: Native Library WEB-INF/lib/libfoo.so already loaded in another classloader 
        at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1525)

...

No Format
<html>

<head>
<meta http-equiv="refresh" content="0;http://mydomain.com/some/path/to/servlet/homepage/">
</head>

<body>
</body>

</html>

This change takes effect immediately and does not require a restart of Tomcat.

How do I redirect System.out and System.err to my web page?

I have met a situation where I needed to redirect a portion of standard ouput (System.out, STDOUT) and standard error (System.err, STDERR) to my web page instead of a log file. An example of such an application is a compiler research platform that our resarch team is putting online for anybody to be able to quickly compile-test their programs on line. Naturally, the compilers dump some of their stuff to STDERR or STDOUT and they are not web application .jar. Thus, I needed badly these streams related to the compiler output to be redirected to my web editor interface. Having found no easy instructions on how to do that lead me writing up this quick HOWTO. The HOWTO is based on Servlets, but similar arrangements can be done for JSPs. The below example shows the essentials, with most non-essentials removed.

No Format

public class WebEditor
extends HttpServlet
{
 ...
	public void doGet
	(
		HttpServletRequest poHTTPRequest,
		HttpServletResponse poHTTPResponse
	)
	throws IOException, ServletException
	{
		poHTTPResponse.setContentType("text/html");

		ServletOutputStream out = poHTTPResponse.getOutputStream();

		out.println("<html>");
		out.println("<body>");
		out.println("<head>");
		out.println("<title>WebEditor Test $Revision: 1.6 $</title>");
		out.println("</head>");
		out.println("<body>");
		out.println("<h3>WebEditor Test $Revision: 1.6 $</h3>");
		out.println("<hr />");

		// Backup the streams
		PrintStream oStdOutBackup = System.out;
		PrintStream oStdErrBackup = System.err;

		// Redired STDOUT and STDERR to the ServletOuputStream
		System.setOut(new PrintStream(out));
		System.setErr(new PrintStream(out));


		try
		{
			// ... call compiler here that produces
			// tons of STDOUT/STDERR messages ...
		}
		catch(Exception e)
		{
			out.println(e.toString());
		}

		// Restore original STDOUT and STDERR
		System.setOut(oStdOutBackup);
		System.setOut(oStdErrBackup);

		out.println("<hr />");
		out.println("</body>");
		out.println("</html>");
	}
}

A few caveats arise, as for instance while the System.out and System.err are deirected as per above, no logging of these is done to files. You will need more legwork to do to make the additional logging. It is important to backup and restore the original streams as the above example does. Also, notice the use of getOutputStream():
when this method is called, the getWriter() method can no longer be used in the same response object.

Corrections and comments are most welcome!