HowTo

*Originally taken from: http://wiki.apache.org/jakarta-tomcat/Tomcat/Howto*

How do I add a question to this page?

Anyone may edit this page to add their own content. That is why this page is part of a Wiki and not a hardcoded static file in the FAQ.

However, do not add questions without answers to this page. If you have a question about how to do something in Tomcat which has not been addressed yet, ask the [http://jakarta.apache.org/tomcat/faq/tomcatuser.html tomcat-user list]. Once you've figured out how to fix your problem, come back and update the Wiki to allow the rest of us to benefit from what you've learned!

How do I set up and run Tomcat on Macintosh OS X?

See ["TomcatOnMacOS"]

How do I load a properties file?

Here are the two most popular ways::

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:

    // 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?

To have Tomcat use log4j universally, place both log4j.jar and the Jakarta commons-logging.jar into the $TOMCAT_HOME/common/lib directory. Create your log4j properties file as $TOMCAT_HOME/common/classes/log4j.properties and configure the root logger. Here is the basic log4j.properties that I used to do this myself:

log4j.rootLogger=info, R
log4j.appender.R=org.apache.log4j.ConsoleAppender
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%-5p %-30.30c{1} %x - %m%n

If you only need to use log4j in your own web app, just include log4j (and any log4j properties file) in your WAR file.

How do I configure Tomcat Connectors?

On the Tomcat FAQ, there is a list of Other Resources which should have information pointing you to the relevant pages.

Each connector has its own configuration, and its own set up. Check them for more information.

In particular, here are a number of locations for Tomcat Connectors:

[http://jakarta.apache.org/tomcat/connectors-doc/index.html Tomcat Connectors Documentation]
[http://jakarta.apache.org/tomcat/connectors-doc/faq.html Tomcat Connectors FAQ]
[http://jakarta.apache.org/tomcat/tomcat-4.1-doc/jk2/config/apache.html Configuring Tomcat Connectors for Apache]

John Turner has an excellent page about [http://johnturner.com/howto/apache-tomcat-howto.html Using Apache HTTP with Apache Tomcat].

Tomcat crashed! What do I do now?

These steps are in no particular order ...

1.#0 Read the Tomcat FAQ

Read the Tomcat RELEASE NOTES - there is something about Linux in it
First look at the stack traces. I hope a stack trace was produced before the failure aborted the JVM process. After you get a few stack traces, see if a pattern appears. Trace back to source code if needed.
Patch (or unpatch!) the operating system as needed.
Patch (or unpatch!) the JVM (Java Virtual Machine).
Linux Problem? - read the RELEASE NOTES!
Look at commercial vendor support for other servlet engines. Sometimes the problem is universal regardless of servlet engine and may be a JVM/OS/application code issue
Search Google for web pages - maybe someone else had this problem. I'll bet they did.
Search Google news groups
If the JVM is from a commercial vendor, (eg: IBM, HP) check their release notes and news groups
Using a database? Make sure JDBC type 4 drivers are used. Check their release notes.
Tweak JVM memory parameters. Setting memory too high can be as bad as having memory too low. If your memory settings are set too high, Java 1.3 JVMs may freeze while waiting for the entire garbage collection to finish. Also if the JVM has too much memory, if may be starving other resources on the machine which are needed which may be causing unforeseen exceptions. In a nutshell, throwing more memory doesn't always solve the problem!
Turn off the Java JIT compiler. See the Java Docs on how to do this.

How do I share sessions across web apps?

You cannot share sessions directly across web apps, as that would be a violation of the Servlet Specification. There are workarounds, including using a singleton class loaded from the common classloader repository to hold shared information, or putting some of this shared information in a database or another data store. Some of these approaches have been discussed on the [http://jakarta.apache.org/tomcat/faq/tomcatuser.html tomcat-user mailing list], whose archives you should search for more information.

Sharing sessions across containers for clustering or replication purposes is a different matter altogether.

Why doesn't the netbeans example build for me?

I have found two issues with the build.xml provided here: http://jakarta.apache.org/struts/faqs/netbeans.html

First, add this to the top of your properties:

<property environment="env" />

Next find this line in the "war" target:

<classes dir="${build.dir}" includes="**/*.properties" />

Change it so it reads like this:

<classes dir="${src.dir}" includes="**/*.properties" />

Now it will work!

I'm encountering classloader problems when using JNI under Tomcat

The important thing to know about using JNI under Tomcat is that one cannot place the native libraries OR their JNI interfaces under the WEB-INF/lib or WEB-INF/classes directories of a web application and expect to be able to reload the webapp without restarting the server. The class that calls System.loadLibrary(String) must be loaded by a classloader that is not affected by reloading the web application itself.

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

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.

Note that under Windows, you'll also need to make sure that the library is in the java.library.path. Either add %CATALINA_HOME%\shared\lib to your Windows PATH environment variable, or place the DLL files in another location that is currently on the java.library.path. There may be a similar requirement for UNIX based system (I haven't checked), in which case you'd also have to add $CATALINA_HOME/shared/lib to the PATH environment variable. (Note: I'm not the original author of this entry.)

The symptom of this problem that I encountered looked something like this -

    java.lang.UnsatisfiedLinkError: Native Library WEB-INF/lib/libfoo.so already loaded in another classloader
        at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1525)

How can I access members of a custom Realm or Principal?

When you create a custom subclass of RealmBase or GenericPrincipal and attempt to use those classes in your webapp code, you'll probably have problems with ClassCastException. This is because the instance returned by request.getUserPrincipal() is of a class loaded by the server's classloader, and you are trying to access it through you webapp's classloader. While the classes maybe otherwise exactly the same, different (sibling) classloaders makes them different classes.

This assumes you created a MyPrincipal class, and put in Tomcat's server/classes (or lib) directory, as well as in your webapp's webinf/classes (or lib) directory. Normally, you would put custom realm and principal classes in the server directory because they depend on other classes there.

Here's what you would like to do, but it throws ClassCastException:

MyPrincipal p = request.getUserPrincipal();
String emailAddress = p.getEmailAddress();

Here are 4 ways you might get around the classloader boundary:

1) Reflection

Principal p = request.getUserPrincipal();
String emailAddress = p.getClass().getMethod("getEmailAddress", null).invoke(p, null);

2) Move classes to a common classloader

You could put your custom classes in a classloader that is common to both the server and your webapp - e.g., either the "common" or bootstrap classloaders. To do this, however, you would also need to move the classes that your custom classes depend on up to the common classloader, and that seems like a bad idea, because there a many of them and they a core server classes.

3) Common Interfaces

Rather than move the implementing custom classes up, you could define interfaces for your customs classes, and put the interfaces in the common directory. You're code would look like this:

public interface MyPrincipalInterface extends java.security.Principal {
  public String getEmailAddress();
}

public class MyPrincipal implements MyPrincipalInterface {
...
  public String getEmailAddress() {
    return emailAddress;
  }
}

public class MyServlet implements Servlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    MyPrincipalInterface p = (MyPrincipalInterface)request.getUserPrincipal();
    String emailAddress = p.getEmailAddress();
...
}

Notice that this method gives you pretty much the webapp code you wanted in the first place

4) Serializing / Deserializing

You might want to try serializing the response of 'request.getUserPrincipal()' and deserialize it to an instance of [webapp]MyPrincipal.

Setting up SSL

Threads from the [http://jakarta.apache.org/tomcat/faq/tomcatuser.html tomcat-user list]

Using Verisign:

Using ["OpenSSL"]:

A description of "what SSL is all about anyway":

http://marc.theaimsgroup.com/?l=tomcat-user&m=106692394104667&w=2

How do I install Tomcat as a service under Unix?

Create a shell program to start Tomcat automatically. Each UNIX varies in how it starts up automatic services, but there are two main variants:

BSD::In a typical BSD system, there are a series of start up scripts in /etc starting with rc.. Look for, or create, a file called /etc/rc.local and enter the appropriate instructions to start up Tomcat there as a shell script.

System V::In a typical UNIX System V setup, there is a directory containing startup scripts, and other directories which contain links to these startup scripts. Create the appropriate startup script for your setup, then create the appropriate links.

For more information on each, check your system documentation.

It also makes a lot of sense to use the JavaServiceWrapper.

How do I get direct access to a Tomcat Realm?

Credit: This code is from a post by Yoav Shapira http://www.yoavshapira.com in the user list

Sometimes access directly into the Tomcat realm object is needed; to do, this the following code can be used. Be aware, however, that by using this, your application is relying on a Tomcat extension and is therefore non-standard.

Note that in order for this to work the Context of the web application in question needs to have its privileged attribute set to "true", otherwise web apps do not have access to the Tomcat classes.

Server server = ServerFactory.getServer();
//Note, this assumes the Container is "Catalina"
Service service = server.findService("Catalina");
Engine engine = (Engine) service.getContainer();
Host host = (Host) engine.findChild(engine.getDefaultHost());
//Note, this assumes your context is "myContext"
Context context = (Context) host.findChild("myContext");
Realm realm = context.getRealm();

How do I make Tomcat startup faster?

See ["HowTo/FasterStartUp"]

How do I contribute to Tomcat's documentation?

Download the source bundle or grab the source XML file from CVS. The docs are in the jakarta-tomcat-catalina CVS module, in the webapps/docs subdirectory. They are in XML format and get processed into the HTML documentation as part of the Tomcat release.

Edit the documentation XML file(s) as you wish. The xdocs format is self-explanatory: use normal HTML markup, and add <section> or <subsection> tags as you see fit. Look at the existing docs as exampels. Make sure you use valid XML markup.

Open a Bugzilla enhancement item with the explanation of your enhancements, and attach a diff -u format of your patch. We will evaluate and commit your patch as needed. Note that the Tomcat web site is updated with every release, so that documentation changes will not be visible as soon as you submit your Bugzilla item.

If you're interested in previewing your changes, you will need to follow the directions for building Tomcat yourself. The docs will be generated in the webapps/tomcat-docs directory just like with any normal Tomcat distributions.

If you'd like to get documentation up and visible to the world before the next Tomcat release, use this wiki site.

If you're not familiar with how to grab files from CVS, see http://www.apache.org/dev/contributors.html.

How do I override the default home page loaded by Tomcat?

After successfully installing Tomcat, you usually test it by loading http://localhost:8080 . The contents of that page are compiled into the index_jsp servlet. The page even warns against modifying the index.jsp files for this reason. Luckily, it is quite easy to override that page. Inside $TOMCAT_HOME/conf/web.xml there is a section called <welcome-file-list> and it looks like this:

    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>

The default servlet attempts to load the index.* files in the order listed. You may easily override the index.jsp file by creating an index.html file at $TOMCAT_HOME/webapps/ROOT. It's somewhat common for that file to contain a new static home page or a redirect to a servlet's main page. A redirect would look like:

<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.

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.setErr(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!

How to run Tomcat without root priviledges?

Is there a way to allow normal user(non-root) to start/stop the tomcat server. Tried assigning permision, did not work. Read thru some articles, stated that only root has permission to port below 1025. How can i allow a non-root user to do so ? thks in adv.

malathi ranjit singh----

One way is to put Apache httpd with mod_jk before your Tomcat servers, and use ports >=1024 in the Tomcat(s). Since we do it that way, it's the only way I know.

BTW, you should read the 1st howto.

using Iptables to redirect Port 80 and 443 to user ports (>1024) ----
/sbin/iptables -A FORWARD -p tcp --destination-port 443 -j ACCEPT
/sbin/iptables -t nat -A PREROUTING -j REDIRECT -p tcp --destination-port 443 --to-ports 8443

/sbin/iptables -A FORWARD -p tcp --destination-port 80 -j ACCEPT
/sbin/iptables -t nat -A PREROUTING -j REDIRECT -p tcp --destination-port 80 --to-ports 8080

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