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WrapperSimpleApp Integration (Linux / UNIX)
WrapperSimpleApp Integration (Linux / UNIX)
Integration Methods
Method 1 - WrapperSimpleApp Integration (Linux / UNIX)
Overview

The first method is to use the WrapperSimpleApp helper class to launch the application. This is by far the simplest way to integrate with the Wrapper, and where possible, it is highly recommended. There are some things to be aware of when using this method however. When the Wrapper shuts down the JVM, there is no direct call to an application requesting that it shutdown cleanly. Rather, the Wrapper will exit the JVM by calling System.exit() from within the JVM. If the application has registered its own shutdown hook, it will be invoked, giving the application a chance to shutdown cleanly. If on the other hand, a shutdown hook is not registered, then the application will suddenly exit. Both cases, with and without a shutdown hook, provide the exact same behavior as if the application was running without the Wrapper and a user pressed CTRL-C in the console.

When integrating with the WrapperSimpleApp helper class, the WrapperSimpleApp class replaces an application's main class. This gives the WrapperSimpleApp class a chance to immediately initialize the WrapperManager and register the JVM with the Wrapper. The WrapperSimpleApp class then manages all interaction with the Wrapper as well as the life-cycle of an application. When the Wrapper sends a start message to the JVM via the WrapperManager, the main method of the application's actual main class is called.

The WrapperSimpleApp helper class is told how to launch the application by passing the application's main class name, followed by any additional application parameters to the main method of the WrapperSimpleApp.

The following section will walk you through a detailed explanation of how to configure JBoss to run within the Wrapper. Most other applications can be integrated by following the same steps.

Detailed Instructions
Install JBoss

This tutorial will start with a clean install of JBoss. We used version 3.0.4 so the exact steps may be slightly different depending on the exact version installed. JBoss was installed in the /usr/lib directory, resulting in a JBoss Home directory of /usr/lib/jboss-3.0.4.

Installing Wrapper Files

There are four files which are required to be able to use the Wrapper. We will also copy over a script which makes it easy to launch and control the Wrapper.

NOTE

Please make sure that you are using the wrapper, and libwrapper.so files which were built for the platform being run. It sounds obvious, but the Linux version will not work on Solaris for example.

bin directory

The Wrapper is shipped with a sh script which can be used to reliably start and stop any Java application controlled by the Java Service Wrapper.

First we will copy the following files into the JBoss bin directory:

{WRAPPER_HOME}/bin/wrapper
{WRAPPER_HOME}/src/bin/sh.script.in

Rename the script file to reflect the name of the application.

{JBOSS_HOME}/bin/jboss

Now open the script into an editor. We need to set the long and short names to reflect that the script is being used to launch JBoss. You will see two variables immediately after the header of the script. APP_NAME and APP_LONG_NAME. Note that the default values of both of these variables are Ant friendly tokens which can easily be replaced as part of a build. Suggested values for these variables are shown below.

APP_NAME="jboss"
APP_LONG_NAME="JBoss Application Server"

These script should not require any additional modification. It does assume that the wrapper.conf file will be located within a conf directory one level up, ../conf/wrapper.conf. If you wish to locate this file someplace else, then that can also be set using the WRAPPER_CONF variable in the script.

NOTE

Important! Before proceeding, please make sure that all three files copied into the bin directory have their executable bit set.

lib directory

Copy the following two files into the JBoss lib directory:

{WRAPPER_HOME}/lib/libwrapper.so
{WRAPPER_HOME}/lib/wrapper.jar

The libwrapper.so file is a native library required by the portion of the Wrapper which runs within the JVM. The wrapper.jar file contains all of the Wrapper classes.

conf directory

The Wrapper requires a configuration file. The standard location for this file is in a conf directory in the application's home directory. JBoss does not have such a directory by default, so we will need to create one. Please do so and copy the template wrapper.conf file to that location:

{WRAPPER_HOME}/src/conf/wrapper.conf.in

Be sure to remove the .in extension so that the file is named wrapper.conf. You should now have:

{JBOSS_HOME}/conf/wrapper.conf

If you wish to relocate the configuration file, you are free to do so. You will need to modify the batch scripts copied into the bin directory above, to reflect the new location.

logs directory

The default wrapper.conf file will place a wrapper.log file in a logs directory under the application home directory. JBoss does not have such a directory by default, so we will need to create one. Please do so. You should now have the following directory:

{JBOSS_HOME}/logs

If you wish to place the log file in another location, you will need to edit the wrapper.conf file and modify the wrapper.logfile property to reflect the new location.

Locate the Application's Java Command Line

Before the Wrapper can be configured to launch an Application, you will need to know the full Java command which is normally used.

Most applications make use of a script to build up the actual command line. These scripts tend to get quite unwieldy and in fact, the ability to avoid having to work with them is one of the benefits of working with the Wrapper.

JBoss is launched by using a script called run.sh. It is launched by first changing the current directory to the bin directory and then run from there. If you open run.sh into an editor, you will notice the following lines towards the end of the file:

    exec $JAVA $JAVA_OPTS \
            -classpath "$JBOSS_CLASSPATH" \
            org.jboss.Main "$@"

The majority of the script has the task of collecting system specific information and storing that information into environment variables. The lines above then expands all of the collected information into the final Java command which launches the application. From looking at the source of the script, we hope you appreciate the complexity and the desire to have to avoid completely writing such scripts yourself.

In order to configure the Wrapper, all that is really needed is the final expanded command line. Rather than reading through the entire script and attempting to understand it, we will use a simple trick to display the final command line in the console. Edit the script by changing it as follows:

    #exec $JAVA $JAVA_OPTS \
    #        -classpath "$JBOSS_CLASSPATH" \
    #        org.jboss.Main "$@"
    echo "exec $JAVA $JAVA_OPTS -classpath $JBOSS_CLASSPATH org.jboss.Main $@"

If you now rerun the script, you will see something like the following in the console (Your output will all be on one line):

exec /opt/IBMJava2-131/bin/java  -Dprogram.name=run.sh
  -classpath /usr/lib/jboss-3.0.4/bin/run.jar:/opt/IBMJava2-131/lib/tools.jar org.jboss.Main
Modifying the wrapper.conf File

In order to be able to use this command with the Wrapper, we need to break up its components. Open the wrapper.conf file into an editor and make the changes below.

NOTE

Where properties are mentioned below, links are provided to their descriptions. Please take the time to review the descriptions of any properties which are modified. In many cases, there are further details on their usage which are not mentioned here.

Java Executable

First is to extract the java executable and assign it to the wrapper.java.command property:

wrapper.java.command=/opt/IBMJava2-131/bin/java
Java Arguments

Most applications provide a number of parameters to the Java executable when it is launched. The Wrapper provides special properties for configuring things like memory, as well as class and library paths. These will be covered below, however any other settings are configured using the wrapper.java.additional.<n> series of properties.

The JBoss command line only has one such property. In this case, we have changed the name of the script used to launch JBoss from run.sh, but for consistency we will leave it as is.:

wrapper.java.additional.1=-Dprogram.name=run.sh

Notice that the full property was copied directly from the command line without any modifications. See the property documentation for details on how to handle properties containing spaces.

Classpath

Next, comes the classpath, which is configured using the wrapper.java.classpath.<n> properties. The Wrapper requires that the classpath be broken up into its individual elements. Then, because we will also be making use of the Wrapper, it is necessary to include the wrapper.jar file as well:

wrapper.java.classpath.1=/usr/lib/jboss-3.0.4/wrapper.jar
wrapper.java.classpath.2=/usr/lib/jboss-3.0.4/bin/run.jar
wrapper.java.classpath.3=/opt/IBMJava2-131/lib/tools.jar
Main Class

The final component of the command used to launch JBoss is the main class, org.jboss.Main. The main class executed by Java when launched is specified by using the wrapper.java.mainclass property. As mentioned above however. Because the JBoss main class does not know how to communicate with the Wrapper, we will set the main class to be the full class name of WrapperSimpleApp. The JBoss main class is then specified as the first application parameter below.

wrapper.java.mainclass=org.tanukisoftware.wrapper.WrapperSimpleApp
Application Parameters

Application parameters are set using the wrapper.app-parameter.<n> properties. Application parameters appear in the Java command line directly after the main class. While JBoss does not have any such parameters, it is still necessary to set one of these properties. This is because we are using the WrapperSimpleApp helper class and as described above, its first parameter is the main class name of the application being run. in this case, org.jboss.Main:

wrapper.app.parameter.1=org.jboss.Main
Library Path

In order to use the Wrapper, there is one more property which much be set. The Wrapper makes use of a native library to control interactions with the system. This file libwrapper.so needs to be specified on the library path supplied to the JVM. JBoss does not have any native libraries of its own, but if it did, the directories where they were located would also need to be specified. The library path is set using the wrapper.java-library-path.<n> properties.

wrapper.java.library.path.1=/usr/lib/jboss-3.0.4/lib
Putting It All Together

Putting it all together, we get the following:

wrapper.java.command=/opt/IBMJava2-131/bin/java

wrapper.java.additional.1=-Dprogram.name=run.sh

wrapper.java.classpath.1=/usr/lib/jboss-3.0.4/wrapper.jar
wrapper.java.classpath.2=/usr/lib/jboss-3.0.4/bin/run.jar
wrapper.java.classpath.3=/opt/IBMJava2-131/lib/tools.jar

wrapper.java.library.path.1=/usr/lib/jboss-3.0.4/lib

wrapper.java.mainclass=org.tanukisoftware.wrapper.WrapperSimpleApp

wrapper.app.parameter.1=org.jboss.Main

Notice what while this will function correctly on this particular machine, it is highly dependent on the directory structure and platform. By taking advantage of the fact that the Wrapper's scripts always set the current directory to the location of the script, and by making use of a single environment variable, we are able to modify the above properties so that they are completely platform and machine independent:

wrapper.java.command=%JAVA_HOME%/bin/java

wrapper.java.additional.1=-Dprogram.name=run.sh

wrapper.java.classpath.1=../lib/wrapper.jar
wrapper.java.classpath.2=./run.jar
wrapper.java.classpath.3=%JAVA_HOME%/lib/tools.jar

wrapper.java.library.path.1=../lib

wrapper.java.mainclass=org.tanukisoftware.wrapper.WrapperSimpleApp

wrapper.app.parameter.1=org.jboss.Main
Trying It Out

JBoss can now be run by simply executing bin/jboss console. Because of the way the Wrapper sets its current directory, it is not necessary to run this script from within the bin directory.

As you will see if you omit a command, the scripts shipped with the wrapper are fairly standard daemon scripts. They accept console, start, stop, restart, and dump commands. The start, stop, and restart commands are common to most daemon scripts and are used to control the wrapper and its application as a daemon process. The status command can be used to find out whether or not the wrapper is currently running. The console command will launch the wrapper in the current shell, making it possible to kill the application with CTRL-C. The final command, dump, will send a kill -3 signal to the wrapper causing the its JVM to do a full thread dump.

Congratulations. Your application should now be up and running.

If you did have any problems, please take a look at the Troubleshooting section for help with tracking down the problem.

by Leif Mortenson

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