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WrapperJarApp Integration (Linux / UNIX)

Method 4 - WrapperJarApp Integration (Linux / UNIX)

Overview

The fourth and final method is to use the WrapperJarApp helper class to launch the application. This is another simple way to integrate with the Wrapper when the application is already configured to run as an executable jar.

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 like pressing CTRL-C in the console (command window). Both cases, with and without a Shutdown Hook, provide the exact same behavior as if the application was running without the Wrapper.

When integrating with this Method 4 (WrapperJarApp helper class), the WrapperJarApp class replaces an application's main class. This gives the WrapperJarApp class a chance to immediately initialize the WrapperManager and register the JVM with the Wrapper. The WrapperJarApp 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 jar's manifest is inspected and its configured main class is called. The WrapperJarApp creates a new ClassLoader which is able to load classes from the executable jar file as well as any other jar files referenced within its manifest file.

The WrapperJarApp helper class is told how to launch the application by passing the absolute or relative location of the executable jar file, followed by any additional application parameters to the main method of the WrapperJarApp.

Detailed Instructions

This section will walk you through a detailed explanation of how to configure Hudson, an integration engine, to run within the Wrapper. Most other applications deployed as executable jars can be integrated by following the same steps.

Install Hudson

This tutorial will start with a clean install of Hudson. We used "Hudson version 1.285" so the exact steps may be slightly different depending on the exact version installed. Hudson is deployed as a file called hudson.war. This is to enable it to be deployed as a web application, but it is also an executable jar. We will install Hudson in a directory, /usr/lib/hudson. Create bin, lib, conf, and logs directories and place the hudson.war file inside the lib directory.

Installing Wrapper Files

There are four directories which are required to be configured in order to be able to use the Wrapper.

NOTE

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

bin directory

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

First, please copy the following files into the Hudson bin directory:

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

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

{HUDSON_HOME}/bin/hudson

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 Hudson. You will see two variables immediately after the header of the script. APP_NAME and APP_LONG_NAME. Suggested values for these variables are shown below.

APP_NAME="hudson"
APP_LONG_NAME="Hudson Integration Engine"

The script should not require any additional modification. However 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 place the wrapper.conf file somewhere else, the WRAPPER_CONF variable in the script will require appropriate modification.

NOTE

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

lib directory

Copy the following two files into the Hudson bin directory:

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

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

NOTE

Note that the native library follows slightly different naming conventions on some platforms. Possible names include; libwrapper.a, libwrapper.sl, libwrapper.so, and libwrapper.jnilib. In any case, the file should be copied over without changing the extension.

conf directory

The Wrapper requires a configuration file "wrapper.conf" for each application. The standard location for this file is in a conf directory in the application's home directory. Please copy the following template file wrapper.conf.in into the conf directory of Hudson.

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

Rename the file as follows. Be sure to remove the .in extension so that the file is named wrapper.conf.

You should now have:

{HUDSON_HOME}/conf/wrapper.conf

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

logs directory

The default configuration file wrapper.conf will place a wrapper.log file in a logs directory under the application's HOME directory.

{HUDSON_HOME}/logs

If you wish to place the wrapper.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.

The Java Command Line

In the case of an executable jar, the Java command line is quite simple. In the case of Hudson, you would simply go to the Hudson directory and execute:

java -jar /usr/lib/hudson/lib/hudson.war

Any arguments would be passed in as follows:

java -jar /usr/lib/hudson/lib/hudson.war arg1 arg2 arg3

Modifying the "wrapper.conf" File

In order to be able to use the above Java command line with the Wrapper, we need to break up the command line's components into a configuration file. 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 the location path to the wrapper.java.command property:

wrapper.java.command=java

Classpath

Next, comes the classpath, which is configured using the wrapper.java.classpath.<n> properties. Java does not actually allow you to specifiy a classpath when running with the -jar parameter. But this integration with the Wrapper works a little differently. The Wrapper requires that its wrapper.jar be specified in the classpath:

wrapper.java.classpath.1=/usr/lib/hudson/lib/wrapper.jar

Main Class

When using the Wrapper and the WrapperJarApp helper class, Java is not executing the jar directly. It is necessary to specify the helper class as the main class of the application. The main class executed by Java when launched is specified by using the wrapper.java.mainclass property as follows:

wrapper.java.mainclass=org.tanukisoftware.wrapper.WrapperJarApp

Application Parameters

Application parameters are set using the wrapper.app-parameter.<n> properties. In this case, the command line to launch Hudson does not specifiy any application parameters, but it is necessary to tell the WrapperJarApp helper class which jar to execute. This is done as follows:

wrapper.app.parameter.1=/usr/lib/hudson/lib/hudson.war

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 library file libwrapper.so needs to be specified on the library path supplied to the JVM.

Hudson 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/hudson/lib

Putting It All Together

Putting it all together, we get the following:

wrapper.java.command=java

wrapper.java.classpath.1=/usr/lib/hudson/lib/wrapper.jar

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

wrapper.java.mainclass=org.tanukisoftware.wrapper.WrapperJarApp

wrapper.app.parameter.1=/usr/lib/hudson/lib/hudson.war

Notice, while these configurations will work 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.classpath.1=../lib/wrapper.jar

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

wrapper.java.mainclass=org.tanukisoftware.wrapper.WrapperJarApp

wrapper.app.parameter.1=../lib/hudson.war

Trying It Out

Hudson can now be run by simply executing the script bin/hudson 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 y 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.