best way to deploy a package

Question

When I finished to write my classes I put them into a package structure and then I jarred all.

Now which is the best way to deploy and use my jar?

1. setting classpath;
2. use CLASSPATH variable;
3. using the extension mechanism.

Answer 1

Best to my opinon is to provide batch files and shell scripts to start the application.

Sophisticated scripts check for environment variables like $JAVA_HOME (%JAVA_HOME%) and use them, if defined or use a default value.

Inside the script you could build the classpath in an internal variable and start the app with a line like

%JAVA_HOME%\bin\java.exe -cp %LIBRARIES% com.example.Main

I would prefer this solution over the java -jar Application.jar alternative, because this one requires that you setup the classpath inside the jars manifest. So deploying an application that depends on existing libraries on the target system is pretty difficults, just because you have to know the library paths before you build the application.

Answer 2

Setting the classpath (using -cp) is the best way, as you can have a different classpath for each application. The CLASSPATH environment variable is global for all Java applications running on the machine, as is the extension mechanism so you probably don't want to use those.

If your code is executable (ie it has a public static void main(String[] args) method) then you can also specify the class that the main method is in, and the associated classpath within the manifest file inside the Jar file. Once you have done that you can do this:

java -jar myJar.jar

And Java will work out the rest.

Answer 3

I you have a main class in that jar that you want to run the best approach is to put a META-INF/MANIFEST.MF file in the jar and launch your class using java -jar mypackage.jar

The manifest should contain a Class-Path and a Main-Class attribute

See http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html#JAR%20Manifest

Answer 4

If you mean by 'deploy and use' that you want to use it in another application, set it on the classpath of that application.

If you use the extension mechanism (I assume you mean putting the jar in pathtojava/lib/ext) every application using that jvm will have the jar loaded, the samecounts for the CLASSPATH as system variable. That is most likely not necessary?

If you ment to execute/use the jar as standalone application; just run it commandline, no classpath stuff needed. If you want to deploy on a server you probably wanted to make a war or ear fiel instead.

Answer 5

Don't update the user's CLASSPATH environment variable because there is a risk that your deployed application will interfere with other Java applications that the user might want to run.

Don't deploy using the Extension mechanism because there is a risk that you will interfere with applications run by any user using the JVM that you have "extended".

The best solution is to create and deploy a wrapper script that uses the "-cp" argument, or a shortcut that runs a self-launching JAR file ... as suggested by other answers.