Creating a runnable jar file:

This quick tutorial gives a step by step process of creating runnable jar files with the help of Ant. It is not the only way to do it, but it is probably the easiest.

A runnable jar file allows a use to run Java classes without having to know class names and type them in a command prompt, rather the user can just double click on the jar file and the program will fire up.  A runnable jar allows Java classes to be loaded just like when a user clicks an exe file.  The easiest way to do this is to use Apache Ant.  Ant is similar to a "make" file in C++, but it is for Java.

• You need to start by installing Apache Ant and you can get the latest release from http://ant.apache.org
• Ant works on an XML file named build.xml, so this must be created for your project.  You also will need a project folder and some subfolders explained below.
  •  Start by creating a directory that will hold will project. You need to create a subdirectory called "build" and another subdirectory called "jar".  Place all of your class files for project in the build directory. We also need to create a file called build.xml in the main project directory. Your build.xml file is where you specify some tags for Ant to use, for our case of creating an runnable jar, we will only need to create one tag. Below is an example of what this tag should look like.
    • <target name="jar">
          <jar destfile="jar/MyProject.jar" basedir="build">
              <manifest>
                  <attribute name="Main-Class" value="MyProjectMain"/>
              </manifest>
          </jar>
      </target>
  • In this example we will get an output file in the jar directory named "MyProject.jar". The key to creating the runnable jar file is to specify a manifest class (Your manifest class is just the class in your project that has main()). In the example above the manifest class is "MyProjectMain".
• To run your Ant build file, open a command prompt, navigate to your project folder and type:
  • > ant jar
  • If you get an error saying "build.xml does not exist" then you are either not located at the root of your project or your build.xml file is not in the root of the project folder.
• At his point you should have a runnable jar file to click on.  If you click on it to open it and you get an error saying that Java can't find your main class, review your build.xml and make sure your paths are setup correctly. If the manifest is not specified correctly Java won't know which class to run as your main class.

If you are having some problems or you want to find out how make Ant do some more neat stuff life automatic compilation, Javadoc, running, etc.. refer to this site http://ant.apache.org/manual/index.html