what is the best practice to create a .jar file from a java project??

Question

what is the best practice to create a .jar file from a java project??

Answer 1

Some points to consider:

• Create proper MANIFEST.MF, which should contain:
  • Build date;
  • Author;
  • Implementation-version;
• Use a script/program - like an Ant task - which takes care of properly creating a manifest file.

---

Here's a simple ant file which builds a java project, adapted from the Ant tutorial:

<project>

<target name="clean">
    <delete dir="build"/>
</target>

<target name="compile">
    <mkdir dir="build/classes"/>
    <javac srcdir="src" destdir="build/classes"/>
</target>

<target name="jar">
    <mkdir dir="build/jar"/>
    <jar destfile="build/jar/HelloWorld.jar" basedir="build/classes">
        <manifest>
            <attribute name="Implementation-Version" value="1.0"/>
        </manifest>
    </jar>
</target>

<target name="run">
    <java jar="build/jar/HelloWorld.jar" fork="true"/>
</target>

</project>

Answer 2

Read up on the basics of Sun's JAR format at this tutorial. In my opinion you should learn the basics -- namely MANIFESTs, the SDK tools -- before jumping into third party tools such as the following.

The Jar command line tool distributed with the Sun JDK:

jar -cf myjar.jar base_src_folder

Where base_src_folder is the parent directory holding your source code.

Alternatively you could use a build tool such as Apache Ant. It has features such as the JAR target to do this for you.

Answer 3

Apache Ant

Answer 4

Ant is not quite easy to begin with. Instead, I would suggest using an IDE, for instance NetBeans, which creates an Ant script under the hood. All you have to do is to hit "build", and you get a .jar file as result.

Answer 5

Apache Maven, for projects which are dependent on other projects.

Admittedly, Maven may be overkill for learning projects, but it is invaluable for larger, distributed ones.

Answer 6

Eclipse IDE is the best way for new comers. Just select the project right click export File, select jar anf filename.

Answer 7

I'm a relative novice (though not newcomber) to java but I will say that for me this thread is missing the mark for jar "Best Practices". It's relatively pedantic to simply "create a jar". The questions I have around best practices are:

1) Is it OK to have numerous versions of a particular class in a jar file? My local utilities tend to consume numerous other local utilities ("set A"). Which, in turn, consume other utilities - some of which consume other "set A" utilities. I end up with duplicate entries in the jar.

2) Is there a particularly good use for "Implementation-Version"? E.g., is that what should be used to provide the --version for an app? If so, is there a good (or any way), perhaps using annotations (?) that allow the jar file version to be displayed from the app?

3) In order to minimize the number of classes I need in the batch wrapper (script that starts the jar), I unjar other jar libraries (e.g., apache commons CLI, etc) and include it in the object jar. Is this frowned on?

Thanks for any suggestions!

• Andy