How can I include external jar on my Netbeans project

I solved this by creating just one jar file with all libraries inside, adding the following to my build.xml file in NetBeans:

<target name="-post-jar">
  <jar jarfile="dist/Combined-dist.jar">
    <zipfileset src="${dist.jar}" excludes="META-INF/*" />
    <zipfileset src="lib/commons-io-1.4.jar" excludes="META-INF/*" />
    <zipfileset src="lib/ninja-utils-3.2.jar" excludes="META-INF/*" />
    <zipfileset src="lib/unicorn-1.0.jar" excludes="META-INF/*" />
    <manifest>
        <attribute name="Main-Class" value="com.example.mypackage.Main"/>
    </manifest>
  </jar>
</target>

This creates a jar file (Combined-dist.jar) which is the combination of the dist jar and the specified library jars (in this case, commons-io-1.4.jar,ninja-utils-3.2.jar and unicorn-1.0.jar). You have to be sure to specify your Main Class package for the new jar file or it won't run when you try to open it.

If you copy your jars into the source code directory, they will be in your final jar. Nevetheless, I am not sure if this will work 100% of the time.

There is a great post at java-forum that states the following:

Except for a select few circumstances, what works best for me is to simply merge the files manually. A .jar is basically a .zip with organized contents, and you can open them in almost any .zip capable archive program (I just use gnome's standard archiver, File Roller, and it works great). Backup your jar file and open it in the archiver of your choice, and do the same for each library jar in the library directory. Drag and drop the working folders (IE, everything EXCEPT the META-INF Directory) from each library into your jar's root path (alongside your META-INF and your app's root package). Now drag the META-INF/MANIFEST.MF file from your jar to your Desktop or any other folder. Open it, and erase the Class-Path and X-COMMENT lines. Don't forget to leave a blank newline at the end of the file! Save the new manifest file and drag it back to your jar's META-INF directory, overwriting the old one. Test the jar.

That's really easy to package every dependent library (*.jar) into one single myProject.jar.

Just follow these steps and you will finally pack every dependent library into single jar. If you are using NetBeans then you can follow exactly or else you need to find your build.xml file in project files.

Follow these steps to edit build.xml

1) Click on Files tab on the left side of the project panel in NetBeans.

2) Double click on the build.xml file and add these lines in it just before </project> line

 <target name="package-for-store" depends="jar">
    <property name="store.jar.name" value="myProject"/>
    <property name="store.dir" value="store"/>
    <property name="store.jar" value="${store.dir}/${store.jar.name}.jar"/>
    <echo message="Packaging ${application.title} into a single JAR at ${store.jar}"/>
    <delete dir="${store.dir}"/>
    <mkdir dir="${store.dir}"/>
    <jar destfile="${store.dir}/temp_final.jar" filesetmanifest="skip">
        <zipgroupfileset dir="dist" includes="*.jar"/>
        <zipgroupfileset dir="dist/lib" includes="*.jar"/>
        <manifest>
            <attribute name="Main-Class" value="${main.class}"/>
        </manifest>
    </jar>
    <zip destfile="${store.jar}">
        <zipfileset src="${store.dir}/temp_final.jar"
        excludes="META-INF/*.SF, META-INF/*.DSA, META-INF/*.RSA"/>
    </zip>
    <delete file="${store.dir}/temp_final.jar"/>
</target>

3) Change value in second line of the code as per your project name which is

<property name="store.jar.name" value="myProject"/> //<---Just value not name

4) Save it and right click on build.xml and choose Run Target and then Other Targets and finally click on Package-for-store

5) And here you done. Now you can go and check just like dist folder there will be a store folder which will be containing your final complete jar including all of your dependent libraries. Now whenever you want to change / add more libraries or so, just follow step 4.

Picture for step 4

You could use Apache Ant since version 1.7 for build the JAR with the required libraries in only one file. You could have a configuration file as follows:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<project default="buildJar">
    <target name="buildJar">
        <!-- Name of jar -->
        <jar destfile="C:/MyJar.jar" filesetmanifest="mergewithoutmain">
            <manifest>
                <!-- Your class with the main method -->
                <attribute name="Main-Class" value="myPackage.MyClass"/>
                <!-- Path in the jar -->
                <attribute name="Class-Path" value="."/>
            </manifest>
            <!-- Dir of compiled class -->
            <fileset dir="C:/NetBeansProjects/MyProject/bin"/>
            <!-- Include required jars -->
            <zipfileset excludes="META-INF/*.SF" 
                src="C:/NetBeansProjects/MyProject/lib/library1.jar"/>
            <zipfileset excludes="META-INF/*.SF" 
                src="C:/NetBeansProjects/MyProject/lib/library2.jar"/>
        </jar>
    </target>
</project>

In Netbeans, place the XML file in your project and run it with the context menu.

See more in Apache Ant User Manual.