Revision as of 10:46, 14 February 2010 by Mdm42 (Talk | contribs)

What is a library wrapper module and how do I use it?

If your module uses some external library, you will probably use a wrapper module to make classes from that library available to your module at runtime.

A wrapper module is a module that contains no code; really the only significant thing about it is its manifest, which does two significant things, in addition to the standard module unique ID/version/etc.:

  • Has a Class-Path entry for one or more JARs, conventionally in the subdirectory ext/ of the directory where the module is.
  • Declares OpenIDE-Module-Public-Packages followed by a list of the packages from the library that other modules should be able to use.

You can use File > New Project > NetBeans Modules > Library Wrapper Module to make a library wrapper.

So a wrapper module acts as a proxy to turn a library into a NB module. Since you can't modify the NetBeans classpath directly ( DevFaqNetBeansClasspath), nor would you want to, this is the way you let your code use third-party libraries. It serves the same function that running with java -cp or setting CLASSPATH would do in a smaller Java application.

There are other options for packaging libraries described in DevFaqWhenUseWrapperModule.

If the above was confusing, read DevFaqModuleDependencies.

Using a wrapper module for an existing project

If you are developing the library yourself, but decide you want to keep the library project separate from any NB module project, you can do so. Just make a plain Java project for the library and build it; and also create a library wrapper module from its JAR output. Here are three ways to hook them up.

  • The first modifies the project so that when the project is built, it builds the target jarfile directly in the wrapper-module's target directory instead of in the original project's dist directory copies the jar to the wrapper module.
  • The second modifies the wrapper module so that the wrapper cleans, builds and picks up the jar.
  • The third modifies the library project's build.xml to copy the library jarfile to into the wrapper-module's target directory, replacing the (outdated) copy already residing there.

The first and third methods may be considered push methods that work to push the new jarfile to the wrapper module whenever the library gets rebuilt; the second method may be considered a pull method where you have to remember to rebuild the wrapper-module whenever you rebuild the library.

Pro Con
Method 1 Wrapper module automatically updated when the library gets rebuilt; nothing to remember. The library jarfile is no longer available in the library/dist directory for other external projects or components.
Method 2 No changes needed to the library project. Must remember to rebuild wrapper module whenever the library gets rebuilt.
Method 3 Wrapper module automatically updated when the library gets rebuilt; nothing to remember. Library project's build.xml gains an awareness of the wrapper-module's location, meaning that changes to directory locations may break the library-project build.

Method 1

To hook them up (since the library wrapper module wizard just copies the JAR you select), you can make the plain Java SE project build into the wrapper. Say your Java SE project is in e.g./src/suite/libs/foo and your NBM wrapper is in /src/suite/foo-wrapper; just edit /src/suite/libs/foo/nbproject/ to specify e.g.:


Now you can just build the Java SE project and it will update the wrapper's JAR file. Also code completion on anything that compiles against the foo library should "see" sources in /src/suite/libs/foo/src (so long as the Java SE project is open).

Method 2

Here's how to have the wrapper module build, clean and pick up the JAR from the Java SE project's original location with source association (even if the Java SE project is not open!). You modify the wrapper's project.xml (to adjust the <class-path-extension>), (to specify extra.module.files) and build.xml (to override the release target) as shown in the following example. harness/README gives the details. See also Issue 70894, which would make it easier.

Example: Having the wrapper module clean and build the project

With these changes to a wrapper module, build/clean on the wrapper, or on the module suite that contains the wrapper, also does build/clean on the project.

For this example, my-wrapper is a library wrapper module for the JAR file produced by the regular Java project called my-project. my-project and my-wrapper are in the same directory; this only affects relative path specifications and is not a general requirement. This example was created on NetBeans 5.5. If you have jars from multiple projects in a wrapper, then this example is extended by using <antsub> instead of <ant> and a FileSet in the release target's <copy> task.

Only the my-wrapper project needs modification.


In my-wrapper/nbproject/project.xml, change <class-path-extension>'s <binary-origin> to reference the jar created by my-project. This change gives code completion with Javadoc and Go to Source when referencing my-project.


Make sure a ../src directory (relative to the JAR location) containing the corresponding sources of the library exists if you want Go to Source functionality to work.


In my-wrapper/nbproject/ specify where my-project's JAR file is installed in the suite's cluster. This puts my-project.jar in the wrapper's NBM; it is needed since the wrapper's release directory is no longer used as a staging area.



Delete the directory my-wrapper/release. The original JAR file was copied here when the wrapper was created. It will interfere if it is left around.


In my-wrapper/build.xml add the following. Customize the first two properties' value= to specify your project's relative location and JAR. The release target is replaced; now it builds my-project then copies the JAR to the suite's cluster. The clean target first cleans as usual, then cleans my-project.

<property name="original.project.dir" value="../my-project"/>
<property name="original.project.jar"

<target name="release">
    <echo message="Building ${original.project.dir}"/>
    <ant dir="${original.project.dir}"
         target="jar" inheritall="false" inheritrefs="false"/>
    <echo message="Done building ${original.project.dir}"/>

    <copy todir="${cluster}/modules/ext"

<target name="clean" depends="projectized-common.clean">
    <echo message="Cleaning ${original.project.dir}"/>
    <ant dir="${original.project.dir}"
         target="clean" inheritall="false" inheritrefs="false"/>
    <echo message="Done cleaning ${original.project.dir}"/>

How do I include native libraries (*.so or *.dll) in my library wrapper module?

Some libraries come with a native counterpart. The current Library Wrapper wizard doesn't cater to this. As per the JNI section in this document, you simply need to create a lib directory under <my-wrapper>/release/modules (which gets created by the wizard), alongside the ext directory mentioned earlier in this document. This directory is where you place your native libraries.

How do I include more that one jar in my library wrapper module?

As explained in this mail and in this README the library wrapper creation wizard will only add one jar. To add more you need to copy the jars to release/modules/ext/ and edit nbproject/project.xml to add extra <class-path-extension> elements.


Applies to: NetBeans 5.5, 6.x

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