问题
Is it possible to specify a Java classpath that includes a JAR file contained within another JAR file?
回答1:
If you're trying to create a single jar that contains your application and its required libraries, there are two ways (that I know of) to do that. The first is One-Jar, which uses a special classloader to allow the nesting of jars. The second is UberJar, (or Shade), which explodes the included libraries and puts all the classes in the top-level jar.
I should also mention that UberJar and Shade are plugins for Maven1 and Maven2 respectively. As mentioned below, you can also use the assembly plugin (which in reality is much more powerful, but much harder to properly configure).
回答2:
You do NOT want to use those "explode JAR contents" solutions. They definitely make it harder to see stuff (since everything is exploded at the same level). Furthermore, there could be naming conflicts (should not happen if people use proper packages, but you cannot always control this).
The feature that you want is one of the top 25 Sun RFEs: RFE 4648386, which Sun, in their infinite wisdom, has designated as being of low priority. We can only hope that Sun wakes up...
In the meanwhile, the best solution that I have come across (which I wish that Sun would copy in the JDK) is to use the custom class loader JarClassLoader.
回答3:
After some research I have found method that doesn't require maven or any 3rd party extension/program.
You can use "Class-Path" in your manifest file.
For example:
Create manifest file MANIFEST.MF
Manifest-Version: 1.0
Created-By: Bundle
Class-Path: ./custom_lib.jar
Main-Class: YourMainClass
Compile all your classes and run jar cfm Testing.jar MANIFEST.MF *.class custom_lib.jar
c stands for create archive
f indicates that you want to specify file
v is for verbose input
m means that we will pass custom manifest file
Be sure that you included lib in jar package. You should be able to run jar in the normal way.
based on: http://www.ibm.com/developerworks/library/j-5things6/
all other information you need about the class-path do you find here
回答4:
Use the zipgroupfileset tag (uses same attributes as a fileset tag); it will unzip all files in the directory and add to your new archive file. More information: http://ant.apache.org/manual/Tasks/zip.html
This is a very useful way to get around the jar-in-a-jar problem -- I know because I have googled this exact StackOverflow question while trying to figure out what to do. If you want to package a jar or a folder of jars into your one built jar with Ant, then forget about all this classpath or third-party plugin stuff, all you gotta do is this (in Ant):
<jar destfile="your.jar" basedir="java/dir">
...
<zipgroupfileset dir="dir/of/jars" />
</jar>
回答5:
If you are building with ant (I am using ant from eclipse), you can just add the extra jar files by saying to ant to add them... Not necessarily the best method if you have a project maintained by multiple people but it works for one person project and is easy.
for example my target that was building the .jar file was:
<jar destfile="${plugin.jar}" basedir="${plugin.build.dir}">
<manifest>
<attribute name="Author" value="ntg"/>
................................
<attribute name="Plugin-Version" value="${version.entry.commit.revision}"/>
</manifest>
</jar>
I just added one line to make it:
<jar ....">
<zipgroupfileset dir="${external-lib-dir}" includes="*.jar"/>
<manifest>
................................
</manifest>
</jar>
where
<property name="external-lib-dir"
value="C:\...\eclipseWorkspace\Filter\external\...\lib" />
was the dir with the external jars. And that's it...
回答6:
Not without writing your own class loader. You can add jars to the jar's classpath, but they must be co-located, not contained in the main jar.
回答7:
You need to build a custom class-loader to do this or a third-party library that supports this. Your best bet is to extract the jar from the runtime and add them to the classpath (or have them already added to the classpath).
回答8:
I use maven for my java builds which has a plugin called the maven assembly plugin.
It does what your asking, but like some of the other suggestions describe - essentially exploding all the dependent jars and recombining them into a single jar
回答9:
If you have eclpise IDE, you just need to export your JAR and choose "Package Required libraries into generated JAR". eclipse will automatically add the required dependant JARs into the generated JAR as well as generated some eclipse custom class loader that load these JARs automatically.
回答10:
I was about to advise to extract all the files at the same level, then to make a jar out of the result, since the package system should keep them neatly separated. That would be the manual way, I suppose the tools indicated by Steve will do that nicely.
回答11:
Winstone is pretty good http://blog.jayway.com/2008/11/28/executable-war-with-winstone-maven-plugin/. But not for complex sites. And that's a shame because all it takes is to include the plugin.
回答12:
Well, there is a very easy way if you're using Eclipse.
Export your project as a "Runnable" Jar file (right-click project folder from within Eclipse, select "Export..."). When you configure the export settings, be sure to select "Extract required libraries into generated Jar." Keep in mind, select "Extract..." and not "Package required libraries...".
Additionally: You must select a run-configuration in your export settings. So, you could always create an empty main( ) in some class and use it for your run configuration.
Anyway, it isn't guaranteed to work 100% of the time - as you will notice a pop-up message telling you to make sure you check the licenses of the Jar files you're including and something about not copying signature files. However, I have been doing this for years and have never encountered a problem.
回答13:
Extracting into an Uber-dir works for me as we s should all be using root:\java and have outlets code in packages with versioning. Ie ca.tecreations-1.0.0. Signing is okay because the jars are intact from their downloaded location. 3rd party signatures intact, extract to c:\java. There’s my project dir. run from launcher so java -cp c:\java Launcher
来源：https://stackoverflow.com/questions/183292/classpath-including-jar-within-a-jar