NoClassDefFoundError on external library project f

Question

I use eclipse for Google Android development.

I've created a library project ([x] Is Library in the Android-settings), which includes an external jar-file (Referenced Libraries). This library project are referenced in another Project (the actual project which will use the library project). This is done by add the project under the Android-settings.

the source compiles but if I want to execute it on the device, I get the NoClassDefFoundError for a class which is inside the jar-file which is included in the library project.

Edit: The jar-file ist added to the exported entries ([x] my.jar on the Order and Export-Tab from the library project)

Is there a clean way to get this working?

Answer 1

Go to project properties -> build path-> libraies

If you see your jar files like this

snmp4j.jar - e:\software\jars

Its may your problem

Add libs folder in your project and copy jar file in that folder. Right click jar file and go build path -> add to build path. Then you can see your jar as

snmp4j.jar  - project_name/libs 

Its worked for me.

Answer 2

I had a similar problem and non of the solutions out here fixed it.

Short version: the JAR was compiled in Java 1.7 and could not be found by Dalvik.

We build an internal JAR that we share across backend and mobile clients with Maven. The problem ended up being that the JAR was compiled with Java 1.7. Androids dalvik only supports Java 1.5 and 1.6. This is why everything works fine in Eclipse as it's not compiled to dalvik at this point.

We even specified the target and source version in the Maven compiler plugin to compile with Java 1.6. This did not work because only JDK 1.7 was installed on the build machine. A small note at the bottom of the Maven page gave us the hint: Note: Merely setting the target option does not guarantee that your code actually runs on a JRE with the specified version.

To see if you have this problem as well, rename your *.jar file to *.zip unpack it, and look in the MANIFEST.MF file for the Build-Jdk: parameter to see what Java version actually compiled your JAR.

Answer 3

It has been clearly stated in offcial API here:

A library project can include a JAR library

You can develop a library project that itself includes a JAR library, however you need to manually edit the dependent application project's build path and add a path to the JAR file

The jar lib must be manually added to the dependent application project's build path, not only the library project build path itself.

Update from SDK r17:

This is automatically handled by ADT now, check out new feature for ADT 17.0.0 release here:

Added feature to automatically setup JAR dependencies. Any .jar files in the /libs folder are added to the build configuration (similar to how the Ant build system works). Also, .jar files needed by library projects are also automatically added to projects that depend on those library projects. (more info)

Answer 4

Another thing to pay attention to is library package names.

If you are using ADT21 and you happen to have libraries that have the same package name, there will be error during compile but it will still compile and run in Eclipse, giving you an APK that is missing some of the resource classes. Hence the crash when you run the app.

If you compile it with ANT then you can see the compile error that says two or more libraries use the same package name.

To fix this, rename your library project by using Android Tools -> Rename Application Package. Then everything will go back to normal.

It took me almost entire day to figure this out...

Answer 5

For those who followed the steps(even check the projects in "Order and Export") and still have the java.lang.ClassNotFoundException in the API 17, the final step is to check that your compiler does not run with Java 1.7. If is 1.7 then you should change it to 1.6 for all your projects. After that it will ask to rebuild all the projects and successfully ran on my phone :)

To change the java compile version in eclipse, this is located in: Project properties > Java Compiler > Compiler Compliance level: 1.6

Answer 6

I had a minor issue when I upgraded to ADT17 where my libs weren't being imported properly. Turns out this is because my librarys were being linked as dependancies from my lib folder not libs!

Seems librarys have to be in the libs folder from now