NoClassDefFoundError on external library project for Android

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-f

Answer 1

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 2

I had two projects using the same library: one working, the other one crashing with java.lang.NoClassDefFoundError. After nothing else helped me, I looked into the file project.properties in the root directory of my project. The working project had the android.library.reference line (the last line below), the crashing one did not:

# Project target.
target=android-17
android.library.reference.1=../my-library-project

I manually added the line and it started working! (Yes, I did try both (project) properties -- java build path -- projects and (project) properties -- java build path -- order and exports -- nothing helped.)

PS By the way, "project properties" has also the "project references" tab. No idea if it would work.

Answer 3

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

Answer 4

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 5

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 6

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...