Can't import library into Google App Engine project

Question

I use the Google App Engine SDK 1.8.5 with Eclipse 3.8 on Ubuntu.

I want to add the Cloud Storage service to my app, so I downloaded guava-gwt-15.0.jar and appengine-gcs-client-0.3.jar, and put them in my apps /war/WEB-INF/lib/ folder. I also added these jars to the build path in Eclipse.

When I fire up my app in dev mode, it runs fine, at least until I try to access a page relevant to the GCS library. When I do that, I get the following error:

java.lang.NoClassDefFoundError: com/google/common/base/Preconditions
at com.google.appengine.tools.cloudstorage.GcsServiceImpl.<init>(GcsServiceImpl.java:35)
at com.google.appengine.tools.cloudstorage.GcsServiceFactory.createGcsService(GcsServiceFactory.java:32)
... etc

I cleaned my project and restarted Eclipse multiple times, and still the problem persists. What to do?

Answer 1

In addition to Guava for GWT, you also need the core Guava library (guava-15.0.jar). Download the .jar to war/WEB-INF/lib and add it to you build path as well.