Google provides a rich set of libraries to access their services.  The Documents List Data API provides access to the Google Documents service:

http://code.google.com/apis/documents/overview.html

The documentation describes how to make raw HTTP requests to access data.  You can also download the Java client library:

http://code.google.com/p/gdata-java-client/

The developer's guide provides several useful examples to get you started:

http://code.google.com/apis/documents/docs/2.0/developers_guide_java.html

The Javadoc can be found here:

http://code.google.com/apis/gdata/javadoc/

Finally, in order to run a sample application to upload a document, you must have the following jars in your classpath:

gdata-base-1.0.jar
gdata-client-1.0.jar
gdata-client-meta-1.0.jar
gdata-core-1.0.jar
gdata-docs-2.0.jar
gdata-docs-meta-2.0.jar
gdata-media-1.0.jar        
                                                                                                                                
You also need to include mail.jar and activation.jar from the Java Mail library and the Activation Framework.