The sun.net.www.http.HttpClient class breaks binary compatability from version 1.3.1 of the JDK to version 1.3.1_01. In particular, the signature of the writeRequests(...) method has changed from:

sun.net.www.http.HttpClient.writeRequests( sun.net.www.MessageHeader );

to:

sun.net.www.http.HttpClient.writeRequests( sun.net.www.MessageHeader, java.io.ByteArrayOutputStream ) throws java.io.IOException;

While our code does not reference this class directly, it is referenced by third-party software that we use. We are filing a bug against this third-party software, but feel that this compatability break should also be addressed in the JDK itself.