As reported in Java.net

KickJava.com has introduced a Java Source Codes Repository of over 20
million lines of codes, with more being added. "The unique feature is
that all source codes are extensively cross-referenced and linked to
JDK APIs, so that it can be used to track the call stack easily." Code
is organized in sections by package, so the top level consists of
"org", "com", "java", etc.

http://kickjava.com/src
http://today.java.net/pub/n/KickJavaSourceRepository