how to download source jar file for your jar
1. google + org.eclipse.jdt.debug.ui (3.6.100.v20120530-1425) source
使用google直接搜索
2. Java Source Attacher
使用Java Source Attacher插件
update site is: http://svn.codespot.com/a/eclipselabs.org/free-plugins/trunk/site/
3. add eclipse related source jar file, please using eclipse update site
如果是eclipse自带的jar包，可以试一试eclipse的update site
http://wiki.eclipse.org/Eclipse_Project_Update_Sites
4. using eclipse site