Java API Source Code

OpenJDK code: Browse here
For example, if you looking for AWTUtilities.java, go here in the above link:

src› share› classes› com› sun› awt› AWTUtilities.java

2. OpenJDK project homepage where they have all the instructions of downloading and building it
3. OpenJDK Mercurial Repo hosted here
4. JDK Documentation here

I'm not sure what you mean, but here is the API documentation

Source for OpenJDK implementation

Install the JDK. The sources for the public classes are packaged in src.zip.

You can also find them online at http://www.docjar.org/.