How to recompile Java Runtime Environment (JRE)?

Question

I thought this would be very easy. I downloaded the JDK, extracted src.zip, modified the JDK to fit my needs and saved the file.

Now, the only thing I need to do is recompile the extracted and update src folder to a "JRE". I tried using javac, but didn't get anywhere. For example, I got the error that no source files were given. I am obviousely not using the right syntax to compile the JRE.

So, can anyone tell me, how do you end up with a working "JRE" folder containing a modified Java Runtime Environment based on the new source folder extracted from the JDK?

Note: I am not going to redistribute the compilation. It is for personal self use only.

Update: thanks to an answer and http://www.javalobby.org/java/forums/t103334.html I got to the following command: "c:\tmp\jdk1.6.0_17\bin\javac" -classpath "c:\tmp\out" -verbose -g -d "c:\tmp\out" -J-Xmx512m -cp "c:\jdk1.6.0_17\jre\lib\rt.jar";"c:\jdk1.6.0_17\lib\tools.jar" @files.txt - unfortunately, while it does seem to process things, when finished the output folder /out is empty. Is something wrong with my command?

Answer 1

Set your classpath to the top of the extract source directory. Compile the files then place their .class files back in the rt.jar.

Answer 2

You will not be able to compile the entire Sun/Oracle JDK given just the sources that are supplied with it, because many of those classes internally make use of proprietary classes in packages like com.sun.*, and of course native methods - and the source of these is not included in the JDK. You have to get them via a special source code release or use OpenJDK (and I have no idea whether getting the native stuff to work is trivial or excruciating). Alternatively, it might be possible to selectively recompile only specific classes - but of course only when you don't change them in ways that make them incompatible with existing usage in the JDK.