近在研究jdk源码，发现debug时无法查看源码里的变量值。 因为sun提供的jdk并不能查看运行中的局部变量，需要重新编译一下rt.jar。
下面这六步是编译jdk的具体步骤：
Step 1: Locate the JDK source
First navigate to the JDK install directory, and locate the src.zip file. This file contains the JDK sources – and is absolutely invaluable for the rest of this process.
Next, unzip this folder to some location, such asc:\src.
Step 2: List all the source files to be compiled
Generate a list of all .java files in the unzipped folder, out to a separate file:
dir /B /S /X c:\src\*.java > jdk-src.txt
Step 3: Compile the source
Compile the source files named in this file, using the–goption.
javac-verbose -nowarn-g -source 1.6 -target 1.6 -J-Xms512m -J-Xmx1024m -bootclasspath C:\java\jdk1.6.0_07\jre\lib\rt.jar;C:\java\jdk1.6.0_07\jre\lib\jce.jar;C:\java\jdk1.6.0_07\jre\lib\jsse.jar;C:\java\jdk1.6.0_07\jre\lib\resources.jar;C:\java\jdk1.6.0_07\jre\lib\charsets.jar;C:\java\jdk1.6.0_07\jre\lib\deploy.jar -sourcepathsrc -classpathsrc -djdk-class @jdk-src.txt
Note the presence of the –bootclasspath flag which makes the stated JARs available to the compiler. This is absolutely critical when trying to build the source distribution of JDK 6.
Step 4: Extract rt.jar
Extract the original rt.jar file, that is found in JAVA_HOME\jre\lib, into a temporary folder.
Step 5: Generate a composite build
Copy the newly compiled .class files from ourjdk-classover the folder where the rt.jar file was expanded. This ensures that the final set has old classes overwritten by newer classes with debug information, while still retaining class files that we couldn't compile.
Step 6: Regenerate rt.jar
Finally, recompress all the files from the composite folder into a new rt.jar file, and overwrite the original rt.jar file with this new one.
如果想在eclipse中跟踪调试，需要在Windows -> Preferences -> Java-Installed JRE下，选择安装的jdk，点edit，然后在列出的jre system libraries列表中选择rt.jar，设置其中的Source attachment为C:\java\jdk1.6.0_07\src.zip。
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下面是一个方便的linux脚本， 只要设置了JAVA_HOME， 就可以轻松搞定上面的事情了:)
#!/bin/sh
if [ -z "$JAVA_HOME" ]
then
echo "Must set JAVA_HOME"
exit 1
fi
cd $JAVA_HOME
mkdir temp
cp src.zip temp/
cd temp/
mkdir out
unzip src.zip
rm src.zip
find . -name *.java > filelist
echo "$(wc -l filelist) java files to compile"
javac -g -d out/ -J-Xmx1024m -cp "../jre/lib/tools.jar:../jre/lib/rt.jar" @filelist
if [ $? != 0 ]
then
echo "compile error!"
exit 1
fi
unzip $JAVA_HOME/jre/lib/rt.jar -d $JAVA_HOME/temp/old_classes
cp -r $JAVA_HOME/temp/out/* $JAVA_HOME/temp/old_classes/
cd $JAVA_HOME/temp/old_classes/
jar cf rt_debug.jar *
cp rt_debug.jar $JAVA_HOME/jre/lib/
mv $JAVA_HOME/jre/lib/rt.jar $JAVA_HOME/lib/rt_old.jar
cd $JAVA_HOME/jre/lib/
ln -s rt_debug.jar rt.jar
rm -rf $JAVA_HOME/temp
