See Java source code in eclipse

How to view the jar source code in the Eclipse SDK such as: *.jar
1. Point "Window", "Preferences", "Java", "Installed JREs"

2. The right side of "Installed JREs" is the list pane, listing the JRE environment in the system, selecting your JRE, and then clicking "Edit ..." on the edge, a window will appear (edit JRE)

3. Select this entry for the Rt.jar file: "C:\Program Files\java\jre_1.5.0_06\lib\*.jar"
Point to the left of the "+" sign to expand it,

4. After expanding, you can see "source Attachment: (None)", point this item, point to the right button "Source Attachment ...", select "Src.zip" file under your JDK directory

5. "OK", end.

See Java source code in eclipse