how to know which class / package/ methods used by given jar file?

Question

I have a jar file. I want to know which external classes and methods are used by classes inside JAR file. Can anyone suggest me any tool?

For example - if below two classes are packaged into Myjar.jar

import java.util.Vector;
class MyJarClass{

    public static void main(String args[]){
        Vector v = new Vector();
        AnotherClass another = new AnotherClass();

        v.addElement("one");
        another.doSomething();

    }
}

class AnotherClass{

    void doSomething(){
    }
}

When I supply that JAR to a tool - the tool should show java.util.Vector and Vector.adElements() are from external source (not present in MyJar.jar)

Forgot to mention, i don't have access to sourcecode.

Answer 1

Easy

import com.example.*;

Possible

List<com.example.MyType> = new ArrayList<com.example.MyType>();

A challenge

Class<?> clazz = Class.forName("com.example.MyType");

Mission impossible

List<String> classes = getClassNamesFromUrl("http://example.com/classes.txt");
for (String className:classes) {
   doSomethingWith(Class.forName(className));
}

I support Jon's advice to look at the byte code (BCEL) but just be aware, that in general it is not possible to read all dependencies from a jar, as they can be dynamic and defined outside the library (see: Mission impossible).

---

Hard to tell if there's a tool, have a look at those directories on java-source.net:

• Open Source ByteCode Libraries in Java
• Open Source Code Analyzers in Java (has some applications to work on jars too, like JDepend. JarAnalyzer sounds promising too, but it is quite old, last update in 2005)

Further reading

• How can I visualize jar (not plugin) dependencies? (especially VonC's answer)

Answer 2

You might want to look at BCEL, which will allow you to parse the class files and find out what they use. I expect it'll be a certain amount of effort though.