Can ASM method-visitors be used with interfaces?

Question

I need to write a tool that lists the classes that call methods of specified interfaces. It will be used as part of the build process of a large java application consisting of many modules. The goal is to automatically document the dependencies between certain java modules.

I found several tools for dependency analysis, but they don't work on the method level, just for packages or jars. Finally I found ASM, that seems to do what I need.

The following code prints the method dependencies of all class files in a given directory:

import java.io.*;
import java.util.*;

import org.objectweb.asm.ClassReader;

public class Test {

    public static void main(String[] args) throws Exception {

        File dir = new File(args[0]);

        List<File> classFiles = new LinkedList<File>();
        findClassFiles(classFiles, dir);

        for (File classFile : classFiles) {
            InputStream input = new FileInputStream(classFile);
            new ClassReader(input).accept(new MyClassVisitor(), 0);
            input.close();
        }
    }

    private static void findClassFiles(List<File> list, File dir) {
        for (File file : dir.listFiles()) {
            if (file.isDirectory()) {
                findClassFiles(list, file);
            } else if (file.getName().endsWith(".class")) {
                list.add(file);
            }
        }
    }
}

---

import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.commons.EmptyVisitor;

public class MyClassVisitor extends EmptyVisitor {

    private String className;

    @Override
    public void visit(int version, int access, String name, String signature,
            String superName, String[] interfaces) {
        this.className = name;
    }

    @Override
    public MethodVisitor visitMethod(int access, String name, String desc,
            String signature, String[] exceptions) {

        System.out.println(className + "." + name);
        return new MyMethodVisitor();
    }
}

---

import org.objectweb.asm.commons.EmptyVisitor;

public class MyMethodVisitor extends EmptyVisitor {

    @Override
    public void visitMethodInsn(int opcode, String owner, String name,
            String desc) {

        String key = owner + "." + name;
        System.out.println("  " + key);
    }
}

---

The Problem:

The code works for regular classes only! If the class file contains an interface, visitMethod is called, but not visitMethodInsn. I don't get any info about the callers of interface methods.

Any ideas?

Answer 1

I have to admit, I was confused...

I thought that asm visitors do some magic to give me the list of all callers of a given method, like a stacktrace. Instead they justs parse classes and method bodies. Fortunatly, this is totally sufficent for my needs as I can build the call tree by myself.

The following code lists all methods that are called by other methods, checking class files in given directory (and subdirectories) only:

---

import java.io.*;
import java.util.*;

import org.objectweb.asm.ClassReader;

public class Test {

    public static void main(String[] args) throws Exception {

        File dir = new File(args[0]);

        Map<String, Set<String>> callMap = new HashMap<String, Set<String>>();

        List<File> classFiles = new LinkedList<File>();
        findClassFiles(classFiles, dir);

        for (File classFile : classFiles) {
            InputStream input = new FileInputStream(classFile);
            new ClassReader(input).accept(new MyClassVisitor(callMap), 0);
            input.close();
        }

        for (Map.Entry<String, Set<String>> entry : callMap.entrySet()) {
            String method = entry.getKey();
            Set<String> callers = entry.getValue();

            if (callers != null && !callers.isEmpty()) {
                System.out.println(method);
                for (String caller : callers) {
                    System.out.println("    " + caller);
                }
            }
        }
    }

    private static void findClassFiles(List<File> list, File dir) {
        for (File file : dir.listFiles()) {
            if (file.isDirectory()) {
                findClassFiles(list, file);
            } else if (file.getName().endsWith(".class")) {
                list.add(file);
            }
        }
    }
}

---

import java.util.*;

import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.commons.EmptyVisitor;

public class MyClassVisitor extends EmptyVisitor {

    private String className;
    private Map<String, Set<String>> callMap;

    public MyClassVisitor(Map<String, Set<String>> callMap) {
        this.callMap = callMap;
    }

    @Override
    public void visit(int version, int access, String name, String signature,
            String superName, String[] interfaces) {
        this.className = name;
    }

    @Override
    public MethodVisitor visitMethod(int access, String name, String desc,
            String signature, String[] exceptions) {

        return new MyMethodVisitor(className + "." + name, callMap);
    }
}

---

import java.util.*;

import org.objectweb.asm.commons.EmptyVisitor;

public class MyMethodVisitor extends EmptyVisitor {

    private String currentMethod;
    private Map<String, Set<String>> callMap;

    public MyMethodVisitor(String currentMethod,
            Map<String, Set<String>> callMap) {
        this.currentMethod = currentMethod;
        this.callMap = callMap;
    }

    @Override
    public void visitMethodInsn(int opcode, String owner, String name,
            String desc) {

        String calledMethod = owner + "." + name;

        Set<String> callers = callMap.get(calledMethod);
        if (callers == null) {
            callers = new TreeSet<String>();
            callMap.put(calledMethod, callers);
        }

        callers.add(currentMethod);
    }
}