Trace.java

package samples.tracing;

import net.sf.cglib.proxy.MethodProxy;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.Enhancer;

/**
 * This class is taken from the regular cglib samples.
 */
public class Trace implements MethodInterceptor {

    public static class Target {
        static int s_count = 0;

        private int m_count;

        public Target() {
            m_count = s_count++;
        }

        public void step1() {
            step2(new Target());
        }

        public void step2(Target arg) {
            step3();
        }

        public void step3() {
        }

        public String toString() {
            return "I am Target " + m_count;
        }
    }

    int ident = 1;
    static Trace callback = new Trace();

    public static Object newInstance(Class clazz) {
        try {
            Enhancer e = new Enhancer();
            e.setSuperclass(clazz);
            e.setCallback(callback);
            return e.create();
        } catch (Throwable e) {
            e.printStackTrace();
            throw new Error(e.getMessage());
        }

    }

    public static void main(String[] args) {
        Target target = (Target) newInstance(Target.class);
        target.step1();
    }


    public Object intercept(Object obj, java.lang.reflect.Method method, Object[] args, MethodProxy proxy)
            throws Throwable {
        printIdent(ident);
        System.out.println(method);
        for (int i = 0; i < args.length; i++) {
            printIdent(ident);
            System.out.print("arg" + (i + 1) + ": ");
            if (obj == args[i]) {
                System.out.println("this");
            } else {
                System.out.println(args[i]);
            }
        }
        ident++;

        Object retValFromSuper = null;
        try {
            retValFromSuper = proxy.invokeSuper(obj, args);
            ident--;
        } catch (Throwable t) {
            ident--;
            printIdent(ident);
            System.out.println("throw " + t);
            System.out.println();
            throw t.fillInStackTrace();
        }

        printIdent(ident);
        System.out.print("return ");
        if (obj == retValFromSuper) {
            System.out.println("this");
        } else {
            System.out.println(retValFromSuper);
        }

        if (ident == 1) {
            System.out.println();
        }

        return retValFromSuper;
    }

    void printIdent(int ident) {
        while (--ident > 0) {
            System.out.print(".......");
        }
        System.out.print("  ");
    }

    private Trace() {
    }
}