pinpoint/src/main/java/com/profiler/TomcatTracer.java

package com.profiler;

import java.lang.instrument.ClassFileTransformer;

import java.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;

import javassist.ByteArrayClassPath;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;

public class TomcatTracer implements ClassFileTransformer {
	protected String agentArgString = "";
	protected Instrumentation instrumentation;
	ClassPool classPool;

	public static void premain(String agentArgs, Instrumentation inst) {
		new TomcatTracer(agentArgs, inst);
	}

	public TomcatTracer(String agentArgs, Instrumentation inst) {
		agentArgString = agentArgs;
		instrumentation = inst;
		instrumentation.addTransformer(this);
		classPool = ClassPool.getDefault();
	}

	@Override
	public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
		String javassistClassName = className.replace('/', '.');

		if (javassistClassName.startsWith("javax.servlet.") || javassistClassName.startsWith("org.apache.tomcat")) {
			if (!javassistClassName.startsWith("org.apache.tomcat.util")) {
				byte[] result = changeCode(javassistClassName, classfileBuffer);
				if (result != null)
					return result;
			}
		}

		return null;
	}

	private byte[] changeCode(String javassistClassName, byte[] classfileBuffer) {
		boolean insertFlag = false;

		classPool.insertClassPath(new ByteArrayClassPath(javassistClassName, classfileBuffer));

		try {
			if (classPool == null) {
				System.out.println("NULL");
				classPool = ClassPool.getDefault();
			}

			CtClass cc = classPool.get(javassistClassName);
			CtMethod[] methodList = cc.getDeclaredMethods();

			for (CtMethod method : methodList) {
				String methodName = method.getLongName();

				if (!method.isEmpty()) {
					System.out.println("***inserted instrument code at " + methodName);
					method.insertBefore("{ System.out.println(\"--- " + methodName + "  is called. \");}");
					insertFlag = true;
				}
			}

			if (insertFlag) {
				byte[] newClassfileBuffer = cc.toBytecode();
				System.out.println("@@@" + javassistClassName + "class's new Buffer generated !!!");

				return newClassfileBuffer;
			}
		} catch (Exception e) {
			System.err.println("!!!!! " + e.getMessage());
		}
		return null;
	}
}