/*
* Javassist, a Java-bytecode translator toolkit.
* Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. Alternatively, the contents of this file may be used under
* the terms of the GNU Lesser General Public License Version 2.1 or later,
* or the Apache License Version 2.0.
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*/
package javassist.util;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.instrument.ClassDefinition;
import java.lang.instrument.Instrumentation;
import java.lang.instrument.UnmodifiableClassException;
import java.util.jar.Attributes;
import java.util.jar.JarEntry;
import java.util.jar.JarOutputStream;
import java.util.jar.Manifest;
import java.lang.management.ManagementFactory;
import com.sun.tools.attach.VirtualMachine;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;
/**
* A utility class for dynamically adding a new method
* or modifying an existing method body.
* This class provides {@link #redefine(Class, CtClass)}
* and {@link #redefine(Class[], CtClass[])}, which replace the
* existing class definition with a new one.
* These methods perform the replacement by
* {@code java.lang.instrument.Instrumentation}. For details
* of acceptable modification,
* see the {@code Instrumentation} interface.
*
* <p>Before calling the {@code redefine} methods, the hotswap agent
* has to be deployed.</p>
*
* <p>To create a hotswap agent, run {@link #createAgentJarFile(String)}.
* For example, the following command creates an agent file named {@code hotswap.jar}.
*
* <pre>
* $ jshell --class-path javassist.jar
* jshell> javassist.util.HotSwapAgent.createAgentJarFile("hotswap.jar")
* </pre>
*
* <p>Then, run the JVM with the VM argument {@code -javaagent:hotswap.jar}
* to deploy the hotswap agent.
* </p>
*
* <p>If the {@code -javaagent} option is not given to the JVM, {@code HotSwapAgent}
* attempts to automatically create and start the hotswap agent on demand.
* This automated deployment may fail. If it fails, manually create the hotswap agent
* and deploy it by {@code -javaagent}.</p>
*
* <p>The {@code HotSwapAgent} requires {@code tools.jar} as well as {@code javassist.jar}.</p>
*
* <p>The idea of this class was given by <a href="https://github.com/alugowski">Adam Lugowski</a>.
* Shigeru Chiba wrote this class by referring
* to his <a href="https://github.com/turn/RedefineClassAgent">{@code RedefineClassAgent}</a>.
* For details, see <a href="https://github.com/jboss-javassist/javassist/issues/119">this discussion</a>.
* </p>
*
* @see #redefine(Class, CtClass)
* @see #redefine(Class[], CtClass[])
* @since 3.22
*/
public class HotSwapAgent {
private static Instrumentation instrumentation = null;
/**
* Obtains the {@code Instrumentation} object.
*
* @return null when it is not available.
*/
public Instrumentation instrumentation() { return instrumentation; }
/**
* The entry point invoked when this agent is started by {@code -javaagent}.
*/
public static void premain(String agentArgs, Instrumentation inst) throws Throwable {
agentmain(agentArgs, inst);
}
/**
* The entry point invoked when this agent is started after the JVM starts.
*/
public static void agentmain(String agentArgs, Instrumentation inst) throws Throwable {
if (!inst.isRedefineClassesSupported())
throw new RuntimeException("this JVM does not support redefinition of classes");
instrumentation = inst;
}
/**
* Redefines a class.
*/
public static void redefine(Class oldClass, CtClass newClass)
throws NotFoundException, IOException, CannotCompileException
{
Class[] old = { oldClass };
CtClass[] newClasses = { newClass };
redefine(old, newClasses);
}
/**
* Redefines classes.
*/
public static void redefine(Class[] oldClasses, CtClass[] newClasses)
throws NotFoundException, IOException, CannotCompileException
{
startAgent();
ClassDefinition[] defs = new ClassDefinition[oldClasses.length];
for (int i = 0; i < oldClasses.length; i++)
defs[i] = new ClassDefinition(oldClasses[i], newClasses[i].toBytecode());
try {
instrumentation.redefineClasses(defs);
}
catch (ClassNotFoundException e) {
throw new NotFoundException(e.getMessage(), e);
}
catch (UnmodifiableClassException e) {
throw new CannotCompileException(e.getMessage(), e);
}
}
/**
* Ensures that the agent is ready.
* It attempts to dynamically start the agent if necessary.
*/
private static void startAgent() throws NotFoundException {
if (instrumentation != null)
return;
try {
File agentJar = createJarFile();
String nameOfRunningVM = ManagementFactory.getRuntimeMXBean().getName();
String pid = nameOfRunningVM.substring(0, nameOfRunningVM.indexOf('@'));
VirtualMachine vm = VirtualMachine.attach(pid);
vm.loadAgent(agentJar.getAbsolutePath(), "");
vm.detach();
}
catch (Exception e) {
throw new NotFoundException("hotswap agent", e);
}
for (int sec = 0; sec < 10 /* sec */; sec++) {
if (instrumentation != null)
return;
try {
Thread.sleep(1000);
}
catch (InterruptedException e) {
Thread.currentThread().interrupt();
break;
}
}
throw new NotFoundException("hotswap agent (timeout)");
}
/**
* Creates an agent file for using {@code HotSwapAgent}.
*/
public static File createAgentJarFile(String fileName)
throws IOException, CannotCompileException, NotFoundException
{
return createJarFile(new File(fileName));
}
private static File createJarFile()
throws IOException, CannotCompileException, NotFoundException
{
File jar = File.createTempFile("agent", ".jar");
jar.deleteOnExit();
return createJarFile(jar);
}
private static File createJarFile(File jar)
throws IOException, CannotCompileException, NotFoundException
{
Manifest manifest = new Manifest();
Attributes attrs = manifest.getMainAttributes();
attrs.put(Attributes.Name.MANIFEST_VERSION, "1.0");
attrs.put(new Attributes.Name("Premain-Class"), HotSwapAgent.class.getName());
attrs.put(new Attributes.Name("Agent-Class"), HotSwapAgent.class.getName());
attrs.put(new Attributes.Name("Can-Retransform-Classes"), "true");
attrs.put(new Attributes.Name("Can-Redefine-Classes"), "true");
JarOutputStream jos = null;
try {
jos = new JarOutputStream(new FileOutputStream(jar), manifest);
String cname = HotSwapAgent.class.getName();
JarEntry e = new JarEntry(cname.replace('.', '/') + ".class");
jos.putNextEntry(e);
ClassPool pool = ClassPool.getDefault();
CtClass clazz = pool.get(cname);
jos.write(clazz.toBytecode());
jos.closeEntry();
}
finally {
if (jos != null)
jos.close();
}
return jar;
}
}