javassist.Loader Maven / Gradle / Ivy
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/*
* 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;
import java.io.*;
import java.util.Hashtable;
import java.util.Vector;
import java.security.ProtectionDomain;
/**
* The class loader for Javassist.
*
* This is a sample class loader using ClassPool.
* Unlike a regular class loader, this class loader obtains bytecode
* from a ClassPool.
*
*
Note that Javassist can be used without this class loader; programmers
* can define their own versions of class loader. They can run
* a program even without any user-defined class loader if that program
* is statically translated with Javassist.
* This class loader is just provided as a utility class.
*
*
Suppose that an instance of MyTranslator implementing
* the interface Translator is responsible for modifying
* class files.
* The startup program of an application using MyTranslator
* should be something like this:
*
*
* import javassist.*;
*
* public class Main {
* public static void main(String[] args) throws Throwable {
* MyTranslator myTrans = new MyTranslator();
* ClassPool cp = ClassPool.getDefault();
* Loader cl = new Loader(cp);
* cl.addTranslator(cp, myTrans);
* cl.run("MyApp", args);
* }
* }
*
*
* Class MyApp is the main program of the application.
*
*
This program should be executed as follows:
*
*
* % java Main arg1 arg2...
*
*
* It modifies the class MyApp with a MyTranslator
* object before the JVM loads it.
* Then it calls main() in MyApp with arguments
* arg1, arg2, ...
*
*
This program execution is equivalent to:
*
*
* % java MyApp arg1 arg2...
*
*
* except that classes are translated by MyTranslator
* at load time.
*
*
If only a particular class must be modified when it is loaded,
* the startup program can be simpler; MyTranslator is
* unnecessary. For example, if only a class test.Rectangle
* is modified, the main() method above will be the following:
*
*
* ClassPool cp = ClassPool.getDefault();
* Loader cl = new Loader(cp);
* CtClass ct = cp.get("test.Rectangle");
* ct.setSuperclass(cp.get("test.Point"));
* cl.run("MyApp", args);
*
* This program changes the super class of the test.Rectangle
* class.
*
*
Note 1:
*
*
This class loader does not allow the users to intercept the loading
* of java.* and javax.* classes (and
* sun.*, org.xml.*, ...) unless
* Loader.doDelegation is false. This is because
* the JVM prohibits a user class loader from loading a system class.
* Also see Note 2.
* If this behavior is not appropriate, a subclass of Loader
* must be defined and loadClassByDelegation() must be overridden.
*
*
Note 2:
*
*
If classes are loaded with different class loaders, they belong to
* separate name spaces. If class C is loaded by a class
* loader CL, all classes that the class C
* refers to are also loaded by CL. However, if CL
* delegates the loading of the class C to CL',
* then those classes that the class C refers to
* are loaded by a parent class loader CL'
* instead of CL.
*
*
If an object of class C is assigned
* to a variable of class C belonging to a different name
* space, then a ClassCastException is thrown.
*
*
Because of the fact above, this loader delegates only the loading of
* javassist.Loader
* and classes included in package java.* and
* javax.* to the parent class
* loader. Other classes are directly loaded by this loader.
*
*
For example, suppose that java.lang.String would be loaded
* by this loader while java.io.File is loaded by the parent
* class loader. If the constructor of java.io.File is called
* with an instance of java.lang.String, then it may throw
* an exception since it accepts an instance of only the
* java.lang.String loaded by the parent class loader.
*
* @see javassist.ClassPool
* @see javassist.Translator
*/
public class Loader extends ClassLoader {
private Hashtable notDefinedHere; // must be atomic.
private Vector notDefinedPackages; // must be atomic.
private ClassPool source;
private Translator translator;
private ProtectionDomain domain;
/**
* Specifies the algorithm of class loading.
*
*
This class loader uses the parent class loader for
* java.* and javax.* classes.
* If this variable doDelegation
* is false, this class loader does not delegate those
* classes to the parent class loader.
*
*
The default value is true.
*/
public boolean doDelegation = true;
/**
* Creates a new class loader.
*/
public Loader() {
this(null);
}
/**
* Creates a new class loader.
*
* @param cp the source of class files.
*/
public Loader(ClassPool cp) {
init(cp);
}
/**
* Creates a new class loader
* using the specified parent class loader for delegation.
*
* @param parent the parent class loader.
* @param cp the source of class files.
*/
public Loader(ClassLoader parent, ClassPool cp) {
super(parent);
init(cp);
}
private void init(ClassPool cp) {
notDefinedHere = new Hashtable();
notDefinedPackages = new Vector();
source = cp;
translator = null;
domain = null;
delegateLoadingOf("javassist.Loader");
}
/**
* Records a class so that the loading of that class is delegated
* to the parent class loader.
*
*
If the given class name ends with . (dot), then
* that name is interpreted as a package name. All the classes
* in that package and the sub packages are delegated.
*/
public void delegateLoadingOf(String classname) {
if (classname.endsWith("."))
notDefinedPackages.addElement(classname);
else
notDefinedHere.put(classname, this);
}
/**
* Sets the protection domain for the classes handled by this class
* loader. Without registering an appropriate protection domain,
* the program loaded by this loader will not work with a security
* manager or a signed jar file.
*/
public void setDomain(ProtectionDomain d) {
domain = d;
}
/**
* Sets the soruce ClassPool.
*/
public void setClassPool(ClassPool cp) {
source = cp;
}
/**
* Adds a translator, which is called whenever a class is loaded.
*
* @param cp the ClassPool object for obtaining
* a class file.
* @param t a translator.
* @throws NotFoundException if t.start() throws an exception.
* @throws CannotCompileException if t.start() throws an exception.
*/
public void addTranslator(ClassPool cp, Translator t)
throws NotFoundException, CannotCompileException {
source = cp;
translator = t;
t.start(cp);
}
/**
* Loads a class with an instance of Loader
* and calls main() of that class.
*
*
This method calls run().
*
* @param args command line parameters.
*
{@code args[0]} is the class name to be loaded.
*
{@code args[1..n]} are parameters passed
* to the target {@code main()}.
*
* @see javassist.Loader#run(String[])
*/
public static void main(String[] args) throws Throwable {
Loader cl = new Loader();
cl.run(args);
}
/**
* Loads a class and calls main() in that class.
*
* @param args command line parameters.
*
*
{@code args[0]} is the class name to be loaded.
*
{@code args[1..n]} are parameters passed
* to the target {@code main()}.
*/
public void run(String[] args) throws Throwable {
int n = args.length - 1;
if (n >= 0) {
String[] args2 = new String[n];
for (int i = 0; i < n; ++i)
args2[i] = args[i + 1];
run(args[0], args2);
}
}
/**
* Loads a class and calls main() in that class.
*
* @param classname the loaded class.
* @param args parameters passed to main().
*/
public void run(String classname, String[] args) throws Throwable {
Class c = loadClass(classname);
try {
c.getDeclaredMethod("main", new Class[] { String[].class }).invoke(
null,
new Object[] { args });
}
catch (java.lang.reflect.InvocationTargetException e) {
throw e.getTargetException();
}
}
/**
* Requests the class loader to load a class.
*/
protected Class loadClass(String name, boolean resolve)
throws ClassFormatError, ClassNotFoundException {
name = name.intern();
synchronized (name) {
Class c = findLoadedClass(name);
if (c == null)
c = loadClassByDelegation(name);
if (c == null)
c = findClass(name);
if (c == null)
c = delegateToParent(name);
if (resolve)
resolveClass(c);
return c;
}
}
/**
* Finds the specified class using ClassPath.
* If the source throws an exception, this returns null.
*
*
This method can be overridden by a subclass of
* Loader. Note that the overridden method must not throw
* an exception when it just fails to find a class file.
*
* @return null if the specified class could not be found.
* @throws ClassNotFoundException if an exception is thrown while
* obtaining a class file.
*/
protected Class findClass(String name) throws ClassNotFoundException {
byte[] classfile;
try {
if (source != null) {
if (translator != null)
translator.onLoad(source, name);
try {
classfile = source.get(name).toBytecode();
}
catch (NotFoundException e) {
return null;
}
}
else {
String jarname = "/" + name.replace('.', '/') + ".class";
InputStream in = this.getClass().getResourceAsStream(jarname);
if (in == null)
return null;
classfile = ClassPoolTail.readStream(in);
}
}
catch (Exception e) {
throw new ClassNotFoundException(
"caught an exception while obtaining a class file for "
+ name, e);
}
int i = name.lastIndexOf('.');
if (i != -1) {
String pname = name.substring(0, i);
if (getPackage(pname) == null)
try {
definePackage(
pname, null, null, null, null, null, null, null);
}
catch (IllegalArgumentException e) {
// ignore. maybe the package object for the same
// name has been created just right away.
}
}
if (domain == null)
return defineClass(name, classfile, 0, classfile.length);
else
return defineClass(name, classfile, 0, classfile.length, domain);
}
protected Class loadClassByDelegation(String name)
throws ClassNotFoundException
{
/* The swing components must be loaded by a system
* class loader.
* javax.swing.UIManager loads a (concrete) subclass
* of LookAndFeel by a system class loader and cast
* an instance of the class to LookAndFeel for
* (maybe) a security reason. To avoid failure of
* type conversion, LookAndFeel must not be loaded
* by this class loader.
*/
Class c = null;
if (doDelegation)
if (name.startsWith("java.")
|| name.startsWith("javax.")
|| name.startsWith("sun.")
|| name.startsWith("com.sun.")
|| name.startsWith("org.w3c.")
|| name.startsWith("org.xml.")
|| notDelegated(name))
c = delegateToParent(name);
return c;
}
private boolean notDelegated(String name) {
if (notDefinedHere.get(name) != null)
return true;
int n = notDefinedPackages.size();
for (int i = 0; i < n; ++i)
if (name.startsWith((String)notDefinedPackages.elementAt(i)))
return true;
return false;
}
protected Class delegateToParent(String classname)
throws ClassNotFoundException
{
ClassLoader cl = getParent();
if (cl != null)
return cl.loadClass(classname);
else
return findSystemClass(classname);
}
}