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Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation
simple. It is a class library for editing bytecodes in Java.
/*
* 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.tools.reflect;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CodeConverter;
import javassist.CtClass;
import javassist.CtField;
import javassist.CtMethod;
import javassist.CtMethod.ConstParameter;
import javassist.CtNewMethod;
import javassist.Modifier;
import javassist.NotFoundException;
import javassist.Translator;
import javassist.bytecode.BadBytecode;
import javassist.bytecode.ClassFile;
import javassist.bytecode.MethodInfo;
/**
* The class implementing the behavioral reflection mechanism.
*
* If a class is reflective,
* then all the method invocations on every
* instance of that class are intercepted by the runtime
* metaobject controlling that instance. The methods inherited from the
* super classes are also intercepted except final methods. To intercept
* a final method in a super class, that super class must be also reflective.
*
*
To do this, the original class file representing a reflective class:
*
*
* class Person {
* public int f(int i) { return i + 1; }
* public int value;
* }
*
*
* is modified so that it represents a class:
*
*
* class Person implements Metalevel {
* public int _original_f(int i) { return i + 1; }
* public int f(int i) { delegate to the metaobject }
*
* public int value;
* public int _r_value() { read "value" }
* public void _w_value(int v) { write "value" }
*
* public ClassMetaobject _getClass() { return a class metaobject }
* public Metaobject _getMetaobject() { return a metaobject }
* public void _setMetaobject(Metaobject m) { change a metaobject }
* }
*
*
* @see javassist.tools.reflect.ClassMetaobject
* @see javassist.tools.reflect.Metaobject
* @see javassist.tools.reflect.Loader
* @see javassist.tools.reflect.Compiler
*/
public class Reflection implements Translator {
static final String classobjectField = "_classobject";
static final String classobjectAccessor = "_getClass";
static final String metaobjectField = "_metaobject";
static final String metaobjectGetter = "_getMetaobject";
static final String metaobjectSetter = "_setMetaobject";
static final String readPrefix = "_r_";
static final String writePrefix = "_w_";
static final String metaobjectClassName = "javassist.tools.reflect.Metaobject";
static final String classMetaobjectClassName
= "javassist.tools.reflect.ClassMetaobject";
protected CtMethod trapMethod, trapStaticMethod;
protected CtMethod trapRead, trapWrite;
protected CtClass[] readParam;
protected ClassPool classPool;
protected CodeConverter converter;
private boolean isExcluded(String name) {
return name.startsWith(ClassMetaobject.methodPrefix)
|| name.equals(classobjectAccessor)
|| name.equals(metaobjectSetter)
|| name.equals(metaobjectGetter)
|| name.startsWith(readPrefix)
|| name.startsWith(writePrefix);
}
/**
* Constructs a new Reflection object.
*/
public Reflection() {
classPool = null;
converter = new CodeConverter();
}
/**
* Initializes the object.
*/
@Override
public void start(ClassPool pool) throws NotFoundException {
classPool = pool;
final String msg
= "javassist.tools.reflect.Sample is not found or broken.";
try {
CtClass c = classPool.get("javassist.tools.reflect.Sample");
rebuildClassFile(c.getClassFile());
trapMethod = c.getDeclaredMethod("trap");
trapStaticMethod = c.getDeclaredMethod("trapStatic");
trapRead = c.getDeclaredMethod("trapRead");
trapWrite = c.getDeclaredMethod("trapWrite");
readParam
= new CtClass[] { classPool.get("java.lang.Object") };
}
catch (NotFoundException e) {
throw new RuntimeException(msg);
} catch (BadBytecode e) {
throw new RuntimeException(msg);
}
}
/**
* Inserts hooks for intercepting accesses to the fields declared
* in reflective classes.
*/
@Override
public void onLoad(ClassPool pool, String classname)
throws CannotCompileException, NotFoundException
{
CtClass clazz = pool.get(classname);
clazz.instrument(converter);
}
/**
* Produces a reflective class.
* If the super class is also made reflective, it must be done
* before the sub class.
*
* @param classname the name of the reflective class
* @param metaobject the class name of metaobjects.
* @param metaclass the class name of the class metaobject.
* @return false if the class is already reflective.
*
* @see javassist.tools.reflect.Metaobject
* @see javassist.tools.reflect.ClassMetaobject
*/
public boolean makeReflective(String classname,
String metaobject, String metaclass)
throws CannotCompileException, NotFoundException
{
return makeReflective(classPool.get(classname),
classPool.get(metaobject),
classPool.get(metaclass));
}
/**
* Produces a reflective class.
* If the super class is also made reflective, it must be done
* before the sub class.
*
* @param clazz the reflective class.
* @param metaobject the class of metaobjects.
* It must be a subclass of
* Metaobject.
* @param metaclass the class of the class metaobject.
* It must be a subclass of
* ClassMetaobject.
* @return false if the class is already reflective.
*
* @see javassist.tools.reflect.Metaobject
* @see javassist.tools.reflect.ClassMetaobject
*/
public boolean makeReflective(Class clazz,
Class metaobject, Class metaclass)
throws CannotCompileException, NotFoundException
{
return makeReflective(clazz.getName(), metaobject.getName(),
metaclass.getName());
}
/**
* Produces a reflective class. It modifies the given
* CtClass object and makes it reflective.
* If the super class is also made reflective, it must be done
* before the sub class.
*
* @param clazz the reflective class.
* @param metaobject the class of metaobjects.
* It must be a subclass of
* Metaobject.
* @param metaclass the class of the class metaobject.
* It must be a subclass of
* ClassMetaobject.
* @return false if the class is already reflective.
*
* @see javassist.tools.reflect.Metaobject
* @see javassist.tools.reflect.ClassMetaobject
*/
public boolean makeReflective(CtClass clazz,
CtClass metaobject, CtClass metaclass)
throws CannotCompileException, CannotReflectException,
NotFoundException
{
if (clazz.isInterface())
throw new CannotReflectException(
"Cannot reflect an interface: " + clazz.getName());
if (clazz.subclassOf(classPool.get(classMetaobjectClassName)))
throw new CannotReflectException(
"Cannot reflect a subclass of ClassMetaobject: "
+ clazz.getName());
if (clazz.subclassOf(classPool.get(metaobjectClassName)))
throw new CannotReflectException(
"Cannot reflect a subclass of Metaobject: "
+ clazz.getName());
registerReflectiveClass(clazz);
return modifyClassfile(clazz, metaobject, metaclass);
}
/**
* Registers a reflective class. The field accesses to the instances
* of this class are instrumented.
*/
private void registerReflectiveClass(CtClass clazz) {
CtField[] fs = clazz.getDeclaredFields();
for (int i = 0; i < fs.length; ++i) {
CtField f = fs[i];
int mod = f.getModifiers();
if ((mod & Modifier.PUBLIC) != 0 && (mod & Modifier.FINAL) == 0) {
String name = f.getName();
converter.replaceFieldRead(f, clazz, readPrefix + name);
converter.replaceFieldWrite(f, clazz, writePrefix + name);
}
}
}
private boolean modifyClassfile(CtClass clazz, CtClass metaobject,
CtClass metaclass)
throws CannotCompileException, NotFoundException
{
if (clazz.getAttribute("Reflective") != null)
return false; // this is already reflective.
clazz.setAttribute("Reflective", new byte[0]);
CtClass mlevel = classPool.get("javassist.tools.reflect.Metalevel");
boolean addMeta = !clazz.subtypeOf(mlevel);
if (addMeta)
clazz.addInterface(mlevel);
processMethods(clazz, addMeta);
processFields(clazz);
CtField f;
if (addMeta) {
f = new CtField(classPool.get("javassist.tools.reflect.Metaobject"),
metaobjectField, clazz);
f.setModifiers(Modifier.PROTECTED);
clazz.addField(f, CtField.Initializer.byNewWithParams(metaobject));
clazz.addMethod(CtNewMethod.getter(metaobjectGetter, f));
clazz.addMethod(CtNewMethod.setter(metaobjectSetter, f));
}
f = new CtField(classPool.get("javassist.tools.reflect.ClassMetaobject"),
classobjectField, clazz);
f.setModifiers(Modifier.PRIVATE | Modifier.STATIC);
clazz.addField(f, CtField.Initializer.byNew(metaclass,
new String[] { clazz.getName() }));
clazz.addMethod(CtNewMethod.getter(classobjectAccessor, f));
return true;
}
private void processMethods(CtClass clazz, boolean dontSearch)
throws CannotCompileException, NotFoundException
{
CtMethod[] ms = clazz.getMethods();
for (int i = 0; i < ms.length; ++i) {
CtMethod m = ms[i];
int mod = m.getModifiers();
if (Modifier.isPublic(mod) && !Modifier.isAbstract(mod))
processMethods0(mod, clazz, m, i, dontSearch);
}
}
private void processMethods0(int mod, CtClass clazz,
CtMethod m, int identifier, boolean dontSearch)
throws CannotCompileException, NotFoundException
{
CtMethod body;
String name = m.getName();
if (isExcluded(name)) // internally-used method inherited
return; // from a reflective class.
CtMethod m2;
if (m.getDeclaringClass() == clazz) {
if (Modifier.isNative(mod))
return;
m2 = m;
if (Modifier.isFinal(mod)) {
mod &= ~Modifier.FINAL;
m2.setModifiers(mod);
}
}
else {
if (Modifier.isFinal(mod))
return;
mod &= ~Modifier.NATIVE;
m2 = CtNewMethod.delegator(findOriginal(m, dontSearch), clazz);
m2.setModifiers(mod);
clazz.addMethod(m2);
}
m2.setName(ClassMetaobject.methodPrefix + identifier
+ "_" + name);
if (Modifier.isStatic(mod))
body = trapStaticMethod;
else
body = trapMethod;
CtMethod wmethod
= CtNewMethod.wrapped(m.getReturnType(), name,
m.getParameterTypes(), m.getExceptionTypes(),
body, ConstParameter.integer(identifier),
clazz);
wmethod.setModifiers(mod);
clazz.addMethod(wmethod);
}
private CtMethod findOriginal(CtMethod m, boolean dontSearch)
throws NotFoundException
{
if (dontSearch)
return m;
String name = m.getName();
CtMethod[] ms = m.getDeclaringClass().getDeclaredMethods();
for (int i = 0; i < ms.length; ++i) {
String orgName = ms[i].getName();
if (orgName.endsWith(name)
&& orgName.startsWith(ClassMetaobject.methodPrefix)
&& ms[i].getSignature().equals(m.getSignature()))
return ms[i];
}
return m;
}
private void processFields(CtClass clazz)
throws CannotCompileException, NotFoundException
{
CtField[] fs = clazz.getDeclaredFields();
for (int i = 0; i < fs.length; ++i) {
CtField f = fs[i];
int mod = f.getModifiers();
if ((mod & Modifier.PUBLIC) != 0 && (mod & Modifier.FINAL) == 0) {
mod |= Modifier.STATIC;
String name = f.getName();
CtClass ftype = f.getType();
CtMethod wmethod
= CtNewMethod.wrapped(ftype, readPrefix + name,
readParam, null, trapRead,
ConstParameter.string(name),
clazz);
wmethod.setModifiers(mod);
clazz.addMethod(wmethod);
CtClass[] writeParam = new CtClass[2];
writeParam[0] = classPool.get("java.lang.Object");
writeParam[1] = ftype;
wmethod = CtNewMethod.wrapped(CtClass.voidType,
writePrefix + name,
writeParam, null, trapWrite,
ConstParameter.string(name), clazz);
wmethod.setModifiers(mod);
clazz.addMethod(wmethod);
}
}
}
public void rebuildClassFile(ClassFile cf) throws BadBytecode {
if (ClassFile.MAJOR_VERSION < ClassFile.JAVA_6)
return;
for (MethodInfo mi:cf.getMethods())
mi.rebuildStackMap(classPool);
}
}