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package sample.evolve;
import javassist.*;
/**
* Evolution provides a set of methods for instrumenting bytecodes.
*
* For class evolution, updatable class A is renamed to B. Then an abstract
* class named A is produced as the super class of B. If the original class A
* has a public method m(), then the abstract class A has an abstract method
* m().
*
* abstract class A abstract m() _makeInstance() | class A --------> class B m()
* m()
*
* Also, all the other classes are translated so that "new A(i)" in the methods
* is replaced with "_makeInstance(i)". This makes it possible to change the
* behavior of the instantiation of the class A.
*/
public class Evolution implements Translator {
public final static String handlerMethod = "_makeInstance";
public final static String latestVersionField = VersionManager.latestVersionField;
public final static String versionManagerMethod = "initialVersion";
private static CtMethod trapMethod;
private static final int initialVersion = 0;
private ClassPool pool;
private String updatableClassName = null;
private CtClass updatableClass = null;
public void start(ClassPool _pool) throws NotFoundException {
pool = _pool;
// Get the definition of Sample.make() and store it into trapMethod
// for later use.
trapMethod = _pool.getMethod("sample.evolve.Sample", "make");
}
public void onLoad(ClassPool _pool, String classname)
throws NotFoundException, CannotCompileException {
onLoadUpdatable(classname);
/*
* Replaces all the occurrences of the new operator with a call to
* _makeInstance().
*/
CtClass clazz = _pool.get(classname);
CtClass absClass = updatableClass;
CodeConverter converter = new CodeConverter();
converter.replaceNew(absClass, absClass, handlerMethod);
clazz.instrument(converter);
}
private void onLoadUpdatable(String classname) throws NotFoundException,
CannotCompileException {
// if the class is a concrete class,
// classname is <updatableClassName>$$<version>.
int i = classname.lastIndexOf("$$");
if (i <= 0)
return;
String orgname = classname.substring(0, i);
if (!orgname.equals(updatableClassName))
return;
int version;
try {
version = Integer.parseInt(classname.substring(i + 2));
}
catch (NumberFormatException e) {
throw new NotFoundException(classname, e);
}
CtClass clazz = pool.getAndRename(orgname, classname);
makeConcreteClass(clazz, updatableClass, version);
}
/*
* Register an updatable class.
*/
public void makeUpdatable(String classname) throws NotFoundException,
CannotCompileException {
if (pool == null)
throw new RuntimeException(
"Evolution has not been linked to ClassPool.");
CtClass c = pool.get(classname);
updatableClassName = classname;
updatableClass = makeAbstractClass(c);
}
/**
* Produces an abstract class.
*/
protected CtClass makeAbstractClass(CtClass clazz)
throws CannotCompileException, NotFoundException {
int i;
CtClass absClass = pool.makeClass(clazz.getName());
absClass.setModifiers(Modifier.PUBLIC | Modifier.ABSTRACT);
absClass.setSuperclass(clazz.getSuperclass());
absClass.setInterfaces(clazz.getInterfaces());
// absClass.inheritAllConstructors();
CtField fld = new CtField(pool.get("java.lang.Class"),
latestVersionField, absClass);
fld.setModifiers(Modifier.PUBLIC | Modifier.STATIC);
CtField.Initializer finit = CtField.Initializer.byCall(pool
.get("sample.evolve.VersionManager"), versionManagerMethod,
new String[] { clazz.getName() });
absClass.addField(fld, finit);
CtField[] fs = clazz.getDeclaredFields();
for (i = 0; i < fs.length; ++i) {
CtField f = fs[i];
if (Modifier.isPublic(f.getModifiers()))
absClass.addField(new CtField(f.getType(), f.getName(),
absClass));
}
CtConstructor[] cs = clazz.getDeclaredConstructors();
for (i = 0; i < cs.length; ++i) {
CtConstructor c = cs[i];
int mod = c.getModifiers();
if (Modifier.isPublic(mod)) {
CtMethod wm = CtNewMethod.wrapped(absClass, handlerMethod, c
.getParameterTypes(), c.getExceptionTypes(),
trapMethod, null, absClass);
wm.setModifiers(Modifier.PUBLIC | Modifier.STATIC);
absClass.addMethod(wm);
}
}
CtMethod[] ms = clazz.getDeclaredMethods();
for (i = 0; i < ms.length; ++i) {
CtMethod m = ms[i];
int mod = m.getModifiers();
if (Modifier.isPublic(mod))
if (Modifier.isStatic(mod))
throw new CannotCompileException(
"static methods are not supported.");
else {
CtMethod m2 = CtNewMethod.abstractMethod(m.getReturnType(),
m.getName(), m.getParameterTypes(), m
.getExceptionTypes(), absClass);
absClass.addMethod(m2);
}
}
return absClass;
}
/**
* Modifies the given class file so that it is a subclass of the abstract
* class produced by makeAbstractClass().
*
* Note: the naming convention must be consistent with
* VersionManager.update().
*/
protected void makeConcreteClass(CtClass clazz, CtClass abstractClass,
int version) throws CannotCompileException, NotFoundException {
int i;
clazz.setSuperclass(abstractClass);
CodeConverter converter = new CodeConverter();
CtField[] fs = clazz.getDeclaredFields();
for (i = 0; i < fs.length; ++i) {
CtField f = fs[i];
if (Modifier.isPublic(f.getModifiers()))
converter.redirectFieldAccess(f, abstractClass, f.getName());
}
CtConstructor[] cs = clazz.getDeclaredConstructors();
for (i = 0; i < cs.length; ++i)
cs[i].instrument(converter);
CtMethod[] ms = clazz.getDeclaredMethods();
for (i = 0; i < ms.length; ++i)
ms[i].instrument(converter);
}
}
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