Javassist操作方法总结

ClassPool pool =ClassPool.getDefault();

//会从classpath中查询该类
CtClass cc = pool.get("test.Rectangle");

//设置.Rectangle的父类
cc.setSuperclass(pool.get("test.Point"));

//输出.Rectangle.class文件到该目录中
cc.writeFile("c://");

//输出成二进制格式

//byte[] b=cc.toBytecode();

//输出并加载class 类，默认加载到当前线程的ClassLoader中，也可以选择输出的ClassLoader。

//Class clazz=cc.toClass();

ClassPool pool =ClassPool.getDefault();

CtClass cc = pool.makeClass("Point");

//新增方法
cc.addMethod(m);

//新增Field
cc.addField(f);

CtClasss cc =...;

    :

cc.writeFile();

cc.defrost();

cc.setSuperclass(...);    //OK since the class is not frozen.

CtClasss cc =...;

cc.stopPruning(true);

    :

cc.writeFile();                             //convert to a class file.

//cc没有被释放

//默认加载方式如pool.insertClassPath(new ClassClassPath(this.getClass()));
ClassPool pool =ClassPool.getDefault();


//从file加载classpath
pool.insertClassPath("/usr/local/javalib")


//从URL中加载
ClassPath cp = new URLClassPath("www.javassist.org", 80, "/java/", "org.javassist.");

pool.insertClassPath(cp);

//从byte[] 中加载

byte[] b = a bytearray;

String name = classname;

cp.insertClassPath(newByteArrayClassPath(name, b));


//可以从输入流中加载class
InputStream ins = an input stream for reading a classfile;

CtClass cc = cp.makeClass(ins);

CtClass cc =... ;

cc.writeFile();

cc.detach();

//ClassPool(true) 会默认加载Jvm的ClassPath
ClassPool cp = new ClassPool(true);

//if needed, append an extra search path by appendClassPath()

ClassPool parent =ClassPool.getDefault();

ClassPool child = newClassPool(parent);

child.insertClassPath("./classes");

ClassPool pool =ClassPool.getDefault();

CtClass cc = pool.get("Point");

cc.setName("Pair");

//重新在classpath加载
CtClass cc1 = pool.get("Point");

ClassPool pool =ClassPool.getDefault();

CtClass cc = pool.get("Point");

cc.writeFile();

//cc.setName("Pair");    wrong since writeFile() has been called.
CtClass cc2 = pool.getAndRename("Point", "Pair");

//当Hello未加载的时候，下面是可以运行的。
ClassPool cp =ClassPool.getDefault();

CtClass cc = cp.get("Hello");

Class c =cc.toClass();

 

//下面这种情况，由于Hello2已加载，所以会出错
Hello2 h=newHello2();

CtClass cc2 = cp.get("Hello2");

Class c2 = cc.toClass();//这里会抛出java.lang.LinkageError 异常

 

//解决加载问题，可以指定一个未加载的ClassLoader
Class c3 = cc.toClass(new MyClassLoader());

 ClassPool pool =ClassPool.getDefault();

 Loader cl = newLoader(pool);

 CtClass ct = pool.get("test.Rectangle");

ct.setSuperclass(pool.get("test.Point"));

Class c = cl.loadClass("test.Rectangle");

Object rect =c.newInstance();

         :

//Translator 为监听器

public class MyTranslator implementsTranslator {

    voidstart(ClassPool pool)

        throwsNotFoundException, CannotCompileException {}

    voidonLoad(ClassPool pool, String classname)

        throwsNotFoundException, CannotCompileException

    {

        CtClass cc =pool.get(classname);

        cc.setModifiers(Modifier.PUBLIC);

    }

}

//示例

public classMain2 {

  public static void main(String[] args) throwsThrowable {

     Translator t = newMyTranslator();

     ClassPool pool =ClassPool.getDefault();

     Loader cl = newLoader();

     cl.addTranslator(pool, t);

     cl.run("MyApp", args);

  }

}

//输出

% java Main2 arg1 arg2...

ClassPool pool =ClassPool.getDefault();

CtClass cc = pool.get("java.lang.String");

CtField f = new CtField(CtClass.intType, "hiddenValue", cc);

f.setModifiers(Modifier.PUBLIC);

cc.addField(f);

cc.writeFile(".");

//运行脚本

% java -Xbootclasspath/p:. MyApp arg1 arg2...

$0, $1, $2, ...    thisand actual parameters

$args    An array of parameters. The type of $args is Object[].

$$    All actual parameters.For example, m($$) is equivalent to m($1,$2,...)

$cflow(...)    cflow variable

$r    The result type. It is used in a cast expression.

$w    The wrapper type. It is used in a cast expression.

$_    The resulting value

$sig    An array of java.lang.Class objects representing the formal parameter types

$type    A java.lang.Class object representing the formal result type.

$class    A java.lang.Class object representing the class currently edited.

    //实际方法

    void move(int dx, intdy)

    //javassist
CtMethod m = cc.getDeclaredMethod("move");

    //打印dx，和dy
m.insertBefore("{ System.out.println($1); System.out.println($2); }");

//原方法

int fact(intn) {

    if (n <= 1)

        returnn;

    else

        return n * fact(n - 1);

}

 

//javassist调用
CtMethod cm =...;

//这里代表使用了cflow
cm.useCflow("fact");

//这里用了cflow，说明当深度为0的时候，就是开始当第一次调用fact的方法的时候，打印方法的第一个参数
cm.insertBefore("if ($cflow(fact) == 0)" + "    System.out.println("fact " + $1);");

Object result =... ;

$_ = ($r)result;

CtMethod m =...;

CtClass etype = ClassPool.getDefault().get("java.io.IOException");

m.addCatch("{ System.out.println($e); throw $e; }", etype);

try{

    the original method body

}

catch(java.io.IOException e) {

    System.out.println(e);

    throwe;

}

$0, $1, $2, ...    thisand actual parameters

$args    An array of parameters. The type of $args is Object[].

$$    All actual parameters.For example, m($$) is equivalent to m($1,$2,...)

$cflow(...)    cflow variable

$r    The result type. It is used in a cast expression.

$w    The wrapper type. It is used in a cast expression.

$sig    An array of java.lang.Class objects representing the formal parameter types

$type    A java.lang.Class object representing the formal result type.

$class    A java.lang.Class object representing the class currently edited.

CtMethod cm =... ;

cm.instrument(

    newExprEditor() {

        public voidedit(MethodCall m)

                      throwsCannotCompileException

        {

            if (m.getClassName().equals("Point")

                          && m.getMethodName().equals("move"))

                m.replace("{ $1 = 0; $_ = $proceed($$); }");

        }

    });

{

　　 before-statements;

  　　$_ =$proceed($$);

　　  after-statements;

}

$0The target object of the method call.

This is not equivalent to this, which represents the caller-side thisobject.

$0 is null if the method is static.

$1, $2, ...    The parameters of the method call.

$_    The resulting value of the method call.

$r    The result type of the method call.

$class    A java.lang.Class object representing the classdeclaring the method.

$sig    An array of java.lang.Class objects representing the formal parameter types

$type    A java.lang.Class object representing the formal result type.

$proceed    The name of the method originally called in the expression.

$0    The target object of the constructor call. This is equivalent to this.

$1, $2, ...    The parameters of the constructor call.

$class    A java.lang.Class object representing the classdeclaring the constructor.

$sig    An array of java.lang.Class objects representing the formal parameter types.

$proceed    The name of the constructor originally called in the expression.

$0    The object containing the field accessed by the expression. This is not equivalent to this.

thisrepresents the object that the method including the expression is invoked on.

$0 is null if the field is static.

$1    The value that would be stored in the field ifthe expression is write access.

Otherwise, $1is not available.

$_    The resulting value of the field access ifthe expression is read access.

Otherwise, the value stored in $_ is discarded.

$r    The type of the field ifthe expression is read access.

Otherwise, $r is void.

$class    A java.lang.Class object representing the classdeclaring the field.

$type    A java.lang.Class object representing the field type.

$proceed    The name of a virtual method executing the original field access. .

$0    null
$1, $2, ...    The parameters to the constructor.

$_    The resulting value of the object creation.

A newly created object must be stored in thisvariable.

$r    The type of the created object.

$sig    An array of java.lang.Class objects representing the formal parameter types

$type    A java.lang.Class object representing the classof the created object.

$proceed    The name of a virtual method executing the original object creation. 

$0    null
$1, $2, ...    The size of each dimension.

$_    The resulting value of the object creation.

A newly created array must be stored in thisvariable.

$r    The type of the created object.

$type    A java.lang.Class object representing the classof the created array .

$proceed    The name of a virtual method executing the original array creation. .

$0    null
$1    The value on the left hand side of the original instanceofoperator.

$_    The resulting value of the expression. The type of $_ is boolean.

$r    The type on the right hand side of the instanceofoperator.

$type    A java.lang.Class object representing the type on the right hand side of the instanceofoperator.

$proceed    The name of a virtual method executing the original instanceofexpression.

It takes one parameter (the type is java.lang.Object) and returns true

ifthe parameter value is an instance of the type on the right hand side of

the original instanceof operator. Otherwise, it returns false.

$0    null
$1The value the type of which is explicitly cast.

$_    The resulting value of the expression. The type of $_ is the same as the type

after the explicit casting, that is, the type surrounded by ( ).

$r    the type after the explicit casting, or the type surrounded by ( ).

$type    A java.lang.Class object representing the same type as $r.

$proceed    The name of a virtual method executing the original type casting.

It takes one parameter of the type java.lang.Object and returns it after

the explicit type casting specified by the original expression.

$1    The exception object caught by the catchclause.

$r    the type of the exception caught by the catchclause. It is used in a cast expression.

$w    The wrapper type. It is used in a cast expression.

$type    A java.lang.Class object representing the type of the exception caught by the catch clause.

CtClass point = ClassPool.getDefault().get("Point");

CtMethod m = CtNewMethod.make("public int xmove(int dx) { x +=dx; }",point);

point.addMethod(m);

CtClass point = ClassPool.getDefault().get("Point");

CtMethod m = CtNewMethod.make("public int ymove(int dy) { $proceed(0, dy); }", point, "this", "move");

CtClass cc =... ;

CtMethod m = new CtMethod(CtClass.intType, "move",newCtClass[] { CtClass.intType }, cc);

cc.addMethod(m);

m.setBody("{ x += $1; }");

cc.setModifiers(cc.getModifiers() & ~Modifier.ABSTRACT);

CtClass cc =... ;

CtMethod m = CtNewMethod.make("public abstract int m(int i);", cc);

CtMethod n = CtNewMethod.make("public abstract int n(int i);", cc);

cc.addMethod(m);

cc.addMethod(n);

m.setBody("{ return ($1 <= 0) ? 1 : (n($1 - 1) * $1); }");

n.setBody("{ return m($1); }");

cc.setModifiers(cc.getModifiers() & ~Modifier.ABSTRACT);

CtClass point = ClassPool.getDefault().get("Point");

CtField f = new CtField(CtClass.intType, "z", point);

point.addField(f);

//point.addField(f, "0");    //initial value is 0.

CtClass point = ClassPool.getDefault().get("Point");

CtField f = CtField.make("public int z = 0;", point);

point.addField(f);

//注解

public @interfaceAuthor {

    String name();

    intyear();

}

//javassist代码
CtClass cc = ClassPool.getDefault().get("Point");

Object[] all =cc.getAnnotations();

Author a = (Author)all[0];

String name =a.name();

int year =a.year();

System.out.println("name: " + name + ", year: " + year);

ClassPool pool =ClassPool.getDefault();

pool.importPackage("java.awt");

CtClass cc = pool.makeClass("Test");

CtField f = CtField.make("public Point p;", cc);

cc.addField(f);

classA {}

class B extendsA {}

class C extendsB {}

 

classX {

    voidfoo(A a) { .. }

    voidfoo(B b) { .. }

}