Java学习之javassist

 1 ClassPool pool = ClassPool.getDefault();
 2 //会从classpath中查询该类
 3 CtClass cc = pool.get("test.Rectangle");
 4 //设置.Rectangle的父类
 5 cc.setSuperclass(pool.get("test.Point"));
 6 //输出.Rectangle.class文件到该目录中
 7 cc.writeFile("c://");
 8 //输出成二进制格式
 9 //byte[] b=cc.toBytecode();
10 //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。
11 //Class clazz=cc.toClass();

1 ClassPool pool = ClassPool.getDefault();
2 CtClass cc = pool.makeClass("Point");
3 //新增方法
4 cc.addMethod(m);
5 //新增Field
6 cc.addField(f);

1 CtClasss cc = ...;
2     :
3 cc.writeFile();
4 cc.defrost();
5 cc.setSuperclass(...);    // OK since the class is not frozen.

1 CtClasss cc = ...;
2 cc.stopPruning(true);
3     :
4 cc.writeFile();                             // convert to a class file.
5 // cc没有被释放

 1 //默认加载方式如pool.insertClassPath(new ClassClassPath(this.getClass()));
 2 ClassPool pool = ClassPool.getDefault();
 3 //从file加载classpath
 4 pool.insertClassPath("/usr/local/javalib")
 5 //从URL中加载
 6 ClassPath cp = new URLClassPath("www.javassist.org", 80, "/java/", "org.javassist.");
 7 pool.insertClassPath(cp);
 8 //从byte[] 中加载
 9 byte[] b = a byte array;
10 String name = class name;
11 cp.insertClassPath(new ByteArrayClassPath(name, b));
12 //可以从输入流中加载class
13 InputStream ins = an input stream for reading a class file;
14 CtClass cc = cp.makeClass(ins);

1 CtClass cc = ... ;
2 cc.writeFile();
3 cc.detach();

1 //ClassPool(true) 会默认加载Jvm的ClassPath
2 ClassPool cp = new ClassPool(true);
3 // if needed, append an extra search path by appendClassPath()

1 ClassPool parent = ClassPool.getDefault();
2 ClassPool child = new ClassPool(parent);
3 child.insertClassPath("./classes");

1 ClassPool pool = ClassPool.getDefault();
2 CtClass cc = pool.get("Point");
3 cc.setName("Pair");
4 //重新在classpath加载
5 CtClass cc1 = pool.get("Point"); 

1 ClassPool pool = ClassPool.getDefault();
2 CtClass cc = pool.get("Point");
3 cc.writeFile(); // has frozened
4 //cc.setName("Pair");    wrong since writeFile() has been called.
5 CtClass cc2 = pool.getAndRename("Point", "Pair"); 

 1 // 当Hello未加载的时候，下面是可以运行的。
 2 ClassPool cp = ClassPool.getDefault();
 3 CtClass cc = cp.get("Hello");
 4 Class c = cc.toClass();
 5 //下面这种情况，由于Hello2已加载，所以会出错
 6 Hello2 h=new Hello2();
 7 CtClass cc2 = cp.get("Hello2");
 8 Class c2 = cc.toClass();//这里会抛出java.lang.LinkageError 异常
 9 //解决加载问题，可以指定一个未加载的ClassLoader
10 Class c3 = cc.toClass(new MyClassLoader());

1  ClassPool pool = ClassPool.getDefault();
2  Loader cl = new Loader(pool);
3  CtClass ct = pool.get("test.Rectangle");
4  ct.setSuperclass(pool.get("test.Point"));
5  Class c = cl.loadClass("test.Rectangle");
6  Object rect = c.newInstance();        :

 1 //Translator 为监听器
 2 public class MyTranslator implements Translator {
 3     void start(ClassPool pool)
 4         throws NotFoundException, CannotCompileException {}
 5     void onLoad(ClassPool pool, String classname)
 6         throws NotFoundException, CannotCompileException
 7     {
 8         CtClass cc = pool.get(classname);
 9         cc.setModifiers(Modifier.PUBLIC);
10     }
11 }
12 //示例
13 public class Main2 {
14   public static void main(String[] args) throws Throwable {
15      Translator t = new MyTranslator();
16      ClassPool pool = ClassPool.getDefault();
17      Loader cl = new Loader();
18      cl.addTranslator(pool, t);
19      cl.run("MyApp", args);
20   }
21 }
22 //输出
23 % 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...

1 //实际方法
2 void move(int dx, int dy) 
3 //javassist
4 CtMethod m = cc.getDeclaredMethod("move");
5 //打印dx，和dy
6 m.insertBefore("{ System.out.println($1); System.out.println($2); }");

1 //原方法
2 move(String a,String b)
3 move($$) 相当于move($1,$2)
4 如果新增一个方法，方法含有move的所有参数，则可以这些写：
5 exMove($$, context) 相当于 exMove($1, $2, context)

 1 //原方法
 2 int fact(int n) {
 3     if (n <= 1)
 4         return n;
 5     else
 6         return n * fact(n - 1);
 7 }
 8 //javassist调用
 9 CtMethod cm = ...;
10 //这里代表使用了cflow
11 cm.useCflow("fact");
12 //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
13 cm.insertBefore("if ($cflow(fact) == 0)"
14               + "    System.out.println(\"fact \" + $1);");

1 CtMethod m = ...;
2 CtClass etype = ClassPool.getDefault().get("java.io.IOException");
3 m.addCatch("{ System.out.println($e); throw $e; }", etype);

1 try {
2     the original method body
3 }
4 catch (java.io.IOException e) {
5     System.out.println(e);
6     throw e;
7 }

 1 CtMethod cm = ... ;
 2 cm.instrument(
 3     new ExprEditor() {
 4         public void edit(MethodCall m)
 5                       throws CannotCompileException
 6         {
 7             if (m.getClassName().equals("Point")
 8                           && m.getMethodName().equals("move"))
 9                 m.replace("{ $1 = 0; $_ = $proceed($$); }");
10         }
11     });

 1 CtClass point = ClassPool.getDefault().get("Point");
 2 CtMethod m = CtNewMethod.make(
 3                  "public int xmove(int dx) { x += dx; }",
 4                  point);
 5 point.addMethod(m);
 6  
 7 在方法中调用其他方法，例如：
 8 CtClass point = ClassPool.getDefault().get("Point");
 9 CtMethod m = CtNewMethod.make(
10                  "public int ymove(int dy) { $proceed(0, dy); }",
11                  point, "this", "move");
12 其效果如下：
13 public int ymove(int dy) { this.move(0, dy); }

1 CtClass cc = ... ;
2 CtMethod m = new CtMethod(CtClass.intType, "move",
3                           new CtClass[] { CtClass.intType }, cc);
4 cc.addMethod(m);
5 m.setBody("{ x += $1; }");
6 cc.setModifiers(cc.getModifiers() & ~Modifier.ABSTRACT);
7 Since Javassist makes a class abstract if an abstract method is added to the class, you have to explicitly change the class back to a non-abstract one after calling setBody().

1 CtClass cc = ... ;
2 CtMethod m = CtNewMethod.make("public abstract int m(int i);", cc);
3 CtMethod n = CtNewMethod.make("public abstract int n(int i);", cc);
4 cc.addMethod(m);
5 cc.addMethod(n);
6 m.setBody("{ return ($1 <= 0) ? 1 : (n($1 - 1) * $1); }");
7 n.setBody("{ return m($1); }");
8 cc.setModifiers(cc.getModifiers() & ~Modifier.ABSTRACT);

1 CtClass point = ClassPool.getDefault().get("Point");
2 CtField f = new CtField(CtClass.intType, "z", point);
3 point.addField(f);
4 //point.addField(f, "0");    // initial value is 0.
5 或者：
6 CtClass point = ClassPool.getDefault().get("Point");
7 CtField f = CtField.make("public int z = 0;", point);
8 point.addField(f);

1 调用removeField()或者removeMethod()。

 1 //注解
 2 public @interface Author {
 3     String name();
 4     int year();
 5 }
 6 //javassist代码
 7 CtClass cc = ClassPool.getDefault().get("Point");
 8 Object[] all = cc.getAnnotations();
 9 Author a = (Author)all[0];
10 String name = a.name();
11 int year = a.year();
12 System.out.println("name: " + name + ", year: " + year);

1 ClassPool pool = ClassPool.getDefault();
2 pool.importPackage("java.awt");
3 CtClass cc = pool.makeClass("Test");
4 CtField f = CtField.make("public Point p;", cc);
5 cc.addField(f);