java javassist库处理类的基本用法

Posted 2022-11-06

public class Dema //获取原方法信息 public static void test01() throws Exception ClassPool pool=ClassPool.getDefault(); CtClass cc=pool.get("cn.sxt.in.Emp"); //获得已有的类 byte[] bytes=cc.toBytecode(); //转换成字节码 System.out.println(cc.getName()); //获取类名 System.out.println(cc.getSimpleName()); //获取简要类名 System.out.println(cc.getSuperclass()); //获取父类 System.out.println(Arrays.toString(bytes)); System.out.println(cc.getInterfaces()); //获取接口，返回的是数组 //添加方法 public static void test02() throws Exception ClassPool pool =ClassPool.getDefault(); CtClass cc=pool.get("cn.sxt.in.Emp"); //创建新方法 CtMethod m=CtNewMethod.make("public int add(int a,int b)return a+b;", cc); //创建新方法 CtMethod m2=new CtMethod(CtClass.intType,"add2",new CtClass[] CtClass.intType,CtClass.intType,cc); m2.setModifiers(Modifier.PUBLIC); //设置权限 m2.setBody("System.out.println(\"yes\");return $1+$2;"); //占位符代替形参名 cc.addMethod(m2); cc.addMethod(m); //通过反射调用新生成的方法 Class clazz=cc.toClass(); Object obj=clazz.newInstance(); //通过调用Emp的无参构造器，创建新的Emp对象 Method method=clazz.getDeclaredMethod("add2",int.class,int.class); Object result=method.invoke(obj, 200,300); System.out.println(result); //修改方法 public static void test03() throws Exception ClassPool pool=ClassPool.getDefault(); CtClass cc=pool.get("cn.sxt.in.Emp"); CtMethod cm=cc.getDeclaredMethod("sayHello",new CtClass[] CtClass.intType); //在方法开头添加内容 cm.insertBefore("System.out.println($1);System.out.println(\"start\");"); //在某一行前面加代码 cm.insertAt(8, "System.out.println(\"ugly\");"); //在方法后面加内容 cm.insertAfter("System.out.println(\"end\");"); Class clazz=cc.toClass(); Object obj=clazz.newInstance(); //通过调用Emp的无参构造器，创建新的Emp对象 Method method=clazz.getDeclaredMethod("sayHello",int.class); method.invoke(obj,300); //修改属性 public static void test04() throws Exception ClassPool pool=ClassPool.getDefault(); CtClass cc=pool.get("cn.sxt.in.Emp"); CtField f1=CtField.make("private int emm;", cc); CtField f2=new CtField(CtClass.intType,"emm2",cc); f2.setModifiers(Modifier.PRIVATE); cc.addField(f1,"100"); //传默认值 cc.addField(f2); //cc.getDeclaredField("ename"); 获取指定属性 //增加相应的set和get方法 cc.addMethod(CtNewMethod.getter("getEmm2", f2)); cc.addMethod(CtNewMethod.getter("setEmm2", f2)); //构造器 public static void test05() throws Exception ClassPool pool=ClassPool.getDefault(); CtClass cc=pool.get("cn.sxt.in.Emp"); CtConstructor[] cs= cc.getConstructors(); for(CtConstructor c:cs) System.out.println(c.getLongName()); //调用注解 public static void test06() throws Exception ClassPool pool=ClassPool.getDefault(); CtClass cc=pool.get("cn.sxt.in.Emp"); Object[] all=cc.getAnnotations(); Author a=(Author)all[0]; String name=a.name(); int year=a.year(); System.out.println("name:"+name+",year:"+year); public static void main(String[] args) throws Exception test06();