字节码操做-Javaassist

下面就是一个具体的demo来介绍利用Javaassist库来建立类，不过要先在工程里面导入Javaassist的架包，

package JavaAasist; import java.lang.reflect.Method; import java.util.Arrays; import javassist.ClassPool; import javassist.CtClass; import javassist.CtConstructor; import javassist.CtField; import javassist.CtMethod; import javassist.CtNewMethod; import javassist.Modifier; /** * 测试javassist的API * @author 尚学堂高淇 www.sxt.cn * */
public class DEmo02 { /** * 处理类的基本用法 * @throws Exception */
public static void test01() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("com.bjsxt.test.Emp"); byte[] bytes = cc.toBytecode(); System.out.println(Arrays.toString(bytes)); 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()); //得到父类
System.out.println(cc.getInterfaces()); //得到接口
 } /** * 测试产生新的方法 * @throws Exception */
public static void test02() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("com.bjsxt.test.Emp"); // CtMethod m = CtNewMethod.make("public int add(int a,int b){return a+b;}", cc);
 CtMethod m = new CtMethod(CtClass.intType,"add", new CtClass[]{CtClass.intType,CtClass.intType},cc); m.setModifiers(Modifier.PUBLIC); m.setBody("{System.out.println(\"www.sxt.cn\");return $1+$2;}"); cc.addMethod(m); //经过反射调用新生成的方法
Class clazz = cc.toClass(); Object obj = clazz.newInstance(); //经过调用Emp无参构造器，建立新的Emp对象
Method method = clazz.getDeclaredMethod("add", int.class,int.class); Object result = method.invoke(obj, 200,300); System.out.println(result); } /** * 修改已有的方法的信息，修改方法体的内容 * @throws Exception */
public static void test03() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("com.bjsxt.test.Emp"); CtMethod cm = cc.getDeclaredMethod("sayHello",new CtClass[]{CtClass.intType}); cm.insertBefore("System.out.println($1);System.out.println(\"start!!!\");"); cm.insertAt(9, "int b=3;System.out.println(\"b=\"+b);"); cm.insertAfter("System.out.println(\"end!!!\");"); //经过反射调用新生成的方法
Class clazz = cc.toClass(); Object obj = clazz.newInstance(); //经过调用Emp无参构造器，建立新的Emp对象
Method method = clazz.getDeclaredMethod("sayHello", int.class); method.invoke(obj, 300); } /** * 属性的操做 * @throws Exception */
public static void test04() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("com.bjsxt.test.Emp"); // CtField f1 = CtField.make("private int empno;", cc);
CtField f1 = new CtField(CtClass.intType,"salary",cc); f1.setModifiers(Modifier.PRIVATE); cc.addField(f1); // cc.getDeclaredField("ename"); //获取指定的属性 //增长相应的set和get方法
cc.addMethod(CtNewMethod.getter("getSalary", f1));; cc.addMethod(CtNewMethod.getter("setSalary", f1));; } /** * 构造方法的操做 * @throws Exception */
public static void test05() throws Exception { ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("com.bjsxt.test.Emp"); CtConstructor[] cs = cc.getConstructors(); for (CtConstructor c : cs) { System.out.println(c.getLongName()); } } public static void test06() throws Exception{ CtClass cc = ClassPool.getDefault().get("com.bjsxt.test.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(); } }

 

运行改代码则在对应路径生成一个java文件，不过该文件须要反编译才能够查看，具体的工具是xjad

 

下面是JavaAssist处理类的demo

package JavaAssist; import java.lang.reflect.Method; import java.util.Arrays; import javassist.ClassPool; import javassist.CtClass; import javassist.CtConstructor; import javassist.CtField; import javassist.CtMethod; import javassist.CtNewMethod; import javassist.Modifier; /** * 测试javassist的API * @author 19579 * */
public class DEmo02 { /** * 处理类的基本用法 * @throws Exception */
public static void test01() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("JavaAssist.Emp"); byte[] bytes = cc.toBytecode(); System.out.println(Arrays.toString(bytes)); 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()); //得到父类
System.out.println(cc.getInterfaces()); //得到接口
 } /** * 测试产生新的方法 * @throws Exception */
public static void test02() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("JavaAssist.Emp"); // CtMethod m = CtNewMethod.make("public int add(int a,int b){return a+b;}", cc);
 CtMethod m = new CtMethod(CtClass.intType,"add", new CtClass[]{CtClass.intType,CtClass.intType},cc); m.setModifiers(Modifier.PUBLIC); m.setBody("{System.out.println(\"www.sxt.cn\");return $1+$2;}");//$1和$2分别指两个形参
 cc.addMethod(m); //经过反射调用新生成的方法
Class clazz = cc.toClass(); Object obj = clazz.newInstance(); //经过调用Emp无参构造器，建立新的Emp对象
Method method = clazz.getDeclaredMethod("add", int.class,int.class); Object result = method.invoke(obj, 200,300); System.out.println(result); } /** * 修改已有的方法的信息，修改方法体的内容 * @throws Exception */
public static void test03() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("JavaAssist.Emp"); CtMethod cm = cc.getDeclaredMethod("sayHello",new CtClass[]{CtClass.intType}); cm.insertBefore("System.out.println($1);System.out.println(\"start!!!\");");//在方法体前加入
cm.insertAt(9, "int b=3;System.out.println(\"b=\"+b);");//具体的第9行加入
cm.insertAfter("System.out.println(\"end!!!\");");//在方法后面加入 //经过反射调用新生成的方法
Class clazz = cc.toClass(); Object obj = clazz.newInstance(); //经过调用Emp无参构造器，建立新的Emp对象
Method method = clazz.getDeclaredMethod("sayHello", int.class); method.invoke(obj, 300); } /** * 属性的操做 * @throws Exception */
public static void test04() throws Exception{ ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("JavaAssist.Emp"); // CtField f1 = CtField.make("private int empno;", cc);
CtField f1 = new CtField(CtClass.intType,"salary",cc); f1.setModifiers(Modifier.PRIVATE); cc.addField(f1); // cc.getDeclaredField("ename"); //获取指定的属性 //增长相应的set和get方法
cc.addMethod(CtNewMethod.getter("getSalary", f1));; cc.addMethod(CtNewMethod.getter("setSalary", f1));; } /** * 构造方法的操做 * @throws Exception */
public static void test05() throws Exception { ClassPool pool = ClassPool.getDefault(); CtClass cc = pool.get("JavaAssist.Emp"); CtConstructor[] cs = cc.getConstructors(); for (CtConstructor c : cs) { System.out.println(c.getLongName()); } } public static void test06() throws Exception{ CtClass cc = ClassPool.getDefault().get("JavaAssist.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(); } }

 

对应的emp类以下

package com.bjsxt.test; @Author(name="gaoqi", year=2014) public class Emp { private int empno; private String ename; public void sayHello(int a){ System.out.println("sayHello,"+a); } public int getEmpno() { return empno; } public void setEmpno(int empno) { this.empno = empno; } public String getEname() { return ename; } public void setEname(String ename) { this.ename = ename; } public Emp(int empno, String ename) { super(); this.empno = empno; this.ename = ename; } public Emp() { } } Author类以下 package com.bjsxt.test; public @interface Author { String name(); int year(); }

 

固然javaAssist也有本身的局限性