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一、S02E216_01字節碼操作_javassist庫、介紹、動態創建新類、屬性、方法、構造器
字節碼操作
常見的字節碼操作類庫
JAVAssist庫
package com.test.javassist;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtConstructor;
import javassist.CtField;
import javassist.CtMethod;
/**
* 測試使用javassist生成一個新的類
*/
public class Demo01 {
public static void main(String[] args) throws CannotCompileException, Exception {
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.makeClass("com.test.bean.Emp");
//創建屬性
CtField f1 = CtField.make("private int empno;",cc);
CtField f2 = CtField.make("private String ename;",cc);
cc.addField(f1);
cc.addField(f2);
//創建方法
CtMethod m1 = CtMethod.make("public int getEmpno(){return empno;}", cc);
CtMethod m2 = CtMethod.make("public void setEmpno(){this.empno = empno;}", cc);
cc.addMethod(m1);
cc.addMethod(m2);
//添加構造器
CtConstructor constructor = new CtConstructor(new CtClass[]{CtClass.intType, pool.get("java.lang.String")},cc);
constructor.setBody("{this.empno = empno; this.ename = ename;}");
cc.addConstructor(constructor);
cc.writeFile("g:/java/test");//將上面構造好的類寫入到指定的工作空間中
System.out.println("生成類,成功!");
}
}
使用XJad反編譯後生成的.java文件
// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) fieldsfirst ansi space
// Source File Name: Emp.java
package com.test.bean;
public class Emp
{
private int empno;
private String ename;
public int getEmpno()
{
return empno;
}
public void setEmpno()
{
empno = empno;
}
public Emp(int i, String s)
{
empno = empno;
ename = ename;
}
}
一、S02E217_01字節碼操作javaassist庫介紹_API詳解
package com.test.javassist;
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;
/**
* 測試javassist的API
*/
public class Demo2 {
public static void main(String[] args) throws Exception {
test06();
}
/**
* 處理類的基本用法
* @throws Exception
*/
public static void test01() throws Exception{
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.test.javassist.Emp");//獲取已有的類
byte[] bytes = cc.toBytecode();
System.out.println(Arrays.toString(bytes));
System.out.println(cc.getName());//獲取類名
System.out.println(cc.getSimpleName());//獲取簡要類名
System.out.println(cc.getSuperclass());//獲取父類
System.out.println(cc.getInterfaces());//獲取接口
}
/**
* 測試產生新的方法
*/
public static void test02() throws Exception{
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.test.javassist.Emp");//獲取已有的類
//CtMethod m = CtNewMethod.make("public int add(int a,int b){return a+b;}", cc);
//另一種方式,參數:返回類型,方法名,可變參數類型,CtClass對象
CtMethod m = new CtMethod(CtClass.intType, "add",
new CtClass[]{CtClass.intType,CtClass.intType}, cc);
m.setModifiers(javassist.Modifier.PUBLIC);
m.setBody("{System.out.println(\"返回方法體中的打印信息\");return $1+$2;}");
cc.addMethod(m);
//通過反射調用新生成的方法
Class clazz = cc.toClass();
Object obj = clazz.newInstance();//調用Emp無參構造器,創建新的Emp對象
Method method = clazz.getDeclaredMethod("add", int.class,int.class);
Object result = method.invoke(obj, 200,300);
System.out.println(result);
}
/**
* 修改已有方法的方法體內容
* @throws Exception
*/
public static void test03() throws Exception{
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.test.javassist.Emp");//獲取已有的類
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!!!\");");
//通過反射調用新生成的方法
Class clazz = cc.toClass();
Object obj = clazz.newInstance();//調用Emp無參構造器,創建新的Emp對象
Method method = clazz.getDeclaredMethod("sayHello", int.class);
method.invoke(obj, 300);
}
/**
* 測試產生新的屬性
*/
public static void test04() throws Exception{
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.test.javassist.Emp");//獲取已有的類
//CtField f1 = CtField.make("private int salary;", cc);
//另一種方式
CtField f1 = new CtField(CtClass.intType, "salary",cc);
f1.setModifiers(Modifier.PRIVATE);
cc.addField(f1);
//cc.getDeclaredField("salary");//獲取指定的屬性
//另一種方式
cc.addMethod(CtNewMethod.getter("getSalary", f1));
cc.addMethod(CtNewMethod.getter("setSalary", f1));
//通過反射調用,省略。。。
}
/**
* 測試構造器
*/
public static void test05() throws Exception{
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.test.javassist.Emp");//獲取已有的類
CtConstructor[] cs = cc.getConstructors();
for (CtConstructor c : cs) {
System.out.println(c.getLongName());
}
}
/**
* 測試註解
*/
public static void test06() throws Exception{
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.test.javassist.Emp");//獲取已有的類
Object[] all = cc.getAnnotations();
Author a = (Author) all[0];
String name = a.name();
int year = a.year();
System.out.println("name:" + name + ",year:" + year);
}
}
javabean
package com.test.javassist;
@Author(name = "test",year= 2016)
public class Emp {
private int empNo;
private String empName;
public Emp() {
}
public Emp(int empNo, String empName) {
super();
this.empNo = empNo;
this.empName = empName;
}
public int getEmpNo() {
return empNo;
}
public void setEmpNo(int empNo) {
this.empNo = empNo;
}
public String getEmpName() {
return empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}
public void sayHello(int a){
System.out.println("sayHello," + a);
}
}
註解
package com.test.javassist;
public @interface Author {
String name();
int year();
}