dubbo源码——javaassist

灰太狼 2022-05-22 10:18 183阅读 0赞

假设要使用javassist创建一个类：

1 package com.alibaba.dubbo.demo.test;
     2 
     3 public class Emp {
     4     //属性
     5     private int    account;
     6     private String name;
     7 
     8     //构造方法
     9     public Emp() {
    10         this.account = 1;
    11         this.name = "xiaona";
    12     }
    13 
    14     //getter
    15     public int getAccount() {
    16         return account;
    17     }
    18 
    19     //setter
    20     public void setAccount(int account) {
    21         this.account = account;
    22     }
    23 
    24     public String getName() {
    25         return name;
    26     }
    27 
    28     public void setName(String name) {
    29         this.name = name;
    30     }
    31 
    32     //普通方法
    33     public void commonMethod() {
    34         System.out.println("haha");
    35     }
    36 }

该类包含属性／构造方法／getter／setter／普通方法。

使用javassist来创建类：

1 package com.alibaba.dubbo.demo.test;
     2 
     3 import javassist.ClassPool;
     4 import javassist.CtClass;
     5 import javassist.CtConstructor;
     6 import javassist.CtField;
     7 import javassist.CtMethod;
     8 import javassist.CtNewMethod;
     9 import javassist.Modifier;
    10 
    11 import java.io.File;
    12 import java.io.FileOutputStream;
    13 
    14 public class TestJavassitCompiler {
    15     public static void main(String[] args) throws Exception {
    16         ClassPool pool = ClassPool.getDefault();
    17         CtClass ctClass = pool.makeClass("com.alibaba.dubbo.demo.test.Emp");
    18         //添加属性:private String name
    19         CtField nameField = new CtField(pool.getCtClass("java.lang.String"), "name", ctClass);
    20         nameField.setModifiers(Modifier.PRIVATE);
    21         ctClass.addField(nameField);
    22         //添加属性:private int account
    23         CtField accountField = new CtField(pool.getCtClass("int"), "account", ctClass);
    24         accountField.setModifiers(Modifier.PRIVATE);
    25         ctClass.addField(accountField);
    26         //getter和setter
    27         ctClass.addMethod(CtNewMethod.getter("getName", nameField));
    28         ctClass.addMethod(CtNewMethod.setter("setName", nameField));
    29         ctClass.addMethod(CtNewMethod.getter("getAccount", accountField));
    30         ctClass.addMethod(CtNewMethod.setter("setAccount", accountField));
    31         //创建构造器
    32         CtConstructor ctConstructor = new CtConstructor(new CtClass[] {}, ctClass);
    33         String body = new StringBuilder("{\nthis.account = 1;\nthis.name = \"xiaona\";\n}").toString();
    34         ctConstructor.setBody(body);
    35         ctClass.addConstructor(ctConstructor);
    36         //普通方法
    37         CtMethod ctMethod = new CtMethod(CtClass.voidType, "commonMethod", new CtClass[] {}, ctClass);
    38         ctMethod.setModifiers(Modifier.PUBLIC);
    39         ctMethod.setBody(new StringBuilder("{\n System.out.println(\"haha\"); \n}").toString());
    40         ctClass.addMethod(ctMethod);
    41 
    42         Class<?> clazz = ctClass.toClass();
    43         Object obj = clazz.newInstance();
    44         obj.getClass().getMethod("commonMethod", new Class[] {}).invoke(obj, new Object[] {});//方法调用
    45 
    46         /**
    47          * 将字节码输出到文件中
    48          */
    49         byte[] codeByteArray = ctClass.toBytecode();
    50         FileOutputStream fos = new FileOutputStream(new File("/Users/jigangzhao/Desktop/Emp.class"));
    51         fos.write(codeByteArray);
    52         fos.close();
    53     }
    54 }

//参考文档：https://github.com/jboss-javassist/javassist/wiki/Tutorial-1