dubbo javassist

javassist提供了两种方法进行动态编译

1. 通过创建class模型对象设置class属性，然后生成class
   CtClass->CtField->CtMethod
2. 直接编译拼凑好的字符串，来生成class
   JavassistCompiler

    package com.enjoy.spi;
    
    import com.alibaba.dubbo.common.compiler.support.JavassistCompiler;
    import javassist.*;
    import org.junit.Test;
    
    import java.lang.reflect.InvocationTargetException;
    
    /**
     * javassist的使用示例
     */
    public class JavassistTest {
    
    	/**
    	 * javassist动态生成类示例
    	 */
    	@Test
    	public void createClassObj() throws NotFoundException, CannotCompileException, IllegalAccessException,
    			InstantiationException, NoSuchMethodException, InvocationTargetException {
    		// ClassPool：Class对象的容器
    		ClassPool pool = ClassPool.getDefault();
    
    		// 通过ClassPool生成一个public类
    		CtClass ctClass = pool.makeClass("com.enjoy.service.DemoImpl");
    
    		// 添加属性 private String name
    		CtField nameFild = new CtField(pool.getCtClass("java.lang.String"), "name", ctClass);
    		nameFild.setModifiers(Modifier.PRIVATE);
    		ctClass.addField(nameFild);
    
    		// 添加属性 private int age
    		CtField ageField = new CtField(pool.getCtClass("int"), "age", ctClass);
    		ageField.setModifiers(Modifier.PRIVATE);
    		ctClass.addField(ageField);
    
    		// 为属性name和age添加getXXX和setXXX方法
    		ctClass.addMethod(CtNewMethod.getter("getName", nameFild));
    		ctClass.addMethod(CtNewMethod.setter("setName", nameFild));
    		ctClass.addMethod(CtNewMethod.getter("getAge", ageField));
    		ctClass.addMethod(CtNewMethod.setter("setAge", ageField));
    
    		// 添加方法 void sayHello(String name) {...}
    		CtMethod ctMethod = new CtMethod(CtClass.voidType, "sayHello", new CtClass[] {}, ctClass);
    		// 方法设置为PUBLIC
    		ctMethod.setModifiers(Modifier.PUBLIC);
    		// 方法体
    		ctMethod.setBody("{\nSystem.out.println(\"hello \" + getName() + \" !\");\n}");
    		ctClass.addMethod(ctMethod);
    
    		// 生成class类
    		Class<?> clazz = ctClass.toClass();
    		// 创建对象
    		Object obj = clazz.newInstance();
    		// 反射 执行方法sayHello
    		obj.getClass().getMethod("setName", new Class[] { String.class }).invoke(obj, new Object[] { "peter" });
    		obj.getClass().getMethod("sayHello", new Class[] {}).invoke(obj, new Object[] {});
    
    	}
    
    	/**
    	 * javassist动态编译类示例
    	 */
    	@Test
    	public void createClassByCompile()
    			throws IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
    		JavassistCompiler compiler = new JavassistCompiler();
    		Class<?> clazz = compiler.compile(
    				"public class DemoImpl implements DemoService {     public String sayHello(String name) {        System.out.println(\"hello \" + name);        return \"Hello, \" + name;   }}",
    				JavassistTest.class.getClassLoader());
    		// 创建对象
    		Object obj = clazz.newInstance();
    		// 反射 执行方法sayHello
    		obj.getClass().getMethod("sayHello", new Class[] { String.class }).invoke(obj, new Object[] { "peter" });
    	}
    }