Javassist修改已有类加新的属性注解

Posted 2022-11-26 HiveDark

一、新建类PersonService

name字段目前是有两个注解Autowired和JsonFormat。

package com.david.test.test_springboot_schema.javassist;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;

import com.fasterxml.jackson.annotation.JsonFormat;

@Controller
public class PersonService 
	@Autowired
	@JsonFormat
	private String name;
	
	public void getPerson()
        System.out.println("get Person");
    

    public void personFly()
        System.out.println("oh my god,I can fly");
    

二、javassist动态修改name属性，增加注解

在原有基础上新增JsonIgnore注解，注意AnnotationsAttribute的获取方式，应先检测是否已经存在，存在则用已有的AnnotationsAttribute，否则新增的会覆盖原有的注解。

private static void testAnnotation2() throws Exception 
		// TODO Auto-generated method stub
		ClassPool classPool = ClassPool.getDefault();
		CtClass ctClass = classPool.get("com.david.test.test_springboot_schema.javassist.PersonService");
		//字段添加注解
		CtField ctField = ctClass.getDeclaredField("name");
		List<AttributeInfo> attributeInfos = ctField.getFieldInfo().getAttributes();
		AnnotationsAttribute annotationsAttribute = !attributeInfos.isEmpty()?(AnnotationsAttribute) attributeInfos.get(0):
						new AnnotationsAttribute(ctField.getFieldInfo().getConstPool(), AnnotationsAttribute.visibleTag);
		Annotation annotation = new Annotation("com.fasterxml.jackson.annotation.JsonIgnore", ctField.getFieldInfo().getConstPool());
		annotationsAttribute.addAnnotation(annotation);
		ctField.getFieldInfo().addAttribute(annotationsAttribute);
		ctClass.writeFile("D:\\\\javassist\\\\");
        //class
		System.out.println("==================TEST=================");
        Class<?> afterClass = ctClass.toClass();
        Field field = afterClass.getDeclaredField("name");
        java.lang.annotation.Annotation[] annotation2 = field.getAnnotations();
        for(java.lang.annotation.Annotation annotation3:annotation2) 
        	System.out.println(annotation3);
        
		ctClass.detach();
	

三、运行结果