什麼是javassist ?

javassist是一個開源的生成java位元組碼的類庫,其優點在於簡單,快速,直接使用javassist就可以動態生成javaBean,或修改類的結構

使用javassist實現動態代理

1.準備需要的jar包

<dependency>
    <groupId>org.javassist</groupId>
	<artifactId>javassist</artifactId>
	<version>3.24.0-GA</version>
</dependency>
 

2.建立被代理的類

public class Person {

	private String userId;
	private String password;
	private String username;
	private Integer age;
    /** setter|getter  **/
	public void writeWork() {
		System.out.println("student is writeing homework ...");
	}

3.建立代理類

public class JavassisForPerson {
	
	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws Exception {
		ProxyFactory proxyFactory = new ProxyFactory();
		//指定父類/proxtfactory會自動生成繼承該類的子類
		proxyFactory.setSuperclass(Person.class);
		
		//設定過濾器,判斷哪些方法需要被攔截
		proxyFactory.setFilter((m) ->{
			if(m.getName().equals("writeWork")) {
				return true;
			}
			return false;
		});
		
		//設定攔截代理
		proxyFactory.setHandler((self,thisMethod,proceed,arg) ->{
			System.out.println("前置通知");
			Object object = proceed.invoke(self, arg);
			System.out.println("後置通知");
			return object;
		});
		
		//建立Person代理類,並建立物件
		Class<?> class1 = proxyFactory.createClass();
		Person person =  (Person) class1.newInstance();
		person.writeWork();
		
	}
}
 

4.執行結果