Spring 自定义注解（上）-白红宇

首先定义一个简单的Service：

public interface IDemoService {    void add(int a, int b);}@Servicepublic class DemoServiceImpl implements  IDemoService {    @Log    public void add(int a, int b) {        System.out.println(Thread.currentThread().getName());        System.out.println(a + b);    }}复制代码

假设@Log注解可以用来记录每个函数的执行情况：

@Target({ElementType.METHOD, ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface Log {}复制代码

使用BeanPostProcesser来生成自定义的代理对象：

@Servicepublic class LogAnnotationBeanPostProcesser extends AbstractBeanFactoryAwareAdvisingPostProcessor {    @Override    public void setBeanFactory(BeanFactory beanFactory) {        super.setBeanFactory(beanFactory);        LogAnnotationAdvisor advisor = new LogAnnotationAdvisor();        advisor.setBeanFactory(beanFactory);        this.advisor = advisor;    }    @Override    public Object postProcessAfterInitialization(Object bean, String beanName) {        Method[] methods = ReflectionUtils.getAllDeclaredMethods(bean.getClass());        for (Method method : methods) {            if (method.isAnnotationPresent(Log.class)) {                ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);                if (!proxyFactory.isProxyTargetClass()) {                    evaluateProxyInterfaces(bean.getClass(), proxyFactory);                }                proxyFactory.addAdvisor(this.advisor);                customizeProxyFactory(proxyFactory);                return proxyFactory.getProxy(getProxyClassLoader());            }        }        return bean;    }}复制代码

LogAnnotationAdvisor用来处理切面:

public class LogAnnotationAdvisor  implements BeanFactoryAware,Advisor{    private Advice advice;    public  LogAnnotationAdvisor(){        this.advice=new LogAnnotationInterceptor();    }    @Override    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {    }    @Override    public Advice getAdvice() {        return this.advice;    }    @Override    public boolean isPerInstance() {        // TODO Auto-generated method stub        return false;    }}复制代码

当然实例处理交给了：

public class LogAnnotationInterceptor    implements MethodInterceptor, Ordered{    @Override    public int getOrder() {        return Ordered.HIGHEST_PRECEDENCE;    }    @Override    public Object invoke(MethodInvocation invocation) throws Throwable {        System.out.println("开始执行");        invocation.proceed();        System.out.println("结束执行");        return null;    }}复制代码

使用：

public class Main {    public static void main(String[] args) {        @SuppressWarnings("resource")        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application-context.xml");             IDemoService demoService = context.getBean(IDemoService.class);    //         AsyncAnnotationBeanPostProcessor             demoService.add(1, 2);    }}复制代码

输出：

开始执行 main 3 结束执行

源代码地址：

解决了如果有一个方法加了@Log注解，那么这个类所有的方法都会执行Log的情况。

至于原理嘛。。下篇讲述。。

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