简介
说明
本文用实例介绍Spring的BeanPostProcessor的应用。
所有的Bean都会走到BeanPostProcessor接口的postProcessBeforeInitialization和postProcessAfterInitialization方法。
Bean的生命周期流程见：Spring-Bean生命周期-流程/原理 – 自学精灵
简单示例
代码
package com.example.processor;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
@Component
public class TestProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("postProcessBeforeInitialization==> " + "bean:" + bean + "; " + "beanName:" + beanName);
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("postProcessAfterInitialization==> " + "bean:" + bean + "; " + "beanName:" + beanName);
return bean;
}
}
运行结果（太长，只贴一部分）
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.3.0.RELEASE) 2021-03-04 23:40:59.246 INFO 5820 --- [ main] com.example.DemoApplication : Starting DemoApplication on DESKTOP-QI6B9ME with PID 5820 (E:\work\Idea_proj\demo_JAVA\demo_SpringBoot\target\classes started by Liu in E:\work\Idea_proj\demo_JAVA\demo_SpringBoot) 2021-03-04 23:40:59.248 INFO 5820 --- [ main] com.example.DemoApplication : No active profile set, falling back to default profiles: default postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat@1136b469; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat@1136b469; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat postProcessBeforeInitialization==> bean:org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory@512d4583; beanName:tomcatServletWebServerFactory postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration@2abc224d; beanName:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration@2abc224d; beanName:org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.TomcatWebSocketServletWebServerCustomizer@2b97cc1f; beanName:websocketServletWebServerCustomizer postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.websocket.servlet.TomcatWebSocketServletWebServerCustomizer@2b97cc1f; beanName:websocketServletWebServerCustomizer postProcessBeforeInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration@64f555e7; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration postProcessAfterInitialization==> bean:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration@64f555e7; beanName:org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration
高级应用：注入属性
简介
Spring开发时，会遇到同一个接口有多个实现类，通常有如下几种方法：
- 通过@Autowired+@Qualify引入接口：@Autowired @Qualify(“helloServiceImpl2”) private HelloService helloService;
- 通过@Autowired+@Primary：在某个实现类上标注@Primary
- 在具体调用的地方通过ApplicationContext根据业务的需要来选择不同的接口实现类，虽然可以在抽象出一个工厂方法，但是还是感觉不够优雅。
其实上边这些方法已经能满足开发需求了，而且推荐使用法1。本处，使用BeanPostProcessor+自定义注解来达到同样的作用。当然，这么写是重复造轮子，本质上是毫无意义的。但是，我们可以从本例子中学到如下几点：
- 给使用了自定义注解的属性赋值的方法
- 代理工厂类的用法
- BeanPostProcessor的用法
接口
package com.example.service;
public interface HelloService {
void sayHello();
}
实现类
package com.example.service.impl;
import com.example.service.HelloService;
import org.springframework.stereotype.Service;
@Service
public class HelloServiceImpl1 implements HelloService {
@Override
public void sayHello() {
System.out.println("我是HelloServiceImpl1");
}
}
package com.example.service.impl;
import com.example.service.HelloService;
import org.springframework.stereotype.Service;
@Service
public class HelloServiceImpl2 implements HelloService {
@Override
public void sayHello() {
System.out.println("我是HelloServiceImpl2");
}
}
自定义注解
package com.example.annotation;
import org.springframework.stereotype.Component;
import java.lang.annotation.*;
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface RountingInjected {
String value() default "helloServiceImpl1";
}
自定义BeanPostProcessor实现类
package com.example.processor;
import com.example.annotation.RountingInjected;
import com.example.factory.RoutingBeanProxyFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanCreationException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;
import java.lang.reflect.Field;
import java.util.Map;
@Component
public class HelloServiceInjectProcessor implements BeanPostProcessor {
@Autowired
private ApplicationContext applicationContext;
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
Class<?> targetCls = bean.getClass();
Field[] targetFld = targetCls.getDeclaredFields();
for (Field field : targetFld) {
//找到指定目标的注解类
if (field.isAnnotationPresent(RountingInjected.class)) {
if (!field.getType().isInterface()) {
throw new BeanCreationException("RoutingInjected field must be declared as an interface:"
+ field.getName() + " @Class " + targetCls.getName());
}
try {
this.handleRoutingInjected(field, bean, field.getType());
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
return bean;
}
private void handleRoutingInjected(Field field, Object bean, Class type) throws IllegalAccessException {
Map<String, Object> candidates = this.applicationContext.getBeansOfType(type);
field.setAccessible(true);
if (candidates.size() == 1) {
field.set(bean, candidates.values().iterator().next());
} else if (candidates.size() == 2) {
String injectVal = field.getAnnotation(RountingInjected.class).value();
Object proxy = RoutingBeanProxyFactory.createProxy(injectVal, type, candidates);
field.set(bean, proxy);
} else {
throw new IllegalArgumentException("Find more than 2 beans for type: " + type);
}
}
}
代理实现类
package com.example.factory;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.framework.ProxyFactory;
import java.util.Map;
public class RoutingBeanProxyFactory {
private final static String DEFAULT_BEAN_NAME = "helloServiceImpl1";
public static Object createProxy(String name, Class type, Map<String, Object> candidates) {
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.setInterfaces(type);
proxyFactory.addAdvice(new VersionRoutingMethodInterceptor(name, candidates));
return proxyFactory.getProxy();
}
static class VersionRoutingMethodInterceptor implements MethodInterceptor {
private Object targetObject;
public VersionRoutingMethodInterceptor(String name, Map<String, Object> beans) {
this.targetObject = beans.get(name);
if (this.targetObject == null) {
this.targetObject = beans.get(DEFAULT_BEAN_NAME);
}
}
@Override
public Object invoke(MethodInvocation invocation) throws Throwable {
return invocation.getMethod().invoke(this.targetObject, invocation.getArguments());
}
}
}
测试类
package com.example.controller;
import com.example.annotation.RountingInjected;
import com.example.service.HelloService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class HelloController {
@RountingInjected(value = "helloServiceImpl2")
private HelloService helloService;
@GetMapping("/test1")
public String test1() {
helloService.sayHello();
return "test1 success";
}
}
测试
访问：http://localhost:8080/test1
后端结果：
我是HelloServiceImpl2
请先 ！