Spring 中的接口知识整理

本想每个小知识一篇随笔，但是那样，看起来有些单薄，所以，就放在一片文章里了。而且，以后还会慢慢在最后不断的追加。

目录：

FactoryBean

BeanPostProcessor

1.FactoryBean

FactoryBean接口，它在Spring框架源码内部，被大量使用，如使用AOP创建bean的代理时，使用了ProxyFactoryBean；从JNDI中查找对象时，使用了JndiObjectFactoryBean。

它在框架外，很少使用。但是为了学习，也得研究研究，您说是不？

它怎么使用？首先看看构造。

 public interface FactoryBean<T> {

　// 返回的是这个工厂管理的对象的实例
 T getObject() throws Exception;
 
　// 返回的是工厂创建的对象的类型
 Class<?> getObjectType();

 boolean isSingleton();

 }

上个例子，看具体东西。

 public class Tool {

     private int id;
     public Tool(int id) {
         this.id = id;
     }
     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }
 }

 public class ToolFactory implements FactoryBean<Tool> {

     private int factoryId;
     private int toolId;
 
　　　　// 创建的是Tool的对象
     @Override
     public Tool getObject() throws Exception {
 8         return new Tool(toolId);
 9     }

     @Override
     public Class<?> getObjectType() {
13         return Tool.class;
14     }

     @Override
     public boolean isSingleton() {
         return false;
     }

     public int getFactoryId() {
         return factoryId;
     }

     public int getToolId() {
         return toolId;
     }

     public void setFactoryId(int factoryId) {
         this.factoryId = factoryId;
     }

     public void setToolId(int toolId) {
         this.toolId = toolId;
     }

 }

 public class Test {

     public static void main(String[] args) {
         @SuppressWarnings("resource")
         ApplicationContext context = new ClassPathXmlApplicationContext("beaFactoryTest.xml");
         Tool tool = (Tool) context.getBean("tool");  
　　　　　　 // 在名字前面加　& 表示要得到工厂类的bean
         ToolFactory tool2 = (ToolFactory) context.getBean("&tool");
         System.out.println("Tool Id is " + tool.getId());
         System.out.println("ToolFactory Id is " + tool2.getFactoryId());

     }
 }

     <bean id="tool" class="com.lee.demo.beanfactory.ToolFactory">
         <property name="factoryId" value="9090"/>
         <property name="toolId" value="108"/>
     </bean>

最后执行结果：

Tool Id is 108
ToolFactory Id is 9090

2.BeanPostProcessor

它叫bean后处理器,也就是处理bean，它针对所有的bean，在初始化前后，对bean进行操作。主要内容我会在例子中描述。

例子：

 public class HelloWorld {
     private String message;

     public void setMessage(String message) {
         this.message = message;
     }

     public void getMessage() {
         System.out.println("Your Message : " + message);
     }
 　　

       // 加上init方法和destory方法，是为了在后面验证他们和postProcessBeforeInitialization  postProcessAfterInitialization 执行的先后顺序
     public void init() {
         System.out.println("Bean is going through init.");
     }

     public void destroy() {
         System.out.println("Bean will destroy now.");
     }
 }

 public class InitHelloWorld implements BeanPostProcessor {
 
　　　　// BeanPostProcessor 接口中主要是下面两个方法 初始化前的后处理 初始化后的后处理
     @Override
     public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

         System.out.println("BeforeInitialization : " + beanName);
         return bean; // you can return any other object as well
     }

     @Override
     public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

         System.out.println("AfterInitialization : " + beanName);
         return bean; // you can return any other object as well
     }

 }

Test.java

 public class Test {

     public static void main(String[] args) {
         @SuppressWarnings("resource")
         AbstractApplicationContext  context = new ClassPathXmlApplicationContext("beaFactoryTest.xml");
         HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
         obj.getMessage();
　　　　　　 // 注册钩子方法
         context.registerShutdownHook();
     }
 }

查看源码：

 @Override
　　　　// 在JVM运行期间，注册一个钩子关闭方法，关闭掉这个context。实际的关闭程序的操作，被代理给doClose方法。
     public void registerShutdownHook() {
         if (this.shutdownHook == null) {
             // No shutdown hook registered yet.
             this.shutdownHook = new Thread() {
                 @Override
                 public void run() {
                     doClose();
                 }
             };
             Runtime.getRuntime().addShutdownHook(this.shutdownHook);
         }
     }

xml文件

     <bean id = "helloWorld" class = "com.lee.demo.beanfactory.HelloWorld"
       init-method = "init" destroy-method = "destroy">
       <property name = "message" value = "Hello World!"/>
    </bean>

    <bean class = "com.lee.demo.beanfactory.InitHelloWorld" />

执行结果：

 BeforeInitialization : helloWorld
 Bean is going through init.
 AfterInitialization : helloWorld
 Your Message : Hello World!
 [org.springframework.context.support.ClassPathXmlApplicationContext] - Closing org.springframework.context.support.ClassPathXmlApplicationContext@6ae40994: startup date [Thu May 17 23:31:53 JST 2018]; root of context hierarchy
 Bean will destroy now.

在这里大致说一下Spring的实例化过程：

实例化Bean对象→设置对象属性→检查Aware相关接口并设置相关依赖→BeanPostProcessor前置处理→检查是否是InitializingBean以决定是否调用afterPropertiesSet方法→

检查是否配置有自定义的init-method方法→BeanPostProcessor后置处理→是否实现DisposableBean接口→是否配置有自定义的destroy方法

3.Aware接口

它是干什么用的呢？作用就是通过上下文（Context)可以获得当前环境。看看它的接口：

我们拿BeanNameAware来举个例子。

 public class User implements GetNameAware {

     private String id;
     private String name;
     private String address;
 6     @Override
 7     public void setBeanName(String name) {
 8         this.id = name;
 9     }
     public String getId() {
         return id;
     }
     public String getName() {
         return name;
     }
     public String getAddress() {
         return address;
     }
     public void setId(String id) {
         this.id = id;
     }
     public void setName(String name) {
         this.name = name;
     }
     public void setAddress(String address) {
         this.address = address;
     }

 }

 public class User2 {

     private String id;
     private String name;
     private String address;
     public String getId() {
         return id;
     }
     public String getName() {
         return name;
     }
     public String getAddress() {
         return address;
     }
     public void setId(String id) {
         this.id = id;
     }
     public void setName(String name) {
         this.name = name;
     }
     public void setAddress(String address) {
         this.address = address;
     }

 }

 public interface GetNameAware extends BeanNameAware {

 }

 public class Test {
     public static void main(String[] args) {
         ApplicationContext ctx = new ClassPathXmlApplicationContext("beaFactoryTest.xml");
         User user = (User) ctx.getBean("user1");
         User2 user2 = (User2) ctx.getBean("user2");
         System.out.println("user id " + user.getId() + " user name " + user.getName() + " user address " + user.getAddress());
         System.out.println("========================================");
         System.out.println("user2 id " + user2.getId() + " user2 name " + user2.getName() + " user2 address " + user2.getAddress());
     }
 }

     <bean id="user1" class="com.lee.demo.aware.User">
         <property name="name" value="lee"/>
         <property name="address" value="China"/>
     </bean>

     <bean id="user2" class="com.lee.demo.aware.User2">
         <property name="name" value="lin"/>
         <property name="address" value="Tokyo"/>
     </bean>

执行结果（user id 因为继承了GetNameAware接口，对BeanName进行了设置）：

 user id user1 user name lee user address China
 ========================================
 user2 id null user2 name lin user2 address Tokyo