Spring 中的接口知识整理

浅浅的花香味﹌ 2021-09-20 13:22 342阅读 0赞

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。

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。

1 public interface FactoryBean<T> {
         
    
    　// 返回的是这个工厂管理的对象的实例 2 T getObject() throws Exception;
    3 
    　// 返回的是工厂创建的对象的类型
    4 Class<?> getObjectType();
    5 
    6 boolean isSingleton();
    7 
    8 }

上个例子，看具体东西。

1 public class Tool {
     2 
     3 
     4     private int id;
     5     public Tool(int id) {
     6         this.id = id;
     7     }
     8     public int getId() {
     9         return id;
    10     }
    11 
    12     public void setId(int id) {
    13         this.id = id;
    14     }
    15 }

1 public class ToolFactory implements FactoryBean<Tool> {
     2 
     3     private int factoryId;
     4     private int toolId;
     5 
    　　　　// 创建的是Tool的对象
     6     @Override
     7     public Tool getObject() throws Exception {
     8         return new Tool(toolId);
     9     }
    10 
    11     @Override
    12     public Class<?> getObjectType() {
    13         return Tool.class;
    14     }
    15 
    16     @Override
    17     public boolean isSingleton() {
    18         return false;
    19     }
    20 
    21     public int getFactoryId() {
    22         return factoryId;
    23     }
    24 
    25     public int getToolId() {
    26         return toolId;
    27     }
    28 
    29     public void setFactoryId(int factoryId) {
    30         this.factoryId = factoryId;
    31     }
    32 
    33     public void setToolId(int toolId) {
    34         this.toolId = toolId;
    35     }
    36 
    37 }

1 public class Test {
     2 
     3     public static void main(String[] args) {  
     4         @SuppressWarnings("resource")
     5         ApplicationContext context = new ClassPathXmlApplicationContext("beaFactoryTest.xml");  
     6         Tool tool = (Tool) context.getBean("tool");  
    　　　　　　 // 在名字前面加　& 表示要得到工厂类的bean  7         ToolFactory tool2 = (ToolFactory) context.getBean("&tool");  
     8         System.out.println("Tool Id is " + tool.getId());
     9         System.out.println("ToolFactory Id is " + tool2.getFactoryId());
    10         
    11     }
    12 }

1     <bean id="tool" class="com.lee.demo.beanfactory.ToolFactory">
    2         <property name="factoryId" value="9090"/>
    3         <property name="toolId" value="108"/>
    4     </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：

1 public class HelloWorld {
     2     private String message;
     3 
     4     public void setMessage(String message) {
     5         this.message = message;
     6     }
     7 
     8     public void getMessage() {
     9         System.out.println("Your Message : " + message);
    10     }
    11 　　
    
           // 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
    12     public void init() {
    13         System.out.println("Bean is going through init.");
    14     }
    15 
    16     public void destroy() {
    17         System.out.println("Bean will destroy now.");
    18     }
    19 }

1 public class InitHelloWorld implements BeanPostProcessor {
     2 
    　　　　// 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
     3     @Override
     4     public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
     5 
     6         System.out.println("BeforeInitialization : " + beanName);
     7         return bean; // you can return any other object as well
     8     }
     9 
    10     @Override
    11     public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    12 
    13         System.out.println("AfterInitialization : " + beanName);
    14         return bean; // you can return any other object as well
    15     }
    16 
    17 }

Test.java

1 public class Test {
     2 
     3     public static void main(String[] args) {  
     4         @SuppressWarnings("resource")
     5         AbstractApplicationContext  context = new ClassPathXmlApplicationContext("beaFactoryTest.xml");  
     6         HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
     7         obj.getMessage();
    　　　　　　 // 注册钩子方法  8         context.registerShutdownHook();
     9     }
    10 }

查看源码：

1 @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。  2     public void registerShutdownHook() {
     3         if (this.shutdownHook == null) {
     4             // No shutdown hook registered yet.
     5             this.shutdownHook = new Thread() {
     6                 @Override
     7                 public void run() {
     8                     doClose();
     9                 }
    10             };
    11             Runtime.getRuntime().addShutdownHook(this.shutdownHook);
    12         }
    13     }

xml文件

1     <bean id = "helloWorld" class = "com.lee.demo.beanfactory.HelloWorld"
    2       init-method = "init" destroy-method = "destroy">
    3       <property name = "message" value = "Hello World!"/>
    4    </bean>
    5 
    6    <bean class = "com.lee.demo.beanfactory.InitHelloWorld" />

执行结果：

1 BeforeInitialization : helloWorld
    2 Bean is going through init.
    3 AfterInitialization : helloWorld
    4 Your Message : Hello World!
    5 [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
    6 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：

![698535-20180519215118698-1692644264.png][]

我们拿BeanNameAware来举个例子。

1 public class User implements GetNameAware {
     2 
     3     private String id;
     4     private String name;
     5     private String address;
     6     @Override
     7     public void setBeanName(String name) {
     8         this.id = name;
     9     }
    10     public String getId() {
    11         return id;
    12     }
    13     public String getName() {
    14         return name;
    15     }
    16     public String getAddress() {
    17         return address;
    18     }
    19     public void setId(String id) {
    20         this.id = id;
    21     }
    22     public void setName(String name) {
    23         this.name = name;
    24     }
    25     public void setAddress(String address) {
    26         this.address = address;
    27     }
    28 
    29 }

1 public class User2 {
     2 
     3     private String id;
     4     private String name;
     5     private String address;
     6     public String getId() {
     7         return id;
     8     }
     9     public String getName() {
    10         return name;
    11     }
    12     public String getAddress() {
    13         return address;
    14     }
    15     public void setId(String id) {
    16         this.id = id;
    17     }
    18     public void setName(String name) {
    19         this.name = name;
    20     }
    21     public void setAddress(String address) {
    22         this.address = address;
    23     }
    24 
    25 }

1 public interface GetNameAware extends BeanNameAware {
    2 
    3 
    4 }

1 public class Test {
     2     public static void main(String[] args) {  
     3         ApplicationContext ctx = new ClassPathXmlApplicationContext("beaFactoryTest.xml");
     4         User user = (User) ctx.getBean("user1");
     5         User2 user2 = (User2) ctx.getBean("user2");
     6         System.out.println("user id " + user.getId() + " user name " + user.getName() + " user address " + user.getAddress());
     7         System.out.println("========================================");
     8         System.out.println("user2 id " + user2.getId() + " user2 name " + user2.getName() + " user2 address " + user2.getAddress());
     9     }
    10 }

1     <bean id="user1" class="com.lee.demo.aware.User">
    2         <property name="name" value="lee"/>
    3         <property name="address" value="China"/>
    4     </bean>
    5     
    6     <bean id="user2" class="com.lee.demo.aware.User2">
    7         <property name="name" value="lin"/>
    8         <property name="address" value="Tokyo"/>
    9     </bean>

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

1 user id user1 user name lee user address China
    2 ========================================
    3 user2 id null user2 name lin user2 address Tokyo

转载于:https://www.cnblogs.com/lihao007/p/9053644.html

[698535-20180519215118698-1692644264.png]: /images/20210726/a81eb22c4a5e4b4caa7bed754488b4fa.png