Spring（IOC/AOP）注解学习

客官°小女子只卖身不卖艺 2022-05-22 10:15 274阅读 0赞

# Spring的初始化顺序 #

在spring的配置文件中配置bean，如下

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
        <bean id="one" class="cn.itcast_04_springannotation.springrunorder.One">
            <constructor-arg name="one" value="one"/>
        </bean>
    
        <bean id="two" class="cn.itcast_04_springannotation.springrunorder.Two">
            <constructor-arg name="two" value="two" />
        </bean>
    
    </beans>

在One类和Two类中，分别实现一个参数的构造如下：

package cn.itcast_04_springannotation.springrunorder;
    
    
    public class One{
        public One(String one) {
            System.out.println(one);
        }
    
    
    }

package cn.itcast_04_springannotation.springrunorder;
    
    public class Two {
        public Two(String two) {
            System.out.println(two);
        }
    }

加载spring配置文件，初始化bean如下：

package cn.itcast_04_springannotation.springrunorder;
    
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class Start { 
        public static void main(String[] args) {
            new ClassPathXmlApplicationContext("spring.xml");
        }
    }

![这里写图片描述][70]

结论：spring会按照bean的顺序依次初始化xml中配置的所有bean

## 通过ApplicationContextAware加载Spring上下文环境 ##

在One中实现ApplicationContextAware接口会出现如何的变换呢？

package cn.itcast_04_springannotation.springrunorder;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.InitializingBean;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    
    public class One implements ApplicationContextAware { 
        public One(String one) {
            System.out.println(one);
        }
    
        @Override
        public void setApplicationContext(ApplicationContext arg0)
                throws BeansException {
                System.out.println("setApplicationContext");
        }
    
    
    }

![这里写图片描述][70 1]

## InitializingBean的作用 ##

在One中实现InitializingBean接口呢?

package cn.itcast_04_springannotation.springrunorder;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.InitializingBean;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    
    public class One implements ApplicationContextAware ,InitializingBean { 
        public One(String one) {
            System.out.println(one);
        }
    
        @Override
        public void setApplicationContext(ApplicationContext arg0)
                throws BeansException {
                System.out.println("setApplicationContext");
        }
    
        @Override
        public void afterPropertiesSet() throws Exception {
            System.out.println("afterPropertiesSet");
        }
    }

![这里写图片描述][70 2]

## 如果使用注解@Component ##

使用@Component注入类，那么它的顺序是如何呢？

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
        <bean id="one" class="cn.itcast_04_springannotation.springrunorder.One">
            <constructor-arg name="one" value="one"/>
        </bean>
        <context:component-scan base-package="cn.itcast_04_springannotation.springrunorder"/>
        <bean id="two" class="cn.itcast_04_springannotation.springrunorder.Two">
            <constructor-arg name="two" value="two" />
        </bean>
    
    </beans>

package cn.itcast_04_springannotation.springrunorder;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class Three {
        public Three() {
            System.out.println("three");
        }
        public Three(String three) {
            System.out.println(three);
        }
    }

![这里写图片描述][70 3]

## 结论 ##

1、 spring先检查注解注入的bean，并将它们实例化  
2、 然后spring初始化bean的顺序是按照xml中配置的顺序依次执行构造  
3、 如果某个类实现了ApplicationContextAware接口，会在类初始化完成后调用setApplicationContext（）方法进行操作  
4、 如果某个类实现了InitializingBean接口，会在类初始化完成后，并在setApplicationContext（）方法执行完毕后，调用afterPropertiesSet（）方法进行操作

# 注解使用回顾 #

1、在spring中，用注解来向Spring容器注册Bean。需要在applicationContext.xml中注册`<context:component-scan base-package="pagkage1[,pagkage2,…,pagkageN]"/>`。  
2、如果某个类的头上带有特定的注解@Component/@Repository/@Service/@Controller，就会将这个对象作为Bean注册进Spring容器  
3、在使用spring管理的bean时，无需在对调用的对象进行new的过程，只需使用@Autowired将需要的bean注入本类即可

# 自定义注解 #

## 解释 ##

1、自定义注解的作用：在反射中获取注解，以取得注解修饰的“类、方法、属性”的相关解释。  
2、java内置注解  
@Target 表示该注解用于什么地方，可能的 ElemenetType 参数包括：  
ElemenetType.CONSTRUCTOR 构造器声明  
ElemenetType.FIELD 域声明（包括 enum 实例）  
ElemenetType.LOCAL\_VARIABLE 局部变量声明  
ElemenetType.METHOD 方法声明  
ElemenetType.PACKAGE 包声明  
ElemenetType.PARAMETER 参数声明  
ElemenetType.TYPE 类，接口（包括注解类型）或enum声明  
@Retention 表示在什么级别保存该注解信息。可选的 RetentionPolicy 参数包括：  
RetentionPolicy.SOURCE 注解将被编译器丢弃  
RetentionPolicy.CLASS 注解在class文件中可用，但会被VM丢弃  
RetentionPolicy.RUNTIME JVM将在运行期也保留注释，因此可以通过反射机制读取注解的信息。

## 实现 ##

1.定义自定义注解

package cn.itcast_04_springannotation.userdefinedannotation.annotation;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    import org.springframework.stereotype.Component;
    
    @Target({ ElementType.TYPE })//注解用在接口上
    @Retention(RetentionPolicy.RUNTIME)//VM将在运行期也保留注释，因此可以通过反射机制读取注解的信息
    @Component
    public @interface RpcService {
    
        String value();
    }

2、将直接类加到需要使用的类上，我们可以通过获取注解，来得到这个类

package cn.itcast_04_springannotation.userdefinedannotation.service.impl;
    
    import cn.itcast_04_springannotation.userdefinedannotation.annotation.RpcService;
    import cn.itcast_04_springannotation.userdefinedannotation.service.HelloService;
    
    
    @RpcService("HelloServicebb")
    public class HelloServiceImpl implements HelloService { 
        public String hello(String name) {
            return "Hello! " + name;
        }
    
        public void test(){
            System.out.println("test");
        }
    }

3、类实现的接口

package cn.itcast_04_springannotation.userdefinedannotation.service;
    
    
    public interface HelloService {
        String hello(String name);
    }

4、通过ApplicationContext获取所有标记这个注解的类

package cn.itcast_04_springannotation.userdefinedannotation.test;
    
    import java.lang.reflect.Method;
    import java.util.Map;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    import org.springframework.stereotype.Component;
    
    import cn.itcast_04_springannotation.userdefinedannotation.annotation.RpcService;
    import cn.itcast_04_springannotation.userdefinedannotation.service.HelloService;
    
    @Component        //ApplicationContextAware会为Component组件调用setApplicationContext方法；
    public class MyServer implements ApplicationContextAware {
        @SuppressWarnings("resource")
        public static void main(String[] args) {
            ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("spring2.xml");
        }
    
    
        public void setApplicationContext(ApplicationContext ctx)
                throws BeansException {
            Map<String, Object> serviceBeanMap = ctx
                    .getBeansWithAnnotation(RpcService.class);
            for (Object serviceBean : serviceBeanMap.values()) {
                try {
                    //获取自定义注解上的value
                    String value = serviceBean.getClass().getAnnotation(RpcService.class).value();
                    System.out.println("注解上的value: " + value);
    
                    //反射被注解类，并调用指定方法
                    Method method = serviceBean.getClass().getMethod("hello",
                            new Class[] { String.class });
                    Object invoke = method.invoke(serviceBean, "bbb");
                    System.out.println(invoke);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    
    }

![这里写图片描述][70 4]

package cn.itcast_04_springannotation.userdefinedannotation.test;
    
    import java.lang.reflect.Method;
    import java.util.Map;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    import org.springframework.stereotype.Component;
    
    import cn.itcast_04_springannotation.userdefinedannotation.annotation.RpcService;
    import cn.itcast_04_springannotation.userdefinedannotation.service.HelloService;
    
    
    public class MyServer2 implements ApplicationContextAware {
        @SuppressWarnings("resource")
        public static void main(String[] args) {
            ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("spring2.xml");
            Map<String, Object> beans = ctx.getBeansWithAnnotation(RpcService.class);
            for(Object obj: beans.values()){
                HelloService hello=(HelloService) obj;
                String hello2 = hello.hello("mmmm");
                System.out.println(hello2);
            }
        }
    
    
    
        public void setApplicationContext(ApplicationContext ctx)
                throws BeansException {
            Map<String, Object> serviceBeanMap = ctx
                    .getBeansWithAnnotation(RpcService.class);
            for (Object serviceBean : serviceBeanMap.values()) {
                try {
                    Method method = serviceBean.getClass().getMethod("hello",
                            new Class[] { String.class });
                    Object invoke = method.invoke(serviceBean, "bbb");
                    System.out.println(invoke);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    
    }

![这里写图片描述][70 5]

5、 结合spring实现junit测试

package cn.itcast_04_springannotation.userdefinedannotation.test;
    
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    import org.springframework.test.context.ContextConfiguration;
    import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
    
    import cn.itcast_04_springannotation.userdefinedannotation.service.HelloService;
    
    @RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration(locations = "classpath:spring2.xml")
    @Component
    public class MyServer3 {
        @Autowired
        HelloService helloService;
    
        @Test
        public void helloTest1() {
            System.out.println("开始junit测试……");
            String hello = helloService.hello("ooooooo");
            System.out.println(hello);
        }
    
    }

![这里写图片描述][70 6]

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