spring3.2--DI(注解注入)

注解注入demo

需要做如下准备：

　　1.加入jar包 spring-aop-5.0.11.RELEASE.jar

　　2.增加约束文件
　　3.注册组件扫描器，为了让spring找到注解的位置
　　4.类上加注解

package com.cn.dao;

import org.springframework.stereotype.Component;

/**@Component 放在类上，作用是创建类的对象
 * 有value 属性
 * 相当于： <bean id="dao" class="com.cn.dao.DoSomeThingsOracleDao" />
 * 调用无参的构造函数创建对象
 */
@Component("dao") 
public class DoSomeThingsOracleDao implements SQLDao{

    
    public void insert(){
        System.out.println("oracle do insert");
    }
}




package com.cn.service;

import javax.annotation.Resource;

import org.springframework.stereotype.Component;

import com.cn.dao.DoSomeThingsOracleDao;
@Component("doSomeService")
public class DoSomeThingsService {

    @Resource
    private DoSomeThingsOracleDao dao;

    @Override
    public String toString() {
        return "DoSomeThingsService [dao=" + dao + "]";
    }
    
}




<?xml version="1.0" encoding="UTF-8"?>
<!-- 增加约束文件 -->
<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"
    >
    
    
    <!-- 使用注解的方式实现DI 
        1.加入jar包  spring-aop-5.0.11.RELEASE.jar
        2.增加约束文件
        3.注册组件扫描器，为了让spring找到注解的位置
        4.类上加注解
     -->
     <!-- 
           base-package 指定注解所在的包名 
           com.cn 扫描这个包下及其子包下的所有类
     -->
     <context:component-scan base-package="com.cn"/>
</beans>





package com.cn.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;

import com.cn.service.DoSomeThingsService;

public class Test {

    public static void main(String[] args) {
        String resource = "applicationContext.xml";
        ApplicationContext ac = new ClassPathXmlApplicationContext(resource);
        
        DoSomeThingsService service=  (DoSomeThingsService) ac.getBean("doSomeService");
        System.out.println(service.toString());
        
    }
}



DoSomeThingsService [dao=com.cn.dao.DoSomeThingsOracleDao@80169cf]

如果 @Component 不赋value值的话，默认beanid是类的首字母小写

package com.cn.service;

import javax.annotation.Resource;

import org.springframework.stereotype.Component;

import com.cn.dao.DoSomeThingsOracleDao;
@Component
public class DoSomeThingsService {

    @Resource
    private DoSomeThingsOracleDao dao;

    @Override
    public String toString() {
        return "DoSomeThingsService [dao=" + dao + "]";
    }
    
}

    public static void main(String[] args) {
        String resource = "applicationContext.xml";
        ApplicationContext ac = new ClassPathXmlApplicationContext(resource);
        
        DoSomeThingsService service=  (DoSomeThingsService) ac.getBean("doSomeThingsService");
        System.out.println(service.toString());
        
    }

指定包的方式

有三种

逗号分隔
<context:component-scan base-package="com.cn.dao,com.cn.service"/>

使用多个标签
<context:component-scan base-package="com.cn.dao"/><context:component-scan base-package="com.cn.service"/>


使用父包

<context:component-scan base-package="com.cn"/>

@Scope("prototype")

package com.cn.service;

import javax.annotation.Resource;

import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

import com.cn.dao.DoSomeThingsOracleDao;
@Component
@Scope("prototype")
public class DoSomeThingsService {

    @Resource
    private DoSomeThingsOracleDao doSomeThingsOracleDao;

    public DoSomeThingsService() {
        System.out.println("service sonstruction");
    }
    @Override
    public String toString() {
        return "DoSomeThingsService [dao=" + doSomeThingsOracleDao + "]";
    }
    
}


    public static void main(String[] args) {
        String resource = "applicationContext.xml";
        ApplicationContext ac = new ClassPathXmlApplicationContext(resource);
        
        DoSomeThingsService service=  (DoSomeThingsService) ac.getBean("doSomeThingsService");
        DoSomeThingsService service1=  (DoSomeThingsService) ac.getBean("doSomeThingsService");
//        System.out.println(service.toString());
        
    }


service sonstruction
service sonstruction

和@Component 类似的注解

和@Component 类似的注解有 @service，@Repository，@Controller。

@service是放在service层的实体类上。创建service对象

@Repository是放在dao层的

@Controller 放在处理器类上的。servlet。

package com.cn.dao;

import org.springframework.stereotype.Repository;

/**@Component 放在类上，作用是创建类的对象
 * 有value 属性
 * 相当于： <bean id="dao" class="com.cn.dao.DoSomeThingsOracleDao" />
 * 调用无参的构造函数创建对象
 */
@Repository
public class DoSomeThingsOracleDao implements SQLDao{

    
    public void insert(){
        System.out.println("oracle do insert");
    }
}




package com.cn.service;

import javax.annotation.Resource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

import com.cn.dao.DoSomeThingsOracleDao;
@Component
//@Scope("prototype")
public class DoSomeThingsService {

    @Value("6")
    private int valInt;
    
    @Resource(name="doSomeThingsOracleDao")
    private DoSomeThingsOracleDao dao;
    
    /**
     * 区别：@Resource 是JDK的,默认按byName注入，注入失败，再按照byType注入。
     * Resource也可以只按照byName注入。"@Resource(name="doSomeThingsOracleDao")"
     * @Autowired 是spring的，默认是按照byType注入的，需要按照byName注入的话，需要配合@Qualifier一起使用
     * @Autowired 必须注入成功。因为 "boolean required() default true;"
     * 
     */
    @Autowired
    @Qualifier("doSomeThingsOracleDao")
    private DoSomeThingsOracleDao dao1;

    public DoSomeThingsService() {
        System.out.println("service sonstruction");
    }

    @Override
    public String toString() {
        return "DoSomeThingsService [valInt=" + valInt + ", dao=" + dao + ", dao1=" + dao1 + "]";
    }
    
}

@PostConstruct  @PreDestroy

    @PostConstruct
    public void initA() {
        System.out.println("initA");
    }
    
    @PreDestroy
    public void preDestroyA() {
        System.out.println("destroyA");
    }



service sonstruction
initA
DoSomeThingsService [valInt=6, dao=com.cn.dao.DoSomeThingsOracleDao@3e77a1ed, dao1=com.cn.dao.DoSomeThingsOracleDao@3e77a1ed]
七月 27, 2019 2:19:49 下午 org.springframework.context.support.ClassPathXmlApplicationContext doClose
信息: Closing org.springframework.context.support.ClassPathXmlApplicationContext@c4437c4: startup date [Sat Jul 27 14:19:49 CST 2019]; root of context hierarchy
destroyA

注解相对配置文件，代码量少。但是需要修改代码

在没有源码的时候，用别的类时，只能用配置文件实现。

如果代码中一个类既有注解，又有配置文件，以配置文件为准。配置文件优先级高于注解。

<?xml version="1.0" encoding="UTF-8"?>
<!-- 增加约束文件 -->
<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"
    >
    
    
    <!-- 使用注解的方式实现DI 
        1.加入jar包  spring-aop-5.0.11.RELEASE.jar
        2.增加约束文件
        3.注册组件扫描器，为了让spring找到注解的位置
        4.类上加注解
     -->
     <!-- 
           base-package 指定注解所在的包名 
           com.cn 扫描这个包下及其子包下的所有类
     -->
     <context:component-scan base-package="com.cn"/>
     <bean id ="service" class="com.cn.service.DoSomeThingsService"/>
</beans>




    public static void main(String[] args) {
        String resource = "applicationContext.xml";
        ApplicationContext ac = new ClassPathXmlApplicationContext(resource);
        
        DoSomeThingsService service=  (DoSomeThingsService) ac.getBean("doSomeThingsService");
        DoSomeThingsService service1=  (DoSomeThingsService) ac.getBean("service");
        System.out.println(service.toString());
        System.out.println(service1.toString());
        
    }


service sonstruction
initA
service sonstruction
initA
DoSomeThingsService [valInt=6, dao=com.cn.dao.DoSomeThingsOracleDao@25359ed8, dao1=com.cn.dao.DoSomeThingsOracleDao@25359ed8]
DoSomeThingsService [valInt=6, dao=com.cn.dao.DoSomeThingsOracleDao@25359ed8, dao1=com.cn.dao.DoSomeThingsOracleDao@25359ed8]


明显是注入了两个一样的类。。
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原文地址：https://www.cnblogs.com/llq1214/p/11232084.html