Spring框架context的注解管理方法之二 使用注解注入对象属性

Posted 2020-10-14 Advancing Swift

首先还是xml的配置文件

<?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"> 
      <!--  开启注解扫描  -->
     <context:component-scan base-package="com.swift"></context:component-scan>
</beans>

接着是假定dao的类

package com.swift;

import org.springframework.stereotype.Component;

@Component(value="dao")
public class Dao {
    public String fun() {
        return "This is Dao\'s fun()........";
        
    }
}

生成一个对象很方便，甚至@Component(value="dao")中的value=都可以不写，变成

@Component("dao")

然后是假定service的类

package com.swift;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component(value="service")
public class Service {
    
    @Autowired
    private Dao dao;
    public String fun() {
        return "This is Service\'s fun()......."+"\\r\\n"+this.dao.fun();
    }
    //注意使用注解方法，不需要自己生成setter方法了
    public void setDao(Dao dao) {
        this.dao = dao;
    }
    
}

与配置文件中使用<bean id="service" class="com.swift.Service"><property name="dao" ref="dao"></property></bean>

不同，注解生成两个对象后，再注解属性

@Autowired

就搞定了，自动装配，自动连线

最后使用Servlet来测试一下

package com.swift;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
@WebServlet("/test")
public class ServletTest extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public ServletTest() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().append("Served at: ").append(request.getContextPath());
        ApplicationContext context=new ClassPathXmlApplicationContext("zhujie.xml");
        Service service=(Service) context.getBean("service");
        String test=service.fun();
        response.getWriter().append(test);
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

浏览器结果如下

自动装载的这种方法   @Autowired    原理是通过类名找到定义的对象，这种注解使用不多，因为多个对象存在的话，注入的是哪个？

所以，使用

另一个注解，可以明确到底注入哪个对象

@Resource(name="dao")
private Dao dao;

这种方法使用较多

 注入基本类型和对象属性

半注解方式

 

package cn.itcast.domain;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
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;

//<bean name="user" class="cn.itcast.domain.User" />
@Component("user")
/*    //注册service层对象
@Service
@Repository        //注册Dao层对象
@Controller        //注册Web层对象*/
//<bean scope="singleton|prototype" >
@Scope("prototype")
public class User {
    @Value("tom") //为name赋值为tom
    private String name;
    private Integer age;
    @Resource(name="car2")
    /*
     * @Autowired 自动注入 有就注入 默认名car开始
     * 注意:如果匹配到多个会抛出异常*/
//     @Autowired
    /*
     *  当自动注入匹配到多个对象时,可以使用@Qualifier 指定具体注入哪一个(不常用)
     */
    @Autowired
    @Qualifier("car2")
    private Car car;

    public User() {
        super();
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    //将赋值注解放到set方法上,可执行方法中判断逻辑
    @Value("18")//为age赋值
    public void setAge(Integer age) {
        System.out.println("public void setAge(Integer age)!");
        this.age = age;
    }

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }
    //<bean init-method="init" >
    @PostConstruct
    public void init() {
        System.out.println("构造之后初始化方法!");
    }
    //<bean destory-method="destory" >
    @PreDestroy
    public void destory() {
        System.out.println("销毁之前销毁方法!");
    }

    @Override
    public String toString() {
        return "User [name=" + name + ", age=" + age + ", car=" + car + "]";
    }
}

 

引用类型Car

package cn.itcast.domain;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class Car {
    
    @Value("哈佛H6")
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

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

XML配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns="http://www.springframework.org/schema/beans" 
    xmlns:context="http://www.springframework.org/schema/context" 
    xsi:schemaLocation="http://www.springframework.org/schema/beans 
                        http://www.springframework.org/schema/beans/spring-beans-4.2.xsd 
                        http://www.springframework.org/schema/context 
                        http://www.springframework.org/schema/context/spring-context-4.2.xsd ">
        
    <!-- 开启ioc注解 -->    
    <context:component-scan base-package="cn.itcast"></context:component-scan>
    
    <!---->
    <bean name="car1" class="cn.itcast.domain.Car" >
        <property name="name" value="五菱宏光"></property>
    </bean>
     <bean name="car2" class="cn.itcast.domain.Car" >
        <property name="name" value="长安CS95" ></property>
    </bean> 
    
</beans>

测试类

package cn.itcast.a_ioc;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import cn.itcast.domain.User;

public class Demo {
    @Test
    public void fun1(){
        
        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
        User u1 = (User) ac.getBean("user");
        User u2 = (User) ac.getBean("user");
        
        System.out.println(u1==u2);
    }
    
    @Test
    public void fun2(){
        
        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
        
        User u1 = (User) ac.getBean("user");
        
        System.out.println(u1);
    }
    
}