Spring 三种装配Bean方式

偏执的太偏执、 2022-05-30 11:52 261阅读 0赞

### 三种方式如下: ###

![这里写图片描述][70]

## 基于注解的配置： ##

--------------------

在resources下创建conf目录建applicationContext.xml ,配置如下

<?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:p="http://www.springframework.org/schema/p" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:jee="http://www.springframework.org/schema/jee" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">
    
        <context:component-scan base-package="com.cyh"/>
    </beans>

> < context:component-scan base-package=”com.cyh”/> 表示注解要扫描包的范围

##### 创建测试类Student #####

package com.cyh.pojo;
    
    import org.springframework.stereotype.Component;
    
    import java.util.List;
    
    @Component
    public class Student {
        private String name;
        private Integer id;
    
        public Student() {
            System.out.println("无参构造");
        }
    get set tostring...

在类上用了@Component注解， 表示这个类是一个组件， 供给其他类使用的， 他有一个value参数，用来指明这个类的名称

##### 创建测试类 #####

import com.cyh.pojo.MyConfig;
    import com.cyh.pojo.Student;
    import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.test.context.ContextConfiguration;
    import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
    
    import javax.annotation.Resource;
    
    @RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration("classpath:conf/applicationContext.xml")
    public class StudentTest {
    
        @Autowired
        private Student student;
    
        @Test
        public void test(){
            System.out.println(student);
        }
    }

上面的测试代码中， 就能输出student对象，输出如下：

无参构造
    Student{name='null', id=null}

看看这几个注解的意思:  
@RunWith 表示运行Spring测试环境  
@ContextConfiguration 表示加载配置文件实例化applicationContext  
@Autowired 表示将student对象自动注入进来

其实@Autowired 还可以用在方法上，好处是不用在类中定义一个 private Student student， 如下将 setStudent使用@Autowired同样可以得到值

@RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration("classpath:conf/applicationContext.xml")
    //@ContextConfiguration(classes = MyConfig.class)
    public class StudentTest { 
    
    // @Autowired
    // private Student student;
    
    
        @Test
        public void test(){
            //System.out.println(student);
        }
    
        @Autowired
        public void setStudent(Student student) {
            System.out.println(student);
        }
    }

如何给属性设置默认的值？ 来看看@Value用法

@Value("张三")
        private String name;
        @Value("10000")
        private Integer id;

运行测试类显示如下：

无参构造
    Student{
       name='张三', id=10000}

## 基于xml装配 ##

修改applicationContext.xml

<?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:p="http://www.springframework.org/schema/p" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:jee="http://www.springframework.org/schema/jee" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">
    
    
        <bean name="stu" class="com.cyh.pojo.Student">
    
        </bean>
    </beans>

再修改Student类，去掉所有注解

public class Student {
        private String name;
        private Integer id;
    ....

运行测试类得到结果如下：

无参构造
    Student{name='null', id=null}

和Student类加注解的效果相同， 在< bean>标签下配置property， 可以达到和@Value的效果

## 基于java类的配置 ##

新建类MyConfig

@Configuration
    @ComponentScan(value = "com.cyh")
    public class MyConfig {
    
    }

@Configuration 就类似与取代了xml文件的配置内容  
@ComponentScan 和< context:component-scan base-package=”com.cyh”/> 效果相同

接着将在恢复Student类上的注解@Component， 清空applicationContext.xml内容, 并修改Test类的注解如下

@RunWith(SpringJUnit4ClassRunner.class)
    //@ContextConfiguration("classpath:conf/applicationContext.xml")
    @ContextConfiguration(classes = MyConfig.class)
    public class StudentTest { 
    
        @Autowired
        private Student student;
    
    
        @Test
        public void test(){
            System.out.println(student);
        }
    
    }

在@ContextConfiguration将参数换成了类, 得到的结果也是和上面方法相同的

[70]: /images/20220530/809eee2147034e93bf4e494dba68a71e.png