spring-ioc的注解 理解-1

简单对象注入的理解 用到了两个对象 Student 、Wife ，一个xml配置(在idea编译器的resource文件下)，主要是为让spring去扫描注解，一个测试类，一个pom.xml,导入需要的依赖。

1.Student

import lombok.Data;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Data
/**
 * 创建对象的注解 一下注解只能加在类上
 * @Component  哪一层都可以
 * @Controller 加在web层
 * @Service 加在service层 也叫业务层
 * @Repository 加在dao层
 */
//使用注解的方式
//该注解的作用：当项目启动时，spring会去扫描注解(spring要想去扫描注解，那么就要通过配置文件去配置)，一旦扫描到该注解，就会给该注解所
//注解的类创建对象，并放入容器中 该容器中对象的唯一标识是类名首字母小写，当然也可以手动
//定义一个唯一标识 @Component("stu")
@Component
public class Student {
    //给属性赋初值 使用注解的方式@Value
    @Value("1")
    private int id;
    @Value("renzhe")
    private String name;
    @Value("18")
    private int age;
    //当容器中有且只有一个wife对象时 用@Autowired注解进行对象的注入，他是根据类型自动注入的
    //相当于Wife w = app.getBean("Wife.class");
    //Wife wife = w;
    @Autowired
    private Wife wife;

    /**
     * 当有多个对象时，要想注入对象，有两种方法
     * 1.@Autowired
     *   @Qualifier（value="名字"）
     *   这两个注解联合使用，@Autowired是根据类型 @Qualifier是根据类型和名字
     *  2.@Resource（name="名字"） 他相当于@Autowired和@Qualifier联合使用
     */

     @Autowired
     private Date date；

}

2.Wife

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

@Data
@Component
public class Wife {
    @Value("1")
    private int id;
    @Value("yu")
    private String name;
    @Value("18")
    private int age;
}

3.applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       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
">
    <!-- 要想扫描注解必须用到context命名空间-->
    <!-- context:component-scan扫描的包以及他的子包-->
<context:component-scan base-package="com.briup.spring.bean"></context:component-scan>

<bean id="now" class="java.util.Date"></bean>

</beans>

4.SpringAnnTest

import com.briup.spring.bean.Student;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringAnnTest {
    @Test
    public void test1(){
      ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
     /*一旦加载这个配置文件 就会去扫描所配置的包以及他的子包 那么就会扫描到Student类上的注解Component，
        就会给Student类创建一个student对象（也叫bean对象）
        并且放入到容器中。
        而默认的bean对象的唯一标识是类名首字母小写 也就是student
        */
       Student student = (Student) app.getBean("student");
        System.out.println(student);
    }
}

5.pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>spring-ioc-ann</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId>
            <version>1.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-io</artifactId>
            <version>1.3.2</version>
        </dependency>

        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.11.0</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.11.0</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.11.0</version>
        </dependency>

        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aop</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-expression</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.2.7.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>