[Java知识库]spring入门 IOC创建对象--来自狂神

User

package com.liu.pojo;

public class User {
    private String name;

    public String getName() {
        return name;
    }

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

    public void show(){
        System.out.println("name="+name);
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                '}';
    }
}

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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

无参构造默认赋值
   <bean id="user" class="com.liu.pojo.User">
       <property name="name" value="向阳"/>
   </bean>

</beans>

MyTest

import com.liu.pojo.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {
    public static void main(String[] args) {
    //获取ApplicationContext;拿到spring容器；
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        //容器在手天下我有，需要啥就get啥
        User user = (User)context.getBean("user");
        System.out.println(user.toString());
    }
}

## 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>myliu-02</artifactId>
    <version>1.0-SNAPSHOT</version>

<!--引入spring坐标-->
    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.3.10</version>
        </dependency>
        <!--引入spring  context坐标-->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.3.10</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

</project>

如果User中存在有参构造

package com.liu.pojo;

public class User {
    private String name;

    private User(String name){
        this.name=name;
    }

    public String getName() {
        return name;
    }

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

    public void show(){
        System.out.println("name="+name);
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                '}';
    }
}

applicationcontext.xml

1.还可以用下标赋值

 <bean id="user" class="com.liu.pojo.User">
        <constructor-arg index="0" value="张三"/>
    </bean>

2.类型赋值

  <bean id="user" class="com.liu.pojo.User">
        <constructor-arg type="java.lang.String" value="张三"/>
    </bean>

无参构造默认赋值

   <bean id="user" class="com.liu.pojo.User">
       <property name="name" value="向阳"/>
   </bean>