2-IOC创建对象的方式

构造器创建对象的方式

• 一个HellWorld的POJO类

public class HelloWorld {
    private String name;

    public HelloWorld() {
        System.out.println("无参构造器创建对象");
    }

    public HelloWorld(String name) {
        this.name = name;
        System.out.println("有参构造器创建对象");
    }

    public String getName() {
        return name;
    }

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

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

1）无参构造器创建对象（默认）

<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="helloWorld" class="com.shang.HelloWorld"></bean>

</beans>

• 测试

public class HelloWorldTest {

    @Test
    public void test(){
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        HelloWorld helloWorld = context.getBean("helloWorld", HelloWorld.class);
        System.out.println(helloWorld);
    }
}

• 结果
  

2）有参构造器创建对象（三种方式）

- 第一种方式

<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="helloWorld" class="com.shang.HelloWorld">
        <constructor-arg index="0" value="shang"/>
    </bean>

</beans>

- 第二种方式

<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="helloWorld" class="com.shang.HelloWorld">
        <constructor-arg name="name" value="shang"/>
    </bean>

</beans>

- 第三种方式（不建议使用）

<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="helloWorld" class="com.shang.HelloWorld">
        <constructor-arg type="java.lang.String" value="shang"/>
    </bean>

</beans>

• 测试

public class HelloWorldTest {

    @Test
    public void test(){
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        HelloWorld helloWorld = context.getBean("helloWorld", HelloWorld.class);
        System.out.println(helloWorld);
    }
}

• 三种方式的结果
  

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