Java Spring框架在何时创建对象的实验

结论：Spring在创建spring容器的时候就创建的类的对象(调用了类的无参构造方法)

1. 下面我们创建一个Person类用于测试

package com.mars.learnspring;

import com.sun.xml.internal.ws.addressing.WsaActionUtil;

public class Person {
    private String name;
    private String gender;
    private Integer age;
    private String email;

    public String getName() {
        return name;
    }

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

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", gender='" + gender + '\'' +
                ", age=" + age +
                ", email='" + email + '\'' +
                '}';
    }

//注意：下面的无参构造方法用于测试
    public Person() {
        System.out.println("Person类的无参构造方法...");
    }
}

 

2.下面是ioc反转控制的xml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"
      xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="person01" class="com.mars.learnspring.Person">
        <property name="name" value="黄晓明"></property>
        <property name="age" value="43"></property>
        <property name="gender" value="男"></property>
        <property name="email" value="huangxiaoming@javaspring.com"></property>
    </bean>

</beans>

 

3. 下面是maven里面创建的测试类

package com.mars.springtest;

import static org.junit.Assert.*;

import com.mars.learnspring.Person;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class PersonTest {

    @Test
    public void test() {
        ApplicationContext ioc=new ClassPathXmlApplicationContext("conf/ioc.xml");

//注意，下面两句被注释掉了，目的就是用来看看无参构造方法何时被调用
//        Person bean=(Person) ioc.getBean("person01");
//        System.out.println(bean);
        }

}

 

4.执行上面第3部的测试类。其结果如下

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" ...
Person类的无参构造方法...

Process finished with exit code 0

 

5.由此可见类的构造方法是子spring容器启动就被调用了。

6.01ioc反转控制里面配置多少个bean就会创建多少个相应的对象

6.02 同一个bean被调用两次，但这个bean对于的对象只会创建一个。

如下代码，我们调用了两次person01这个bean，但是它创建的对象却还是一个而不是两个，所以system.out里面输出结果为true。

  @Test
    public void test() {
        ApplicationContext ioc=new ClassPathXmlApplicationContext("conf/ioc.xml");
        Person bean1=(Person) ioc.getBean("person01");
        Person bean2=(Person) ioc.getBean("person01");
        System.out.println(bean1==bean2);
        }

 

输出结果

Person类的无参构造方法...
Person类的无参构造方法...
true

Process finished with exit code 0