Bean的两种类型

定义一个class

package com.hhm.spring5;

public class User {
    public void add(){
        System.out.println("add.......");
    }
}

定义xml

测试方法：

@Test
public void testAdd() {
    //1.加载spring配置文件
    ApplicationContext context =
            new ClassPathXmlApplicationContext("bean1.xml");
    User user = context.getBean("user", User.class);
    System.out.println(user);
    user.add();
}

新建 MyBean类

package com.hhm.spring5;

import org.springframework.beans.factory.FactoryBean;

public class MyBean implements FactoryBean {
    @Override
    public Object getObject() throws Exception {
        return null;
    }

    @Override
    public Class getObjectType() {
        return null;
    }

    @Override
    public boolean isSingleton() {
        return false;
    }
}

定义xml

测试方法：

@Test
public void testMyBean() {
    //1.加载spring配置文件
    ApplicationContext context =
            new ClassPathXmlApplicationContext("bean1.xml");
    MyBean mybean = context.getBean("mybean", MyBean.class);
    System.out.println(mybean);
}

发现会报错：
错误为：

org.springframework.beans.factory.BeanNotOfRequiredTypeException: 
Bean named 'mybean' is expected to be of type 
'com.hhm.spring5.MyBean' but was actually of type 
'org.springframework.beans.factory.support.NullBean'

意思是期望是 com.hhm.spring5.MyBean 可实际上是 org.springframework.beans.factory.support.NullBean

如果MyBean类的代码改成：

@Override
public Object getObject() throws Exception {
    return "hello";
}

又会报错为:

org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'mybean' is expected to be of type 'com.hhm.spring5.MyBean' but was actually of type 'java.lang.String'

期望的是 com.hhm.spring5.MyBean 结果实际上是 java.lang.String

也就是说这边会动态返回你指定的类型。
再次改造一下：注意接口中加入了字符串的类型

public class MyBean implements FactoryBean {
    @Override
    public String getObject() throws Exception {
        return "hello world!";
    }

测试类也需要定义返回的类型：

@Test
public void testMyBean() {
    //1.加载spring配置文件
    ApplicationContext context =
            new ClassPathXmlApplicationContext("bean1.xml");
    String mybean = context.getBean("mybean", String.class);
    System.out.println(mybean);
}

结果输出：

hello world!

============================================================================
其实按默认就好， return返回什么类型，测试的时候强转即可。

public class MyBean implements FactoryBean {
    @Override
    public Object getObject() throws Exception {
        return "hello world!";
    }

@Test
public void testMyBean() {
    //1.加载spring配置文件
    ApplicationContext context =
            new ClassPathXmlApplicationContext("bean1.xml");
    Object mybean = context.getBean("mybean", Object.class);
    System.out.println(mybean);
}

输出：

hello world!

或者：

@Override
public Object getObject() throws Exception {
    return new User(); //实际中不会这么创建
}

@Test
public void testMyBean() {
    //1.加载spring配置文件
    ApplicationContext context =
            new ClassPathXmlApplicationContext("bean1.xml");
    Object mybean = context.getBean("mybean", Object.class);
    User user = (User)mybean;
    user.add();
}

输出：

add.......