【Spring学习及总结05】从IOC容器中获取bean对象

首先写一个实体类：

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Person {
    private String lastName;
    private int age;
    private String gender;
}

其次在spring.xml中配置两个Person对象，person01和person02

<bean id="person01" class="com.hh.pojo.Person">
    <property name="lastName" value="张三"/>
    <property name="gender" value="男"/>
    <property name="age" value="12"/>
</bean>

1.根据bean的id从IOC容器中获取bean对象

写一个测试类，根据bean的id获取bean的实例

public class MyTest {
public class MyTest {
    //根据spring的配置文件得到ioc容器对象
    ApplicationContext context =
            new ClassPathXmlApplicationContext("spring.xml");
    @Test
    public void test(){
        Person person = (Person)context.getBean("person01");
        System.out.println(person);
    }
    @Test
    public void test2(){
        Person person = (Person)context.getBean("person02");
        System.out.println(person);
    }
}

2.根据bean的class类型从IOC容器中获取bean对象

现在spring.xml中只注册了一个bean对象

<bean id="person01" class="com.hh.pojo.Person">
    <property name="lastName" value="张三"/>
    <property name="gender" value="男"/>
    <property name="age" value="12"/>
</bean>

测试根据bean的类型从IOC容器中获取bean对象

public class MyTest2 {
    //根据spring的配置文件得到ioc容器对象
    ApplicationContext context =
            new ClassPathXmlApplicationContext("spring.xml");
    @Test
    public void test2(){
        Person person = context.getBean(Person.class);
        System.out.println(person);
    }
}

这样获取bean对象有一个好处就是不用返回值类型不用强制转换
那么问来了，如果spring.xml中注册了两个bean对象呢？

<bean id="person01" class="com.hh.pojo.Person">
  <property name="lastName" value="张三"/>
  <property name="gender" value="男"/>
  <property name="age" value="12"/>
</bean>

<bean id="person02" class="com.hh.pojo.Person">
  <property name="lastName" value="李四"/>
</bean>

此时按照bean的类型来找时，就会报错

遇到这种情况，我们只能通过bean的id来获取bean对象，那么我们又不想类型强转怎么办？？

public class MyTest2 {
    //根据spring的配置文件得到ioc容器对象
    ApplicationContext context =
            new ClassPathXmlApplicationContext("spring.xml");

    @Test
    public void test(){
        Person person = context.getBean("person01",Person.class);
        System.out.println(person);
    }
    @Test
    public void test2(){
        Person person = context.getBean(Person.class);
        System.out.println(person);
    }
}

3.总结