@Autowired
private ApplicationContext applicationContext; //IOC容器對象

Object getBean(String name)

<T> T getBean(Class<T> requiredType)

<T> T getBean(String name, Class<T> requiredType)

@SpringBootTest
class SpringbootTheoryApplicationTests {

    @Autowired
    private ApplicationContext applicationContext; //IOC容器對象

    //獲取bean對象
    @Test
    public void testGetBean(){
        //根據(jù)bean的名稱獲取
        MyController bean1 = (MyController) applicationContext.getBean("myController");
        System.out.println(bean1);

        //根據(jù)bean的類型獲取
        MyController bean2 = applicationContext.getBean(MyController.class);
        System.out.println(bean2);

        //根據(jù)bean的名稱 及 類型獲取
        MyController bean3 = applicationContext.getBean("myController", MyController.class);
        System.out.println(bean3);
    }

}

//當(dāng)我們未加@Scope注解時(shí)，默認(rèn)bean的作用域?yàn)椋篅Scope("singleton") (單例模式)
@Lazy //延遲加載(第一次使用bean對象時(shí)，才會(huì)創(chuàng)建bean對象并交給ioc容器管理)
@RestController
public class MyController {

    @Autowired
    private MyService myService;

    public MyController(){
        System.out.println("MyController 構(gòu)造方法執(zhí)行了...");
    }
}

@SpringBootTest
class SpringbootTheoryApplicationTests {

    @Autowired
    private ApplicationContext applicationContext; //IOC容器對象

    //獲取bean對象
    @Test
    public void testGetBean(){
        //根據(jù)bean的名稱獲取
        MyController bean1 = (MyController) applicationContext.getBean("myController");
        System.out.println(bean1);

        //根據(jù)bean的類型獲取
        MyController bean2 = applicationContext.getBean(MyController.class);
        System.out.println(bean2);

        //根據(jù)bean的名稱 及 類型獲取
        MyController bean3 = applicationContext.getBean("myController", MyController.class);
        System.out.println(bean3);
    }
}

@Lazy //延遲加載(第一次使用bean對象時(shí)，才會(huì)創(chuàng)建bean對象并交給ioc容器管理)
@Scope("prototype")
@RestController
public class MyController {

    @Autowired
    private MyService myService;

    public MyController(){
        System.out.println("MyController 構(gòu)造方法執(zhí)行了...");
    }
}

@SpringBootApplication
public class SpringbootTheoryApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringbootTheoryApplication.class, args);
    }

    //聲明第三方bean
    @Bean //將當(dāng)前方法的返回值對象交給IOC容器管理, 成為IOC容器bean
    public ObjectMapper objectMapper(){
        return new ObjectMapper();
    }
}

@SpringBootTest
class SpringbootWebConfig2ApplicationTests {

    @Autowired
    private ObjectMapper objectMapper;

    // 第三方bean的管理
    @Test
    public void testThirdBean() throws Exception {
        // 將 JSON 字符串轉(zhuǎn)換為 Java 對象
        String json = "{\"name\":\"zhangsan\",\"age\":21}";
        Person person = objectMapper.readValue(json, Person.class);

        System.out.println(person.getName() + " : " + person.getAge());
    }

    // 用于測試的簡單 POJO 類
    static class Person {
        private String name;
        private int age;


        public String getName() {
            return name;
        }

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

        public int getAge() {
            return age;
        }

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

@Configuration //聲明一個(gè)配置類
public class ObjectMapperConfig {
    
    @Bean
    public ObjectMapper objectMapper() {
        return new ObjectMapper();
    }
}