SpringBoot向容器注册bean的方法详解

2022-11-13 08:11:51 方法容器详解

简介

本文用示例介绍SpringBoot如何向容器注册bean（即：将对象加入容器）。

法1：@Component

(@Controller/@Service/@Repository也可以，因为它里边包含@Component)

默认是加载和Application类所在同一个目录下的所有类，包括所有子目录下的类。

当启动类和@Component分开时，如果启动类在某个包下，需要在启动类中增加注解@ComponentScan，配置需要扫描的包名。例如：

@springBootApplication(scanBasePackages="com.test.chapter4")

此注解其实是@ComponentScan的basePackages，通过查看scanBasePackages即可得知。

@SpringBootApplication只会扫描@SpringBootApplication注解标记类包下及其子包的类，将这些类纳入到spring容器，只要类有@Component注解即可。

有的注解的定义中已加入@Component，所以这些注解也会被扫描到：@Controller，@Service，@Configuration，@Bean

@ComponentScan+@Configuration+@Component

DemoConfig在扫描路径之内

@Configuration
@ComponentScan(basePackages = { "com.example.demo.mybeans" })
public class DemoConfig {
}

MyBean1在com.example.demo.mybeans下

@Component
public class MyBean1{
}

法2：@Configuration+@Bean

使用场景：将没有Component等注解的类导入。例如：第三方包里面的组件、将其他jar包中的类。

public class User {
    //@Value("Tom")
    public String username;
 
    public User(String s) {
        this.username = s;
    }
}
 
@Configuration
public class ImportConfig {
    @Bean
    public User user(){
        return new User("Lily");
    }
}
 
@RestController
public class ImportDemoController {
    @Autowired
    private User user;
 
    @RequestMapping("/importDemo")
    public String demo() throws Exception {
        String s = user.username;
        return "ImportDemo@SpringBoot " + s;
    }
}

法3：@Import等

简介

@Import(要导入到容器中的组件)；容器会自动注册这个组件，id默认是全类名。（@Import是Spring的注解。）

ImportSelector:返回需要导入的组件的全类名数组；

ImportBeanDefinitionReGIStrar:手动注册bean到容器中

@Import方式

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import({ImportDemoConfig.class})
public @interface EnableImportDemo {
}
 
public class ImportDemoConfig{
    @Bean
    public User user(){
        return new User("Lily");
    }
}
 
@EnableImportDemo
@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}
 
@RestController
public class ImportDemoController {
    @Autowired
    private User user;
 
    @RequestMapping("/importDemo")
    public String demo() {
        String s = user.getName();
        return "user.getName():" + s;
    }
}

ImportSelector方式

//自定义逻辑返回需要导入的组件
public class MyImportSelector implements ImportSelector {
 
    //返回值，就是到导入到容器中的组件全类名
    //AnnotationMetadata:当前标注@Import注解的类的所有注解信息
    @Override
    public String[] selectImports(AnnotationMetadata importinGClaSSMetadata) {
        //当前类的所有注解
        Set<String> annotationTypes = importingClassMetadata.getAnnotationTypes();
        System.out.println("当前配置类的注解信息："+annotationTypes);
        //注意不能返回null,不然会报NullPointException
        return new String[]{"com.paopaoedu.springboot.bean.user01","com.paopaoedu.springboot.bean.user02"};
    }
}
 
public class User01 {
	public String username;
 
    public User01() {
        System.out.println("user01...constructor");
    }
}
 
public class User02 {
    public String username;
 
    public User02() {
        System.out.println("user02...constructor");
    }
}
 
@Configuration
@Import({ImportDemo.class, MyImportSelector.class})
public class ImportConfig {
    @Bean
    public User user(){
        return new User("Lily");
    }
}
 
@RestController
public class ImportDemoController {
    @Autowired
    private User user;
 
    @Autowired
    private ImportDemo importDemo;
 
    @Autowired
    private User01 user01;
 
    @RequestMapping("/importDemo")
    public String demo() throws Exception {
        importDemo.doSomething();
        user01.username = "user01";
        String s = user.username;
        String s1 = user01.username;
 
        return "ImportDemo@SpringBoot " + s + " " + s1;
    }
}

ImportBeanDefinitionRegistrar方式

public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
                   BeanDefinitionRegistry registry) {
 
        boolean definition = registry.containsBeanDefinition("com.paopaoedu.springboot.bean.User01");
        boolean definition2 = registry.containsBeanDefinition("com.paopaoedu.springboot.bean.User02");
        if(definition && definition2){
            //指定Bean定义信息作用域都可以在这里定义；（Bean的类型，Bean。。。）
            RootBeanDefinition beanDefinition = new RootBeanDefinition(User03.class);
            //注册一个Bean，指定bean名
            registry.registerBeanDefinition("User03", beanDefinition);
        }
    }
}

public class User03 {
    public String username;
 
    public User03() {
        System.out.println("user03...constructor");
    }
}

使用上和前面的类似就不举例了。

法4：FactoryBean

默认获取到的是工厂bean调用getObject创建的对象。

要获取工厂Bean本身，我们需要给id前面加一个&。例如：&xxxFactoryBean 注意类名是X，这里就是小写的x

public class UserFactoryBean implements FactoryBean<User04> {
    @Override
    public User04 getObject() throws Exception {
        // TODO Auto-generated method stub
        System.out.println("UserFactoryBean...getObject...");
        return new User04("User04");
    }
 
    @Override
    public Class<?> getObjectType() {
        // TODO Auto-generated method stub
        return User04.class;
    }
 
    //是否单例？
    //true：这个bean是单实例，在容器中保存一份
    //false：多实例，每次获取都会创建一个新的bean；
    @Override
    public boolean isSingleton() {
        return true;
    }
}
 
public class User04 {
    public String username;
    public User04(String s) {
        String nowtime= DateUtil.now();
        username=s+" "+nowtime;
    }
}
 
@Configuration
@Import({ImportDemo.class, MyImportSelector.class, MyImportBeanDefinitionRegistrar.class})
public class ImportConfig {
 
    // 要获取工厂Bean本身，需要给id前面加一个&，&userFactoryBean
    @Bean
    public UserFactoryBean userFactoryBean(){
        return new UserFactoryBean();
    }
 
    @Bean
    public User user(){
        return new User("Lily");
    }
}
 
@RestController
public class ImportDemoController {
    @Autowired
    private User user;
 
    @Autowired
    private ImportDemo importDemo;
 
    @Autowired
    private User01 user01;
 
    @Autowired
    private UserFactoryBean userFactoryBean;
 
    @RequestMapping("/importDemo")
    public String demo() throws Exception {
        importDemo.doSomething();
        user01.username = "user01";
        String s = user.username;
        String s1 = user01.username;
        String s4 = userFactoryBean.getObject().username;
 
        return "ImportDemo@SpringBoot " + s + " " + s1 + " " + s4;
    }
}
 
@SpringBootApplication
public class SpringBootLearningApplication {
 
    public static void main(String[] args) {
        SpringApplication.run(SpringBootLearningApplication.class, args);
 
        AnnotationConfigApplicationContext context =
                new AnnotationConfigApplicationContext("com.paopaoedu.springboot.config");
        ImportDemo importDemo = context.getBean(ImportDemo.class);
        importDemo.doSomething();
        printClassName(context);
 
        Object bean1 = context.getBean("userFactoryBean");
        Object bean2 = context.getBean("userFactoryBean");
        System.out.println(bean1 == bean2);
    }
 
    private static void printClassName(AnnotationConfigApplicationContext annotationConfigApplicationContext){
        String[] beanDefinitionNames = annotationConfigApplicationContext.getBeanDefinitionNames();
        for (int i = 0; i < beanDefinitionNames.length; i++) {
            System.out.println("匹配的类"+beanDefinitionNames[i]);
        }
    }
}

测试结果

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