Spring Bean四种注入方式(Springboot环境)

阅读此文建议参考本人写的Spring常用注解:https://blog.csdn.net/21aspJava
强烈推介IDEA2020.2破解激活,IntelliJ IDEA 注册码,2020.2 IDEA 激活码

阅读此文建议参考本人写的Spring常用注解:https://blog.csdn.net/21aspnet/article/details/104042826

给容器中注册组件的四种方法:

 1.@ComponentScan包扫描+组件标注注解@Component(@Controller@Service@Repository)
使用场景:自己写的代码,可以方便的加@Controller/@Service/@Repository/@Component

@SpringBootApplication
源码
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication

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。

2.@Configuration+@Bean   
使用场景:导入的第三方包里面的组件,将其他jar包中的类(类没有Component等注解),加载到容器中。

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;
    }
}

3.@Import快速给容器中导入一个组件
         1)@Import(要导入到容器中的组件);容器中就会自动注册这个组件,id默认是全类名
         2)ImportSelector:返回需要导入的组件的全类名数组;
         3)ImportBeanDefinitionRegistrar:手动注册bean到容器中

 

@Import方式

public class ImportDemo {
    public void doSomething () {
        System.out.println("ImportDemo.doSomething()");
    }
}

@Configuration
@Import({ImportDemo.class})
public class ImportConfig{
@Bean
    public User user(){
        return new User("Lily");
    }
}


@RestController
public class ImportDemoController {

    @Autowired
    private User user;

    @Autowired
    private ImportDemo importDemo;

    @RequestMapping("/importDemo")
    public String demo() throws Exception {
        importDemo.doSomething();
        
        String s = user.username;
        

        return "ImportDemo@SpringBoot " + 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) {
        // TODO Auto-generated method stub
        //importingClassMetadata
        //方法不要返回null值
        //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 {

    /**
     * 给容器中注册组件;
     * 1)、包扫描+组件标注注解(@Controller/@Service/@Repository/@Component)[自己写的类]
     * 2)、@Bean[导入的第三方包里面的组件]
     * 3)、@Import[快速给容器中导入一个组件]
     * 		1)、@Import(要导入到容器中的组件);容器中就会自动注册这个组件,id默认是全类名
     * 		2)、ImportSelector:返回需要导入的组件的全类名数组;
     * 		3)、ImportBeanDefinitionRegistrar:手动注册bean到容器中
     * 4)、使用Spring提供的 FactoryBean(工厂Bean);
     * 		1)、默认获取到的是工厂bean调用getObject创建的对象
     * 		2)、要获取工厂Bean本身,我们需要给id前面加一个&,&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;

    

    @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 {

    /**
     * AnnotationMetadata:当前类的注解信息
     * BeanDefinitionRegistry:BeanDefinition注册类;
     * 		把所有需要添加到容器中的bean;调用
     * 		BeanDefinitionRegistry.registerBeanDefinition手工注册进来
     */
    @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。

4.使用Spring提供的 FactoryBean(工厂Bean)
         1)默认获取到的是工厂bean调用getObject创建的对象
         2)要获取工厂Bean本身,我们需要给id前面加一个&
            &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() {
        // TODO Auto-generated method stub
        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 {

    /**
     * 给容器中注册组件;
     * 1)、包扫描+组件标注注解(@Controller/@Service/@Repository/@Component)[自己写的类]
     * 2)、@Bean[导入的第三方包里面的组件]
     * 3)、@Import[快速给容器中导入一个组件]
     * 		1)、@Import(要导入到容器中的组件);容器中就会自动注册这个组件,id默认是全类名
     * 		2)、ImportSelector:返回需要导入的组件的全类名数组;
     * 		3)、ImportBeanDefinitionRegistrar:手动注册bean到容器中
     * 4)、使用Spring提供的 FactoryBean(工厂Bean);
     * 		1)、默认获取到的是工厂bean调用getObject创建的对象
     * 		2)、要获取工厂Bean本身,我们需要给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]);
        }
    }
}

 Spring Bean四种注入方式(Springboot环境)

 

Spring Bean四种注入方式(Springboot环境)

如果基础不够可以再看看此文: 

https://blog.csdn.net/qq_27470131/category_7502799.html 

本文来源164,由架构君转载发布,观点不代表Java架构师必看的立场,转载请标明来源出处:https://javajgs.com/archives/2084

发表评论