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 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 {
/**
* 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。
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{ @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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