自定义注解开发

需求

设想现有这样的需求，程序需要接收不同的命令CMD，
然后根据命令调用不同的处理类Handler。
很容易就会想到用Map来存储命令和处理类的映射关系。

由于项目可能是多个成员共同开发，不同成员实现各自负责的命令的处理逻辑。
因此希望开发成员只关注Handler的实现，不需要主动去Map中注册CMD和Handler的映射。

• 定义注解类

@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Component
public @interface CmdMapping {
    int value() ;
}

• 处理器接口类

public interface ICmdHandler {
    Object handle();
}

• 处理器实现类

@CmdMapping(Cmd.REGISTER)
public class RegisterHandler implements ICmdHandler
{
    @Override public Object handle()
    {
        return "handle register request";
    }
}

@CmdMapping(Cmd.LOGOUT)
public class LogoutHandler implements ICmdHandler {
    @Override
    public Object handle() {
        return "handle logout request";
    }
}

@CmdMapping(Cmd.LOGIN)
public class LoginHandler implements ICmdHandler {
    @Override
    public Object handle() {
       return  "handle login request";
    }
}

• 注册处理类

@Component
public class HandlerDispatcherServlet implements
        InitializingBean, ApplicationContextAware
{

    private ApplicationContext context;

    private Map<Integer, ICmdHandler> handlers = new HashMap<>();

    public Object handle(int cmd) {
        Object handle=null;
        try
        {
            handle = handlers.get(cmd).handle();

        }catch (RuntimeException e){

            return "没有这个命令";
        }
      return handle;
    }

    public void afterPropertiesSet() {

        String[] beanNames = this.context.getBeanNamesForType(ICmdHandler.class);

        System.out.println(Arrays.toString(beanNames));
        for (String beanName : beanNames) {
            Class<?> beanType = this.context.getType(beanName);

            if (beanType != null) {

                CmdMapping annotation = AnnotatedElementUtils.findMergedAnnotation(
                        beanType, CmdMapping.class);

                if(annotation != null) {
                    handlers.put(annotation.value().getCode(), (ICmdHandler) context.getBean(beanType));
                }
            }
        }

    }

    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException
    {
        this.context = applicationContext;
    }

}

• controller类

@RestController
public class TestController {

    @Autowired
    private HandlerDispatcherServlet handlerDispatcherServlet;

    @RequestMapping("/test")
    public Object test(@RequestParam int cmd){
      return  handlerDispatcherServlet.handle(cmd);
    }
}

• 最终结果

localhost:8081/test?cmd=1
handle register request