项目中如何优雅的消除if-else
消除if-else的方法有很多种，本文结合spring中ArgumentResolver的应用，提供一种优雅地方式。
先看ArgumentResolver的应用方式
public class UserArgumentResolver implements HandlerMethodArgumentResolver {
private static final String TOKEN_KEY = "token";
@Override
public boolean supportsParameter(MethodParameter parameter) {
return parameter.hasParameterAnnotation(LoginUser.class);
}
@Override
public Object resolveArgument(MethodParameter parameter,
ModelAndViewContainer mavContainer,
NativeWebRequest webRequest,
WebDataBinderFactory binderFactory) throws Exception {
// 通过session取userid
String token = webRequest.getHeader(TOKEN_KEY);
User user = null;
// 从redis中获取user json
// user = JSON.parse(redis.get(token),User.class);
return user;
}
}controller 需要注入参数的地方
@RequestMapping(value = "/doSth", method = RequestMethod.POST)
public String feed(@LoginUser User user) {
System.out.println("userId: " + JSON.toJsonString(user));
return "success";
}声明注解LoginUser
@Target(ElementType.TYPE,ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RestController {
String value() default "";
}配置类添加
@Configuration
public class WebConfiguration implements WebMvcConfigurer {
@Override
public void addArgumentResolvers (List<HandlerMethodArgumentResolver> resolvers) {
resolvers.add(new UserArgumentResolver());
}
}有多个ArgumentResolver在WebConfiguration中配置即可。
if-else消除
常用代码 如交通方式有 bike, bus,subway,train,plan
if (bike) {
} else if (bus) {
} else if (subway) {
} else if (train) {
} else if (plan) {
}else {
}编写不同的reslover
定义统一的接口
public interface TrafficResolver {
boolean support(String type);
Object resolver(Object argument);
}定义实现类BusTrafficResolver，其他省略
@Compoment
public class BusTrafficResolver implements TrafficResolver{
@Override
public boolean support (String type) {
return "BUS".equals(type);
}
@Override
public Object resolver (Object argument) {
// doSth
return "bus resolver";
}
}真正消除if-else的服务类
List 若没有bean则需要required 比提供默认值new ArrayList<>() ,有bean 可以去掉。
@Service
public class TrafficService {
// required = false
@Autowired(required = false)
List<TrafficResolver> trafficResolverList = new ArrayList<>();
public Object traffic(String type,Object argument){
System.out.printf("trafficResolverList "+trafficResolverList.size());
TrafficResolver resolver = getFirstResolver(type);
if(resolver!=null){
return resolver.resolver(argument);
}
return "traffic not find. type: "+type;
}
private TrafficResolver getFirstResolver(String type){
TrafficResolver resolver = trafficResolverList.stream()
.filter(item -> item.support(type))
.findFirst()
.orElse(null);
return resolver;
}
}通过此种方式完成了对if-else调用类的解耦，实现了高扩展性。遵循了面向修改关闭，面向扩展开放的原则。
消除if-else完成，当然可以用注解的方式，通过注解类型判断是否支持。
其实if-else挺好用，除非考虑扩展性很强的地方，否则不要过度设计。
