撸了今年阿里、头条和美团的面试，我有一个重要发现.......>>>

需求

根据Restful API，前端传给后台的参数，动态的调用具体的service。不用手动写if else进行判断。

service

UserService.java

package com.vincent.service;public interface UserService {String getGender(String gender); }

两个service实现类分别实现这个UserService接口

FemaleServiceImpl.java

package com.vincent.service.impl;import com.vincent.service.UserService; import org.elasticsearch.action.search.SearchResponse; import org.elasticsearch.client.Client; import org.elasticsearch.index.query.QueryBuilders; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service;@Service("female") public class FemaleServiceImpl implements UserService {@Autowiredprivate Client client;@Overridepublic String getGender(String name) {SearchResponse test = client.prepareSearch("test").setQuery(QueryBuilders.boolQuery().must(QueryBuilders.termQuery("name", name))).setSize(0).get();System.out.println("female" + test.getHits().totalHits);return null;} }

MaleServiceImpl.java

package com.vincent.service.impl;import com.vincent.service.UserService; import org.elasticsearch.action.search.SearchResponse; import org.elasticsearch.client.Client; import org.elasticsearch.index.query.QueryBuilders; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service;@Service("male") public class MaleServiceImpl implements UserService {@Autowiredprivate Client client;@Overridepublic String getGender(String name) {SearchResponse test = client.prepareSearch("test").setQuery(QueryBuilders.boolQuery().must(QueryBuilders.termQuery("name", name))).setSize(0).get();System.out.println("male:" + test.getHits().totalHits);return null;} }

如何自动根据参数选择具体的UserService实现类？

新建FactoryForStratge.java

package com.vincent.service.impl;import com.vincent.service.UserService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service;import java.util.Map; import java.util.concurrent.ConcurrentHashMap;@Service public class FactoryForStrategy {@AutowiredMap<String, UserService> strategys = new ConcurrentHashMap<>(3);public UserService getStrategy(String component) throws Exception{UserService strategy = strategys.get(component);if(strategy == null) {throw new RuntimeException("no strategy defined");}return strategy;}}

根据bean的name来选择。

工厂类FactoryStrategy负责创建策略的工厂，代码比较简单，比较关键的一点是AutoWired一个Map<String, UserService> 这个会在初始化的时候将所有的UserService自动加载到Map中，是不是很方便。使用concurrentHashMap是防止多线程操作的时候出现问题。

UserController.java

package com.vincent.controller;import com.vincent.service.UserService; import com.vincent.service.impl.FactoryForStrategy; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController;@RestController public class UserController {@AutowiredFactoryForStrategy factoryForStrategy;@GetMapping("/gender2/{gender}/{name}")public String getGender2(@PathVariable String gender, @PathVariable String name) {try {UserService strategy = factoryForStrategy.getStrategy(gender);String gender1 = strategy.getGender(name);return "success";} catch (Exception e) {e.printStackTrace();return "failed";}}}

这样就可以根据参数来选择具体的service实现类了。

代码：https://github.com/vincentduan/springboot-test

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