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在开发中，一个对外暴露的接口可能会面临瞬间的大量重复请求，如果想过滤掉重复请求造成对业务的伤害，那就需要实现幂等
幂等：
任意多次执行所产生的影响均与一次执行的影响相同。最终的含义就是 对数据库的影响只能是一次性的，不能重复处理。
解决方案：
数据库建立唯一性索引，可以保证最终插入数据库的只有一条数据
token机制，每次接口请求前先获取一个token，然后再下次请求的时候在请求的header体中加上这个token，后台进行验证，如果验证通过删除token，下次请求再次判断token（本次案例使用）
悲观锁或者乐观锁，悲观锁可以保证每次for update的时候其他sql无法update数据(在数据库引擎是innodb的时候,select的条件必须是唯一索引,防止锁全表)
先查询后判断，首先通过查询数据库是否存在数据，如果存在证明已经请求过了，直接拒绝该请求，如果没有存在，就证明是第一次进来，直接放行
一、搭建Redis服务
package com.ckw.idempotence.service;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.data.redis.core.RedisTemplate;import org.springframework.data.redis.core.ValueOperations;import org.springframework.data.redis.serializer.RedisSerializer;import org.springframework.data.redis.serializer.StringRedisSerializer;import org.springframework.stereotype.Component;import java.io.Serializable;import java.util.concurrent.TimeUnit;@Componentpublic class RedisService { private RedisTemplate redisTemplate; @Autowired(required = false) public void setRedisTemplate(RedisTemplate redisTemplate) { RedisSerializer stringSerializer = new StringRedisSerializer(); redisTemplate.setKeySerializer(stringSerializer); redisTemplate.setValueSerializer(stringSerializer); redisTemplate.setHashKeySerializer(stringSerializer); redisTemplate.setHashValueSerializer(stringSerializer); this.redisTemplate = redisTemplate; } public boolean set(final String key, Object value) { boolean result = false; try { ValueOperations operations = redisTemplate.opsForValue(); operations.set(key, value); result = true; } catch (Exception e) { e.printStackTrace(); } return result; } public boolean setEx(final String key, Object value, Long expireTime) { boolean result = false; try { ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue(); operations.set(key, value); redisTemplate.expire(key, expireTime, TimeUnit.SECONDS); result = true; } catch (Exception e) { e.printStackTrace(); } return result; } public boolean exists(final String key) { return redisTemplate.hasKey(key); } public Object get(final String key) { Object o = null; ValueOperations valueOperations = redisTemplate.opsForValue(); return valueOperations.get(key); } public Boolean remove(final String key) { if(exists(key)){ return redisTemplate.delete(key); } return false; }}二、自定义注解
作用：拦截器拦截请求时，判断调用的地址对应的Controller方法是否有自定义注解，有的话说明该接口方法进行 幂等
package com.ckw.idempotence.annotion;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target({ElementType.METHOD})@Retention(RetentionPolicy.RUNTIME)public @interface AutoIdempotent {}三、Token创建和校验
package com.ckw.idempotence.service;import com.ckw.idempotence.exectionhandler.BaseException;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import org.springframework.util.StringUtils;import javax.servlet.http.HttpServletRequest;import java.util.UUID;@Servicepublic class TokenService { @Autowired RedisService redisService;//创建token public String createToken() { //使用UUID代表token UUID uuid = UUID.randomUUID(); String token = uuid.toString(); //存入redis boolean b = redisService.setEx(token, token, 10000L); return token; }//检验请求头或者请求参数中是否有token public boolean checkToken(HttpServletRequest request) { String token = request.getHeader("token"); //如果header中是空的 if(StringUtils.isEmpty(token)){ //从request中拿 token = request.getParameter("token"); if(StringUtils.isEmpty(token)){ throw new BaseException(20001, "缺少参数token"); } } //如果从header中拿到的token不正确 if(!redisService.exists(token)){ throw new BaseException(20001, "不能重复提交-------token不正确、空"); } //token正确 移除token if(!redisService.remove(token)){ throw new BaseException(20001, "token移除失败"); } return true; }}这里用到了自定义异常和自定义响应体如下
自定义异常：
package com.ckw.idempotence.exectionhandler;import lombok.AllArgsConstructor;import lombok.Data;import lombok.NoArgsConstructor;@Data@AllArgsConstructor@NoArgsConstructorpublic class BaseException extends RuntimeException { private Integer code; private String msg;}设置统一异常处理：
package com.ckw.idempotence.exectionhandler;import com.ckw.idempotence.utils.R;import org.springframework.web.bind.annotation.ControllerAdvice;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.ResponseBody;@ControllerAdvicepublic class GlobalExceptionHandler { @ExceptionHandler(Exception.class) @ResponseBody public R error(Exception e){ e.printStackTrace(); return R.error(); } @ExceptionHandler(BaseException.class) @ResponseBody public R error(BaseException e){ e.printStackTrace(); return R.error().message(e.getMsg()).code(e.getCode()); }}自定义响应体：
package com.ckw.idempotence.utils;import lombok.Data;import java.util.HashMap;import java.util.Map;@Datapublic class R { private Boolean success; private Integer code; private String message; private Map<String, Object> data = new HashMap<String, Object>(); private R() { } //封装返回成功 public static R ok(){ R r = new R(); r.setSuccess(true); r.setCode(ResultCode.SUCCESS); r.setMessage("成功"); return r; } //封装返回失败 public static R error(){ R r = new R(); r.setSuccess(false); r.setCode(ResultCode.ERROR); r.setMessage("失败"); return r; } public R success(Boolean success){ this.setSuccess(success); return this; } public R message(String message){ this.setMessage(message); return this; } public R code(Integer code){ this.setCode(code); return this; } public R data(String key, Object value){ this.data.put(key, value); return this; } public R data(Map<String, Object> map){ this.setData(map); return this; }}自定义响应码：
package com.ckw.idempotence.utils;import lombok.Data;import java.util.HashMap;import java.util.Map;@Datapublic class R { private Boolean success; private Integer code; private String message; private Map<String, Object> data = new HashMap<String, Object>(); private R() { } //封装返回成功 public static R ok(){ R r = new R(); r.setSuccess(true); r.setCode(ResultCode.SUCCESS); r.setMessage("成功"); return r; } //封装返回失败 public static R error(){ R r = new R(); r.setSuccess(false); r.setCode(ResultCode.ERROR); r.setMessage("失败"); return r; } public R success(Boolean success){ this.setSuccess(success); return this; } public R message(String message){ this.setMessage(message); return this; } public R code(Integer code){ this.setCode(code); return this; } public R data(String key, Object value){ this.data.put(key, value); return this; } public R data(Map<String, Object> map){ this.setData(map); return this; }}四、拦截器配置
拦截器配置类
package com.ckw.idempotence.config;import com.ckw.idempotence.interceptor.AutoIdempotentInterceptor;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.annotation.Configuration;import org.springframework.web.servlet.config.annotation.InterceptorRegistry;import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configurationpublic class WebConfiguration implements WebMvcConfigurer { @Autowired private AutoIdempotentInterceptor autoIdempotentInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(autoIdempotentInterceptor); }}拦截器类
package com.ckw.idempotence.interceptor;import com.ckw.idempotence.annotion.AutoIdempotent;import com.ckw.idempotence.service.TokenService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Component;import org.springframework.web.method.HandlerMethod;import org.springframework.web.servlet.HandlerInterceptor;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.lang.reflect.Method;@Componentpublic class AutoIdempotentInterceptor implements HandlerInterceptor { @Autowired private TokenService tokenService; @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { if(!(handler instanceof HandlerMethod)) return true; HandlerMethod handlerMethod = (HandlerMethod) handler; Method method = handlerMethod.getMethod(); //拿到方法上面的自定义注解 AutoIdempotent annotation = method.getAnnotation(AutoIdempotent.class); //如果不等于null说明该方法要进行幂等 if(null != annotation){ return tokenService.checkToken(request); } return true; }}五、正常Sevice类
package com.ckw.idempotence.service;import org.springframework.stereotype.Service;@Servicepublic class TestService { public String testMethod(){ return "正常业务逻辑"; }}六、Controller类
package com.ckw.idempotence.controller;import com.ckw.idempotence.annotion.AutoIdempotent;import com.ckw.idempotence.service.TestService;import com.ckw.idempotence.service.TokenService;import com.ckw.idempotence.utils.R;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.*;@RestController@CrossOrigin@RequestMapping("/Idempotence")public class TestController { @Autowired private TokenService tokenService; @Autowired private TestService testService; @GetMapping("/getToken") public R getToken(){ String token = tokenService.createToken(); return R.ok().data("token",token); } //相当于添加数据接口（测试时 连续点击添加数据按钮 看结果是否是添加一条数据还是多条数据） @AutoIdempotent @PostMapping("/test/addData") public R addData(){ String s = testService.testMethod(); return R.ok().data("data",s); }}七、测试
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第二次点击：
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