使用拦截器对GET请求结果进行缓存

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前言

在接口服务中，如果每个接口单独添加缓存的话会存在很多的重复的逻辑，所以通过拦截器可以简化。

1. 通过拦截器实现对请求的拦截，在拦截器中实现缓存的命中。
2. 缓存的处理中，仅针对GET请求处理，

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一、使用步骤

1.引入库

使用redis做缓存，引入坐标

       <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>

2. application

  redis:
    host: 192.X.X.X
    port: 6379
#    password: root@123456
    database: 0  #使用0号数据库
    
#是否开启数据缓存
cache:
  enable: true

3. 自定义注解

代码如下（示例）：

import java.lang.annotation.*;

/**
 * 被标记为Cache的Controller进行缓存，其他情况不进行缓存
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented //标记注解
public @interface Cache {

    /**
     * 缓存时间，默认为60秒
     * @return
     */
    String time() default "60";
}

4. 响应结果写入到缓存

import com.fasterxml.jackson.databind.ObjectMapper;
import net.fff.rege.annotation.Cache;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.MethodParameter;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

import java.util.concurrent.TimeUnit;

@ControllerAdvice
public class MyResponseBodyAdvice implements ResponseBodyAdvice {

    @Value("${cache.enable}")
    private Boolean enable;

    @Autowired
    private RedisTemplate<String, String> redisTemplate;

    private static final ObjectMapper MAPPER = new ObjectMapper();

    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        // 开关处于开启状态  是get请求  包含了@Cache注解
        return enable && returnType.hasMethodAnnotation(GetMapping.class)
                && returnType.hasMethodAnnotation(Cache.class);
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType,
                                  ServerHttpRequest request, ServerHttpResponse response) {
        if (null == body) {
            return null;
        }

        try {

            String redisValue = null;
            if (body instanceof String) {
                redisValue = (String) body;
            } else {
                redisValue = MAPPER.writeValueAsString(body);
            }

            String redisKey = RedisCacheInterceptor.createRedisKey(((ServletServerHttpRequest) request).getServletRequest());

            Cache cache = returnType.getMethodAnnotation(Cache.class);

            //缓存的时间单位是秒
            this.redisTemplate.opsForValue().set(redisKey, redisValue, Long.valueOf(cache.time()), TimeUnit.SECONDS);

        } catch (Exception e) {
            e.printStackTrace();
        }

        return body;
    }

5. 采用拦截器进行缓存获取

import com.fasterxml.jackson.databind.ObjectMapper;
import net.fff.rege.annotation.Cache;
import org.apache.commons.codec.digest.DigestUtils;
import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.HandlerInterceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@Component
public class RedisCacheInterceptor implements HandlerInterceptor {

    @Value("${cache.enable}")
    private Boolean enable;

    @Autowired
    private RedisTemplate<String, String> redisTemplate;

    private static final ObjectMapper MAPPER = new ObjectMapper();

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //缓存的全局开关的校验
        if (!enable) {
            return true;
        }

        //校验handler是否是HandlerMethod
        if (!(handler instanceof HandlerMethod)) {
            return true;
        }

        //判断是否为get请求
        if (!((HandlerMethod) handler).hasMethodAnnotation(GetMapping.class)) {
            return true;
        }

        //判断是否添加了@Cache注解
        if (!((HandlerMethod) handler).hasMethodAnnotation(Cache.class)) {
            return true;
        }

        //缓存命中
        String redisKey = createRedisKey(request);
        String cacheData = this.redisTemplate.opsForValue().get(redisKey);
        if(StringUtils.isEmpty(cacheData)){
            //缓存未命中
            return true;
        }

        // 将data数据进行响应
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/json; charset=utf-8");
        response.getWriter().write(cacheData);

        return false;
    }

    /**
     * 生成redis中的key，规则：SERVER_CACHE_DATA_MD5(url + param + token)
     *
     * @param request
     * @return
     */
    public static String createRedisKey(HttpServletRequest request) throws Exception {
        String url = request.getRequestURI();
        String param = MAPPER.writeValueAsString(request.getParameterMap());
        String token = request.getHeader("Authorization");

        String data = url + "_" + param + "_" + token;
        return "SERVER_CACHE_DATA_" + DigestUtils.md5Hex(data);
    }
}

6. 注册拦截器到Spring容器

import net.fff.rege.interceptor.RedisCacheInterceptor;

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;

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    private RedisCacheInterceptor redisCacheInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(this.redisCacheInterceptor).addPathPatterns("/**");
    }
}

7. 测试

   @GetMapping("/page")
   @Cache(time = "90")
    public Result getInfoByPage(int page, int pageSize) {
        //分页查询员工信息
        IPage pageInfo = catService.getInfoByPage(page, pageSize);
        return Result.success(pageInfo);
    }