springboot+redis+mybatis体会布隆过滤器

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1.建立数据库表和对应实体类

CREATE TABLE `user` (`id` int(11) NOT NULL AUTO_INCREMENT,`uname` varchar(50) DEFAULT NULL,`usex` varchar(20) DEFAULT NULL,`uage` int(11) DEFAULT NULL,PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=1319 DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;

public class User {private String id;private String uname;private String usex;private String uage;public String getUname() {return uname;}public void setUname(String uname) {this.uname = uname;}public String getUsex() {return usex;}public void setUsex(String usex) {this.usex = usex;}public String getUage() {return uage;}public void setUage(String uage) {this.uage = uage;}public String getId() {return id;}public void setId(String id) {this.id = id;}
}

2.编写Controller，新增用户和获取用户

@Controller
public class BloomController {@Autowiredprivate BloomService bloomService;@RequestMapping(value = "/addUser")@ResponseBodypublic void addUser(){for(int i=0;i<100;i++){User user = new User();user.setUsex(i + "");user.setUname("user:" + i);user.setUage("26");bloomService.addUser(user);}}@RequestMapping(value = "/getUser")@ResponseBodypublic User getUser(HttpServletRequest request){String userId = request.getParameter("userId");User user = bloomService.getUser(userId);return  user;}}

3.编写servie，实现具体的业务逻辑

public interface BloomService {void addUser(User user);User getUser(String userId);List<String> getUserIds();
}

@Service
public class BloomServiceImpl implements BloomService {public static final String redisKey = "USER:";@Resourceprivate BloomDao bloomDao;@Autowiredprivate RedisTemplate redisTemplate;@Autowiredprivate BloomCheckUtil bloomCheckUtil;@Overridepublic void addUser(User user) {int i = bloomDao.addUser(user);if(i>0){//mysql插入成功，将数据存入redisUser currentUser = bloomDao.getUser(user.getId());redisTemplate.opsForValue().set(redisKey+user.getId(), JSONObject.toJSONString(currentUser));}}@Overridepublic User getUser(String userId) {User user = null;//1.先从布隆过滤器中获取数据，若没有则直接返回if(!bloomCheckUtil.check(userId)){System.out.println("该用户id：" + userId +"不在合法用户内！！！！");return user;}//2.从redis中查找String rediskey = redisKey + userId;String jsonObj = Optional.ofNullable(redisTemplate.opsForValue().get(rediskey)).map(Object::toString).orElse(null);if(jsonObj == null){//3.redis中没有，查询数据库user = bloomDao.getUser(userId);if(user != null){//4.redis无mysql有,把查询出的数据写入到redis缓存redisTemplate.opsForValue().set(rediskey,JSONObject.toJSONString(user));}return user;}user =JSONObject.parseObject(jsonObj, User.class) ;return user;}@Overridepublic List<String> getUserIds() {return bloomDao.getUserIds();}
}

4.编写dao和mapper，实现数据库操作

public interface BloomDao {int addUser(@Param("user") User user);User getUser(@Param("id")String id);List<String> getUserIds();
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.cn.study.redis.dao.BloomDao"><insert id="addUser"  parameterType="com.cn.study.redis.pojo.User" useGeneratedKeys="true" keyProperty="id">insert into user(uname,usex,uage) values (#{user.uname},#{user.usex},#{user.uage})</insert><select id="getUser" resultType="com.cn.study.redis.pojo.User">select u.id ,u.uname ,u.usex ,u.uage  from user u where u.id = #{id}</select><select id="getUserIds" resultType="String">select id from user</select>
</mapper>

5.编写布隆过滤器和工具类

@Component
public class BloomFilter {public static final String key = "LEGITIMATE_USER";@Autowiredprivate RedisTemplate redisTemplate;@Autowiredprivate BloomService bloomService;@PostConstructpublic void init(){//初始化布隆过滤器//1.从数据库查出user表中的所有id，计算hash值List<String> userIdList = bloomService.getUserIds();for(int i=0;i<userIdList.size();i++){//对每个userId计算hash值并取绝对值int hashValue = Math.abs(("USER:" + userIdList.get(i)).hashCode());//使用hash值对2的32次方取余，得到下标long index = (long)(hashValue % Math.pow(2,32));System.out.println("id为：" + userIdList.get(i)+"的用户产生的hash值为：" + hashValue +",下标为：" + index);//将redis中对应下标的bitmap的值更新成1redisTemplate.opsForValue().setBit(key,index,true);}}
}

@Component
public class BloomCheckUtil {private static final String key = "LEGITIMATE_USER";@Autowiredprivate RedisTemplate redisTemplate;public boolean check(String userId){boolean flag = false;int hashValue = Math.abs(("USER:" + userId).hashCode());long index = (long)(hashValue % Math.pow(2,32));flag = redisTemplate.opsForValue().getBit(key,index);return flag;}}

7.验证

由于第一次启动项目的时候，BloomFilter 类中的init方法会在一开始执行，此时我还并没有调用addUser方法添加用户，数据库中没有任何用户信息，所以第一次启动项目的时候，布隆过滤器中不会有任何的数据。
我们启动项目后，手动调用下addUser方法，新增100条用户数据。
然后重启项目，将用户信息加载到布隆过滤器中。
我们调用getUser方法尝试获取用户信息，当我们传了一个数据库不存在的用户id时，当请求到布隆过滤器，布隆过滤器发现没有此数据，则直接返回，不会再往下查redis和mysql