springboot+redis+mybatis体会布隆过滤器

1.建立数据库表和对应实体类

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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;

bash 复制代码

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

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@Controller
public class BloomController {
    @Autowired
    private BloomService bloomService;

    @RequestMapping(value = "/addUser")
    @ResponseBody
    public 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")
    @ResponseBody
    public 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

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public interface BloomService {
    void addUser(User user);

    User getUser(String userId);

    List<String> getUserIds();
}

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@Service
public class BloomServiceImpl implements BloomService {

    public static final String redisKey = "USER:";

    @Resource
    private BloomDao bloomDao;

    @Autowired
    private RedisTemplate redisTemplate;

    @Autowired
    private BloomCheckUtil bloomCheckUtil;

    @Override
    public void addUser(User user) {
        int i = bloomDao.addUser(user);
        if(i>0){
            //mysql插入成功，将数据存入redis
            User currentUser = bloomDao.getUser(user.getId());
            redisTemplate.opsForValue().set(redisKey+user.getId(), JSONObject.toJSONString(currentUser));
        }


    }

    @Override
    public 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;
    }

    @Override
    public List<String> getUserIds() {

        return bloomDao.getUserIds();
    }
}

4.编写dao和mapper，实现数据库操作

bash 复制代码

public interface BloomDao {
    int addUser(@Param("user") User user);

    User getUser(@Param("id")String id);

    List<String> getUserIds();
}

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<?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

bash 复制代码

@Component
public class BloomFilter {

    public static final String key = "LEGITIMATE_USER";

    @Autowired
    private RedisTemplate redisTemplate;

    @Autowired
    private BloomService bloomService;


    @PostConstruct
    public 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1
            redisTemplate.opsForValue().setBit(key,index,true);
        }
    }
}

bash 复制代码

@Component
public class BloomCheckUtil {


    private static final String key = "LEGITIMATE_USER";

    @Autowired
    private 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