Get complete Map from Redis if a key contains a String - redis

Question

I am able to add and get a particular user object from Redis I am adding object like this:
private static final String USER_PREFIX = ":USER:";
public void addUserToRedis(String serverName,User user) {
redisTemplate.opsForHash().put(serverName + USER_PREFIX + user.getId(),
Integer.toString(user.getId()),user);
}
If a userId is 100 I am able to get by key: SERVER1:USER:100
Now I want to retrieve all Users as Map<String,List<User>> ,
For example, get all users by this key SERVER1:USER: Is it possible ? Or I need to modify my addUserToRedis method? Please suggest me.

Answer 1

I would recommend not using the "KEYS" command in production as this can severely impact REDIS latencies (can even bring down the cluster if you have a large number of keys stored)
Instead, you would want to use a different command than plain GET/SET.
It would be better if you use a Sets or Hashes
127.0.0.1:6379> sadd server1 user1 user2
(integer) 2
127.0.0.1:6379> smembers server1
1) "user2"
2) "user1"
127.0.0.1:6379>
Using sets you can simply add your users to server keys and get the entire list of users on a server.
If you really need a map of < server, list < users > > you can use hashes with stringified user data and then convert it to actual User POJO at application layer
127.0.0.1:6379> hset server2 user11 name
(integer) 1
127.0.0.1:6379> hset server2 user13 name
(integer) 1
127.0.0.1:6379> hgetall server2
1) "user11"
2) "name"
3) "user13"
4) "name"
127.0.0.1:6379>
Also do note that keeping this much big data into a single key is not an ideal thing to do.

Answer 2

i dont use java but here's how to use SCAN
const Redis = require('ioredis')
const redis = new Redis()
async function main() {
const stream = redis.scanStream({
match: "*:user:*",
count: 100,
})
stream.on("data", (resultKeys) => {
for (let i = 0; i < resultKeys.length; i++) {
// console.log(resultKeys[i])
// do your things here
}
});
stream.on("end", () => {
console.log("all keys have been visited");
});
}
main()

Answer 3

Finally I came up with this solution with wildcard search and avoiding KEYS, and here is my complete method:
public Map<String, User> getUserMapFromRedis(String serverName){
Map<String, User> users=new HashMap<>();
RedisConnection redisConnection = null;
try {
redisConnection = redisTemplate.getConnectionFactory().getConnection();
ScanOptions options = ScanOptions.scanOptions().match(serverName + USER_PREFIX+"*").build();
Cursor<byte[]> scan = redisConnection.scan(options);
while (scan.hasNext()) {
byte[] next = scan.next();
String key = new String(next, StandardCharsets.UTF_8);
String[] keyArray=key.split(":");
String userId=keyArray[2];
User user=//get User by userId From Redis
users.put(userId, user);
}
try {
scan.close();
} catch (IOException e) {
}
}finally {
redisConnection.close(); //Ensure closing this connection.
}
return users;
}