Run a redis container using Docker (just make sure Docker Engine is running before executing the below command)
docker run --name some-redis --publish=6379:6379 -d redis
<dependency>
<groupId>redis.clients</groupId>
<artifactId>jedis</artifactId>
<version>5.2.0</version>
</dependency>Redis strings store sequences of bytes, including text, serialized objects, and binary arrays. As such, strings are the simplest type of value you can associate with a Redis key.
import redis.clients.jedis.Jedis;
public class Test {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String res1 = jedis.set("user:1", "Mahtab Alam");
System.out.println(res1); // OK
String res2 = jedis.get("user:1");
System.out.println(res2); // Mahtab Alam
jedis.setex("active:partition", 10, "edf833-hju87iols-kla12");
Thread.sleep(6000);
System.out.println("Active Partition :" + jedis.get("active:partition"));
Thread.sleep(5000);
System.out.println("Active Partition :" + jedis.get("active:partition"));
} catch (Exception e) {
e.printStackTrace();
}
}
}OK
Mahtab Alam
Active Partition :edf833-hju87iols-kla12
Active Partition :null
import redis.clients.jedis.Jedis;
public class CounterTest {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
jedis.set("counter", "0");
jedis.incr("counter");
System.out.println("counter :" + jedis.get("counter"));
jedis.incrBy("counter", 5);
System.out.println("counter :" + jedis.get("counter"));
jedis.decr("counter");
System.out.println("counter :" + jedis.get("counter"));
jedis.decrBy("counter", 2);
System.out.println("counter :" + jedis.get("counter"));
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
}counter :1
counter :6
counter :5
counter :3
Redis hashes are record types modeled as collections of field-value pairs.
import redis.clients.jedis.Jedis;
import java.util.Map;
public class Hashes {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String hashKey = "user:1001";
// Add fields to the hash using HSET
jedis.hset(hashKey, "name", "Mahtab Alam");
jedis.hset(hashKey, "age", "31");
jedis.hset(hashKey, "city", "Bangalore");
// Retrieve a specific field using HGET
String name = jedis.hget(hashKey, "name");
System.out.println("Name: " + name);
// Retrieve all fields and values using HGETALL
Map<String, String> userDetails = jedis.hgetAll(hashKey);
System.out.println("User Details:");
userDetails.forEach((field, value) -> System.out.println(field + ": " + value));
// Increment a numeric field using HINCRBY
jedis.hincrBy(hashKey, "age", 1);
System.out.println("Updated Age: " + jedis.hget(hashKey, "age"));
// HKEYS returns a Set containing all keys in a hash
System.out.println("Fields: " + jedis.hkeys(hashKey));
// HVALS returns a List containing all values in a hash
System.out.println("Values: " + jedis.hvals(hashKey));
// Delete a field using HDEL
jedis.hdel(hashKey, "city");
System.out.println("After deleting 'city', fields: " + jedis.hkeys(hashKey));
// Check if a field exists using HEXISTS
boolean hasCity = jedis.hexists(hashKey, "city");
System.out.println("Does 'city' exist? " + hasCity);
} catch (Exception e) {
e.printStackTrace();
}
}
}Name: Mahtab Alam
User Details:
name: Mahtab Alam
city: Bangalore
age: 31
Updated Age: 32
Fields: [city, name, age]
Values: [Mahtab Alam, 32, Bangalore]
After deleting 'city', fields: [name, age]
Does 'city' exist? false
Redis lists are lists of strings sorted by insertion order. You can add/pop element from either the head or tail end of the list.
import redis.clients.jedis.Jedis;
public class RedisList {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String listKey = "myList";
// Clear the list if it already exists
jedis.del(listKey);
// RPUSH to add elements at the end of the list(tail)
jedis.rpush(listKey, "Value1");
jedis.rpush(listKey, "Value2");
jedis.rpush(listKey, "Value3");
// LRANGE listKey 0 -1 retrieves all elements from start (0) to end (-1)
System.out.println("All Elements in list: " + jedis.lrange(listKey, 0, -1));
System.out.println("Last two elements : " + jedis.lrange(listKey, -2, -1));
} catch (Exception e) {
System.err.println("Error interacting with Redis: " + e.getMessage());
}
}
}All Elements in list: [Value1, Value2, Value3]
Last two elements : [Value2, Value3]
import redis.clients.jedis.Jedis;
public class RedisList {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String listKey = "myList";
// Clear the list if it already exists
jedis.del(listKey);
// LPUSH to add elements at the head of the list
jedis.lpush(listKey, "Value1");
jedis.lpush(listKey, "Value2");
jedis.lpush(listKey, "Value3");
// LRANGE listKey 0 -1 retrieves all elements from start (0) to end (-1)
System.out.println("All Elements in list: " + jedis.lrange(listKey, 0, -1));
System.out.println("Last two elements : " + jedis.lrange(listKey, -2, -1));
} catch (Exception e) {
System.err.println("Error interacting with Redis: " + e.getMessage());
}
}
}All Elements in list: [Value3, Value2, Value1]
Last two elements : [Value2, Value1]
import redis.clients.jedis.Jedis;
public class ListOperations {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String listKey = "myList";
// Clear the list if it already exists
jedis.del(listKey);
// RPUSH to add elements at tail, LPUSH for adding at the head
jedis.rpush(listKey, "Value1");
jedis.rpush(listKey, "Value2");
jedis.rpush(listKey, "Value3");
jedis.lpush(listKey, "Value0");
System.out.println("First element at the head :" + jedis.lindex(listKey, 0));
System.out.println("First 5 elements from the head:" + jedis.lrange(listKey, 0, 4));
System.out.println("Last 3 elements from the end:" + jedis.lrange(listKey, -3, -1));
System.out.println("Pop last element from end of the list :" + jedis.rpop(listKey));
System.out.println("Pop first element from the head of the list :" + jedis.lpop(listKey));
} catch (Exception e) {
System.err.println("Error interacting with Redis: " + e.getMessage());
}
}
}First element at the head :Value0
First 5 elements from the head:[Value0, Value1, Value2, Value3]
Last 3 elements from the end:[Value1, Value2, Value3]
Pop last element from end of the list :Value3
Pop first element from the head of the list :Value0
Redis sets are unordered collections of unique strings that act like the sets, present in almost all the programming languages (e.g. Java HashSet, Python set and similarly for other languages)
import redis.clients.jedis.Jedis;
public class RedisSetExample {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String setKey = "mySet";
jedis.sadd(setKey, "element1", "element2", "element3");
jedis.sadd(setKey, "element4");
System.out.println("Elements in the set:");
for (String element : jedis.smembers(setKey)) {
System.out.print(element + " ");
}
System.out.println();
String elementToCheck = "element2";
boolean exists = jedis.sismember(setKey, elementToCheck);
System.out.println(elementToCheck + " exists in the set? " + exists);
// Remove an element from the set
jedis.srem(setKey, "element1");
System.out.println("Removed 'element1' from the set");
// Retrieve and display the updated set
System.out.println("Updated elements in the set:");
for (String element : jedis.smembers(setKey)) {
System.out.println(element);
}
// Clean up: delete the set
jedis.del(setKey);
System.out.println("Deleted the set");
} catch (Exception e) {
e.printStackTrace();
}
}
}Elements in the set:
element1 element2 element3 element4
element2 exists in the set? true
Removed 'element1' from the set
Updated elements in the set:
element2
element3
element4
Deleted the set
Redis sorted sets are collections of unique strings that maintain order by each string's associated score.
import redis.clients.jedis.Jedis;
import redis.clients.jedis.resps.Tuple;
public class RedisSortedSetExample {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String sortedSetKey = "leaderboard";
jedis.zadd(sortedSetKey, 100.0, "Player4");
jedis.zadd(sortedSetKey, 20.0, "Player1");
jedis.zadd(sortedSetKey, 0.0, "Player2");
jedis.zadd(sortedSetKey, 200.0, "Player3");
jedis.zadd(sortedSetKey, 150.0, "Player5");
// Retrieve all elements by score (by default ascending order of score)
System.out.println("Players sorted by rank (score):");
for (String player : jedis.zrange(sortedSetKey, 0, -1)) {
System.out.println(player);
}
// Retrieve all elements with scores
System.out.println("\nPlayers with their scores:");
for (Tuple entry : jedis.zrangeWithScores(sortedSetKey, 0, -1)) {
System.out.println(entry.getElement() + " - Score: " + entry.getScore());
}
// Retrieve players with scores within a range
System.out.println("\nPlayers with scores between 100 and 200:");
for (String player : jedis.zrangeByScore(sortedSetKey, 100.0, 200.0)) {
System.out.println(player);
}
// Get the rank of a specific player
Long rank = jedis.zrank(sortedSetKey, "Player3");
System.out.println("\nRank of Player3: " + rank);
// Remove a player from the sorted set
jedis.zrem(sortedSetKey, "Player1");
System.out.println("\nRemoved Player1 from the sorted set");
// Retrieve updated players
System.out.println("Updated players in the sorted set:");
for (String player : jedis.zrange(sortedSetKey, 0, -1)) {
System.out.println(player);
}
// Clean up: delete the sorted set
jedis.del(sortedSetKey);
System.out.println("\nDeleted the sorted set");
} catch (Exception e) {
e.printStackTrace();
}
}
}Players sorted by rank (score):
Player2
Player1
Player4
Player5
Player3
Players with their scores:
Player2 - Score: 0.0
Player1 - Score: 20.0
Player4 - Score: 100.0
Player5 - Score: 150.0
Player3 - Score: 200.0
Players with scores between 100 and 200:
Player4
Player5
Player3
Rank of Player3: 4
Removed Player1 from the sorted set
Updated players in the sorted set:
Player2
Player4
Player5
Player3
Deleted the sorted setimport redis.clients.jedis.Jedis;
import redis.clients.jedis.resps.Tuple;
public class RedisSortedSetDescendingExample {
public static void main(String[] args) {
try (Jedis jedis = new Jedis("localhost", 6379)) {
String sortedSetKey = "leaderboard";
jedis.zadd(sortedSetKey, 100.0, "Player4");
jedis.zadd(sortedSetKey, 20.0, "Player1");
jedis.zadd(sortedSetKey, 0.0, "Player2");
jedis.zadd(sortedSetKey, 200.0, "Player3");
jedis.zadd(sortedSetKey, 150.0, "Player5");
// Retrieve all elements by descending order of score
System.out.println("Players sorted by score:");
for (String player : jedis.zrevrange(sortedSetKey, 0, -1)) {
System.out.println(player);
}
// Retrieve all elements with scores
System.out.println("\nPlayers with their scores:");
for (Tuple entry : jedis.zrevrangeWithScores(sortedSetKey, 0, -1)) {
System.out.println(entry.getElement() + " - Score: " + entry.getScore());
}
// Retrieve players with scores within a range
System.out.println("\nPlayers with scores between 200 and 100:");
for (String player : jedis.zrevrangeByScore(sortedSetKey, 200.0, 100.0)) {
System.out.println(player);
}
// Get the rank of a specific player
Long rank = jedis.zrevrank(sortedSetKey, "Player3");
System.out.println("\nRank of Player3: " + rank);
// Remove a player from the sorted set
jedis.zrem(sortedSetKey, "Player1");
System.out.println("\nRemoved Player1 from the sorted set");
// Retrieve updated players
System.out.println("Updated players in the sorted set:");
for (String player : jedis.zrevrange(sortedSetKey, 0, -1)) {
System.out.println(player);
}
// Clean up: delete the sorted set
jedis.del(sortedSetKey);
System.out.println("\nDeleted the sorted set");
} catch (Exception e) {
e.printStackTrace();
}
}
}Players sorted by score:
Player3
Player5
Player4
Player1
Player2
Players with their scores:
Player3 - Score: 200.0
Player5 - Score: 150.0
Player4 - Score: 100.0
Player1 - Score: 20.0
Player2 - Score: 0.0
Players with scores between 200 and 100:
Player3
Player5
Player4
Rank of Player3: 0
Removed Player1 from the sorted set
Updated players in the sorted set:
Player3
Player5
Player4
Player2
Deleted the sorted set
Redis stores data as strings, hashes, lists, sets, and other simple data types. To save a Java object, you must transform it into a byte stream or string that Redis can understand.
Most of the time you would use a library to serialize the Java object into a type that redis support e.g. String. In below example we use Jackson library to serialize Java object into a JSON, returned as a String. The returned String is saved in the Redis cache, redis returns the String value on get operation, the application code then deserialize the JSON string back to Java Object using Jackson library.
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.15.2</version>
</dependency>// User.java
public class User {
private String id;
private String name;
private int age;
// Constructors
public User() {
}
public User(String id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
// Getters and Setters
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "name=" + name + ", id=" + id + ", age=" + age;
}
}
// Test.java
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import redis.clients.jedis.Jedis;
public class Test {
public static void main(String[] args) {
// Jackson ObjectMapper for serialization and deserialization
ObjectMapper objectMapper = new ObjectMapper();
User user = new User("1", "Mahtab Alam", 31);
try (Jedis jedis = new Jedis("localhost", 6379)) {
// Serialize User object to JSON, and return as a String
String userJsonAsString = objectMapper.writeValueAsString(user);
System.out.println("Serialized User: " + userJsonAsString);
String key = "user:1";
jedis.set("user:1", userJsonAsString);
// Retrieve JSON from Redis
String retrievedJson = jedis.get(key);
// Deserialize JSON String to User object
if (retrievedJson != null) {
User cachedUser = objectMapper.readValue(retrievedJson, User.class);
System.out.println("Cached User: " + cachedUser);
} else {
System.out.println("Cache miss for key: " + key);
}
} catch (JsonProcessingException e) {
System.err.println("Error in JSON processing: " + e.getMessage());
} catch (Exception e) {
System.err.println("Error connecting to Redis: " + e.getMessage());
}
}
}Serialized User: {"id":"1","name":"Mahtab Alam","age":31}
Cached User: name=Mahtab Alam, id=1, age=31