Redis with Java (Jedis, Lettuce) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Jedis command sequence?

Given a Jedis connection, what will be the output of the following commands?

jedis.set("key1", "value1");
String val = jedis.get("key1");
System.out.println(val);

Redis

jedis.set("key1", "value1");
String val = jedis.get("key1");
System.out.println(val);

A Throws NullPointerException

B null

C Throws JedisConnectionException

D value1

💡 Hint

Remember that set stores a string value and get retrieves it.

The set command stores the string 'value1' under 'key1'. The get command retrieves it, so the output is 'value1'.

📝 Syntax

intermediate

Which option correctly initializes a Lettuce Redis client?

Choose the correct Java code snippet to create a Lettuce Redis client connected to localhost on default port 6379.

A RedisClient client = RedisClient.connect("localhost");

B RedisClient client = new RedisClient("localhost", 6379);

C RedisClient client = RedisClient.create("redis://localhost:6379");

D RedisClient client = RedisClient.create("http://localhost:6379");

💡 Hint

Lettuce uses URI format starting with redis://

The correct way to create a Lettuce client is using RedisClient.create with a redis:// URI.

❓ optimization

advanced

How to optimize multiple Redis commands in Jedis?

You want to execute multiple Redis commands efficiently in Jedis. Which approach reduces network overhead the most?

A Open and close a new Jedis connection for each command

B Use Jedis pipelining to batch commands before sending

C Use multiple threads each with its own Jedis instance

D Send commands one by one synchronously

💡 Hint

Batching commands reduces round-trip time.

Pipelining batches commands and sends them in one network call, reducing overhead.

🔧 Debug

advanced

Why does this Lettuce code throw a NullPointerException?

Consider this Lettuce code snippet:

RedisClient client = RedisClient.create("redis://localhost:6379");
StatefulRedisConnection connection = null;
RedisCommands syncCommands = connection.sync();
syncCommands.set("key", "value");

What causes the NullPointerException?

Redis

RedisClient client = RedisClient.create("redis://localhost:6379");
StatefulRedisConnection<String, String> connection = null;
RedisCommands<String, String> syncCommands = connection.sync();
syncCommands.set("key", "value");

A connection is null, so calling sync() causes NullPointerException

B RedisClient.create returns null causing failure

C set command is invalid syntax in Lettuce

D syncCommands is null because set returns null

💡 Hint

Check which variable is null before method call.

The connection variable is null, so calling connection.sync() throws NullPointerException.

🧠 Conceptual

expert

What is the main difference between Jedis and Lettuce clients?

Which statement best describes the key difference between Jedis and Lettuce Redis clients in Java?

A Jedis is synchronous and blocking; Lettuce supports asynchronous and reactive APIs

B Jedis supports clustering; Lettuce does not support clustering

C Lettuce is only for Redis 6+; Jedis supports all Redis versions

D Jedis uses Netty; Lettuce uses raw sockets

💡 Hint

Think about how each client handles command execution style.

Jedis primarily offers synchronous blocking calls, while Lettuce supports asynchronous and reactive programming models.