[Solved] Given this Kafka Streams topology:builder.stream("input") .mapValues(v -> v.toUpperCase()) .to("output"); // Input message: key=1, value="hello" // What is the output message in "output" topic? | Kafka

Kafka - Advanced Stream Processing

Given this Kafka Streams topology:

builder.stream("input")
  .mapValues(v -> v.toUpperCase())
  .to("output");
// Input message: key=1, value="hello"
// What is the output message in "output" topic?

Akey=1, value="HELLO"

Bkey=1, value="hello"

Ckey=null, value="HELLO"

Dkey=1, value=null

Step-by-Step Solution

Solution:

Step 1: Understand mapValues transformation
mapValues changes the message value to uppercase, key remains unchanged.
Step 2: Apply transformation to input
Input value "hello" becomes "HELLO", key stays 1.
Final Answer:
key=1, value="HELLO" -> Option A
Quick Check:
mapValues changes value only [OK]

Quick Trick: mapValues transforms only the value, key stays same [OK]

Common Mistakes:

Assuming key changes
Confusing mapValues with map
Expecting null values

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Given this Kafka Streams topology:

Step 1: Understand mapValues transformation

Step 2: Apply transformation to input

Final Answer:

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