Skip to main content
Version: 3.2.x

Tutorials

Write a function for word count

note

The following example is a stateful function. By default, the state of a function is disabled. See Enable stateful functions for more instructions.

To write a function for word count, complete the following steps.

  1. Write the function in Java using the SDK for Java.

     package org.example.functions;

    import org.apache.pulsar.functions.api.Context;
    import org.apache.pulsar.functions.api.Function;

    import java.util.Arrays;

    public class WordCountFunction implements Function<String, Void> {
    // This function is invoked every time a message is published to the input topic
    @Override
    public Void process(String input, Context context) throws Exception {
    Arrays.asList(input.split(" ")).forEach(word -> {
    String counterKey = word.toLowerCase();
    context.incrCounter(counterKey, 1);
    });
    return null;
    }
    }
  2. Bundle and build the JAR file, and then deploy it in your Pulsar cluster using the pulsar-admin command.

    bin/pulsar-admin functions create \
    --jar target/my-jar-with-dependencies.jar \
    --classname org.example.functions.WordCountFunction \
    --tenant public \
    --namespace default \
    --name word-count \
    --inputs persistent://public/default/sentences \
    --output persistent://public/default/count

Write a function for content-based routing

To write a function for content-based routing, complete the following steps.

  1. Write the function in Python using the SDK for Python.

     from pulsar import Function

    class RoutingFunction(Function):
    def __init__(self):
    self.fruits_topic = "persistent://public/default/fruits"
    self.vegetables_topic = "persistent://public/default/vegetables"

    def is_fruit(item):
    return item in [b"apple", b"orange", b"pear", b"other fruits..."]

    def is_vegetable(item):
    return item in [b"carrot", b"lettuce", b"radish", b"other vegetables..."]

    def process(self, item, context):
    if self.is_fruit(item):
    context.publish(self.fruits_topic, item)
    elif self.is_vegetable(item):
    context.publish(self.vegetables_topic, item)
    else:
    warning = "The item {0} is neither a fruit nor a vegetable".format(item)
    context.get_logger().warn(warning)
  2. Suppose this code is stored in ~/router.py, then you can deploy it in your Pulsar cluster using the pulsar-admin command.

    bin/pulsar-admin functions create \
    --py ~/router.py \
    --classname router.RoutingFunction \
    --tenant public \
    --namespace default \
    --name route-fruit-veg \
    --inputs persistent://public/default/basket-items

Write a window function for word count

note

Currently, window functions are only available in Java.

This example demonstrates how to use the language-native interface to write a window function in Java.

Each input message is a sentence that is split into words and each word is counted. The built-in counter state is used to keep track of the word count in a persistent and consistent manner.

public class WordCountFunction implements Function<String, Void> {
@Override
public Void process(String input, Context context) {
Arrays.asList(input.split("\\s+")).forEach(word -> context.incrCounter(word, 1));
return null;
}
}