Debug with localrun mode

In localrun mode, a function consumes and produces actual data to a Pulsar cluster, and mirrors how the function runs in a Pulsar cluster. This provides a way to test your function and allows you to launch a function instance on your local machine as a thread for easy debugging.

note

Debugging with localrun mode is only available for Java functions in Pulsar 2.4.0 or later versions.

Before using localrun mode, you need to add the following dependency.

<dependency>
    <groupId>org.apache.pulsar</groupId>
    <artifactId>pulsar-functions-local-runner-original</artifactId>
    <version>${pulsar.version}</version>
</dependency>

<dependency>
    <groupId>com.google.protobuf</groupId>
    <artifactId>protobuf-java</artifactId>
    <version>3.21.9</version>
</dependency>

For example, you can run your function in the following manner.

FunctionConfig functionConfig = new FunctionConfig();
functionConfig.setName(functionName);
functionConfig.setInputs(Collections.singleton(sourceTopic));
functionConfig.setClassName(ExclamationFunction.class.getName());
functionConfig.setRuntime(FunctionConfig.Runtime.JAVA);
functionConfig.setOutput(sinkTopic);

LocalRunner localRunner = LocalRunner.builder().functionConfig(functionConfig).build();
localRunner.start(true);

You can debug functions using an IDE. Set breakpoints and manually step through a function to debug with real data.

The following code example shows how to run a function in localrun mode.

public class ExclamationFunction implements Function<String, String> {

    @Override
    public String process(String s, Context context) throws Exception {
        return s + "!";
    }

    public static void main(String[] args) throws Exception {
        FunctionConfig functionConfig = new FunctionConfig();
        functionConfig.setName("exclamation");
        functionConfig.setInputs(Collections.singleton("input"));
        functionConfig.setClassName(ExclamationFunction.class.getName());
        functionConfig.setRuntime(FunctionConfig.Runtime.JAVA);
        functionConfig.setOutput("output");

        LocalRunner localRunner = LocalRunner.builder().functionConfig(functionConfig).build();
        localRunner.start(false);
    }
}