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Example Fn Java FDK : Notifications

This example provides a Function to consume a Notification. The function accepts a typed message event.

Source

  • Notifications appends metadata to the headers Standard header metadata
  • The Notification message body is a user specified Schema or String. Note: This library currently supports JSON and String types.
  • Limits for Notifications Notification limits

Dependencies

Demonstrated FDK features

This example showcases how to use the fn-event NotificationFunction to use a Function to consume messages from a Notification topic.

Step by step

Set up the Notification Topic with Function Subscription:

The Function entrypoint extends the NotificationFunction abstract class. Note: the func.yaml entrypoint remains the class which extends NotificationFunction e.g. cmd: com.fnproject.fn.examples.Function::handler

Function.java

package com.fnproject.fn.examples;

import com.fnproject.events.NotificationFunction;
import com.fnproject.events.input.NotificationMessage;

public class Function extends NotificationFunction<Employee> {

    public NotificationService notificationService;

    public Function() {
        this.notificationService = new NotificationService();
    }

    @Override
    public void handler(NotificationMessage<Employee> content) {
        notificationService.readNotification(content);
    }
}

The NotificationMessage.java content contains the message body.

The class Employee.java is the schema for the message content.

Function.java public class Function extends NotificationFunction<Employee>.

To return an error response, throw RuntimeException.class. Doing so will cause the Function to return a 502 Retry policy

Test walkthrough

Unit testing NotificationFunction is supported with the NotificationTestFeature and FnTestingRule.

First of all, the class initializes the FnTestingRule harness, as explained in Testing Functions.

FunctionTest.java

package com.fnproject.fn.examples;

import static org.junit.Assert.assertEquals;
import com.fnproject.events.input.NotificationMessage;
import com.fnproject.events.testing.NotificationTestFeature;
import com.fnproject.fn.api.Headers;
import com.fnproject.fn.testing.FnResult;
import com.fnproject.fn.testing.FnTestingRule;
import org.junit.Rule;
import org.junit.Test;

public class FunctionTest {

    @Rule
    public FnTestingRule fn = FnTestingRule.createDefault();

    private final NotificationTestFeature connectorHubTestFeature = NotificationTestFeature.createDefault(fn);

    @Test
    public void testInvokeFunctionWithLoggingData() throws Exception {
        NotificationMessage<Employee> event = createMinimalRequest();
        connectorHubTestFeature.givenEvent(event).enqueue();

        fn.thenRun(Function.class, "handler");

        FnResult result = fn.getOnlyResult();
        assertEquals(200, result.getStatus().getCode());
    }

    private static NotificationMessage createMinimalRequest() {
        Employee employee = new Employee();
        employee.setName("foo");

        return new NotificationMessage<>(employee, Headers.emptyHeaders());
    }
}

Use connectorHubTestFeature.givenEvent(event).enqueue(); to queue the request event and invoke the Function with fn.thenRun(Function.class, "handler");.

To verify the Subscription is working, check Notification metrics