reference-client-sdk-java.md

title	description	author	ms.author	ms.service	ms.custom	ms.topic	ms.date
Reference - Java Client-side SDK for Azure Web PubSub	This reference describes the Java client-side SDK for Azure Web PubSub service.	kevinguo-ed	kevinguo	azure-web-pubsub	devx-track-extended-java	conceptual	07/17/2023

Azure WebPubSub client library for Java

Note

Details about the terms used here are described in key concepts article.

The client-side SDK aims to speed up developer's workflow; more specifically,

• simplifies managing client connections
• simplifies sending messages among clients
• automatically retries after unintended drops of client connection
• reliably deliveries messages in number and in order after recovering from connection drops

As shown in the diagram, your clients establish WebSocket connections with your Web PubSub resource.

:::image type="content" source="./media/reference-client-sdk-java/flow-overview.png" alt-text="Screenshot showing clients establishing WebSocket connection with a Web PubSub resource":::

Getting started

Prerequisites

• Java Development Kit (JDK) with version 8 or above
• Azure subscription
• An existing Web PubSub instance

Adding the package to your product

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-messaging-webpubsub-client</artifactId>
    <version>1.0.0-beta.1</version>
</dependency>

Authenticate the client

A client uses a Client Access URL to connect and authenticate with the service. The URL follows a pattern of wss://<service_name>.webpubsub.azure.com/client/hubs/<hub_name>?access_token=<token>. There are multiple ways to get a Client Access URL. As a quick start, you can copy and paste from Azure portal, and for production, you usually need a negotiation server to generate the URL. See details.

Use Client Access URL from Azure portal

As a quick start, you can go to Azure portal and copy the Client Access URL from Keys blade.

:::image type="content" source="./media/reference-client-sdk-java/get-client-access-url.png" alt-text="Screenshot showing how to get Client Access Url on Azure portal":::

As shown in the diagram, the client is granted permission of sending messages to specific groups and joining specific groups. Learn more about client permission, see permissions.

WebPubSubClient client = new WebPubSubClientBuilder()
    .clientAccessUrl("<client-access-url>")
    .buildClient();

Use negotiation server to generate Client Access URL

In production, a client usually fetches the Client Access URL from a negotiation server. The server holds the connection string and generates the Client Access URL through WebPubSubServiceClient. As a sample, the code snippet just demonstrates how to generate the Client Access URL inside a single process.

// WebPubSubServiceAsyncClient is from com.azure:azure-messaging-webpubsub
// create WebPubSub service client
WebPubSubServiceAsyncClient serverClient = new WebPubSubServiceClientBuilder()
    .connectionString("<connection-string>")
    .hub("<hub>>")
    .buildAsyncClient();

// wrap WebPubSubServiceAsyncClient.getClientAccessToken as WebPubSubClientCredential
WebPubSubClientCredential clientCredential = new WebPubSubClientCredential(Mono.defer(() ->
    serverClient.getClientAccessToken(new GetClientAccessTokenOptions()
            .setUserId("<user-name>")
            .addRole("webpubsub.joinLeaveGroup")
            .addRole("webpubsub.sendToGroup"))
        .map(WebPubSubClientAccessToken::getUrl)));

// create WebPubSub client
WebPubSubClient client = new WebPubSubClientBuilder()
    .credential(clientCredential)
    .buildClient();

Features to differentiate WebPubSubClient and WebPubSubServiceClient.

Class Name	WebPubSubClient	WebPubSubServiceClient
Package Name	azure-messaging-webpubsub-client	azure-messaging-webpubsub
Features	Used on client side. Publish messages and subscribe to messages.	Used on server side. Generate Client Access URL and manage clients.

Examples

Consume messages from the server and groups

A client can add callbacks to consume messages from the server and groups. Note, clients can only receive group messages that it has joined.

client.addOnGroupMessageEventHandler(event -> {
    System.out.println("Received group message from " + event.getFromUserId() + ": "
        + event.getData().toString());
});
client.addOnServerMessageEventHandler(event -> {
    System.out.println("Received server message: "
        + event.getData().toString());
});

Add callbacks for connected, disconnected, and stopped events

When a client connection is connected to the service, the connected event is triggered.

When a client connection is disconnected and fails to recover, the disconnected event is triggered.

When a client is stopped, which means the client connection is disconnected and the client stops trying to reconnect, the stopped event is triggered. This usually happens after the client.StopAsync() is called, or disabled AutoReconnect. If you want to restart the client, you can call client.StartAsync() in the Stopped event.

client.addOnConnectedEventHandler(event -> {
    System.out.println("Connection is connected: " + event.getConnectionId());
});
client.addOnDisconnectedEventHandler(event -> {
    System.out.println("Connection is disconnected");
});
client.addOnStoppedEventHandler(event -> {
    System.out.println("Client is stopped");
});

Operation and retry

By default, the operation such as client.joinGroup(), client.leaveGroup(), client.sendToGroup(), client.sendEvent() has three reties. You can use WebPubSubClientBuilder.retryOptions() to change. If all retries have failed, an error is thrown. You can keep retrying by passing in the same ackId as previous retries, thus the service can help to deduplicate the operation with the same ackId.

try {
    client.joinGroup("testGroup");
} catch (SendMessageFailedException e) {
    if (e.getAckId() != null) {
        client.joinGroup("testGroup", e.getAckId());
    }
}

Troubleshooting

Enable logs

You can set the following environment variable to get the debug logs when using this library.

export AZURE_LOG_LEVEL=verbose

For more detailed instructions on how to enable logs, you can look at the @azure/logger package docs.

Live Trace

Use Live Trace tool from Azure portal to inspect live message traffic through your Web PubSub resource.