--- title: ASP.NET Core SignalR Java client author: mikaelm12 description: Learn how to use the ASP.NET Core SignalR Java client. monikerRange: '>= aspnetcore-2.2' ms.author: wpickett ms.custom: mvc ms.date: 11/12/2019 uid: signalr/java-client --- # ASP.NET Core SignalR Java client By [Mikael Mengistu](https://twitter.com/MikaelM_12) The Java client enables connecting to an ASP.NET Core SignalR server from Java code, including Android apps. Like the [JavaScript client](xref:signalr/javascript-client) and the [.NET client](xref:signalr/dotnet-client), the Java client enables you to receive and send messages to a hub in real time. The Java client is available in ASP.NET Core 2.2 and later. The sample Java console app referenced in this article uses the SignalR Java client. [View or download sample code](https://github.com/dotnet/AspNetCore.Docs/tree/main/aspnetcore/signalr/java-client/sample) ([how to download](xref:index#how-to-download-a-sample)) ## Install the SignalR Java client package The *signalr-7.0.0* JAR file allows clients to connect to SignalR hubs. To find the latest JAR file version number, see the [Maven search results](https://search.maven.org/search?q=g:com.microsoft.signalr%20AND%20a:signalr). If using Gradle, add the following line to the `dependencies` section of your *build.gradle* file: ```gradle implementation 'com.microsoft.signalr:signalr:7.0.0' ``` If using Maven, add the following lines inside the `` element of your `pom.xml` file: [!code-xml[pom.xml dependency element](java-client/sample/pom.xml?name=snippet_dependencyElement)] ## Connect to a hub To establish a `HubConnection`, the `HubConnectionBuilder` should be used. The hub URL and log level can be configured while building a connection. Configure any required options by calling any of the `HubConnectionBuilder` methods before `build`. Start the connection with `start`. [!code-java[Build hub connection](java-client/sample/src/main/java/Chat.java?range=16-17)] ## Call hub methods from client A call to `send` invokes a hub method. Pass the hub method name and any arguments defined in the hub method to `send`. [!code-java[send method](java-client/sample/src/main/java/Chat.java?range=28)] > [!NOTE] > Calling hub methods from a client is only supported when using the Azure SignalR Service in *Default* mode. For more information, see [Frequently Asked Questions (azure-signalr GitHub repository)](https://github.com/Azure/azure-signalr/blob/dev/docs/faq.md#what-is-the-meaning-of-service-mode-defaultserverlessclassic-how-can-i-choose). ## Call client methods from hub Use `hubConnection.on` to define methods on the client that the hub can call. Define the methods after building but before starting the connection. [!code-java[Define client methods](java-client/sample/src/main/java/Chat.java?range=19-21)] ## Add logging The SignalR Java client uses the [SLF4J](https://www.slf4j.org/) library for logging. It's a high-level logging API that allows users of the library to choose their own specific logging implementation by bringing in a specific logging dependency. The following code snippet shows how to use `java.util.logging` with the SignalR Java client. ```gradle implementation 'org.slf4j:slf4j-jdk14:1.7.25' ``` If you don't configure logging in your dependencies, SLF4J loads a default no-operation logger with the following warning message: ``` SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder". SLF4J: Defaulting to no-operation (NOP) logger implementation SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details. ``` This can safely be ignored. ## Android development notes With regards to Android SDK compatibility for the SignalR client features, consider the following items when specifying your target Android SDK version: * The SignalR Java Client will run on Android API Level 16 and later. * Connecting through the Azure SignalR Service will require Android API Level 20 and later because the [Azure SignalR Service](/azure/azure-signalr/signalr-overview) requires TLS 1.2 and doesn't support SHA-1-based cipher suites. Android [added support for SHA-256 (and above) cipher suites](https://developer.android.com/reference/javax/net/ssl/SSLSocket) in API Level 20. ## Configure bearer token authentication In the SignalR Java client, you can configure a bearer token to use for authentication by providing an "access token factory" to the [HttpHubConnectionBuilder](/java/api/com.microsoft.signalr.httphubconnectionbuilder?view=aspnet-signalr-java&preserve-view=true). Use [withAccessTokenFactory](/java/api/com.microsoft.signalr.httphubconnectionbuilder.withaccesstokenprovider?view=aspnet-signalr-java&preserve-view=true) to provide an [RxJava](https://github.com/ReactiveX/RxJava) [Single\](https://reactivex.io/documentation/single.html). With a call to [Single.defer](https://reactivex.io/RxJava/javadoc/io/reactivex/Single.html#defer-java.util.concurrent.Callable-), you can write logic to produce access tokens for your client. ```java HubConnection hubConnection = HubConnectionBuilder.create("YOUR HUB URL HERE") .withAccessTokenProvider(Single.defer(() -> { // Your logic here. return Single.just("An Access Token"); })).build(); ``` :::moniker range=">= aspnetcore-5.0" ### Passing Class information in Java When calling the `on`, `invoke`, or `stream` methods of `HubConnection` in the Java client, users should pass a `Type` object rather than a `Class` object to describe any generic `Object` passed to the method. A `Type` can be acquired using the provided `TypeReference` class. For example, using a custom generic class named `Foo`, the following code gets the `Type`: ```java Type fooType = new TypeReference>() { }).getType(); ``` For non-generics, such as primitives or other non-parameterized types like `String`, you can simply use the built-in `.class`. When calling one of these methods with one or more object types, use the generics syntax when invoking the method. For example, when registering an `on` handler for a method named `func`, which takes as arguments a String and a `Foo` object, use the following code to set an action to print the arguments: ```java hubConnection.>on("func", (param1, param2) ->{ System.out.println(param1); System.out.println(param2); }, String.class, fooType); ``` This convention is necessary because we can not retrieve complete information about complex types with the `Object.getClass` method due to type erasure in Java. For example, calling `getClass` on an `ArrayList` would not return `Class>`, but rather `Class`, which does not give the deserializer enough information to correctly deserialize an incoming message. The same is true for custom objects. :::moniker-end ## Known limitations :::moniker range=">= aspnetcore-5.0" * Transport fallback and the Server Sent Events transport aren't supported. :::moniker-end :::moniker range=">= aspnetcore-3.0 < aspnetcore-5.0" * Transport fallback and the Server Sent Events transport aren't supported. * Only the JSON protocol is supported. :::moniker-end :::moniker range="< aspnetcore-3.0" * Only the JSON protocol is supported. * Only the WebSockets transport is supported. * Streaming isn't supported yet. :::moniker-end ## Additional resources * [Java API reference](/java/api/com.microsoft.signalr?view=aspnet-signalr-java&preserve-view=true) * * * * [Azure SignalR Service serverless documentation](/azure/azure-signalr/signalr-concept-serverless-development-config)