Get started with Relay Hybrid Connections HTTP requests in Java

Article
01/08/2024

NET
Node.js

In this quickstart, you create Java sender and receiver applications that send and receive messages by using the HTTP protocol. The applications use Hybrid Connections feature of Azure Relay. To learn about Azure Relay in general, see Azure Relay.

In this quickstart, you take the following steps:

Create a Relay namespace by using the Azure portal.
Create a hybrid connection in that namespace by using the Azure portal.
Write a server (listener) console application to receive messages.
Write a client (sender) console application to send messages.
Run applications.

Prerequisites

Java. Ensure that you're running JDK 1.8+
Maven. Ensure that you have Maven installed
Azure Relay SDK. Review Java SDK
An Azure subscription. If you don't have one, create a free account before you begin.

Create a namespace using the Azure portal

Sign in to the Azure portal.
Select All services on the left menu. Select Integration, search for Relays, move the mouse over Relays, and then select Create.
On the Create namespace page, follow these steps:
1. Choose an Azure subscription in which to create the namespace.
2. For Resource group, choose an existing resource group in which to place the namespace, or create a new one.
3. Enter a name for the Relay namespace.
4. Select the region in which your namespace should be hosted.
5. Select Review + create at the bottom of the page.
6. On the Review + create page, select Create.
7. After a few minutes, you see the Relay page for the namespace.

Get management credentials

On the Relay page, select Shared access policies on the left menu.
On the Shared access policies page, select RootManageSharedAccessKey.
Under SAS Policy: RootManageSharedAccessKey, select the Copy button next to Primary Connection String. This action copies the connection string to your clipboard for later use. Paste this value into Notepad or some other temporary location.
Repeat the preceding step to copy and paste the value of Primary key to a temporary location for later use.

Create a hybrid connection using the Azure portal

On the Relay page for your namespace, follow these steps to create a hybrid connection.

On the left menu, Under Entities, select Hybrid Connections, and then select + Hybrid Connection.
On the Create Hybrid Connection page, enter a name for the hybrid connection, and select Create.

Create a server application (listener)

To listen and receive messages from the Relay, write a Java console application.

Create a Java application

If you disabled the "Requires Client Authorization" option when creating the Relay, you can send requests to the Hybrid Connections URL with any browser. For accessing protected endpoints, you need to create and pass a token in the ServiceBusAuthorization header, which is shown here.

Here's a simple Maven project structure and a Java class that demonstrates sending requests to a Hybrid Connections URL with client authorization utilizing the Azure Relay library.

Add the Relay package

Modify your pom.xml file in your maven application package to include the Azure Relay package.

<dependency>
    <groupId>com.microsoft.azure</groupId>
    <artifactId>azure-relay</artifactId>
    <version>0.0.6</version>
</dependency>

Run mvn dependency:copy-dependencies -DoutputDirectory=lib in your mvn project to add the dependency jar file in the lib directory of your project. It imports all dependencies of the azure-relay mvn package. This package provides functions to construct Relay uniform resource identifiers (URIs) and tokens.

Write some code to send messages

Add the dependency jar files to the ClassPath of your Listener.java file.
```
javac -cp lib/* src/main/java/com/example/listener/Listener.Java
```

Import the dependencies into your Listener.java class.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.Scanner;
import com.microsoft.azure.relay.HybridConnectionListener;
import com.microsoft.azure.relay.RelayConnectionStringBuilder;
import com.microsoft.azure.relay.RelayedHttpListenerResponse;
import com.microsoft.azure.relay.TokenProvider;

Add the following constants to the top of the Listener.java file to a createConnectionString java function for the hybrid connection details.
```
public static String createConnectionString(){
    StringBuilder connectionString = new StringBuilder();
    connectionString.append("Endpoint=sb://");
    connectionString.append("{namespace}");
    connectionString.append(".servicebus.windows.net/;SharedAccessKeyName=");
    connectionString.append("{keyrule}");
    connectionString.append(";SharedAccessKey=");
    connectionString.append("{key}");
    connectionString.append(";EntityPath=");
    connectionString.append("{path}");
    return connectionString.toString();
}
```
Replace the placeholders in brackets with the values you obtained when you created the hybrid connection.
- namespace - The Relay namespace. Be sure to use the fully qualified namespace name; for example, {namespace}.servicebus.windows.net.
- path - The name of the hybrid connection.
- keyrule - Name of your Shared Access Policies key, which is RootManageSharedAccessKey by default.
- nst key - The primary key of the namespace you saved earlier.

Add the following code to the Listener.java file. The main function should look like the following code:

public static void main( String[] args ) throws URISyntaxException
{
    String CONNECTION_STRING_ENV_VARIABLE_NAME = createConnectionString();
    RelayConnectionStringBuilder connectionParams = new RelayConnectionStringBuilder(CONNECTION_STRING_ENV_VARIABLE_NAME);
    TokenProvider tokenProvider = TokenProvider.createSharedAccessSignatureTokenProvider(
                connectionParams.getSharedAccessKeyName(),
                connectionParams.getSharedAccessKey());
    HybridConnectionListener listener = new HybridConnectionListener(new URI(connectionParams.getEndpoint().toString() + connectionParams.getEntityPath()), tokenProvider);

    // The "context" object encapsulates both the incoming request and the outgoing response
    listener.setRequestHandler((context) -> {
        String receivedText = "";
        if (context.getRequest().getInputStream() != null) {
            try (BufferedReader reader = new BufferedReader(new InputStreamReader(context.getRequest().getInputStream(), "UTF8"))) {
                StringBuilder builder = new StringBuilder();
                String inputLine;
                while ((inputLine = reader.readLine()) != null) {
                    builder.append(inputLine);
                }
                receivedText = builder.toString();
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        }
        System.out.println("requestHandler received " + receivedText);

        RelayedHttpListenerResponse response = context.getResponse();
        response.setStatusCode(202);
        response.setStatusDescription("OK");

        try {
            response.getOutputStream().write(("Echo: " + receivedText).getBytes());
        } catch (IOException e) {
            e.printStackTrace();
        }

        // The context MUST be closed for the message to be sent
        response.close();
    });

    listener.openAsync().join();

    Scanner in = new Scanner(System.in);
    System.out.println("Press ENTER to terminate this program.");
    in.nextLine();

    listener.close();
    in.close();
}

Here's what your Listener.java file should look like:

package com.example.listener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.Scanner;
import com.microsoft.azure.relay.HybridConnectionListener;
import com.microsoft.azure.relay.RelayConnectionStringBuilder;
import com.microsoft.azure.relay.RelayedHttpListenerResponse;
import com.microsoft.azure.relay.TokenProvider;

 public class Listener
 {
    public static String createConnectionString(){
        StringBuilder connectionString = new StringBuilder();
        connectionString.append("Endpoint=sb://");
        connectionString.append("{namespace}");
        connectionString.append(".servicebus.windows.net/;SharedAccessKeyName=");
        connectionString.append("{keyrule}");
        connectionString.append(";SharedAccessKey=");
        connectionString.append("{key}");
        connectionString.append(";EntityPath=");
        connectionString.append("{path}");
        return connectionString.toString();
    }

    public static void main( String[] args ) throws URISyntaxException
    {
        String CONNECTION_STRING_ENV_VARIABLE_NAME = createConnectionString();
        RelayConnectionStringBuilder connectionParams = new RelayConnectionStringBuilder(CONNECTION_STRING_ENV_VARIABLE_NAME);
        TokenProvider tokenProvider = TokenProvider.createSharedAccessSignatureTokenProvider(
                    connectionParams.getSharedAccessKeyName(),
                    connectionParams.getSharedAccessKey());
        HybridConnectionListener listener = new HybridConnectionListener(new URI(connectionParams.getEndpoint().toString() + connectionParams.getEntityPath()), tokenProvider);

        // The "context" object encapsulates both the incoming request and the outgoing response
        listener.setRequestHandler((context) -> {
            String receivedText = "";
            if (context.getRequest().getInputStream() != null) {
                try (BufferedReader reader = new BufferedReader(new InputStreamReader(context.getRequest().getInputStream(), "UTF8"))) {
                    StringBuilder builder = new StringBuilder();
                    String inputLine;
                    while ((inputLine = reader.readLine()) != null) {
                        builder.append(inputLine);
                    }
                    receivedText = builder.toString();
                } catch (IOException e) {
                    System.out.println(e.getMessage());
                }
            }
            System.out.println("requestHandler received " + receivedText);

            RelayedHttpListenerResponse response = context.getResponse();
            response.setStatusCode(202);
            response.setStatusDescription("OK");

            try {
                response.getOutputStream().write(("Echo: " + receivedText).getBytes());
            } catch (IOException e) {
                e.printStackTrace();
            }

            // The context MUST be closed for the message to be sent
            response.close();
        });

        listener.openAsync().join();

        Scanner in = new Scanner(System.in);
        System.out.println("Press ENTER to terminate this program.");
        in.nextLine();

        listener.close();
        in.close();
    }
}

Create a client application (sender)

To send messages to the Relay, you can use any HTTP client, or write a Java console application.

Create a Java application

Here's a simple Maven project structure and a Java class that demonstrates sending requests to a Hybrid Connections URL with client authorization utilizing the Azure Relay library.

Add the Relay package

Modify your pom.xml file in your maven application package to include the Azure Relay package.

<dependency>
	<groupId>com.microsoft.azure</groupId>
	<artifactId>azure-relay</artifactId>
	<version>0.0.6</version>
</dependency>

Run mvn dependency:copy-dependencies -DoutputDirectory=lib in your mvn project to add the dependency jar file in the lib directory of your project. It also imports all dependencies of the azure-relay mvn package. This package provides functions to construct Relay uniform resource identifiers (URIs) and tokens.

Write some code to send messages

Add the dependency jar files to the ClassPath of your Sender.java file.
```
javac -cp lib/* src/main/java/com/example/sender/Sender.Java
```

Import the dependencies into your Sender.java class.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.time.Duration;
import java.util.Scanner;
import com.microsoft.azure.relay.RelayConnectionStringBuilder;
import com.microsoft.azure.relay.TokenProvider;

Add the following constants to the top of the Sender.java file to a createConnectionString java function for the hybrid connection details.
```
public static String createConnectionString(){
    StringBuilder connectionString = new StringBuilder();
    connectionString.append("Endpoint=sb://");
    connectionString.append("{namespace}");
    connectionString.append(".servicebus.windows.net/;SharedAccessKeyName=");
    connectionString.append("{keyrule}");
    connectionString.append(";SharedAccessKey=");
    connectionString.append("{key}");
    connectionString.append(";EntityPath=");
    connectionString.append("{path}");
    return connectionString.toString();
}
```
Replace the placeholders in brackets with the values you obtained when you created the hybrid connection.
- namespace - The Relay namespace. Be sure to use the fully qualified namespace name; for example, {namespace}.servicebus.windows.net.
- path - The name of the hybrid connection.
- keyrule - Name of your Shared Access Policies key, which is RootManageSharedAccessKey by default.
- nst key - The primary key of the namespace you saved earlier.

Add the following code to the Sender.java file. The main function should look like the following code.

public static void main(String[] args) throws IOException {
    String CONNECTION_STRING_ENV_VARIABLE_NAME = createConnectionString();
    if (CONNECTION_STRING_ENV_VARIABLE_NAME == null || CONNECTION_STRING_ENV_VARIABLE_NAME.isEmpty()){
        System.err.println("Connection string is null or empty. Please check your createConnectionString method.");
        return;
    }
    RelayConnectionStringBuilder connectionParams = new RelayConnectionStringBuilder(CONNECTION_STRING_ENV_VARIABLE_NAME);
    TokenProvider tokenProvider = TokenProvider.createSharedAccessSignatureTokenProvider(
            connectionParams.getSharedAccessKeyName(), 
            connectionParams.getSharedAccessKey());
    URL url = buildHttpConnectionURL(connectionParams.getEndpoint().toString(), connectionParams.getEntityPath());
    String tokenString = tokenProvider.getTokenAsync(url.toString(), Duration.ofHours(1)).join().getToken();
    Scanner in = new Scanner(System.in);
    while (true) {
        System.out.println("Press ENTER to terminate this program.");
        String message = in.nextLine();
        int value = System.in.read();
        if (value == '\n' || value == '\r') {
            System.out.println("Terminating the program...");
            break;}
        // Starting a HTTP connection to the listener
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        // Sending an HTTP request to the listener
        // To send a message body, use POST
        conn.setRequestMethod((message == null || message.length() == 0) ? "GET" : "POST");
        conn.setRequestProperty("ServiceBusAuthorization", tokenString);
        conn.setDoOutput(true);
        OutputStreamWriter out = new OutputStreamWriter(conn.getOutputStream());
        out.write(message, 0, message.length());
        out.flush();
        out.close();
        // Reading the HTTP response
        String inputLine;
        BufferedReader reader = null;
        StringBuilder responseBuilder = new StringBuilder();
        try {
            InputStream inputStream = conn.getInputStream();
            reader = new BufferedReader(new InputStreamReader(inputStream));
            System.out.println("status code: " + conn.getResponseCode());
            while ((inputLine = reader.readLine()) != null) {
                responseBuilder.append(inputLine);
            }
            System.out.println("received back " + responseBuilder.toString());
        } catch (IOException e) {
            System.out.println("The listener is offline or could not be reached.");
            break;
        } finally {
            if (reader != null) {
                reader.close();
            }
        }
    }
    in.close();
}

static URL buildHttpConnectionURL(String endpoint, String entity) throws MalformedURLException {
    StringBuilder urlBuilder = new StringBuilder(endpoint + entity);

    // For HTTP connections, the scheme must be https://
    int schemeIndex = urlBuilder.indexOf("://");
    if (schemeIndex < 0) {
        throw new IllegalArgumentException("Invalid scheme from the given endpoint.");
    }
    urlBuilder.replace(0, schemeIndex, "https");
    return new URL(urlBuilder.toString());
}

Here's what your Sender.java file should look like:

package com.example.sender;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.time.Duration;
import java.util.Scanner;
import com.microsoft.azure.relay.RelayConnectionStringBuilder;
import com.microsoft.azure.relay.TokenProvider;

public class Sender
{
    public static String createConnectionString(){
        StringBuilder connectionString = new StringBuilder();
        connectionString.append("Endpoint=sb://");
        connectionString.append("{namespace}");
        connectionString.append(".servicebus.windows.net/;SharedAccessKeyName=");
        connectionString.append("{keyrule}");
        connectionString.append(";SharedAccessKey=");
        connectionString.append("{key}");
        connectionString.append(";EntityPath=");
        connectionString.append("{path}");
        return connectionString.toString();
        }
    public static void main(String[] args) throws IOException {
        String CONNECTION_STRING_ENV_VARIABLE_NAME = createConnectionString();
        if (CONNECTION_STRING_ENV_VARIABLE_NAME == null || CONNECTION_STRING_ENV_VARIABLE_NAME.isEmpty()){
            System.err.println("Connection string is null or empty. Please check your createConnectionString method.");
            return;
        }
        RelayConnectionStringBuilder connectionParams = new RelayConnectionStringBuilder(CONNECTION_STRING_ENV_VARIABLE_NAME);
        TokenProvider tokenProvider = TokenProvider.createSharedAccessSignatureTokenProvider(
                connectionParams.getSharedAccessKeyName(), 
                connectionParams.getSharedAccessKey());
        URL url = buildHttpConnectionURL(connectionParams.getEndpoint().toString(), connectionParams.getEntityPath());
        String tokenString = tokenProvider.getTokenAsync(url.toString(), Duration.ofHours(1)).join().getToken();
        Scanner in = new Scanner(System.in);
        while (true) {
            System.out.println("Press ENTER to terminate this program.");
            String message = in.nextLine();
            int value = System.in.read();
            if (value == '\n' || value == '\r') {
                System.out.println("Terminating the program...");
                break;}
            // Starting a HTTP connection to the listener
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            // Sending an HTTP request to the listener
            // To send a message body, use POST
            conn.setRequestMethod((message == null || message.length() == 0) ? "GET" : "POST");
            conn.setRequestProperty("ServiceBusAuthorization", tokenString);
            conn.setDoOutput(true);
            OutputStreamWriter out = new OutputStreamWriter(conn.getOutputStream());
            out.write(message, 0, message.length());
            out.flush();
            out.close();
            // Reading the HTTP response
            String inputLine;
            BufferedReader reader = null;
            StringBuilder responseBuilder = new StringBuilder();
            try {
                InputStream inputStream = conn.getInputStream();
                reader = new BufferedReader(new InputStreamReader(inputStream));
                System.out.println("status code: " + conn.getResponseCode());
                while ((inputLine = reader.readLine()) != null) {
                    responseBuilder.append(inputLine);
                }
                System.out.println("received back " + responseBuilder.toString());
            } catch (IOException e) {
                System.out.println("The listener is offline or could not be reached.");
                break;
            } finally {
                if (reader != null) {
                    reader.close();
                }
            }
        }
        in.close();
    }

    static URL buildHttpConnectionURL(String endpoint, String entity) throws MalformedURLException {
        StringBuilder urlBuilder = new StringBuilder(endpoint + entity);

        // For HTTP connections, the scheme must be https://
        int schemeIndex = urlBuilder.indexOf("://");
        if (schemeIndex < 0) {
            throw new IllegalArgumentException("Invalid scheme from the given endpoint.");
        }
        urlBuilder.replace(0, schemeIndex, "https");
        return new URL(urlBuilder.toString());
    }
}

Note

The sample code in this article uses a connection string to authenticate to an Azure Relay namespace to keep the tutorial simple. We recommend that you use Microsoft Entra ID authentication in production environments, rather than using connection strings or shared access signatures, which can be more easily compromised. For detailed information and sample code for using the Microsoft Entra ID authentication, see Authenticate and authorize an application with Microsoft Entra ID to access Azure Relay entities and Authenticate a managed identity with Microsoft Entra ID to access Azure Relay resources.

Run the applications

Run the server application: from a Java command prompt or application type java -cp <jar_dependency_path> com.example.listener.Listener.java.
Run the client application: from a Java command prompt or application type java -cp <jar_dependency_path> com.example.sender.Sender.java, and enter some text.
Ensure that the server application console outputs the text that was entered in the client application.

Congratulations, you have created an end-to-end Hybrid Connections application using Java!

Next steps

In this quickstart, you created Java client and server applications that used HTTP to send and receive messages. The Hybrid Connections feature of Azure Relay also supports using WebSockets to send and receive messages. To learn how to use WebSockets with Azure Relay Hybrid Connections, see the WebSockets quickstart.

In this quickstart, you used Java to create client and server applications. To learn how to write client and server applications using .NET Framework, see the .NET WebSockets quickstart or the .NET HTTP quickstart.

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Get started with Relay Hybrid Connections HTTP requests in Java

Prerequisites

Create a namespace using the Azure portal

Get management credentials

Create a hybrid connection using the Azure portal

Create a server application (listener)

Create a Java application

Add the Relay package

Write some code to send messages

Create a client application (sender)

Create a Java application

Add the Relay package

Write some code to send messages

Run the applications

Next steps

Feedback

Additional resources