MCP Client SDK Setup

Install Dependency

We’ll need the AJ MCP SDK for making API requests. Install them with:

<dependency>
    <groupId>com.ajaxjs</groupId>
    <artifactId>aj-mcp-client</artifactId>
    <version>1.2</version>
</dependency>

We can find the latest version:

Concepts

The client SDK implementation consists of two main components:

• Transport: Manages the subprocess and handles low-level message exchange.
• MCP Client: Provides a high-level API for using the transport, implementing the MCP protocol.

To start using the MCP client, you must first these two main components: first to create a appropriate transport instance, and then to create a client instance with that transport. The client supports different transport mechanisms, primarily Server-Sent Events (SSE) and standard I/O (stdio).

Setup the Transport

First, we need to create the transport. There are two types of transport you can choose from for your application, depending on the type of your MCP server.

Stdio Transport

'Stdio' stands for Standard Input/Output, by using command line to interact between the programme and human in short. But here is between the MCP Client and the MCP Server. Usually, we use stdio for the local application, such as a *.exe programme or a Java Jar programme, and so on.

// The MCP server is a Java programme, runs on stdio.
McpTransport transport = StdioTransport.builder()
    .command(Arrays.asList("java", "-jar", "C:\\app\\my-app-jar-with-dependencies.jar"))
    .logEvents(true)
    .build();

Let's take a look at a .exe programme as an example:

// The MCP server is an executable programme, runs on stdio.
McpTransport transport = StdioTransport.builder()
    .command("C:\\app\\my-app.exe", "-token", "dd4df2sx32ds"))
    .logEvents(true)
    .build();

If you want to check out the fully logs of the client, you can set logEvents to true. This approach is beneficial for debugging purposes or for gaining a deeper understanding of the MCP protocol's JSON-based messaging format.

SSE Transport

The SSE Transport enables bidirectional communication between MCP clients and servers using the HTTP protocol with Server-Sent Events. This transport method is particularly useful for web-based applications

McpTransport transport = HttpMcpTransport.builder()
    .sseUrl("http://localhost:8080/sse")
    .logRequests(true)
    .logResponses(true)
    .build();

The sseUrl is required. It specifies the URL of the SSE endpoint where the MCP server is listening for incoming connections.

McpClient

The MCP Client serves as a bridge between local applications and remote tool implementations.

McpClient mcpClient = McpClient.builder()
        .clientName("my-host")
        .clientVersion("1.2")
        .transport(transport)
        .build();

Usually we fill the clientName and clientVersion properties. The clientName property is used to identify the client to the MCP server, while the clientVersion property is used to indicate the version of the client.

All properties are listing below:

Please note that after creating the McpClient, you should call mcpClient.initialize(); right away. We'll talk about the initialization of MCP in next section.

McpClient mcpClient = McpClient.builder()
        .clientName("my-host")
        .clientVersion("1.2")
        .transport(sseTransport)
        .build();
        
mcpClient.initialize();

Finally, please remember to close the McpClient resources by calling the close() method, or using autocloseable.

try(IMcpClient mcpClient2 = McpClient.builder().transport(transport).build()){
    ...
} catch (Exception e) {
   throw new RuntimeException(e);
}

The MCP Client follows a layered architecture with a clean separation between the interface definition and its implementation. The client relies on the transport layer for actual communication with the server, abstracting the communication details to support different transport mechanisms.