LSP4J-MCP

Overview

LSP4J-MCP is a Java-based MCP server that bridges the gap between AI assistants and Java development environments by wrapping Eclipse JDT Language Server using LSP4J. It exposes key IDE features like symbol search, reference finding, definition lookup, and document analysis through the MCP protocol, enabling AI assistants to understand and navigate Java codebases. The server architecture connects Claude Code to JDTLS via LSP4J, allowing for rich interaction with Java projects.

Try asking AI

After installing, here are 7 things you can ask your AI assistant:

• find_symbols

  Search for Java symbols (classes, methods, fields) by name

  Try:Find all classes named Repository in this projectTry:Search for methods containing 'save' in their nameTry:Where is the UserService class defined?
• find_references

  Find all references to a symbol at a given file location

  Try:Find all usages of the `processOrder` method at line 45 in OrderService.javaTry:Where is the `CustomerRepository` interface used throughout the codebase?Try:Show me all places that call the constructor at line 12 of PaymentGateway.java
• find_definition

  Go to the definition of a symbol

  Try:What is the definition of the method being called at line 78, column 15 in CheckoutController.java?Try:Take me to the implementation of the interface method at line 23 in MyService.java
• document_symbols

  Get all symbols defined in a Java file

  Try:List all methods and fields in the Customer.java fileTry:What symbols are defined in src/main/java/com/example/service/OrderService.java?Try:Give me an overview of the structure of ConfigurationManager.java
• find_interfaces_with_method

  Find all interfaces containing a method with a given name

  Try:Which interfaces define a method called 'findById'?Try:Find all classes that have a method named 'process'Try:Show me all interfaces containing the 'validate' method

Comparable tools

Installation

mvn clean package

{
  "mcpServers": {
    "java-lsp": {
      "command": "java",
      "args": [
        "-jar",
        "/path/to/LSP4J-MCP/target/lsp4j-mcp-1.0.0-SNAPSHOT.jar",
        "/path/to/your/java/project",
        "jdtls"
      ],
      "env": {
        "LOG_FILE": "/tmp/lsp4j-mcp.log"
      }
    }
  }
}

FAQ

What Java IDE features does this MCP server provide?

The server provides symbol search, reference finding, definition lookup, document symbols, and interface method discovery - essentially key Java IDE navigation features.

Can I use this with other AI assistants besides Claude?

The README specifically mentions Claude, but since it implements the standard MCP protocol, it should work with any MCP-compatible AI assistant that supports tool calling.

Does it work with non-Maven Java projects?

The README doesn't explicitly specify, but since it connects to JDTLS which is IDE-agnostic, it should work with any standard Java project structure.

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