[BUG] jdtls-lsp Plugin Fails on Windows Due to Incorrect File URI Construction

Summary

The jdtls-lsp plugin fails to initialize on Windows because Claude Code's LSP client constructs invalid file URIs using backslashes and only two slashes instead of three.

Environment

• OS: Windows 10 (MINGW64_NT-10.0-19045)
• Claude Code Version: 2.1.17
• Plugin: jdtls-lsp@claude-plugins-official v1.0.0
• Java Version: 21+
• Working Directory: C:\code\agentic-app

Actual Behavior

The LSP client constructs invalid file URIs:

file://C:\code\agentic-app

(Two slashes, backslashes in path)

Expected Behavior

The LSP client should construct valid file URIs following RFC 8089 for Windows paths:

file:///C:/code/agentic-app

(Three slashes, forward slashes in path)

Error Messages/Logs

## Error Message

2026-01-23T10:25:10.076Z [DEBUG] [LSP SERVER plugin:jdtls-lsp:jdtls] Jan 23, 2026 10:25:10 A.M. org.eclipse.lsp4j.jsonrpc.RemoteEndpoint fallbackResponseError
SEVERE: Internal error: Illegal character in authority at index 9: file://C:\code\agentic-app
java.lang.IllegalArgumentException: Illegal character in authority at index 9: file://C:\code\agentic-app
    at java.base/java.net.URI.create(URI.java:932)
    at org.eclipse.jdt.ls.core.internal.ResourceUtils.canonicalFilePathFromURI(ResourceUtils.java:225)
    at org.eclipse.jdt.ls.core.internal.handlers.BaseInitHandler.handleInitializationOptions(BaseInitHandler.java:109)
    ...
Caused by: java.net.URISyntaxException: Illegal character in authority at index 9: file://C:\code\agentic-app
   ...
2026-01-23T10:25:10.080Z [DEBUG] [LSP PROTOCOL plugin:jdtls-lsp:jdtls] Received response 'initialize - (0)' in 10271ms. Request failed: Internal error. (-32603).

Steps to Reproduce

1. Install Claude Code on Windows
2. Install jdtls-lsp plugin: claude plugin install jdtls-lsp
3. Navigate to any directory with Java files (e.g., C:\code\agentic-app)
4. Start Claude with debug flag: claude --debug
5. Try to use LSP functionality on a Java file
6. Check debug logs in C:\Users\<username>\.claude\debug\<session-id>.txt

Additional Context

• The jdtls wrapper script at C:\Users\<username>\bin\jdtls is working correctly
• The Eclipse JDT.LS server itself is properly installed and functional
• This appears to be a Windows-specific path handling issue in the LSP client

Root Cause

The issue is in Claude Code's built-in LSP client for Windows, not in the jdtls script itself. The LSP client is sending incorrectly formatted file URIs during the initialization handshake.

Problems:

1. Using file:// (2 slashes) instead of file:/// (3 slashes)
2. Using backslashes (\) in the path instead of forward slashes (/)
3. The backslashes are interpreted as illegal characters in the URI authority component

Impact

• jdtls-lsp plugin is completely non-functional on Windows
• Users cannot get Java language server features (autocomplete, go-to-definition, refactoring, etc.)
• Affects all Windows users trying to use Java development features in Claude Code

Workaround

None currently available. The issue is in Claude Code's core LSP client implementation.

Claude Model

Sonnet (default)

Is this a regression?

No

Last Working Version

n/a

Claude Code Version

2.1.17

Platform

AWS Bedrock

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_