Java — LSP setup

• Builtin server: jdtls — jdtls
• Extensions: .java
• Install hint: https://github.com/eclipse-jdtls/eclipse.jdt.ls

Install

• macOS: brew install jdtls
• Linux: Download from eclipse-jdtls/eclipse.jdt.ls releases, extract, and wrap the launcher as jdtls on PATH (some distros package it as jdtls/jdt-language-server).
• Windows: Download the release archive and add the jdtls launcher (bin/jdtls.bat or the Python wrapper) to PATH.

Requires a JDK 17+ to run the language server itself (the project may target an older Java version).

Confirm it resolves:

command -v jdtls

Configure

Builtin — usually NO config needed (auto-resolved by extension). Configure only to set priority, init options, override extensions, or disable. Same JSON shape in .codex/lsp-client.json (Codex) AND .opencode/lsp.json (OpenCode/omo):

{ "lsp": { "jdtls": { "priority": 100 } } }

For builtin ids in a PROJECT config, command is supplied automatically — only set priority/initialization/extensions/disabled/env. A fully custom (non-builtin) server with its own command must go in the USER config (~/.codex/lsp-client.json).

Initialization options (only if commonly needed)

jdtls maintains a per-project workspace data directory and the first index is slow (it resolves the full classpath and builds). Point JAVA_HOME at a JDK 17+ if jdtls cannot find one:

{ "lsp": { "jdtls": { "env": { "JAVA_HOME": "/Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home" } } } }

Most settings (runtimes, format, import order) are passed via settings.java.* initialization options; defaults work for Maven/Gradle projects with a standard layout.

Alternatives

• No mainstream alternative. jdtls (Eclipse JDT Language Server) is the de-facto standard and powers the official VS Code Java extension.

Troubleshooting

• PATH: jdtls on PATH; reopen shell after install.
• No JDK found: server exits immediately — set JAVA_HOME to a JDK 17+.
• Slow / no completions at first: the initial classpath index can take a minute or more on large Maven/Gradle projects; wait for it to finish.
• Stale state: delete the jdtls workspace data dir to force a clean re-index if results go wrong after big dependency changes.
• Build tool required: keep pom.xml / build.gradle valid; a broken build descriptor breaks symbol resolution.

Verify

bun ../../scripts/verify-lsp.ts path/to/File.java