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Java — java-direct

Proxies jdtls (Eclipse JDT.LS launcher) over HTTP. One server per workspace.

Install prereq

brew install jdtls          # macOS — bundles Eclipse JDT.LS + launcher
# Linux: yay -S jdtls (Arch AUR), or download from https://download.eclipse.org/jdtls/snapshots/
java -version               # MUST report 17 or later (JDK, not JRE)

Verify: command -v jdtls (Homebrew formula installs a wrapper script that handles the Equinox bootstrap).

Workspace markers (walk-up order)

  1. pom.xml
  2. build.gradle.kts
  3. build.gradle
  4. settings.gradle.kts
  5. settings.gradle
  6. .project

If none found, wrapper uses current working directory.

Invocation

java-direct start                                                   # cwd walk-up
java-direct start /abs/path/to/project                              # explicit
java-direct call textDocument/documentSymbol \
  '{"textDocument":{"uri":"file:///abs/path/to/Foo.java"}}'

java-direct call textDocument/hover \
  '{"textDocument":{"uri":"file:///abs/path/to/Foo.java"},
    "position":{"line":10,"character":5}}'

java-direct call workspace/symbol '{"query":"UserService"}'

Op surface

Standard LSP 3.17 methods jdtls implements: textDocument/documentSymbol, textDocument/hover, textDocument/definition, textDocument/references, textDocument/implementation, textDocument/typeDefinition, textDocument/completion, textDocument/signatureHelp, textDocument/prepareCallHierarchy, callHierarchy/incomingCalls, callHierarchy/outgoingCalls, workspace/symbol, textDocument/foldingRange, textDocument/codeAction, textDocument/rename.

Quirks

  • Background "Building workspace" job: jdtls runs an asynchronous indexer after start. workspace/symbol may return empty for the first few seconds even though the server responds. Typical settle time: 5-15s on a small project, longer for Maven/Gradle imports that resolve transitive deps.
  • Eclipse ~/.eclipse directory: Equinox launcher extracts native libraries to ~/.eclipse on first run. Sandboxed environments must allow writes there.
  • Per-workspace -data dir: wrapper passes -data $STATE_DIR/jdt-data so each workspace's Eclipse metadata is isolated and removed on stop.
  • JDK 17+ required: jdtls uses Java 17 language features. JDK 21 (LTS) is fine. JRE-only installs fail at startup.
  • Maven/Gradle imports: first start of a real project triggers dependency resolution. For projects with hundreds of deps, expect cold start of 30-120s; subsequent starts are seconds (Eclipse caches the resolved model under jdt-data).

Timing (rough, on a modern laptop, fixture project)

  • Cold start (server boot to /health ready): ~2s
  • Cold call (first request after start): ~900ms (incl. file load + indexing)
  • Warm: ~80-100ms per call (HTTP round-trip dominates)

State directory

~/.cache/java-direct/<workspace-hash>/{pid,port,workspace,log,jdt-data/}

Inspect log if startup fails (Eclipse stack traces are verbose; look for !STACK or Operation not permitted).