Enterprise Java Development in Emacs

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My current Java setup utilises lsp-java and dap-java which together gives me a good Java coding and debugging experience in Emacs, including code navigation, auto completion, documentation lookup, on the fly de-compiling 3rd party libraries and remote debugging an application servers.

Everything works pretty much out of the box, once you've wired up lsp-java and dap-java, it'll figure out your Maven project by itself and download whatever it needs in the background. I've used this setup for a good while now on a code base with around 5000 Java files and 65 Maven modules and the performance is impeccable.

You can see my setup in action in the screencast below.

Support for Lombok

(setq lsp-java-vmargs
      (list
         "-noverify"
         "-Xmx1G"
         "-XX:+UseG1GC"
         "-XX:+UseStringDeduplication"
         "-javaagent:/path/to/lombok-1.18.6.jar"))

Trouble shooting

If lsp-java doesn't work, a good place to start is to look in the Eclipse server log file:

$ tail -f ~/.emacs.d/workspace/.metadata/.log

java.lang.NoSuchMethodError: java.nio.ByteBuffer.limit(I)Ljava/nio/ByteBuffer;

You need to make the language server use Java 9 and it must be OpenJDK:

(setq lsp-java-java-path
      "/usr/lib/jvm/java-9-openjdk-amd64/bin/java")

See this ticket over at jira.mongodb.org for a good explanation of why these errors happen

java.security.InvalidAlgorithmParameterException

java.security.InvalidAlgorithmParameterException: the
trustAnchors parameter must be non-empty

The easiest solution is to just use OpenJDK instead of Oracle Java to run the Eclipse server (I just did apt-get install openjdk-9-jdk), you can set this in your .emacs by setting lsp-java-java-path, see above.

NoClassDefFoundError: javax/annotation/processing/AbstractProcessor

!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.core.resources".
!STACK 0
java.lang.NoClassDefFoundError: javax/annotation/processing/AbstractProcessor
    at java.base/java.lang.ClassLoader.findBootstrapClass(Native Method)
    at java.base/java.lang.ClassLoader.findBootstrapClassOrNull(ClassLoader.java:1248)
    at java.base/java.lang.System$2.findBootstrapClassOrNull(System.java:2123)

The problem was that by having Lombok on the boot classpath it would interfere with the annotation processing mechanism in the Eclipse server. The remedy was to remove -Xbootclasspath/a:/path/to/lombok-1.16.18.jar and only specify Lombok in the javaagent parameter.

Wipe the slate clean

To remove all generated files and caches related to LSP, do:

$ rm -rf ~/.emacs.d/workspace \
         ~/.emacs.d/.cache/lsp

This can be worth trying before going mad about something not working.

Also, there's a minimal .emacs config on the lsp-java website that you can try without your own configuration to ensure your problems are not due to your own (combination of) configuration.

Other Java extensions for Emacs I've used

Licensed under CC BY Creative Commons License ~ ✉ torstein.k.johansen @ gmail ~ 🐘 @skybert@hachyderm.io ~ 🐦 @torsteinkrause