A swank server for clojure with jpda
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Ritz is a swank server for running clojure in slime.


  • Break on exceptions and breakpoints.
  • Allows stepping from breakpoints
  • Allows evaluation of expressions in the context of a stack frame
  • Inspection of locals in any stack frame
  • Disassembly of functions from symbol or stack frame

Should work with any version of clojure from 1.2.0.


The install has two parts. The first is to install the slime components into emacs, the second is to enable Leiningen to use ritz.


Install the slime-ritz.el contrib from marmalade.

A compatible slime.el is in slime/slime.el. It is available as a package.el package file you can download and install with M-x package-install-file. Note that you may need to remove this package to use swank-clojure again.

lein 2

To make ritz available in all your projects, add the lein-ritz plugin to your :user profile in ~/.lein/profiles.clj.

{:user {:plugins [[lein-ritz "0.3.0-SNAPSHOT"]]}}

To enable ritz on a per project basis, add it to your project.clj's :dev profile.

{:dev {:plugins [[lein-ritz "0.3.0-SNAPSHOT"]]}}

Lein 1

To make ritz available in all your projects, install the lein-ritz plugin.

lein plugin install lein-ritz "0.3.0-SNAPSHOT"

Add [lein-ritz "0.3.0-SNAPSHOT"] to your project.clj :dev-dependencies.

Experimental 'jack-in' support

There is experimental support to "jack in" from an existing project using Leiningen:

  • Install clojure-mode either from Marmalade or from git.
  • lein plugin install lein-ritz "0.3.0-SNAPSHOT"
  • in your .emacs file, add the following and evalulate it (or restart emacs)
(setq clojure-swank-command
  (if (or (locate-file "lein" exec-path) (locate-file "lein.bat" exec-path))
    "lein ritz-in %s"
    "echo \"lein ritz-in %s\" | $SHELL -l"))
  • From an Emacs buffer inside a project, invoke M-x clojure-jack-in

Maven Plugin

See zi.

Sun/Oracle JDK and OpenJDK

To use the Sun/Oracle JDK, and possibly OpenJDK, you need to add tools.jar from your JDK install to your classpath. This is not required on OS X, where tools.jar does not exist.

For lein, add the tools.jar to the dev-resources-path:

:dev-resources-path "/usr/lib/jvm/java-6-sun/lib/tools.jar"

For lein2, add the tools.jar to your :user profile:

:user {:plugins [[lein-ritz "0.3.0-SNAPSHOT"]]
       :resource-paths ["/usr/lib/jvm/java-6-sun/lib/tools.jar"]}

If you are using maven then there are instructions in the FAQ.

For cake, add the following (with the correct jdk path), to PROJECT_ROOT/.cake/config: project.classpath = /usr/lib/jvm/java-6-sun/lib/tools.jar

If you are missing tools.jar from the classpath, you will see an exception like java.lang.ClassNotFoundException: com.sun.jdi.VirtualMachine.

Source Browsing

If you would like to browse into java sources then add the source jars to your :dev-dependencies, with the appropriate versions.

[org.clojure/clojure "1.2.1" :classifier "sources"]

For clojure 1.2.0, you will need the following instead:

[clojure-source "1.2.0"]

To be able to see Java sources when using openjdk, add the src.zip to you classpath. e.g. for lein:

:dev-resources-path "/usr/lib/jvm/java-6-openjdk/src.zip"

lein 2

In lein 2 this is simplified. You can add a hook to your user profile to have source jars automatically put on the classpath.

:hooks [ritz.add-sources]

To obtain source jars for your project you can use

lein pom; mvn dependency:sources;


To run ritz with debugging capabilities (notice that it will need to spawn an extra JVM process):

lein ritz

To run ritz with no debugging capabilities:

lein ritz 4005 localhost :server-ns ritz.repl

To run with a maven project:

mvn zi:ritz


To set a breakpoint, put the cursor on the line where you want a breakpoint, and M-x slime-line-breakpoint.

Note that breakpoints disappear on recompilation at the moment.

To list breakpoints, use M-x slime-list-breakpoints or press b in the slime-selector. In the listing you can use the following keys

  • e enable
  • d disable
  • g refresh list
  • k remove breakpoint
  • v view source location

Exception filtering

To filter which exceptions break into the debugger, there is an IGNORE restart, that will ignore an exception type.

To list breakpoints, use M-x slime-list-exception-filters or press f in the slime-selector. In the listing you can use the following keys

  • e enable
  • d disable
  • g refresh list
  • k remove exception filter
  • s save the exception filters

Exception filters are saved to .ritz-exception-filters, which is read by ritz on startup.


Specify the location of local javadoc using slime-javadoc-local-paths in your .emacs file. Note that this requires a connection, so should be in your slime-connected-hook or ritz-connected-hook. e.g.

(defun my-javadoc-setup ()
    (list (concat (expand-file-name "~") "/lisp/docs/java"))))

(add-hook 'slime-connected-hook 'my-javadoc-setup)

The command slime-javadoc, bound to C-c b by default, will open javadoc in the browser you have set up in emacs.

SLIME configuration

If you use slime with multiple lisps, you can isolate clojure specific setup by using ritz-connected-hook and ritz-repl-mode-hook.

Open Problems

Recompilation of clojure code creates new classes, with the same location as the code they replace. Recompilation therefore looses breakpoints, which are set on the old code. Setting breakpoints by line number finds all the old code too.


Allow customisations of which exceptions are trapped by ritz.

A pure JDI backend, that doesn't require swank in the target VM is certainly a possibility.

A slime-eval-symbol-at-point would be useful (requires determining the frame in the current sldb stacktrace using file and line number).

Add watchpoints with logging of locals to an emacs buffer or file.

Use Cases


Run swank server and JDI debugger in the same process to have a single JVM and keep memory usage down


Run swank and debugger in a seperate JVM process. Attach to any -Xdebug enabled JVM process.

Production server

Run swank server in process and attach slime as required. This requires the debugger to run in process.


Ritz was originally based on swank-clojure and was originally called swank-clj. The last swank-clj release is 0.1.6.


Copyright (C) 2010, 2011, 2012 Hugo Duncan

Distributed under the Eclipse Public License.