I have been using the Clojure REPL to debug a large Java server app.
It's great for exploratory testing and for validating assumptions
about how the system works. I wanted to post the code here in case
someone else finds this useful.
1. Stick this in a class that is loaded early in the server/app.
public static class Repl {
public static final String PORT = "18081";
public static final String NS = "user";
private final String initResult; public String getInitResult() {
return initResult; }
public Object invoke(String fn) { try { return
clojure.lang.RT.var(NS, fn).invoke(); } catch (Exception e) { return
null; } }
public Object invoke(String fn, Object arg1) { try { return
clojure.lang.RT.var(NS, fn).invoke(arg1); } catch (Exception e) {
return null; } }
public Object invoke(String fn, Object arg1, Object arg2) { try {
return clojure.lang.RT.var(NS, fn).invoke(arg1, arg2); } catch
(Exception e) { return null; } }
public Object invoke(String fn, Object arg1, Object arg2, Object
arg3) { try { return clojure.lang.RT.var(NS, fn).invoke(arg1, arg2,
arg3); } catch (Exception e) { return null; } }
public Repl() {
String result;
try {
clojure.lang.Var eval = clojure.lang.RT.var("clojure.core", "eval");
clojure.lang.Var read =
clojure.lang.RT.var("clojure.core", "read-string");
String create_repl_server =
"(do " +
"(use '[clojure.contrib.server-socket :only
[create-repl-server]])" +
"(create-repl-server " + PORT + ")" + ")";
result = eval.invoke(read.invoke(create_repl_server)).toString();
} catch (Exception e) {
result = e.toString();
}
initResult = result;
}
}
public static final Repl REPL = new Repl();
2. Use this on the command line to start the REPL:
rlwrap --logfile $HOME/tmp/clj.log telnet localhost 18081
Now from the REPL you can create Java objects and call methods at will.
3. To call a Clojure function called some-function in "user" namespace
from Java, use something like this:
REPL.invoke("some-function", "arg1"));
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