idiomatic clojure of this java style ?

[gary ng]

Hi,

As a newbie learning clojure, I would like to code in clojure rather than 'java disguised as clojure' and I am wondering what would it looks like for the following typical java(shown below) implementation. which has:

1. a static class member for the logger

2. and typical imperative style coding

=============================================================

public class xmpp extends HttpServlet {

    public static final Logger _log = Logger.getLogger(xmpp.class.getName());

    @Override

    public void doPost(HttpServletRequest req, HttpServletResponse resp)

              throws IOException

    {

        try {

            String strStatus = "";

            XMPPService xmpp = XMPPServiceFactory.getXMPPService();

            //STEP 2

            

            Message msg = xmpp.parseMessage(req);

            JID fromJid = msg.getFromJid();

            String body = msg.getBody();

            _log.info("Received a message from " + fromJid + " and body = " + body);

            //STEP 3

            String msgBody = "You sent me : " + body;

            Message replyMessage = new MessageBuilder()

            .withRecipientJids(fromJid)

            .withBody(msgBody)

            .build();

            //STEP 4

            boolean messageSent = false;

            SendResponse status = xmpp.sendMessage(replyMessage);

            messageSent = (status.getStatusMap().get(fromJid) == SendResponse.Status.SUCCESS);

            //STEP 5

            if (messageSent) {

            strStatus = "Message has been sent successfully";

            }

            else {

            strStatus = "Message could not be sent";

            }

            _log.info(strStatus);

        }

        catch (Exception e)

        {

            _log.log(Level.SEVERE,e.getMessage());

        }

    }

--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clo...@googlegroups.com
Note that posts from new members are moderated - please be patient with your first post.
To unsubscribe from this group, send email to
clojure+u...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

[Allen Johnson]

Here's my attempt. I don't think you can do much about the imperative
style when you are calling Java APIs unless someone was nice and wrote
a clojure wrapper. But I'm just a n00b.

---
(ns example.servlet.xmpp
(:use [clojure.contrib.logging])
(:import [xmpp.package.here XMPPServiceFactory MessageBuilder]
[xmpp.package.here SendResponse SendResponse$Status])
(:gen-class
:extends javax.servlet.http.HttpServlet))

(defn create-message [recipient body]
(let [builder (doto (MessageBuilder.)
(.withRecipientJids recipient)
(.witBody body))]
(.build builder)))

(defn send-message! [xmpp recipient body]
(let [status (.sendMessage xmpp (create-message recipient body))
result (.. status getStatusMap (get from))]
(= SendResponse$Status/SUCCESS result)))

(defn -doPost [req res]
(try
(let [xmpp (XMPPServiceFactory/getXMPPService)
msg (.parseMessage xmpp req)
from (.getFromJid msg)
body (.getBody msg)]
(info (str "Received a message from " from " and body " body))
(if (send-message! xmpp from (str "You sent me: " body))
(info "Message has been sent successfully.")
(info "Message could not be sent.")))
(catch Exception e
(fatal "Error sending message:" e))))

[Allen Johnson]

Oops, just saw the error in send-message as I replied. StatusMap
should (get recipient).

(defn send-message! [xmpp recipient body]
(let [status (.sendMessage xmpp (create-message recipient body))

result (.. status getStatusMap (get recipient))]
(= SendResponse$Status/SUCCESS result)))

[gary ng]

On Sat, Apr 24, 2010 at 12:56 PM, Allen Johnson <akjoh...@gmail.com> wrote:

Here's my attempt. I don't think you can do much about the imperative
style when you are calling Java APIs unless someone was nice and wrote
a clojure wrapper. But I'm just a n00b.

thanks for the help. When deployed to GAE, I got the following exception related to the logging function. Just from browsing the logging code in clojure-contrib, it seems that the 'import should be catched and ignored, not sure why it happens.

Error for /_ah/xmpp/message/chat/
java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory
	at clojure.contrib.logging$fn__49$fn__51.invoke(logging.clj:188)
	at clojure.lang.AFn.applyToHelper(AFn.java:173)
	at clojure.lang.AFn.applyTo(AFn.java:164)
	at clojure.core$apply__4370.invoke(core.clj:436)
	at clojure.core$memoize__6537$fn__6539.doInvoke(core.clj:4328)
	at clojure.lang.RestFn.invoke(RestFn.java:413)
	at guestbook.xmppc$_doPost__16.invoke(xmppc.clj:31)
	at guestbook.xmppc.doPost(Unknown Source)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:713)
	at guestbook.xmppc.service(Unknown Source)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
	at guestbook.xmppc.service(Unknown Source)
	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
	at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:97)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
	at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:238)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at org.mortbay.jetty.Server.handle(Server.java:326)
	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
	at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
	at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
	at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:135)
	at com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:243)
	at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5838)
	at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5836)
	at com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24)
	at com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:398)
	at com.google.net.rpc.impl.Server$2.run(Server.java:852)
	at com.google.tracing.LocalTraceSpanRunnable.run(LocalTraceSpanRunnable.java:56)
	at com.google.tracing.LocalTraceSpanBuilder.internalContinueSpan(LocalTraceSpanBuilder.java:576)
	at com.google.net.rpc.impl.Server.startRpc(Server.java:807)
	at com.google.net.rpc.impl.Server.processRequest(Server.java:369)
	at com.google.net.rpc.impl.ServerConnection.messageReceived(ServerConnection.java:442)
	at com.google.net.rpc.impl.RpcConnection.parseMessages(RpcConnection.java:319)
	at com.google.net.rpc.impl.RpcConnection.dataReceived(RpcConnection.java:290)
	at com.google.net.async.Connection.handleReadEvent(Connection.java:474)
	at com.google.net.async.EventDispatcher.processNetworkEvents(EventDispatcher.java:831)
	at com.google.net.async.EventDispatcher.internalLoop(EventDispatcher.java:207)
	at com.google.net.async.EventDispatcher.loop(EventDispatcher.java:103)
	at com.google.net.rpc.RpcService.runUntilServerShutdown(RpcService.java:251)
	at com.google.apphosting.runtime.JavaRuntime$RpcRunnable.run(JavaRuntime.java:404)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory
	at com.google.appengine.runtime.Request.process-03b3a9395bcfd590(Request.java)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClassInternal(Unknown Source) 

... 53 more