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POExposing a remote interface or object model
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copied!<p>I have a question on the best way of exposing an asynchronous remote interface.</p> <p>The conditions are as follows:</p> <ul> <li>The protocol is asynchronous</li> <li>A third party can modify the data at any time</li> <li>The command round-trip can be significant</li> <li>The model should be well suited for UI interaction</li> <li>The protocol supports queries over certain objects, and so must the model</li> </ul> <p>As a means of improving my lacking skills in this area (and brush up my Java in general), I have started a <a href="http://Telharmonium.devjavu.com/" rel="nofollow noreferrer">project</a> to create an Eclipse-based front-end for <a href="http://xmms2.xmms.se" rel="nofollow noreferrer">xmms2</a> (described below).</p> <p>So, the question is; how should I expose the remote interface as a neat data model (In this case, track management and event handling)?</p> <p>I welcome anything from generic discussions to pattern name-dropping or concrete examples and patches :)</p> <hr> <p>My primary goal here is learning about this class of problems in general. If my project can gain from it, fine, but I present it strictly to have something to start a discussion around.</p> <p>I've implemented a protocol abstraction which I call <a href="http://telharmonium.devjavu.com/browser/trunk/xmms2-client" rel="nofollow noreferrer">'client'</a> (for legacy reasons) which allows me to access most exposed features using method calls which I am happy with even if it's far from perfect.</p> <p>The features provided by the xmms2 daemon are things like track searching, meta-data retrieval and manipulation, change playback state, load playlists and so on and so forth.</p> <p>I'm in the middle of updating to the latest stable release of xmms2, and I figured I might as well fix some of the glaring weaknesses of my current implementation.</p> <p>My plan is to build a better abstraction on top of the protocol interface, one that allows a more natural interaction with the daemon. The current <a href="http://telharmonium.devjavu.com/browser/trunk/xmms2-model" rel="nofollow noreferrer">'model'</a> implementation is hard to use and is frankly quite ugly (not to mention the UI-code which is truly horrible atm).</p> <p>Today I have the <a href="http://telharmonium.devjavu.com/browser/trunk/xmms2-model/src/se/fnord/xmms2/model/Tracks.java" rel="nofollow noreferrer">Tracks</a> interface which I can use to get instances of <a href="http://telharmonium.devjavu.com/browser/trunk/xmms2-model/src/se/fnord/xmms2/model/Track.java" rel="nofollow noreferrer">Track</a> classes based on their id. Searching is performed through the <a href="http://telharmonium.devjavu.com/browser/trunk/xmms2-model/src/se/fnord/xmms2/model/Collections.java" rel="nofollow noreferrer">Collections</a> interface (unfortunate namespace clash) which I'd rather move to Tracks, I think.</p> <p>Any data can be modified by a third party at any time, and this should be properly reflected in the model and change-notifications distributed</p> <p>These interfaces are exposed when connecting, by returning an object hierarchy that looks like this:</p> <ul> <li>Connection <ul> <li>Playback getPlayback() <ul> <li>Play, pause, jump, current track etc</li> <li>Expose playback state changes</li> </ul></li> <li>Tracks getTracks() <ul> <li>Track getTrack(id) etc</li> <li>Expose track updates</li> </ul></li> <li>Collections getCollection() <ul> <li>Load and manipulate playlists or named collections</li> <li>Query media library</li> <li>Expose collection updates</li> </ul></li> </ul></li> </ul>

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