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POJava Exception Handling via Strategy Pattern?
 

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  1. POJava Exception Handling via Strategy Pattern?
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    <p>I cooked up a class <code>ExceptionHandler&lt;T extends Exception, OptionalReturnType&gt;</code> (see below) to eliminate some (what I view as) boilerplate code which was cluttering up actual implementation, while still providing a hook for explicit Exception handling if desired in the future. For the most part, in my application (essential a scientific computation), there is no such thing as recovery from exceptions - I need a log of the problem so I can fix it, but otherwise I'm just going to re-run once the problem is corrected.</p> <p>Do other people do this (at least, in my specific application situation)? Is it dumb to do so (if yes, some explanation as to why would be nice)?</p> <p>ExceptionHandler:</p> <pre><code>public abstract class ExceptionHandler&lt;ExceptionType extends Exception,OptionalReturn&gt; { public abstract OptionalReturn handle(ExceptionType e); //assorted boilerplate ExceptionHandling, e.g.: public static &lt;ET extends Exception&gt; ExceptionHandler&lt;ET, ?&gt; swallower(final boolean printStackTrace, final String string) { return new ExceptionHandler&lt;ET,Object&gt;() { @Override public Object handle(ET e) { if(printStackTrace) { e.printStackTrace(); } if(string!=null &amp;&amp; !string.isEmpty()) { System.err.println(string); } return null; } }; } public static &lt;ET extends Exception&gt; ExceptionHandler&lt;ET, ?&gt; swallower() { return swallower(false,null); } } </code></pre> <p>example use (which I'm in the process of chopping down so I'm actually not writing quite so much):</p> <pre><code>public class Getter&lt;From&gt; implements Function&lt;Future&lt;? extends From&gt;, From&gt; { private ExceptionHandler&lt;InterruptedException,?&gt; IEH; private ExceptionHandler&lt;ExecutionException,?&gt; EEH; public static final ExceptionHandler&lt;InterruptedException,?&gt; IEH_SWALLOWER = ExceptionHandler.swallower(true,"Returning null."); public static final ExceptionHandler&lt;ExecutionException,?&gt; EEH_SWALLOWER = ExceptionHandler.swallower(true,"Returning null."); private Getter() { this(IEH_SWALLOWER,EEH_SWALLOWER); } private Getter(ExceptionHandler&lt;InterruptedException,?&gt; IEH, ExceptionHandler&lt;ExecutionException,?&gt; EEH) { this.IEH = IEH; this.EEH = EEH; } public static &lt;T&gt; Getter&lt;T&gt; make() { return new Getter&lt;T&gt;(); } public static &lt;T&gt; Getter&lt;T&gt; make(ExceptionHandler&lt;InterruptedException,?&gt; IEH, ExceptionHandler&lt;ExecutionException,?&gt; EEH) { return new Getter&lt;T&gt;(IEH, EEH); } @Override public From apply(Future&lt;? extends From&gt; from) { if (from==null) throw new NullPointerException("Null argument in call with Getter."); return getter(from, IEH, EEH); } private static &lt;T&gt; T getter(Future&lt;T&gt; src, ExceptionHandler&lt;InterruptedException,?&gt; IEH, ExceptionHandler&lt;ExecutionException,?&gt; EEH) { try { return src.get(); } catch (InterruptedException e) { IEH.handle(e); } catch (ExecutionException e) { EEH.handle(e); } return null; } } </code></pre> <p>which is used with the <a href="http://code.google.com/p/guava-libraries/" rel="nofollow noreferrer">Guava</a> libraries to do some embarrassingly-parallel calculations, and makes the actual Iterable transformation of Futures into something like <code>Iterables.transform(futureCollection,Getter.make())</code> instead of tangle of inner-classes and exception handling.</p>
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    1. COCould you please indent the example code a little better? It looks interesting, but it's hard to read.
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      1. USChristoffer Hammarström
 

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