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    <p>Following up on my comment, the Javadocs for <code>TaggedInputSplit</code> confirms that you are probably wrongly casting the input split to a FileSplit:</p> <pre><code>/** * An {@link InputSplit} that tags another InputSplit with extra data for use * by {@link DelegatingInputFormat}s and {@link DelegatingMapper}s. */ </code></pre> <p>My guess is your setup method looks something like this:</p> <pre><code>@Override protected void setup(Context context) throws IOException, InterruptedException { FileSplit split = (FileSplit) context.getInputSplit(); } </code></pre> <p>Unfortunately <code>TaggedInputSplit</code> is not public visible, so you can't easily do an <code>instanceof</code> style check, followed by a cast and then call to <code>TaggedInputSplit.getInputSplit()</code> to get the actual underlying FileSplit. So either you'll need to update the source yourself and re-compile&amp;deploy, post a JIRA ticket to ask this to be fixed in future version (if it already hasn't been actioned in 2+) or perform some nasty <em>nasty</em> reflection hackery to get to the underlying InputSplit</p> <p>This is completely untested:</p> <pre><code>@Override protected void setup(Context context) throws IOException, InterruptedException { InputSplit split = context.getInputSplit(); Class&lt;? extends InputSplit&gt; splitClass = split.getClass(); FileSplit fileSplit = null; if (splitClass.equals(FileSplit.class)) { fileSplit = (FileSplit) split; } else if (splitClass.getName().equals( "org.apache.hadoop.mapreduce.lib.input.TaggedInputSplit")) { // begin reflection hackery... try { Method getInputSplitMethod = splitClass .getDeclaredMethod("getInputSplit"); getInputSplitMethod.setAccessible(true); fileSplit = (FileSplit) getInputSplitMethod.invoke(split); } catch (Exception e) { // wrap and re-throw error throw new IOException(e); } // end reflection hackery } } </code></pre> <p><strong>Reflection Hackery Explained:</strong></p> <p>With TaggedInputSplit being declared protected scope, it's not visible to classes outside the <code>org.apache.hadoop.mapreduce.lib.input</code> package, and therefore you cannot reference that class in your setup method. To get around this, we perform a number of reflection based operations:</p> <ol> <li><p>Inspecting the class name, we can test for the type TaggedInputSplit using it's fully qualified name</p> <p><code>splitClass.getName().equals("org.apache.hadoop.mapreduce.lib.input.TaggedInputSplit")</code></p></li> <li><p>We know we want to call the <code>TaggedInputSplit.getInputSplit()</code> method to recover the wrapped input split, so we utilize the <code>Class.getMethod(..)</code> reflection method to acquire a reference to the method:</p> <p><code>Method getInputSplitMethod = splitClass.getDeclaredMethod("getInputSplit");</code></p></li> <li><p>The class still isn't public visible so we use the setAccessible(..) method to override this, stopping the security manager from throwing an exception</p> <p><code>getInputSplitMethod.setAccessible(true);</code></p></li> <li><p>Finally we invoke the method on the reference to the input split and cast the result to a FileSplit (optimistically hoping its a instance of this type!):</p> <p><code>fileSplit = (FileSplit) getInputSplitMethod.invoke(split);</code></p></li> </ol>
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    1. USChris White
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    1. COIt is exactly the same as what you guessed. I tried your code and it is working now. You are so pro!
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    2. COI read the codes again but I am still not sure how it works. Can you give a brief explanation about reflection hackery? Thanks.
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    3. COSee the added section at the end
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