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7ChainMapper (Hadoop 0.20.1 API)
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91org.apache.hadoop.mapred.lib</FONT>
92<BR>
93Class ChainMapper</H2>
94<PRE>
95<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">java.lang.Object</A>
96  <IMG SRC="../../../../../resources/inherit.gif" ALT="extended by "><B>org.apache.hadoop.mapred.lib.ChainMapper</B>
97</PRE>
98<DL>
99<DT><B>All Implemented Interfaces:</B> <DD><A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true" title="class or interface in java.io">Closeable</A>, <A HREF="../../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A>, <A HREF="../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</A></DD>
100</DL>
101<HR>
102<DL>
103<DT><PRE>public class <B>ChainMapper</B><DT>extends <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A><DT>implements <A HREF="../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</A></DL>
104</PRE>
105
106<P>
107The ChainMapper class allows to use multiple Mapper classes within a single
108 Map task.
109 <p/>
110 The Mapper classes are invoked in a chained (or piped) fashion, the output of
111 the first becomes the input of the second, and so on until the last Mapper,
112 the output of the last Mapper will be written to the task's output.
113 <p/>
114 The key functionality of this feature is that the Mappers in the chain do not
115 need to be aware that they are executed in a chain. This enables having
116 reusable specialized Mappers that can be combined to perform composite
117 operations within a single task.
118 <p/>
119 Special care has to be taken when creating chains that the key/values output
120 by a Mapper are valid for the following Mapper in the chain. It is assumed
121 all Mappers and the Reduce in the chain use maching output and input key and
122 value classes as no conversion is done by the chaining code.
123 <p/>
124 Using the ChainMapper and the ChainReducer classes is possible to compose
125 Map/Reduce jobs that look like <code>[MAP+ / REDUCE MAP*]</code>. And
126 immediate benefit of this pattern is a dramatic reduction in disk IO.
127 <p/>
128 IMPORTANT: There is no need to specify the output key/value classes for the
129 ChainMapper, this is done by the addMapper for the last mapper in the chain.
130 <p/>
131 ChainMapper usage pattern:
132 <p/>
133 <pre>
134 ...
135 conf.setJobName("chain");
136 conf.setInputFormat(TextInputFormat.class);
137 conf.setOutputFormat(TextOutputFormat.class);
138 <p/>
139 JobConf mapAConf = new JobConf(false);
140 ...
141 ChainMapper.addMapper(conf, AMap.class, LongWritable.class, Text.class,
142   Text.class, Text.class, true, mapAConf);
143 <p/>
144 JobConf mapBConf = new JobConf(false);
145 ...
146 ChainMapper.addMapper(conf, BMap.class, Text.class, Text.class,
147   LongWritable.class, Text.class, false, mapBConf);
148 <p/>
149 JobConf reduceConf = new JobConf(false);
150 ...
151 ChainReducer.setReducer(conf, XReduce.class, LongWritable.class, Text.class,
152   Text.class, Text.class, true, reduceConf);
153 <p/>
154 ChainReducer.addMapper(conf, CMap.class, Text.class, Text.class,
155   LongWritable.class, Text.class, false, null);
156 <p/>
157 ChainReducer.addMapper(conf, DMap.class, LongWritable.class, Text.class,
158   LongWritable.class, LongWritable.class, true, null);
159 <p/>
160 FileInputFormat.setInputPaths(conf, inDir);
161 FileOutputFormat.setOutputPath(conf, outDir);
162 ...
163 <p/>
164 JobClient jc = new JobClient(conf);
165 RunningJob job = jc.submitJob(conf);
166 ...
167 </pre>
168<P>
169
170<P>
171<HR>
172
173<P>
174
175<!-- ======== CONSTRUCTOR SUMMARY ======== -->
176
177<A NAME="constructor_summary"><!-- --></A>
178<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
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180<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
181<B>Constructor Summary</B></FONT></TH>
182</TR>
183<TR BGCOLOR="white" CLASS="TableRowColor">
184<TD><CODE><B><A HREF="../../../../../org/apache/hadoop/mapred/lib/ChainMapper.html#ChainMapper()">ChainMapper</A></B>()</CODE>
185
186<BR>
187&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Constructor.</TD>
188</TR>
189</TABLE>
190&nbsp;
191<!-- ========== METHOD SUMMARY =========== -->
192
193<A NAME="method_summary"><!-- --></A>
194<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
195<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
196<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
197<B>Method Summary</B></FONT></TH>
198</TR>
199<TR BGCOLOR="white" CLASS="TableRowColor">
200<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
201<CODE>static
202<TABLE BORDER="0" CELLPADDING="0" CELLSPACING="0" SUMMARY="">
203<TR ALIGN="right" VALIGN="">
204<TD NOWRAP><FONT SIZE="-1">
205<CODE>&lt;K1,V1,K2,V2&gt; 
206<BR>
207void</CODE></FONT></TD>
208</TR>
209</TABLE>
210</CODE></FONT></TD>
211<TD><CODE><B><A HREF="../../../../../org/apache/hadoop/mapred/lib/ChainMapper.html#addMapper(org.apache.hadoop.mapred.JobConf, java.lang.Class, java.lang.Class, java.lang.Class, java.lang.Class, java.lang.Class, boolean, org.apache.hadoop.mapred.JobConf)">addMapper</A></B>(<A HREF="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</A>&nbsp;job,
212          <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends <A HREF="../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</A>&lt;K1,V1,K2,V2&gt;&gt;&nbsp;klass,
213          <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends K1&gt;&nbsp;inputKeyClass,
214          <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends V1&gt;&nbsp;inputValueClass,
215          <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends K2&gt;&nbsp;outputKeyClass,
216          <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends V2&gt;&nbsp;outputValueClass,
217          boolean&nbsp;byValue,
218          <A HREF="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</A>&nbsp;mapperConf)</CODE>
219
220<BR>
221&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Adds a Mapper class to the chain job's JobConf.</TD>
222</TR>
223<TR BGCOLOR="white" CLASS="TableRowColor">
224<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
225<CODE>&nbsp;void</CODE></FONT></TD>
226<TD><CODE><B><A HREF="../../../../../org/apache/hadoop/mapred/lib/ChainMapper.html#close()">close</A></B>()</CODE>
227
228<BR>
229&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Closes  the ChainMapper and all the Mappers in the chain.</TD>
230</TR>
231<TR BGCOLOR="white" CLASS="TableRowColor">
232<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
233<CODE>&nbsp;void</CODE></FONT></TD>
234<TD><CODE><B><A HREF="../../../../../org/apache/hadoop/mapred/lib/ChainMapper.html#configure(org.apache.hadoop.mapred.JobConf)">configure</A></B>(<A HREF="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</A>&nbsp;job)</CODE>
235
236<BR>
237&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Configures the ChainMapper and all the Mappers in the chain.</TD>
238</TR>
239<TR BGCOLOR="white" CLASS="TableRowColor">
240<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
241<CODE>&nbsp;void</CODE></FONT></TD>
242<TD><CODE><B><A HREF="../../../../../org/apache/hadoop/mapred/lib/ChainMapper.html#map(java.lang.Object, java.lang.Object, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">map</A></B>(<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A>&nbsp;key,
243    <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A>&nbsp;value,
244    <A HREF="../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&nbsp;output,
245    <A HREF="../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;reporter)</CODE>
246
247<BR>
248&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Chains the <code>map(...)</code> methods of the Mappers in the chain.</TD>
249</TR>
250</TABLE>
251&nbsp;<A NAME="methods_inherited_from_class_java.lang.Object"><!-- --></A>
252<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
253<TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor">
254<TH ALIGN="left"><B>Methods inherited from class java.lang.<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A></B></TH>
255</TR>
256<TR BGCOLOR="white" CLASS="TableRowColor">
257<TD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#clone()" title="class or interface in java.lang">clone</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#equals(java.lang.Object)" title="class or interface in java.lang">equals</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#finalize()" title="class or interface in java.lang">finalize</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#getClass()" title="class or interface in java.lang">getClass</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#hashCode()" title="class or interface in java.lang">hashCode</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#notify()" title="class or interface in java.lang">notify</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#notifyAll()" title="class or interface in java.lang">notifyAll</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#toString()" title="class or interface in java.lang">toString</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait()" title="class or interface in java.lang">wait</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait(long)" title="class or interface in java.lang">wait</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait(long, int)" title="class or interface in java.lang">wait</A></CODE></TD>
258</TR>
259</TABLE>
260&nbsp;
261<P>
262
263<!-- ========= CONSTRUCTOR DETAIL ======== -->
264
265<A NAME="constructor_detail"><!-- --></A>
266<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
267<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
268<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
269<B>Constructor Detail</B></FONT></TH>
270</TR>
271</TABLE>
272
273<A NAME="ChainMapper()"><!-- --></A><H3>
274ChainMapper</H3>
275<PRE>
276public <B>ChainMapper</B>()</PRE>
277<DL>
278<DD>Constructor.
279<P>
280</DL>
281
282<!-- ============ METHOD DETAIL ========== -->
283
284<A NAME="method_detail"><!-- --></A>
285<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
286<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
287<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
288<B>Method Detail</B></FONT></TH>
289</TR>
290</TABLE>
291
292<A NAME="addMapper(org.apache.hadoop.mapred.JobConf, java.lang.Class, java.lang.Class, java.lang.Class, java.lang.Class, java.lang.Class, boolean, org.apache.hadoop.mapred.JobConf)"><!-- --></A><H3>
293addMapper</H3>
294<PRE>
295public static &lt;K1,V1,K2,V2&gt; void <B>addMapper</B>(<A HREF="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</A>&nbsp;job,
296                                           <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends <A HREF="../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</A>&lt;K1,V1,K2,V2&gt;&gt;&nbsp;klass,
297                                           <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends K1&gt;&nbsp;inputKeyClass,
298                                           <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends V1&gt;&nbsp;inputValueClass,
299                                           <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends K2&gt;&nbsp;outputKeyClass,
300                                           <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Class.html?is-external=true" title="class or interface in java.lang">Class</A>&lt;? extends V2&gt;&nbsp;outputValueClass,
301                                           boolean&nbsp;byValue,
302                                           <A HREF="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</A>&nbsp;mapperConf)</PRE>
303<DL>
304<DD>Adds a Mapper class to the chain job's JobConf.
305 <p/>
306 It has to be specified how key and values are passed from one element of
307 the chain to the next, by value or by reference. If a Mapper leverages the
308 assumed semantics that the key and values are not modified by the collector
309 'by value' must be used. If the Mapper does not expect this semantics, as
310 an optimization to avoid serialization and deserialization 'by reference'
311 can be used.
312 <p/>
313 For the added Mapper the configuration given for it,
314 <code>mapperConf</code>, have precedence over the job's JobConf. This
315 precedence is in effect when the task is running.
316 <p/>
317 IMPORTANT: There is no need to specify the output key/value classes for the
318 ChainMapper, this is done by the addMapper for the last mapper in the chain
319 <p/>
320<P>
321<DD><DL>
322</DL>
323</DD>
324<DD><DL>
325<DT><B>Parameters:</B><DD><CODE>job</CODE> - job's JobConf to add the Mapper class.<DD><CODE>klass</CODE> - the Mapper class to add.<DD><CODE>inputKeyClass</CODE> - mapper input key class.<DD><CODE>inputValueClass</CODE> - mapper input value class.<DD><CODE>outputKeyClass</CODE> - mapper output key class.<DD><CODE>outputValueClass</CODE> - mapper output value class.<DD><CODE>byValue</CODE> - indicates if key/values should be passed by value
326 to the next Mapper in the chain, if any.<DD><CODE>mapperConf</CODE> - a JobConf with the configuration for the Mapper
327 class. It is recommended to use a JobConf without default values using the
328 <code>JobConf(boolean loadDefaults)</code> constructor with FALSE.</DL>
329</DD>
330</DL>
331<HR>
332
333<A NAME="configure(org.apache.hadoop.mapred.JobConf)"><!-- --></A><H3>
334configure</H3>
335<PRE>
336public void <B>configure</B>(<A HREF="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</A>&nbsp;job)</PRE>
337<DL>
338<DD>Configures the ChainMapper and all the Mappers in the chain.
339 <p/>
340 If this method is overriden <code>super.configure(...)</code> should be
341 invoked at the beginning of the overwriter method.
342<P>
343<DD><DL>
344<DT><B>Specified by:</B><DD><CODE><A HREF="../../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure(org.apache.hadoop.mapred.JobConf)">configure</A></CODE> in interface <CODE><A HREF="../../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A></CODE></DL>
345</DD>
346<DD><DL>
347<DT><B>Parameters:</B><DD><CODE>job</CODE> - the configuration</DL>
348</DD>
349</DL>
350<HR>
351
352<A NAME="map(java.lang.Object, java.lang.Object, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><!-- --></A><H3>
353map</H3>
354<PRE>
355public void <B>map</B>(<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A>&nbsp;key,
356                <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A>&nbsp;value,
357                <A HREF="../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A>&nbsp;output,
358                <A HREF="../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A>&nbsp;reporter)
359         throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
360<DL>
361<DD>Chains the <code>map(...)</code> methods of the Mappers in the chain.
362<P>
363<DD><DL>
364<DT><B>Specified by:</B><DD><CODE><A HREF="../../../../../org/apache/hadoop/mapred/Mapper.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">map</A></CODE> in interface <CODE><A HREF="../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</A></CODE></DL>
365</DD>
366<DD><DL>
367<DT><B>Parameters:</B><DD><CODE>key</CODE> - the input key.<DD><CODE>value</CODE> - the input value.<DD><CODE>output</CODE> - collects mapped keys and values.<DD><CODE>reporter</CODE> - facility to report progress.
368<DT><B>Throws:</B>
369<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
370</DD>
371</DL>
372<HR>
373
374<A NAME="close()"><!-- --></A><H3>
375close</H3>
376<PRE>
377public void <B>close</B>()
378           throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
379<DL>
380<DD>Closes  the ChainMapper and all the Mappers in the chain.
381 <p/>
382 If this method is overriden <code>super.close()</code> should be
383 invoked at the end of the overwriter method.
384<P>
385<DD><DL>
386<DT><B>Specified by:</B><DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true#close()" title="class or interface in java.io">close</A></CODE> in interface <CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true" title="class or interface in java.io">Closeable</A></CODE></DL>
387</DD>
388<DD><DL>
389
390<DT><B>Throws:</B>
391<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
392</DD>
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