XMLInputFormat is an implementation that reads records which are delimited by a specific begin/end tag. This is useful when providing logical file splits to the mapper based on a single start and end tag irrespective of the physical splits of the file.
Consider the following XML
<catalog>
<book>
<author>Gambardella, Matthew</author>
<title>XML Developer's Guide</title>
<genre>Computer</genre>
<price>44.95</price>
<publish_date>2000-10-01</publish_date>
<description>An in-depth look at creating applications
with XML.</description>
</book>
<book>
<author>Ralls, Kim</author>
<title>Midnight Rain</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2000-12-16</publish_date>
<description>A former architect battles corporate zombies,
an evil sorceress, and her own childhood to become queen
of the world.</description>
</book>
<book>
<author>Corets, Eva</author>
<title>Maeve Ascendant</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2000-11-17</publish_date>
<description>After the collapse of a nanotechnology
society in England, the young survivors lay the
foundation for a new society.</description>
</book> .....
</catalog>Setting the start_tag as <book> and end_tag as </book> for the XMLInputFormat :
Configuration conf = new Configuration();
conf.set(XmlInputFormat.START_TAG_KEY, "<book>");
conf.set(XmlInputFormat.END_TAG_KEY, "</book>");
....Job job = new Job(conf, "XML Processing Processing");
job.setInputFormatClass(XmlInputFormat.class);
....This will ensure that every mapper gets one logical entity irrespective of the physical split of the file on HDFS. (Of course the XML file on HDFS must be well-formed)
However this is not useful when you would like to extract records based on multiple start and end tags.
Consider the following XML
<catalog>
<book>
<author>Gambardella, Matthew</author>
<title>XML Developer's Guide</title>
<genre>Computer</genre>
<price>44.95</price>
<publish_date>2000-10-01</publish_date>
<description>An in-depth look at creating applications
with XML.</description>
</book>
<book>
<author>Ralls, Kim</author>
<title>Midnight Rain</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2000-12-16</publish_date>
<description>A former architect battles corporate zombies,
an evil sorceress, and her own childhood to become queen
of the world.</description>
</book>
<book>
<author>Corets, Eva</author>
<title>Maeve Ascendant</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2000-11-17</publish_date>
<description>After the collapse of a nanotechnology
society in England, the young survivors lay the
foundation for a new society.</description>
</book>
<article>
<author>Corets, Eva</author>
<title>Oberon's Legacy</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2001-03-10</publish_date>
<description>In post-apocalypse England, the mysterious
agent known only as Oberon helps to create a new life
for the inhabitants of London. Sequel to Maeve
Ascendant.</description>
</article>
<paper>
<author>Corets, Eva</author>
<title>The Sundered Grail</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2001-09-10</publish_date>
<description>The two daughters of Maeve, half-sisters,
battle one another for control of England. Sequel to
Oberon's Legacy.</description>
</paper>
<article>
<author>Randall, Cynthia</author>
<title>Lover Birds</title>
<genre>Romance</genre>
<price>4.95</price>
<publish_date>2000-09-02</publish_date>
<description>When Carla meets Paul at an ornithology
conference, tempers fly as feathers get ruffled.</description>
</article>
<paper>
<author>Thurman, Paula</author>
<title>Splish Splash</title>
<genre>Romance</genre>
<price>4.95</price>
<publish_date>2000-11-02</publish_date>
<description>A deep sea diver finds true love twenty
thousand leagues beneath the sea.</description>
</paper>
.....
</catalog>If you want to grab all those entities within <book></book>, <article></article>,<paper></paper> use this XMLInputFormatWithMultipleTags as :
Configuration conf = new Configuration();
conf.set(XmlInputFormatWithMultipleTags.START_TAG_KEYS, "<book>,<article>,<paper>");
conf.set(XmlInputFormatWithMultipleTags.END_TAG_KEYS, "</book>,</article>,</paper>");Note that multiple tags are delimeted by a comma (,)
Job job = new Job(conf, XmlInputFormatWithMultipleTags.class);
....
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