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BATCH-667:Added a section to Chapter 3 about the 'saveSate' property.

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lucasward
2008-07-07 18:51:48 +00:00
parent eb7e8f7ebb
commit dbd859f106
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docs/src/site/docbook/reference/readersAndWriters.xml
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@@ -2199,6 +2199,52 @@
</section>
</section>
<section>
<title>Preventing state persistence</title>
<para>By default, all of the <classname>ItemReader</classname> and
<classname>ItemWriter</classname> implementations store their current
state in the <classname>ExecutionContext</classname> before it is
committed. However, this may not always be the desired behavior. For
example, many developers choose to make their database readers
'rerunnable' by using a process indicator. An extra column is added to the
input data to indicate whether or not it has been processed. When a
particular record is being read (or written out) the processed flag is
flipped from false to true. The SQL statement can then contain an extra
statement in the where clause, such as: "where PROCESSED_IND = false",
thereby insuring that only unprocessed records will be returned in the
case of a restart. In this scenario, it is prefereable to not store any
state, such as the current row number, since it will be irrelevant upon
restart. For this reason, all readers and writers include the 'saveState'
property:</para>
<programlisting>
&lt;bean id="playerSummarizationSource"
class="org.springframework.batch.item.database.JdbcCursorItemReader"&gt;
&lt;property name="dataSource" ref="dataSource" /&gt;
&lt;property name="mapper"&gt;
&lt;bean class="org.springframework.batch.sample.mapping.PlayerSummaryMapper" /&gt;
&lt;/property&gt;
&lt;property name="saveState" value="false" /&gt;
&lt;property name="sql"&gt;
&lt;value&gt;
SELECT games.player_id, games.year_no, SUM(COMPLETES),
SUM(ATTEMPTS), SUM(PASSING_YARDS), SUM(PASSING_TD),
SUM(INTERCEPTIONS), SUM(RUSHES), SUM(RUSH_YARDS),
SUM(RECEPTIONS), SUM(RECEPTIONS_YARDS), SUM(TOTAL_TD)
from games, players where players.player_id =
games.player_id group by games.player_id, games.year_no
&lt;/value&gt;
&lt;/property&gt;
&lt;/bean&gt;
</programlisting>
<para>The <classname>ItemReader</classname> configured above will not make
any entries in the <classname>ExecutionContext</classname> for any
executions it participates in.</para>
</section>
<section>
<title id="infrastructure.1.1">Creating Custom ItemReaders and
ItemWriters</title>