Multi-threading with Spring batch File Item Reader

Question

In a Spring Batch I am trying to read a CSV file and want to assign each row to a separate thread and process it. I have tried to achieve it by using TaskExecutor, but what is happening all the thread is picking the same row at a time. I also tried to implement the concept using Partioner, there also same thing happening. Please see below my Configuration Xml.

Step Description

    <step id="Step2">
        <tasklet task-executor="taskExecutor">
            <chunk reader="reader" processor="processor" writer="writer" commit-interval="1" skip-limit="1">
            </chunk>
        </tasklet> 
    </step>

              <bean id="reader" class="org.springframework.batch.item.file.FlatFileItemReader">
<property name="resource" value="file:cvs/user.csv" />

<property name="lineMapper">
    <bean class="org.springframework.batch.item.file.mapping.DefaultLineMapper">
      <!-- split it -->
      <property name="lineTokenizer">
            <bean
          class="org.springframework.batch.item.file.transform.DelimitedLineTokenizer">
            <property name="names" value="userid,customerId,ssoId,flag1,flag2" />
        </bean>
      </property>
      <property name="fieldSetMapper">   

          <!-- map to an object -->
          <bean
            class="org.springframework.batch.item.file.mapping.BeanWrapperFieldSetMapper">
            <property name="prototypeBeanName" value="user" />
          </bean>           
      </property>

      </bean>
  </property>

       </bean>

      <bean id="taskExecutor" class="org.springframework.core.task.SimpleAsyncTaskExecutor">
 <property name="concurrencyLimit" value="4"/>   

I have tried with different types of task executor, but all of them are behaving in same way. How can I assign each row to a separate thread?

Answer 1

FlatFileItemReader is not thread-safe. In your example you can try to split the CSV file to smaller CSV files and then use a MultiResourcePartitioner to process each one of them. This can be done in 2 steps, one for splitting the original file(like 10 smaller files) and the other for processing splitted files.This way you won't have any issues since each file will be processed by one thread.

Example:

<batch:job id="csvsplitandprocess">
     <batch:step id="step1" next="step2master">
    <batch:tasklet>
        <batch:chunk reader="largecsvreader" writer="csvwriter" commit-interval="500">
        </batch:chunk>
    </batch:tasklet>
    </batch:step>
    <batch:step id="step2master">
    <partition step="step2" partitioner="partitioner">
        <handler grid-size="10" task-executor="taskExecutor"/>
    </partition>
</batch:step>
</batch:job>

<batch:step id="step2">
    <batch:tasklet>
        <batch:chunk reader="smallcsvreader" writer="writer" commit-interval="100">
        </batch:chunk>
    </batch:tasklet>
</batch:step>


<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
            <property name="corePoolSize" value="10" />
            <property name="maxPoolSize" value="10" />
    </bean>

<bean id="partitioner" 
class="org.springframework.batch.core.partition.support.MultiResourcePartitioner">
<property name="resources" value="file:cvs/extracted/*.csv" />
</bean>

The alternative instead of partitioning might be a Custom Thread-safe Reader who will create a thread for each line, but probably partitioning is your best choice

Answer 2

You're problem is that you reader is not in scope step .

That's means : all your threads share the same input Stream (Resource file).

To have for each thread one row to process you need to :

1. Be sure that all threads read the file from the start to the end of file (Each thread should open the stream and close it for each execution context )
2. The partitioner must inject the start and end position for each execution context.
3. You're reader must read the file with this positions.

I write some code and this is the output :

Code of com.test.partitioner.RangePartitioner class :

public Map<String, ExecutionContext> partition() {

    Map < String, ExecutionContext > result = new HashMap < String, ExecutionContext >();

    int range = 1;
    int fromId = 1;
    int toId = range;

    for (int i = 1; i <= gridSize; i++) {
        ExecutionContext value = new ExecutionContext();

        log.debug("\nStarting : Thread" + i);
        log.debug("fromId : " + fromId);
        log.debug("toId : " + toId);

        value.putInt("fromId", fromId);
        value.putInt("toId", toId);

        // give each thread a name, thread 1,2,3
        value.putString("name", "Thread" + i);

        result.put("partition" + i, value);

        fromId = toId + 1;
        toId += range;

    }

    return result;
}

--> Look at the outPut console

Starting : Thread1 fromId : 1 toId : 1

Starting : Thread2 fromId : 2 toId : 2

Starting : Thread3 fromId : 3 toId : 3

Starting : Thread4 fromId : 4 toId : 4

Starting : Thread5 fromId : 5 toId : 5

Starting : Thread6 fromId : 6 toId : 6

Starting : Thread7 fromId : 7 toId : 7

Starting : Thread8 fromId : 8 toId : 8

Starting : Thread9 fromId : 9 toId : 9

Starting : Thread10 fromId : 10 toId : 10

Look at the configuration bellow :

http://www.springframework.org/schema/batch/spring-batch-2.2.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd">

<import resource="../config/context.xml" />
<import resource="../config/database.xml" />

<bean id="mouvement" class="com.test.model.Mouvement" scope="prototype" />

<bean id="itemProcessor" class="com.test.processor.CustomItemProcessor" scope="step">
    <property name="threadName" value="#{stepExecutionContext[name]}" />
</bean>
<bean id="xmlItemWriter" class="com.test.writer.ItemWriter" />

<batch:job id="mouvementImport" xmlns:batch="http://www.springframework.org/schema/batch">
    <batch:listeners>
        <batch:listener ref="myAppJobExecutionListener" />
    </batch:listeners>

    <batch:step id="masterStep">
        <batch:partition step="slave" partitioner="rangePartitioner">
            <batch:handler grid-size="10" task-executor="taskExecutor" />
        </batch:partition>
    </batch:step>
</batch:job>

<bean id="rangePartitioner" class="com.test.partitioner.RangePartitioner" />

<bean id="taskExecutor" class="org.springframework.core.task.SimpleAsyncTaskExecutor" />

<batch:step id="slave">
    <batch:tasklet>
        <batch:listeners>
            <batch:listener ref="stepExecutionListener" />
        </batch:listeners>

        <batch:chunk reader="mouvementReader" writer="xmlItemWriter" processor="itemProcessor" commit-interval="1">
        </batch:chunk>

    </batch:tasklet>
</batch:step>



<bean id="stepExecutionListener" class="com.test.listener.step.StepExecutionListenerCtxInjecter" scope="step" />

<bean id="myAppJobExecutionListener" class="com.test.listener.job.MyAppJobExecutionListener" />

<bean id="mouvementReaderParent" class="org.springframework.batch.item.file.FlatFileItemReader" scope="step">

    <property name="resource" value="classpath:XXXXX/XXXXXXXX.csv" />

    <property name="lineMapper">
        <bean class="org.springframework.batch.item.file.mapping.DefaultLineMapper">
            <property name="lineTokenizer">
                <bean class="org.springframework.batch.item.file.transform.DelimitedLineTokenizer">
                    <property name="delimiter" value="|" />
                    <property name="names"
                        value="id,numen,prenom,grade,anneeScolaire,academieOrigin,academieArrivee,codeUsi,specialiteEmploiType,natureSupport,dateEffet,modaliteAffectation" />
                </bean>
            </property>
            <property name="fieldSetMapper">
                <bean class="com.test.mapper.MouvementFieldSetMapper" />
            </property>
        </bean>
    </property>

</bean>

<!--    <bean id="itemReader" scope="step" autowire-candidate="false" parent="mouvementReaderParent">-->
<!--        <property name="resource" value="#{stepExecutionContext[fileName]}" />-->
<!--    </bean>-->

<bean id="mouvementReader" class="com.test.reader.MouvementItemReader" scope="step">
    <property name="delegate" ref="mouvementReaderParent" />
    <property name="parameterValues">
        <map>
            <entry key="fromId" value="#{stepExecutionContext[fromId]}" />
            <entry key="toId" value="#{stepExecutionContext[toId]}" />
        </map>
    </property>
</bean>

<!--    <bean id="xmlItemWriter" class="org.springframework.batch.item.xml.StaxEventItemWriter">-->
<!--        <property name="resource" value="file:xml/outputs/Mouvements.xml" />-->
<!--        <property name="marshaller" ref="reportMarshaller" />-->
<!--        <property name="rootTagName" value="Mouvement" />-->
<!--    </bean>-->

<bean id="reportMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
    <property name="classesToBeBound">
        <list>
            <value>com.test.model.Mouvement</value>
        </list>
    </property>
</bean>

TODO : Change my reader on other that read with position (start and end position) like with Scanner Class in java.

Hope this help.