JPAReaderPattern
The JPAReaderPattern pattern is used to retrieve data from a database using OpenJPA.
Supporting classes
The JPAReader class performs the tasks of obtaining an entity manager, running user provided queries, and iterating over the results of the query. A persistence.xml file needs to be packaged with the user application.
Required properties
The following properties are required for the pattern.
Property name | Value |
---|---|
PATTERN_IMPL_CLASS | Class implementing JPAReader Pattern interface |
PERSISTENT_UNIT | The OpenJPA persistent unit name. |
Optional properties
The following properties are optional for the pattern.
Property name | Value | Description |
---|---|---|
debug | true or false (default is false) | Enables detailed tracing on this batch data stream. |
openjpa.Log | DefaultLevel=WARN,SQL=TRACE |
JPA log settings |
EnablePerformanceMeasurement | true or false (default is false) | Calculates the total time spent in the batch data streams and the processRecord method, if you are using the GenericXDBatchStep. |
EnableDetailedPerformanceMeasurement | true or false (default is false) | Provides a more detailed breakdown of time spent in each method of the batch data streams. |
Interface definition
public interface JPAReaderPattern {
/**
* This method is invoked during the job setup phase.
*
* @param props properties provided in the xJCL
*/
public void initialize(Properties props);
/**
* This method should retrieve values for the various columns for the current row from
* the given Iterator object. Typically this data would be used to populate an intermediate
* object which would be returned.
* @param listIt
* @return
*/
public Object fetchRecord(Iterator listIt);
/**
* This method should return a JPQL query that will be used during setup of the stream to
* retrieve all relevant data that would be processed part of the job steps.
* @return object to be used during process step.
*/
public String getInitialLookupQuery();
/**
* This method gets called during Job Restart. The restart token should be used to create
* a JPQL query that retrieves previously unprocessed records. Typically the restart token
* is the primary key in the table and the query would get all rows with
* primary key value > restarttoken
* @param restartToken
* @return The restart query
*/
public String getRestartQuery(String restartToken);
/**
* This method gets called just before a checkpoint is taken.
* @return The method should return a string value identifying the last record read by the stream.
*/
public String getRestartTokens();
}
xJCL example
<batch-data-streams>
<bds>
<logical-name>inputStream</logical-name>
<props>
<prop name="PERSISTENT_UNIT" value="hellojpa"/>
<prop name="debug" value="true"/>
<prop name="PATTERN_IMPL_CLASS" value="com.ibm.websphere.samples.JPAInputStream"/>
</props>
<impl-class>com.ibm.websphere.batch.devframework.datastreams.patterns.JPAReader</impl-class>
</bds>
</batch-data-streams>