JPAReaderPattern
JPAReaderPattern 模式用于从使用 OpenJPA 的数据库检索数据。
支持类
JPAReader 类执行以下任务:获取实体管理器,运行用户提供的查询以及对查询的结果进行迭代处理。需要将 persistence.xml 文件打包在用户应用程序中。
必需属性
以下属性对于该模式是必需的。
属性名称 | 值 |
---|---|
PATTERN_IMPL_CLASS | 实现 JPAReader 模式接口的类 |
PERSISTENT_UNIT | OpenJPA 持久性单元名称。 |
可选属性
以下属性对于该模式是可选的。
属性名称 | 值 | 描述 |
---|---|---|
debug | true 或 false(缺省值为 false) | 在此批处理数据流上启用详细跟踪。 |
openjpa.Log | DefaultLevel=WARN,SQL=TRACE | JPA 日志设置 |
EnablePerformanceMeasurement | true 或 false(缺省值为 false) | 如果正使用 GenericXDBatchStep,那么计算批处理数据流和 processRecord 方法中所花的总时间。 |
EnableDetailedPerformanceMeasurement | true 或 false(缺省值为 false) | 提供在批处理数据流的每个方法中花费的更为详细的时间细目。 |
接口定义
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 示例
<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>