我遇到了一段代码,它读取了一些数据,如下所示:
public class StudioReader implements ItemReader<List<Studio>> {
@Setter private AreaDao areaDao;
@Getter @Setter private BatchContext context;
private HopsService hopsService = new HopsService();
@Override
public List<Studio> read() throws Exception {
List<Studio> list = hopsService.getStudioHops();
if (!isEmpty(list)) {
for (Studio studio : list) {
log.info("Studio being read: {}", studio.getCode());
List areaList = areaDao.getArea(studio
.getCode());
if (areaList.size() > 0) {
studio.setArea((String) areaList.get(0));
log.info("Area {1} is fetched for studio {2}", areaList.get(0), studio.getCode());
}
this.getContext().setReadCount(1);
}
}
return list;
}
但是,当我运行该作业时,此读取正在循环中运行.我从另一个stackoverflow answer发现它是预期的行为.那么我的问题是,在这个特定的例子中,最佳解决方案是什么?从JdbcCursorItemReader扩展StudioReader?我找到了一个定义xml中我不想要的东西的例子.这是读者的context.xml部分:
<bean class="org.springframework.batch.core.scope.StepScope" />
<bean id="ItemReader" class="com.syc.studio.reader.StudioReader" scope="step">
<property name="context" ref="BatchContext" />
<property name="areaDao" ref="AreaDao" />
</bean>
这是xml中的作业定义:
<bean id="StudioJob" class="org.springframework.batch.core.job.SimpleJob">
<property name="steps">
<list>
<bean id="StudioStep" parent="SimpleStep" >
<property name="itemReader" ref="ItemReader"/>
<property name="itemWriter" ref="ItemWriter"/>
<property name="retryableExceptionClasses">
<map>
<entry key="com.syc.studio.exception.CustomException" value="true"/>
</map>
</property>
<property name="retryLimit" value="2" />
</bean>
</list>
</property>
<property name="jobRepository" ref="jobRepository" />
</bean>
作家:
public void write(List<? extends Object> obj) throws Exception {
List<Studio> list = (List<Studio>) obj.get(0);
for (int i = 0; i <= list.size(); i++) {
Studio studio = list.get(i);
if (apiClient == null) {
apiClient = new APIClient("v2");
}
this.uploadXML(studio);
}
@ holi-java建议后的read方法:
public List<Studio> read() throws Exception {
if (this.listIterator == null) {
this.listIterator = initializing();
}
return this.listIterator.hasNext() ? this.listIterator.next() : null;
}
private Iterator<List<Studio>> initializing() {
List<Studio> listOfStudiosFromApi = hopsService.getStudioLocations();
for (Studio studio : listOfStudiosFromApi) {
log.info("Studio being read: {}", studio.getCode());
List areaList = areaDao.getArea(studio.getCode());
if (areaList.size() > 0) {
studio.setArea((String) areaList.get(0));
log.info("Area {1} is fetched for studio {2}", areaList.get(0), studio.getCode());
}
this.getContext().setReadCount(1);
}
return Collections.singletonList(listOfStudiosFromApi).iterator();
}
最佳答案 ItemReader.read断言的弹簧批文档:
Implementations must return null at the end of the input data set.
但是你的read方法总是返回一个List,应该是这样的:
public Studio read() throws Exception {
if (this.results == null) {
List<Studio> list = hopsService.getStudioHops();
...
this.results=list.iterator();
}
return this.results.hasNext() ? this.results.next() : null;
}
如果你想让你的read方法返回一个List,你必须像这样分页结果:
public List<Studio> read() throws Exception {
List<Studio> results=hopsService.getStudioHops(this.page++);
...
return results.isEmpty()?null:results;
}
如果您无法从服务中分页结果,您可以这样解决:
public List<Studio> read() throws Exception {
if(this.results==null){
this.results = Collections.singletonList(hopsService.getStudioHops()).iterator();
}
return this.results.hasNext()?this.results.next():null;
}
最好不要读取列表< Studio>项目列表,而是在Studio时刻读取项目.当您阅读项目列表时,您可能会重复在编写器和处理器之间迭代逻辑,因为您已在注释中显示演示.如果您有大量的数据列表要处理,您可以在阅读器中组合分页,例如:
public Studio read() throws Exception {
if (this.results == null || !this.results.hasNext()) {
List<Studio> list = hopsService.getStudioHops(this.page++);
...
this.results=list.iterator();
}
return this.results.hasNext() ? this.results.next() : null;
}
也许你需要看step processing mechanism.
> ItemReader – 一次阅读一个项目.
> ItemProcessor – 一次处理一个项目.
> ItemWriter – 写出entire chunk of items.