简介
为了从数据库中提取一些数据,我正在尝试设置一个基本的 Hibernate 和 Spring Batch 项目。目标是提供一个查询(HQL),并基于此查询,Spring Batch 应用程序将所有数据提取到一个平面文件中。
应用程序的要求之一是用户不必配置列的映射。因此,我试图创建一个 DynamicRecordProcessor,它评估输入并将输入(例如地址的表)传递给编写器,以便平面文件项编写器可以使用 PassThroughFieldExtractor。
读取器-处理器-写入器 xml 配置下方:
<!-- Standard Spring Hibernate Reader -->
<bean id="hibernateItemReader" class="org.springframework.batch.item.database.HibernateCursorItemReader">
<property name="sessionFactory" ref="sessionFactory" />
<property name="queryString" value="from Address" />
</bean>
<!-- Custom Processor -->
<bean id="dynamicRecordProcessor" class="nl.sander.mieras.processor.DynamicRecordProcessor"/>
<!-- Standard Spring Writer -->
<bean id="itemWriter" class="org.springframework.batch.item.file.FlatFileItemWriter">
<property name="resource" value="file:target/extract/output.txt" />
<property name="lineAggregator">
<bean class="org.springframework.batch.item.file.transform.DelimitedLineAggregator">
<property name="delimiter" value="|"/>
<property name="fieldExtractor">
<bean class="org.springframework.batch.item.file.transform.PassThroughFieldExtractor"/>
</property>
</bean>
</property>
</bean>
编辑: 以及作业配置:
<bean id="jobLauncher" class="org.springframework.batch.core.launch.support.SimpleJobLauncher">
<property name="jobRepository" ref="jobRepository" />
</bean>
<bean id="jobRepository" class="org.springframework.batch.core.repository.support.MapJobRepositoryFactoryBean">
<property name="transactionManager" ref="transactionManager"/>
</bean>
<bean id="sessionFactory" class="org.springframework.orm.hibernate5.LocalSessionFactoryBean">
<property name="configLocation" value="classpath:hibernate.cfg.xml"/>
<property name="cacheableMappingLocations" value="classpath*:META-INF/mappings/*.hbm.xml"/>
</bean>
<bean id="transactionManager" class="org.springframework.orm.hibernate5.HibernateTransactionManager" lazy-init="true">
<property name="sessionFactory" ref="sessionFactory" />
</bean>
问题
我的处理器如下所示:
public class DynamicRecordProcessor<Input,Output> implements ItemProcessor<Input,Output> {
private static final String DELIMITER = "|";
private boolean areNamesSetup = false;
private List<String> names = new ArrayList<String>();
private Input item;
@SuppressWarnings("unchecked")
@Override
public Output process(Input item) throws Exception {
this.item = item;
initMapping();
return (Output) extract();
}
private void initMapping() {
if (!areNamesSetup) {
mapColumns();
}
areNamesSetup = true;
}
private void mapColumns() {
Field[] allFields = item.getClass().getDeclaredFields();
for (Field field : allFields) {
if (!field.getType().equals(Set.class) && Modifier.isPrivate(field.getModifiers())) {
names.add(field.getName());
}
}
}
private Object extract() {
List<Object> values = new ArrayList<Object>();
BeanWrapper bw = new BeanWrapperImpl(item);
for (String propertyName : this.names) {
values.add(bw.getPropertyValue(propertyName));
}
return StringUtils.collectionToDelimitedString(values, DELIMITER);
}
}
表地址具有以下字段:
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="city_id", nullable=false)
public City getCity() {
return this.city;
}
城市对应的列:
@Column(name="city_id", unique=true, nullable=false)
public Short getCityId() {
return this.cityId;
}
当使用 values.add(bw.getPropertyValue(propertyName));
且 propertyName 为“city”时,会发生以下异常:
org.hibernate.SessionException: proxies cannot be fetched by a stateless session
at org.hibernate.internal.StatelessSessionImpl.immediateLoad(StatelessSessionImpl.java:292)
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:156)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:260)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:68)
at nl.sander.mieras.localhost.sakila.City_$$_jvstc2c_d.toString(City_$$_jvstc2c_d.java)
at java.lang.String.valueOf(String.java:2982)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at org.springframework.util.StringUtils.collectionToDelimitedString(StringUtils.java:1132)
at org.springframework.util.StringUtils.collectionToDelimitedString(StringUtils.java:1148)
at nl.sander.mieras.processor.DynamicRecordProcessor.extract(DynamicRecordProcessor.java:52)
at nl.sander.mieras.processor.DynamicRecordProcessor.process(DynamicRecordProcessor.java:27)
具体问题:如何获得值 300?
我尝试使用反射 API 获取值,但无法达到我想要获取的实际值...
重现
我已经设置了一个公共(public)存储库。但是,您仍然需要本地数据库才能准确重现问题。 https://github.com/Weirdfishees/hibernate-batch-example 。我们非常欢迎任何关于如何进一步隔离此问题的建议。
最佳答案
只需使用 useStatelessSession
属性将您的阅读器切换为全状态而不是无状态:
<!-- Standard Spring Hibernate Reader -->
<bean id="hibernateItemReader" class="org.springframework.batch.item.database.HibernateCursorItemReader">
<property name="sessionFactory" ref="sessionFactory" />
<property name="queryString" value="from Address" />
<property name="useStatelessSession" value="false" />
</bean>
关于java - 如何使用 Spring Batch 和 Hibernate 从 @JoinColumn 获取值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/36893089/