我正在使用Eclipselink JPA,并且我想要写一个数据库实体的集合,以防我的数据库连接在后续查询中不可用。我想使用Moxy简单地编组我的整个结果集,然后在以后的时间解密该文件,从而重新创建我的原始结果集(这是我的JPA实体对象)。由于Eclipselink和Moxy有些集成,我想在我的JPA代码中知道例如:
public void getDataFROMDATABASE() {
factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME,getProperties());
EntityManager em = factory.createEntityManager();
// Read the existing entries and write to console
TypedQuery<CtoPolicyMatrix> query = em.createQuery("SELECT pm FROM CtoPolicyMatrix pm", CtoPolicyMatrix.class);
List<CtoPolicyMatrix> results = query.getResultList();
**//NOW PRESIST RESULTS to file IN CASE OF DB CONNECTION FAILURE**
presistMatrixData(results);
em.close();
}
public void presistMatrixData(List results){
// Save CtoPolicyMatrix to XML
try {
jc = JAXBContext.newInstance(CtoPolicyMatrix.class);
Marshaller marshaller = jc.createMarshaller();
StringWriter writer = new StringWriter();
marshaller.marshal(results, writer);
**???? NOT SURE WHAT TO DO HERE TO WRITE MY COLLECTION TO FILE**
} catch (JAXBException e) {
e.printStackTrace();
}
}
public void retrieveMatrixData(List results){
// Load CtoPolicyMatrix from XML
**???? REALLY NOT SURE HOW TO RETRIEVE MY JPA ENTITY COLLECTION FROM FILE**
Unmarshaller unmarshaller;
try {
unmarshaller = jc.createUnmarshaller();
StringReader reader = new StringReader(writer.toString());
List<CtoPolicyMatrix> savedResults = (List<CtoPolicyMatrix>)
Unmarshaller.unmarshal(reader);
} catch (JAXBException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
感谢您提供的任何帮助。
答案 0 :(得分:2)
你走在正确的轨道上。为了使事情变得尽可能简单,我建议创建一个包装器对象来包含结果列表,然后编组/解组该包装器对象。
包装器对象可能如下所示:
import java.util.List;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement
public class MatrixData {
private List<CtoPolicyMatrix> data;
public List<CtoPolicyMatrix> getData() {
return data;
}
public void setData(List<CtoPolicyMatrix> data) {
this.data = data;
}
}
你的persistMatrixData方法如下所示:
public void persistMatrixData(List results) {
// Save CtoPolicyMatrix to XML
try {
MatrixData data = new MatrixData();
data.setData(results);
File file = new File("D:/Temp/MatrixData.xml");
jc = JAXBContext.newInstance(MatrixData.class);
Marshaller marshaller = jc.createMarshaller();
marshaller.marshal(data, file);
} catch (JAXBException e) {
e.printStackTrace();
}
}
阅读它们:
public void retrieveMatrixData(List results) {
// Load CtoPolicyMatrix from XML
Unmarshaller unmarshaller;
try {
File file = new File("D:/Temp/MatrixData.xml");
unmarshaller = jc.createUnmarshaller();
MatrixData data = (MatrixData) u.unmarshal(file);
List<CtoPolicyMatrix> savedResults = data.getData();
} catch (JAXBException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
希望这有帮助,
瑞克