我在使用Java時顯示一些JPA實體時出現問題。我對這門語言並不是很熟悉,所以我不確定是否可以結合我現在所做的事情。我有這個Student
類,這顯然代表了學生:顯示JPA實體的Java
@Entity
@Table
public class Student implements Serializable {
@Id
@GeneratedValue
private Integer id;
@Email
private String email;
@Column(unique=true)
private String studentNumber;
private String firstName;
private String lastName;
public Student() {}
public Student(String studentNumber, String firstName, String lastName, String email) {
this.studentNumber = studentNumber;
this.firstName = firstName;
this.lastName = lastName;
this.email = email;
}
現在的想法是有一個RESTful服務,並能夠通過找到他們的學生人數,顯示所有的學生,或只是那些。因此,我有這個在我的堅持類:
@Override
public Student findByStudentNumber(String studentNumber) {
Object entity = em.createQuery("SELECT * FROM students st where st.studentNumber = :val")
.setParameter("val", studentNumber).getSingleResult();
return (Student) entity;
}
@Override
public List<Student> getAll() {
List<Student> students = em.createQuery(criteriaQuery).getResultList();
return students;
}
我的控制器:
@Path("/students")
public class StudentController {
@Inject
private StudentPersistence studentPersistence;
@GET
@Path("/get")
public List<Student> getAll() {
List<Student> all = studentPersistence.getAll();
return all;
}
@GET
@Path("{studentNr}")
public Student getStudent(@PathParam("studentNr") String id) {
return studentPersistence.findByStudentNumber(id);
}
但是,我似乎無法讓他們到控制器,因爲它不斷拋出500內部服務器錯誤。我的問題是:這是結合這種方式,還是有更好的方式來顯示這些實體?
編輯:一種用於我的500錯誤堆棧跟蹤:
01-Aug-2017 14:04:24.769 SEVERE [http-nio-8081-exec-1] com.sun.jersey.spi.container.ContainerResponse.logException Mapped exception to response: 500 (Internal Server Error)
javax.ws.rs.WebApplicationException: com.sun.jersey.api.MessageException: A message body writer for Java class models.Student, and Java type class models.Student, and MIME media type application/xml was not found
at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:285)
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1479)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1391)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1381)
at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:538)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:716)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at filters.CorsFilter.doFilter(CorsFilter.java:33)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.sun.jersey.api.MessageException: A message body writer for Java class models.Student, and Java type class models.Student, and MIME media type application/xml was not found
... 33 more
500內部服務器錯誤意味着代碼有問題。請添加完整的堆棧跟蹤 – StanislavL
@StanislavL我明白了,現在就在那裏! – dnsko
@dnsko,根據你的異常判斷,你缺少的是負責將'Student' java對象轉換爲'XML'形式的代碼。 –