springmvc4+jpa在service查询关联关系表的时候返回懒加载数据，当希望获取懒加载的时候发现session已经关闭了，然而我们不希望在service层就关闭session，懒加载的数据可能还需获取。例如一对多关联关系。

一对多关系

实体类：Teacher.java//懒加载

@OneToMany(fetch= FetchType.LAZY,cascade = CascadeType.ALL)

@JoinColumn(name="teacher_id")

public Set getStudents() {

return students;

}

实体类：Student.java//懒加载

@ManyToOne(fetch= FetchType.LAZY)

@JoinColumn(name="teacher_id")

public Teacher getTeacher() {

return teacher;

}

Teacher和Student表，一对多关联关系，并加上了懒加载。

关联关系懒加载

例如在查询一条学生信息，Student关联了Teacher。

在用Jpa Repository 查询完的时候已经session已经关闭，在获取Teacher的时候抛出could not initialize proxy - no Session@Autowired

private StudentRepository studentRepository;

@Override

public Student findById(Long id){

Student student = studentRepository.findOne(id);

Teacher teacher = student.getTeacher();

System.out.println(teacher);

Set students = teacher.getStudents();

System.out.println(students);

return student;

}

解决办法

很简单的，springmvc已经为我们提供了事务注解。直接注解@Transactional就OK。import org.springframework.transaction.annotation.Transactional;

...

@Override

@Transactional(readOnly = true)//查询的只读就行

public Student findById(Long id){

Student student = studentRepository.findOne(id);

Teacher teacher = student.getTeacher();

System.out.println(teacher);

Set students = teacher.getStudents();

System.out.println(students);

return student;

}

注解不生效

1、是否开启了对注解的解析，如：

...

...

2、spring初始化是否加入

contextConfigLocation

classpath:spring-*.xml

异常参考严重: Servlet.service() for servlet [spring] in context with path [] threw exception [Request processing failed; nested exception is org.hibernate.LazyInitializationException: could not initialize proxy - no Session] with root cause

org.hibernate.LazyInitializationException: could not initialize proxy - no Session

at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:165)

at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:286)

at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)

at com.weizhixi.entity.Teacher_$$_jvst6e0_1.toString(Teacher_$$_jvst6e0_1.java)

at java.lang.String.valueOf(String.java:2847)

at java.io.PrintStream.println(PrintStream.java:821)

at org.apache.tomcat.util.log.SystemLogHandler.println(SystemLogHandler.java:269)

at com.weizhixi.service.impl.StudentServiceImpl.findById(StudentServiceImpl.java:29)

at com.weizhixi.controller.IndexController.find(IndexController.java:31)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:606)

at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)

at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)

at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)

at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)

at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)

at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)

at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)

at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)

at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)

at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)

at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:442)

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1083)

at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:640)

at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)

at java.lang.Thread.run(Thread.java:745)

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