我已经花了两天时间试图在我的项目中解决json序列化问题，其中我有一堆实体类，它们以一对多的关系相互映射。所以错误是
org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: com.softcons.cas.entities.CASWeightageMaster.casQuestionMaster, could not initialize proxy - no Session (through reference chain: com.softcons.cas.rest.CASQuestionMasterResource["casQuestionDescriptions"]->org.hibernate.collection.internal.PersistentBag[0]->com.softcons.cas.entities.CASQuestionDescription["casQuestionMaster"]->com.softcons.cas.entities.CASQuestionMaster["casWeightageMaster"]->com.softcons.cas.entities.CASWeightageMaster["casQuestionMaster"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.softcons.cas.entities.CASWeightageMaster.casQuestionMaster, could not initialize proxy - no Session (through reference chain: com.softcons.cas.rest.CASQuestionMasterResource["casQuestionDescriptions"]->org.hibernate.collection.internal.PersistentBag[0]->com.softcons.cas.entities.CASQuestionDescription["casQuestionMaster"]->com.softcons.cas.entities.CASQuestionMaster["casWeightageMaster"]->com.softcons.cas.entities.CASWeightageMaster["casQuestionMaster"])
org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.writeInternal(MappingJackson2HttpMessageConverter.java:244)
org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:207)
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:148)
org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:125)
org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:71)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:122)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:690)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:168)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:205)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213)
org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176)
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344)
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261)
QuestionMaster＆amp; amp;之间存在一对多的关系。问题描述也在QuestionMaster＆amp;权衡主实体存在多对一关系。我需要获取QuestionMaster的单个记录，其中嵌入了QuestionDescription记录列表。为此我在QuestionMaster＆amp; amp; QuestionDescription，在我引入这个List<QuestionDescription>作为json转换的资源之前，都已经习惯了。我一直收到上述错误。不知道在哪里修改，因为我尝试过在网上找到的内容。
question_master
@Entity
@Table(name = "cas_question_master")
public class CASQuestionMaster extends BasicEntity {
private String question;
private boolean self;
private boolean peer;
private boolean supervisor;
private boolean subordinate;
private boolean deleteFlag;
private boolean inactive;
private Long deletedBy;
private Date deletedOn;
private CASWeightageMaster casWeightageMaster;
private String questionDef;
private List<CASQuestionDescription> casQuestionDescription;
@OneToMany(targetEntity = CASQuestionDescription.class, mappedBy = "casQuestionMaster", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
public List<CASQuestionDescription> getCasQuestionDescription() {
return casQuestionDescription;
}
public void setCasQuestionDescription(
List<CASQuestionDescription> casQuestionDescription) {
this.casQuestionDescription = casQuestionDescription;
}
@Column(name = "question", length = 2000)
public String getQuestion() {
return question;
}
public void setQuestion(String question) {
this.question = question;
}
@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name = "weightage_id_fk", nullable = false)
public CASWeightageMaster getCasWeightageMaster() {
return casWeightageMaster;
}
public void setCasWeightageMaster(CASWeightageMaster casWeightageMaster) {
this.casWeightageMaster = casWeightageMaster;
}
}
question_description
@Entity
@Table(name = "cas_question_description")
public class CASQuestionDescription extends BasicEntity {
private CASQuestionMaster casQuestionMaster;
private String Description;
private boolean deleteFlag;
private Long deletedBy;
private Date deletedOn;
@ManyToOne
@JoinColumn(name="question_id_fk", nullable=false)
public CASQuestionMaster getCasQuestionMaster() {
return casQuestionMaster;
}
public void setCasQuestionMaster(CASQuestionMaster casQuestionMaster) {
this.casQuestionMaster = casQuestionMaster;
}
@Column(name="description", nullable=false)
public String getDescription() {
return Description;
}
public void setDescription(String description) {
Description = description;
}
}
weightage_master
@Entity
@Table(name = "cas_weightage_master")
public class CASWeightageMaster extends BasicEntity {
private int weightage;
private List<CASQuestionMaster> casQuestionMaster;
@Column(name = "weightage", nullable=false)
public int getWeightage() {
return weightage;
}
public void setWeightage(int weightage) {
this.weightage = weightage;
}
@OneToMany(targetEntity = CASQuestionMaster.class, mappedBy = "casWeightageMaster", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
public List<CASQuestionMaster> getCasQuestionMaster() {
return casQuestionMaster;
}
public void setCasQuestionMaster(List<CASQuestionMaster> casQuestionMaster) {
this.casQuestionMaster = casQuestionMaster;
}
}
控制器代码
@RequestMapping(value="/findAll", method=RequestMethod.GET)
public ResponseEntity<CASQuestionMasterListResource> findAll()
{
try {
CASQuestionMasterList casQuestionMasterList = new CASQuestionMasterList();
casQuestionMasterList.setCasQuestionMasterList(casQuestionMasterService.findAll());
CASQuestionMasterListResource res = new CASQuestionMasterListAsm().toResource(casQuestionMasterList);
return new ResponseEntity<CASQuestionMasterListResource>(res, HttpStatus.OK);
} catch(Exception exception)
{
throw new NotFoundException(exception);
}
}
我使用Spring HATEOS作为json格式。以下是用于转换为json的资源文件。以下是用于json转换的资源文件
QuestionMasterResource
public class CASQuestionMasterResource extends ResourceSupport {
private Long questionId;
private String question;
private Long casWeightageMasterId;
private List<CASQuestionDescription> casQuestionDescriptions;
public List<CASQuestionDescription> getCasQuestionDescriptions() {
return casQuestionDescriptions;
}
public void setCasQuestionDescriptions(
List<CASQuestionDescription> casQuestionDescriptions) {
this.casQuestionDescriptions = casQuestionDescriptions;
}
public String getQuestion() {
return question;
}
public Long getQuestionId() {
return questionId;
}
public void setQuestionId(Long questionId) {
this.questionId = questionId;
}
public void setQuestion(String question) {
this.question = question;
}
public Long getCasWeightageMasterId() {
return casWeightageMasterId;
}
public void setCasWeightageMasterId(Long casWeightageMaster) {
this.casWeightageMasterId = casWeightageMaster;
}
public CASQuestionMaster toQuestionMaster(CASWeightageMaster casWeightageMaster){
CASQuestionMaster casQuestionMaster = new CASQuestionMaster();
casQuestionMaster.setId(this.questionId);
casQuestionMaster.setCasWeightageMaster(casWeightageMaster);
casQuestionMaster.setQuestion(this.question);
return casQuestionMaster;
}
}
QuestionMasterListResource
public class CASQuestionMasterListResource extends ResourceSupport {
private List<CASQuestionMasterResource> casQuestionMasterResources = new ArrayList<CASQuestionMasterResource>();
public List<CASQuestionMasterResource> getCasQuestionMasterResources() {
return casQuestionMasterResources;
}
public void setCasQuestionMasterResources(
List<CASQuestionMasterResource> casQuestionMasterResources) {
this.casQuestionMasterResources = casQuestionMasterResources;
}
}
QuestionMasterList汇编程序
public class CASQuestionMasterListAsm extends ResourceAssemblerSupport<CASQuestionMasterList, CASQuestionMasterListResource>{
public CASQuestionMasterListAsm() {
super(CASQuestionMasterController.class, CASQuestionMasterListResource.class);
}
@Override
public CASQuestionMasterListResource toResource(CASQuestionMasterList casQuestionMasterList) {
List<CASQuestionMasterResource> casQuestionMasterResources = new CASQuestionMasterAsm().toResources(casQuestionMasterList.getCasQuestionMasterList());
CASQuestionMasterListResource casQuestionMasterListResource = new CASQuestionMasterListResource();
casQuestionMasterListResource.setCasQuestionMasterResources(casQuestionMasterResources);
return casQuestionMasterListResource;
}
}
记录最终注释以检查问题主实体的记录是否被急切地记录正确记录。真的没有到达我错的地方。
答案 0 :(得分：0)
序列化为JSON可以触发集合的获取，并且由于此时您没有进行休眠会话，因此您将获得异常。
您可以使用jackson-datatype-hibernate来控制此行为，文档说明您将如何配置
public class HibernateAwareObjectMapper extends ObjectMapper {
public HibernateAwareObjectMapper() {
registerModule(new Hibernate4Module());
}
}
而不是注册
<mvc:annotation-driven>
<mvc:message-converters>
<!-- Use the HibernateAware mapper instead of the default -->
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper">
<bean class="path.to.your.HibernateAwareObjectMapper" />
</property>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
该模块具有 Feature.FORCE_LAZY_LOADING 设置，用于指示是否应强制加载对象然后进行序列化，默认设置为 false 。此设置意味着您不会获得异常，但该列表将不会包含在json响应中。
如果您想在响应中使用该列表，您可以在您的代码中，在您拥有有效会话的地方（如服务中），通过调用例如Hibernate.initialize(casQuestionMaster.getCasQuestionDescription())甚至可以更好地调用列表中的任何属性，例如getCasQuestionDescription().size()，或将FORCE_LAZY_LOADING设置为true，但这会尝试加载所有延迟加载的集合