Json序列化，有多对一和多对多关系时出现的问题
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/** * 这是一张 单表中的双向一对多，多对一 关系。自己跟自己一对多多对一 */ @Entity @Table(name="tb_test") public class CreditsEventBean implements Serializable{ private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) private Integer id; //序号 /** * 上级分类 */ @ManyToOne @JoinColumn(name = "pid") private CreditsEventBean pid; /** * 下级分类 */ @OneToMany(mappedBy="pid") private List<CreditsEventBean> creditsEventBean;
※ 上面的实体被使用时会出现死循环的问题 如图：
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:478) ~[tomcat-embed-core-8.0.30.jar:8.0.30] at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.sendServerError(DefaultHandlerExceptionResolver.java:488) ~[spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.handleHttpMessageNotWritable(DefaultHandlerExceptionResolver.java:402) ~[spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.doResolveException(DefaultHandlerExceptionResolver.java:146) ~[spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver.resolveException(AbstractHandlerExceptionResolver.java:137) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.handler.HandlerExceptionResolverComposite.resolveException(HandlerExceptionResolverComposite.java:74) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.DispatcherServlet.processHandlerException(DispatcherServlet.java:1182) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1020) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:871) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:648) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.jasig.cas.client.util.AssertionThreadLocalFilter.doFilter(AssertionThreadLocalFilter.java:50) [cas-client-core-3.3.3.jar:3.3.3] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.jasig.cas.client.util.HttpServletRequestWrapperFilter.doFilter(HttpServletRequestWrapperFilter.java:70) [cas-client-core-3.3.3.jar:3.3.3] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.jasig.cas.client.validation.AbstractTicketValidationFilter.doFilter(AbstractTicketValidationFilter.java:238) [cas-client-core-3.3.3.jar:3.3.3] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.jasig.cas.client.authentication.AuthenticationFilter.doFilter(AuthenticationFilter.java:152) [cas-client-core-3.3.3.jar:3.3.3] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:87) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:521) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1096) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:674) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500) [tomcat-embed-core-8.0.30.jar:8.0.30] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456) [tomcat-embed-core-8.0.30.jar:8.0.30] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_181] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_181] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.0.30.jar:8.0.30] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_181]
解决方法：
@Entity @Table(name="tb_test") public class CreditsEventBean implements Serializable{ private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) private Integer id; //序号 /** @JsonBackReference和@JsonManagedReference：这两个标注通常配对使用，通常用在父子关系中。 */ /** * 上级分类 */ @JsonBackReference //标注的属性在序列化（serialization，即将对象转换为json数据）时，会被忽略（即结果中的json数据不包含该属性的内容） @ManyToOne @JoinColumn(name = "pid") private CreditsEventBean pid; /** * 下级分类 */ @JsonManagedReference//标注的属性则会被序列化。 @OneToMany(mappedBy="pid") private List<CreditsEventBean> creditsEventBean;
如果想不忽略 pid字段 （注意：被忽略的字段前端是拿不到值的）则：
@Entity @Table(name="tb_test") public class CreditsEventBean implements Serializable{ private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) private Integer id; //序号 /** * 上级分类 */ @ManyToOne @JoinColumn(name = "pid") private CreditsEventBean pid; /** * 下级分类 */ @OneToMany(mappedBy="pid") @JsonIgnoreProperties("pid") //指定字段不会被序列化 private List<CreditsEventBean> creditsEventBean;
除此之外还可以：
@JsonIgnore：直接忽略某个属性，以断开无限递归，序列化或反序列化均忽略。当然如果标注在get、set方法中，则可以分开控制，序列化对应的是get方法，反序列化对应的是set方法。
@JsonIgnore跟@JsonBackReference和@JsonManagedReference最大的区别：在父子关系中，当反序列化时，@JsonIgnore不会自动注入被忽略的属性值（父或子）
后记：在序列化时，@JsonBackReference的作用相当于@JsonIgnore，此时可以没有@JsonManagedReference。但在反序列化（deserialization，即json数据转换为对象）时，如果没有@JsonManagedReference，则不会自动注入@JsonBackReference标注的属性（被忽略的父或子）；如果有@JsonManagedReference，则会自动注入自动注入@JsonBackReference标注的属性。
@Entity
@Table(name="tb_credits_event")
public class CreditsEventBean implements Serializable{
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id; //序号
private String imagePath;//图片路径
private String title; //标题
private String content; //内容
private String eventRule; //活动规则
private Integer credit; //积分值
private Integer creditStatus;//事件类型 0消费，1获取
private Integer activityShop;//属于活动的商品 0：常规商品 1：活动商品
private Integer isShopEvent; //是商品兑换还是活动兑换 0商品兑换 1活动兑换
private String activityStartCreditsDT;//开始时间
private String activityEndCreditsDT;//结束时间
private String userName; //创建者
private String creteateTime;//创建时间 （活动发布时间）
private String cutOffTime;//活动报名截止日期
private String address;//兑换(参与)地址
private Integer maxPlayers; //活动限制人数
private Integer remaining; //剩余人数
private Integer sort = 1;//排序 -- 用于内容展示时 过期内容的下沉（默认为1）
@OneToOne
@JoinColumn(name="role_id")//与权限表一对一
private CreditsRoleBean roleBean;//活动有权限设置
/**
* 上级分类
*/
// @JsonBackReference
@ManyToOne
@JoinColumn(name = "pid")
private CreditsEventBean pid;
/**
* 下级分类
*/
// @JsonManagedReference
@OneToMany(mappedBy="pid")
// @JsonIgnoreProperties("pid") //指定字段不会被序列化
private List<CreditsEventBean> creditsEventBean;//活动跟商品之间关联
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