Java集合sort排序报错UnsupportedOperationException处理

报错场景

• 我们使用的是PostgreSQL数据库，存储业务数据，业务代码使用的是Spring JPA
• 我们做的是智慧交通信控平台，有个功能是查询展示区域的交通态势，需要按照不同维度排序展示
• 区域态势指标计算，15分钟一次，每次计算存储所有区域指标。我们的实时态势展示，每次展示当前最新结果
• 业务要求，要按照区域交通流量、拥堵指数、拥堵里程分别倒序展示，写在了一个接口里，先查询后排序
• 我们使用的默认自增的主键策略，故获取最新一次区域态势结果，可以使用id倒序，按照区域数量获取
• 查询的业务逻辑比较简单，代码很快就写完了，使用JPA查询语句，构造查询和排序条件。得到查询结果list后，再根据业务需要，按照不同的字段排序
• 但在部署测试环境后发现，排序代码执行报错，报错 null Not Implemented
• 具体业务代码如下

    /*** 获取所有区域实时态势* @param targetIndex 排序字段* @return */public List<SituationAnalysisRegion> getCurrentRegionSituationList(String targetIndex) {// 获取所有子区List<SubRegion> allSubRegions = getAllSubRegion();Map<Integer, SubRegion> idSubRegionMap = new HashMap<>();allSubRegions.forEach(e -> idSubRegionMap.put(e.getId().intValue(), e));// 获取所有子区态势排名倒序Specification<SituationAnalysisRegion> specification = (root, query, cb)->{List<Predicate> predicates = new ArrayList<>();predicates.add(cb.greaterThan(root.get("timeStamp").as(Instant.class), LocalDateTime.now().plusMinutes(-15).plusSeconds(-30).atZone(ZoneId.systemDefault()).toInstant()));Predicate[] pre = new Predicate[predicates.size()];pre = predicates.toArray(pre);return query.where(pre).getRestriction();};Sort orders = Sort.by("id").descending();Pageable pageable = PageRequest.of(0, allSubRegions.size(), orders);List<SituationAnalysisRegion> situationAnalysisRegions = analysisRegionRepository.findAll(specification, pageable).getContent();// 排序要求if (null == targetIndex || StringUtils.isEmpty(targetIndex)) {situationAnalysisRegions.sort((o1, o2) -> (int)(o2.getCongestionMileage() - o1.getCongestionMileage()));} else if (targetIndex.equals("trafficFlow")) {situationAnalysisRegions.sort((o1, o2) -> o2.getTrafficFlow() - o1.getTrafficFlow());} else if (targetIndex.equals("congestionIndex")) {situationAnalysisRegions.sort((o1, o2) -> (int)(o2.getCongestionIndex() - o1.getCongestionIndex()));} else {situationAnalysisRegions.sort((o1, o2) -> (int)(o2.getCongestionMileage() - o1.getCongestionMileage()));}return situationAnalysisRegions;}

• 具体报错日志如下：

2023-08-29 16:12:56.168 ERROR 12860 --- [  XNIO-1 task-1] o.z.problem.spring.common.AdviceTraits   : Not Implementedjava.lang.UnsupportedOperationException: nullat java.base/java.util.Collections$UnmodifiableList.sort(Collections.java:1332)at com.newatc.api.situationanalysis.service.SituationAnalysisRegionExtentService.getCurrentRegionSituationList(SituationAnalysisRegionExtentService.java:88)at com.newatc.api.situationanalysis.service.SituationAnalysisRegionExtentService.getRegionSituationList(SituationAnalysisRegionExtentService.java:104)at com.newatc.api.rest.SituationAnalysisController.getRegionSituationList(SituationAnalysisController.java:112)at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.base/java.lang.reflect.Method.invoke(Method.java:566)at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1070)at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)at javax.servlet.http.HttpServlet.service(HttpServlet.java:497)at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)at javax.servlet.http.HttpServlet.service(HttpServlet.java:584)at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)at com.newatc.api.redis.RequestFilter.doFilter(RequestFilter.java:58)at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:327)at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:115)at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:81)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:122)at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:116)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:126)at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:81)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.oauth2.client.web.OAuth2AuthorizationCodeGrantFilter.doFilterInternal(OAuth2AuthorizationCodeGrantFilter.java:168)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:109)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:149)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.oauth2.server.resource.web.BearerTokenAuthenticationFilter.doFilterInternal(BearerTokenAuthenticationFilter.java:125)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.oauth2.client.web.OAuth2AuthorizationRequestRedirectFilter.doFilterInternal(OAuth2AuthorizationRequestRedirectFilter.java:178)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:103)at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:89)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90)at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:112)at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:82)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:55)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.session.DisableEncodeUrlFilter.doFilterInternal(DisableEncodeUrlFilter.java:42)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:211)at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:183)at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:354)at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:267)at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:96)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)at io.undertow.servlet.handlers.ServletChain$1.handleRequest(ServletChain.java:68)at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)at io.undertow.servlet.handlers.RedirectDirHandler.handleRequest(RedirectDirHandler.java:68)at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:117)at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)at io.undertow.servlet.handlers.SendErrorPageHandler.handleRequest(SendErrorPageHandler.java:52)at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)at io.undertow.servlet.handlers.SessionRestoringHandler.handleRequest(SessionRestoringHandler.java:119)at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:275)at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:79)at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:134)at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:131)at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:255)at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:79)at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:100)at io.undertow.server.Connectors.executeRootHandler(Connectors.java:387)at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:852)at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:2019)at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1558)at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1449)at org.xnio.XnioWorker$WorkerThreadFactory$1$1.run(XnioWorker.java:1282)at java.base/java.lang.Thread.run(Thread.java:834)2023-08-29 16:12:56.227  WARN 12860 --- [  XNIO-1 task-1] .m.m.a.ExceptionHandlerExceptionResolver : Resolved [java.lang.UnsupportedOperationException]

排查解决

• 日志核心打印：Not Implemented、 java.lang.UnsupportedOperationException: null、at java.base/java.util.Collections$UnmodifiableList.sort(Collections.java:1332)

• 一开始看着报错null，以为是空指针异常，想着是不是没查询到数据，或者排序字段的值有null值

• 查看了数据库数据，发现没问题，只好本地debug排查

• 加了断点，进行debug，确认返回结果list有值，且排序字段也都有值，继续执行，还是这个报错

• 想着要进行更细粒度的debug，于是按着 F5 继续调试，结果发现，也是直接一步走进报错，在这一行（Collections.sort）
  

• 一下子没法排查了，这个报错之前也没注意过，于是继续去网上搜索相应报错，还真找到了

• 还是要回到报错日志，核心是这一句：at java.base/java.util.Collections$UnmodifiableList.sort(Collections.java:1332)

• 在执行Collections.sort()方法时，发现传入的集合list，是一个不可修改的UnmodifiableList.，不能直接拿来排序

• 但是可以通过新建一个list，来解决这个问题

        List<SituationAnalysisRegion> situationAnalysisRegions = analysisRegionRepository.findAll(specification, pageable).getContent();// 重新赋值，排除 UnmodifiableList 报错List<SituationAnalysisRegion> result = new ArrayList<>(situationAnalysisRegions);// 排序要求if (null == targetIndex || StringUtils.isEmpty(targetIndex)) {result.sort((o1, o2) -> (int)(o2.getCongestionMileage() - o1.getCongestionMileage()));} else if (targetIndex.equals("trafficFlow")) {result.sort((o1, o2) -> o2.getTrafficFlow() - o1.getTrafficFlow());} else if (targetIndex.equals("congestionIndex")) {result.sort((o1, o2) -> (int)(o2.getCongestionIndex() - o1.getCongestionIndex()));} else {result.sort((o1, o2) -> (int)(o2.getCongestionMileage() - o1.getCongestionMileage()));}return result;

• 现在问题很明确了，JPA的查询代码，返回的list，是个不可修改的list。在网上查询该问题时，发现其他的一些类似查询，也可能返回一个不可修改的list，如 MongoDB的Java查询语句
• 以后如果看到Collections$UnmodifiableList.sort报错，就要考虑到这种情况，都可以类似处理

UnmodifiableList类介绍

• UnmodifiableList类是Collections的内部类
• Java的Collections框架提供了UnmodifiableList类作为不可变列表的一种实现
• UnmodifiableList实现了List接口，但是在其基础上增加了一些限制，例如不允许修改列表中的元素、不允许添加新元素以及不允许删除已有元素。因此，可以使用UnmodifiableList来保护某些关键数据，防止其他程序修改它们
• 使用方式非常简单，通过Collections.unmodifiableList(List list)方法可以将一个可变的列表转换为一个不可变的列表，例如：

List<String> mutableList = new ArrayList<>();
mutableList.add("apple");
mutableList.add("banana");
mutableList.add("orange");List<String> immutableList = Collections.unmodifiableList(mutableList);

• 这样，immutableList就成为了一个不可变的列表，任何尝试修改、添加或删除其中的元素的操作都会抛出UnsupportedOperationException异常。