java.lang.ClassCastException: [Ljava.lang.Object; не может быть передан com.entity.survey.SurveyReport

Question

try{ 
System.out.println(surveyReportList.get(0).getEmploymentStatus()); 
} 
catch(Exception e){ 
System.out.println(e.getCause()); 
e.printStackTrace(); 
} 

Я пытаюсь получить одно из значений поля в моем списке, и я получаю исключение ClassCastException. Я получаю правильный размер своего списка, используя surveyReportList.size();.

Вот стопка и мой surveyReportList имеет тип List<SurveyReport> Линия 103 находится внутри этого блока try.

at com.action.survey.SurveyReportAction.generateReports(SurveyReportAction.java:103) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
    at java.lang.reflect.Method.invoke(Unknown Source) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:441) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:280) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:243) 
    at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:165) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:252) 
    at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:179) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:90) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:130) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:165) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:179) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237) 
    at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54) 
    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:510) 
    at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:434) 
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) 
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) 
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) 
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298) 
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) 
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) 
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) 
    at java.lang.Thread.run(Unknown Source) 

Answer 1

Скорее всего, неправильное использование дженериков. surveyReportList, вероятно, имеет тип List<SurveyReport>, но в какой-то момент у вас есть некоторые предупреждения о компиляторе о непроверенных операциях, и как-то что-то, что не является SurveyReport, добавляется в этот список. Посмотрите, откуда и откуда создается список.

В качестве конкретного примера, следующий код будет создать такое же исключение, что вы видите:

List untyped = new ArrayList(); 
untyped.add(new Object[0]); 
List<String> strings = untyped; 
System.out.println(strings.get(0).length()); 

Результат:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to java.lang.String 

Это ClassCastException, потому что компилятор в основном получается

strings.get(0).length() 

((String) strings.get(0)).length()