java - 迭代器 - Spring MVC Controller 中的 java.util.NoSuchElementException

Question

我有 Java spring MVC 应用程序。

通过 AngularJS。我从客户端上传一个文件，并将一些其他数据发布到服务器。

我的 Java Controller 类

@Controller
public class FileUploadController {

    @RequestMapping(value="/fileUpload", method = RequestMethod.POST)
    public void UploadFile(MultipartHttpServletRequest request, HttpServletResponse response) {
        System.out.println(request.getFileNames());
        Iterator<String> itr=request.getFileNames();
        System.out.println(itr.hashCode());
        MultipartFile file=request.getFile(itr.next());
        String fileName=file.getOriginalFilename();
        System.out.println(fileName);
          }
}

当我运行这个程序时，我会打印前两行，然后出现异常。

java.util.LinkedHashMap$KeyIterator@471164ef
1190767452

错误

java.util.NoSuchElementException
    at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(LinkedHashMap.java:396)
    at java.util.LinkedHashMap$KeyIterator.next(LinkedHashMap.java:405)
    at com.uploaddemo.web.FileUploadController.UploadFile(DocumentUploadController.java:21)
    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.invoke(InvocableHandlerMethod.java:219)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:920)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:827)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:801)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:744)

这是什么意思？服务器正在获取文件还是在服务器 Controller 中我做错了？

因为当我打印迭代器的哈希码时，它被打印出来，这意味着它不为空。(如果我错了，请纠正我)。

我正在从客户端发送文件和其他数据。

Answer 1

我猜您的请求中没有文件。 getFileNames 永远不会返回 null:如果没有文件，它是空集合上的迭代器。要知道是否存在文件，可以调用itr.hasNext()。