GWT 文件上传表单提交 POST 请求无法读取文件

Question

我已经尝试使用 FileUpload 引用 GWT 源文档。因为我想将它添加到不同的选项卡上，所以我为此创建了 GWT 页面并在那里添加了 FileUpload。 自从在其根页面中实施以来，未实施 entryPoint。 我没有使用 onModuleLoad 方法，我只是创建显示元素的方法并将其添加到 FormPanel。

我能够提交 POST 请求，但无法捕获 servlet 上的文件。我是在 GWT 端还是 servlet 端做错了什么。

我在 GWT 端使用过类似的代码

public class FormPanelExample implements Composite {

  public void FormPanelExample() {
    // Create a FormPanel and point it at a service.
    final FormPanel form = new FormPanel();
    form.setAction("/myFormHandler");

    // Because we're going to add a FileUpload widget, we'll need to set the
    // form to use the POST method, and multipart MIME encoding.
    form.setEncoding(FormPanel.ENCODING_MULTIPART);
    form.setMethod(FormPanel.METHOD_POST);

    // Create a panel to hold all of the form widgets.
    VerticalPanel panel = new VerticalPanel();
    form.setWidget(panel);

    // Create a TextBox, giving it a name so that it will be submitted.
    final TextBox tb = new TextBox();
    tb.setName("textBoxFormElement");
    panel.add(tb);

    // Create a ListBox, giving it a name and some values to be associated with
    // its options.
    ListBox lb = new ListBox();
    lb.setName("listBoxFormElement");
    lb.addItem("foo", "fooValue");
    lb.addItem("bar", "barValue");
    lb.addItem("baz", "bazValue");
    panel.add(lb);

    // Create a FileUpload widget.
    FileUpload upload = new FileUpload();
    upload.setName("uploadFormElement");
    panel.add(upload);

    // Add a 'submit' button.
    panel.add(new Button("Submit", new ClickHandler() {
      public void onClick(ClickEvent event) {
        form.submit();
      }
    }));

    // Add an event handler to the form.
    form.addSubmitHandler(new FormPanel.SubmitHandler() {
      public void onSubmit(SubmitEvent event) {
        // This event is fired just before the form is submitted. We can take
        // this opportunity to perform validation.
        if (tb.getText().length() == 0) {
          Window.alert("The text box must not be empty");
          event.cancel();
        }
      }
    });
    form.addSubmitCompleteHandler(new FormPanel.SubmitCompleteHandler() {
      public void onSubmitComplete(SubmitCompleteEvent event) {
        // When the form submission is successfully completed, this event is
        // fired. Assuming the service returned a response of type text/html,
        // we can get the result text here (see the FormPanel documentation for
        // further explanation).
        Window.alert(event.getResults());
      }
    });

    RootPanel.get().add(form);
  }
}

在Servlet端

if (!ServletFileUpload.isMultipartContent(request)) {                                 
            throw new FileUploadException("error multipart request not found");              
        }       

        DiskFileItemFactory factory = new DiskFileItemFactory();            

        ServletFileUpload upload = new ServletFileUpload(factory);

        List<FileItem> items = upload.parseRequest(request);

        if (items == null) {            
            response.getWriter().write("File not correctly uploaded");
            return;
        }

        Iterator<FileItem> iter = items.iterator();

当我调用 iter.next() 时，它给出错误 no such elementFound Exception 作为例外，它看起来在提交文件中没有提交到 servlet 请求。

Answer 1

尝试使用 postman 调用端点并将文件直接上传到正在运行的 Servlet 以确保其正常工作。

我检查了我自己对这段代码的实现，它几乎完全匹配你的，除了我没有使用面板上的 FileUpload 之外的任何东西。移除 TextBox 和 ListBox 以便我们可以检查是否只有文件部分在自己工作，然后介绍每个项目并单独测试。

我发现这在服务器端更可靠

FileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload servletFileUpload = new ServletFileUpload(factory);
FileItemIterator iter = servletFileUpload.getItemIterator(request);