将字符串值解析为整数不起作用

Question

我对某些代码未提供预期响应的问题：

Intellij / Payara提供此错误：

[[2019-10-26T21：26：35.875 + 0200] [Payara 5.193] [警告] [] [javax.enterprise.web] [tid：_ThreadID = 30 _ThreadName = http-thread-pool :: http-listener- 1（3）] [timeMillis：1572117995875] [levelValue：900] [[StandardWrapperValve [FileUploadServlet]：Servlet FileUploadServlet的Servlet.service（）抛出异常java.lang.NullPointerException在FileUploadServlet.doPost（FileUploadServlet.java:27）

特定行号包含用于将字符串数据类型解析为int的代码。

public class FileUploadServlet extends HttpServlet {

    String result = "";

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        HttpSession file = request.getSession(true);
        int uploadcode = Integer.parseInt(request.getParameter("uploadcode"));
        int code = 1111;
        boolean checkcode = check(uploadcode, code);

        if ((checkcode && ((uploadcode != 0))){
            try {
                Part filePart = request.getPart("fileToUpload");
                InputStream fileInputStream = filePart.getInputStream();
                File fileToSave = new File("filepath" +filePart.getSubmittedFileName());
                Files.copy(fileInputStream, fileToSave.toPath(), StandardCopyOption.REPLACE_EXISTING);
                result = "File send and saved";
                file.setAttribute("Bericht", result);
            } catch (Exception ex){
                result = "File not sent, please try again.";
                file.setAttribute("Bericht", result);
            } finally{
                result = "File sent and saved";
                file.setAttribute("Bericht", result);
                getServletContext().getRequestDispatcher("/Upload.jsp").forward(request, response);
            }
        } else {
            result = "incorrect upload code.";
            file.setAttribute("Bericht", result);
            getServletContext().getRequestDispatcher("/Upload.jsp").forward(request, response);
        }
    }
    public boolean check(int a, int b) {
        return a == b;
    }
}

我希望代码与输入匹配，然后将文件保存到磁盘。有指针吗？谢谢：）

问题可能是表格吗？

<form id="form1" enctype="multipart/form-data" method="post"
    action="FileUploadServlet">
    <div id="fileName"></div>
    <div id="fileSize"></div>
    <div id="fileType"></div>
    <input type="number" name="uploadcode" id="uploadcode"
        placeholder="Enter upload code" required>
    <div>
        Select the file to upload:
        <br>
        <input type="file" name="fileToUpload" id="fileToUpload"
                accept="image/*" />
        <br>
        <br>
        <ul class="actions">
            <li>
                <input type="submit" class="button alt"
                    value="Send Message" />
            </li>
        </ul>
    </div>
    <div id="progressNumber"></div>
    <div id="text"></div>
</form>

或者可能是Java脚本上传：

function uploadFile() {
    var fd = new FormData();
    fd.append("fileToUpload", document.getElementById('fileToUpload').files[0]);
    var xhr = new XMLHttpRequest();
    xhr.upload.addEventListener("progress", uploadProgress, false);
    xhr.addEventListener("load", uploadComplete, false);
    xhr.addEventListener("error", uploadFailed, false);
    xhr.addEventListener("abort", uploadCanceled, false);
    xhr.open("POST", "FileUploadServlet");
    xhr.send(fd);
}

不幸的是（26-10-2019 23:10），不同的错误：

[2019-10-26T22:57:54.019+0200] [Payara 5.193] [WARNING] [] [javax.enterprise.web] [tid: _ThreadID=29 _ThreadName=http-thread-pool::http-listener-1(2)] [timeMillis: 1572123474019] [levelValue: 900] [[
  StandardWrapperValve[FileUploadServlet]: Servlet.service() for     servlet FileUploadServlet threw exception
java.lang.NumberFormatException: For input string: ""

在servlet之后，我使用这些将变量传递给JSP：

<%
  HttpSession file = request.getSession(false);
  String resultaat= (String)file.getAttribute("Bericht");
%>

和：

<%out.println(resultaat);%>

通过设置正确的文件属性已解决。

Answer 1

传入请求根本不包含名为uploadcode的参数。这意味着request.getParameter()调用返回null，然后尝试通过Integer.parseInt将其转换为int会生成NullPointerException。

因此，您输入了uploadcode，或者您的JavaScript和/或HTML中存在错误。