请求通过 ajax 下载 servlet 文件(请不要使用 jquery)

Question

过程是这样的：

1. 从web（jsp）我上传了一些pdf文件（通过ajax提交）
2. 在后端我合并这些pdf
3. 我通过 ajax 得到响应（合并的 pdf）>开始文件下载...

我在第三步有问题。

我

只包含了相关代码，我在其中提交文件上传（发布请求）并开始下载。我还放了一个直接链接，它在 get 方法中调用相同的步骤并工作。

我的问题在哪里？提前感谢...

这是 jsp 身体标签

<a href="/TestAjaxServletDownload/DownloadServlet" >
    download
</a>
<p><input id="sampleFile5" name="sampleFile5" type="file" /></p>
<p><input id="uploadBtn" type="button" value="Upload" onClick="javascript:performAjaxSubmit();"></input></p>

这是我的javascript标签内容

function performAjaxSubmit() {
        var sampleFile1 = document.getElementById("sampleFile5").files[0];
        var formdata = new FormData();
        formdata.append("sampleFile", sampleFile1);
        var xhr = new XMLHttpRequest();       
        xhr.onload = function() {
            if(xhr.readyState == 4 && xhr.status == 200) {
//              alert("ok..." + xhr.responseText);
                //?????????????????????????????
                document.location=xhr.responseText;               
            }
        };   
        xhr.open("POST","/TestAjaxServletDownload/DownloadServlet", true);
        xhr.send(formdata);
    }

这是我的网络.xml servlet 映射标签

<servlet>
    <description></description>
    <display-name>DownloadServlet</display-name>
    <servlet-name>DownloadServlet</servlet-name>
    <servlet-class>test.DownloadServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>DownloadServlet</servlet-name>
    <url-pattern>/DownloadServlet</url-pattern>
  </servlet-mapping>

这是我的 servlet 代码

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("DO GET SERVLET MERGE");
        execute (request, response);
    }
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        System.out.println("DO POST SERVLET MERGE");
        execute (request, response);
    }

    protected void execute(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        File downloadFile = new File("c:\data\example.pdf");
        System.out.println("++++" + downloadFile.getAbsolutePath());
//      System.out.println(uploadPathTemp+mergeFileName);
        FileInputStream inStream = new FileInputStream(downloadFile);
         // obtains ServletContext
         ServletContext context = getServletContext();
         // gets MIME type of the file
         String mimeType = context.getMimeType(downloadFile.getCanonicalPath());
         if (mimeType == null) {        
             // set to binary type if MIME mapping not found
             mimeType = "application/octet-stream";
         }
         // modifies response
         response.setContentType(mimeType);
         response.setContentLength((int) downloadFile.length());
         // forces download
         String headerKey = "Content-Disposition";
         String headerValue = String.format("attachment; filename="%s"", downloadFile.getName());
         System.out.println(downloadFile.getName());
         response.setHeader(headerKey, headerValue);
         // obtains response's output stream
         OutputStream outStream = response.getOutputStream();
         byte[] buffer = new byte[4096];
         int bytesRead = -1;
         while ((bytesRead = inStream.read(buffer)) != -1) {
             outStream.write(buffer, 0, bytesRead);
         }
         inStream.close();
         outStream.close();
    }

Answer 1

如何更改

<a href="/TestAjaxServletDownload/DownloadServlet" > download </a>

自

<a id="pdfLink" href="/TestAjaxServletDownload/DownloadServlet" > download </a>

然后使用 document.getElementById('pdfLink').click() ？