从Java Servlet获取PDF后，Blob对象生成空PDF文件问题求助

从AEM环境的Java Servlet获取到有效PDF文件，但前端用JavaScript创建Blob对象后，生成的PDF为空。接收的数据形态看似正常，但PDF无法正常显示。

Java端PDF流处理代码 #

private void streamPDF (final SlingHttpServletResponse response, final Resource pdfRes) throws IOException {
        String fileName = pdfRes.getPath().substring(pdfRes.getPath().lastIndexOf("/") + 1);

        response.setContentType("application/pdf");
        response.setHeader("Content-disposition", "attachment; filename=" + fileName);

        Asset asset = pdfRes.adaptTo(Asset.class);
        final InputStream in = asset.getOriginal().getStream();

        final OutputStream out = response.getOutputStream();

        IOUtils.copy(in, out);

        out.close();

        in.close();
    }

JavaScript端请求及Blob创建代码 #

sendServletDownload: function (title, path) {
        let url = "myurl.pdf";
        $.ajax({
           url: url,
           type: 'GET',
           data: {
               path: path
           },
           success: function (data) {
               var blob = new Blob([data], { type: 'application/pdf' });

               // Create an URL object for the Blob
               var url = window.URL.createObjectURL(blob);

               // Configure the download link with the Blob's URL and the filename
               var downloadLink = document.getElementById('downloadLink');
               downloadLink.href = url;

               downloadLink.download = title + '.pdf';

               // Simulate a click in the link to iniciate the download
               downloadLink.click();

               // Free the URL of the object when it's not necessary anymore
               window.URL.revokeObjectURL(url);
           }, error: function (XMLHttpRequest, textStatus, errorThrown) {
              console.log("Error: {}", errorThrown);
           },
            xhrFields: {
                responseType: 'arraybuffer' // Stablish responseType to 'arraybuffer'
            }
       });
    }

尝试过的base64解码代码 #

function base64ToArrayBuffer(data) {
    var binaryString = window.atob(data);
    var binaryLen = binaryString.length;
    var bytes = new Uint8Array(binaryLen);
    for (var i = 0; i < binaryLen; i++) {
        var ascii = binaryString.charCodeAt(i);
        bytes[i] = ascii;
    }
    return bytes;
};

解决方案 #

1. 修正Java端流处理逻辑 #

• 确保输出流在复制完成后flush，避免缓冲区数据未写入响应：

  IOUtils.copy(in, out);
  out.flush(); // 新增flush操作
  out.close();
  in.close();
  

• 添加Content-Length响应头，让前端明确数据大小：

  long contentLength = asset.getOriginal().getSize();
  response.setContentLengthLong(contentLength);
  

• 改用try-with-resources自动管理流，避免手动关闭时的异常或遗漏：

  private void streamPDF (final SlingHttpServletResponse response, final Resource pdfRes) throws IOException {
      String fileName = pdfRes.getPath().substring(pdfRes.getPath().lastIndexOf("/") + 1);
  
      response.setContentType("application/pdf");
      response.setHeader("Content-disposition", "attachment; filename=" + fileName);
  
      Asset asset = pdfRes.adaptTo(Asset.class);
      try (InputStream in = asset.getOriginal().getStream();
           OutputStream out = response.getOutputStream()) {
          response.setContentLengthLong(asset.getOriginal().getSize());
          IOUtils.copy(in, out);
          out.flush();
      }
  }
  

2. 前端AJAX处理优化 #

• 确认responseType: 'arraybuffer'生效，可改用原生XMLHttpRequest测试，避免jQuery潜在的参数覆盖问题：

  sendServletDownload: function (title, path) {
      let url = "myurl.pdf?path=" + encodeURIComponent(path);
      let xhr = new XMLHttpRequest();
      xhr.open('GET', url, true);
      xhr.responseType = 'arraybuffer';
      xhr.onload = function() {
          if (xhr.status === 200) {
              var blob = new Blob([xhr.response], { type: 'application/pdf' });
              var url = window.URL.createObjectURL(blob);
              var downloadLink = document.getElementById('downloadLink');
              downloadLink.href = url;
              downloadLink.download = title + '.pdf';
              downloadLink.click();
              window.URL.revokeObjectURL(url);
          }
      };
      xhr.send();
  }
  

• 无需将arraybuffer类型数据转base64再解码，直接用原始响应数据创建Blob即可，转码会破坏二进制结构。

3. 排查响应头问题 #

• 检查Servlet返回的响应头是否存在Transfer-Encoding: chunked，设置Content-Length后该头会被自动禁用，避免前端处理二进制数据异常。
• 确认没有其他AEM过滤器或组件向响应流中添加额外字符，这会导致PDF文件损坏。

内容的提问来源于stack exchange，提问作者Daniel Culebras