multipart/form-data 根据PDFurl上传PDF文件

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调用微信的上传文件接口时，该接口要求必须要通过multipart/form-data的方式上传，于是研究了一下multipart/form-data。

multipart/form-data是一种post提交数据的一种方式，用来指定请求内容的数据编码格式，并且指定传输数据为二进制类型，比如图片、mp3、文件。

通过boundary来进行分割请求头与请求体，为了防止boundary与正文内容重复，boundary内容一般为一串随机的字符串。

//上传PDFurl
private final static String uploadPdfUrl = "https://api.weixin.qq.com/card/invoice/platform/setpdf";

private final static String HEAD = "Odcddwssf2exwM16BY25kVBgf";

//上传pdf
public String uploadPdf(String pdfUrl) {
    String name= "123123123.pdf";
    //通过文件地址获取对应的文件流
    ByteArrayOutputStream outputStream = readUrl(pdfUrl);
    InputStreamReader inputStreamReader = null;
    InputStream inputStream = null;
    BufferedReader in = null;
    try {
        MultipartEntity multipartEntity = new MultipartEntity(HttpMultipartMode.BROWSER_COMPATIBLE, "----------" + HEAD, Charset.defaultCharset());
        multipartEntity.addPart("pdf", new ByteArrayBody(outputStream.toByteArray(), name));
        HttpPost request = new HttpPost(uploadPdfUrl);
        request.setEntity(multipartEntity);
        //设置请求的header,设置为multipart/form-data，同时设置boundary的内容为随机字符串
        request.addHeader("Content-Type", "multipart/form-data; boundary=----------" + HEAD);

        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpResponse response = httpClient.execute(request);

        inputStream = response.getEntity().getContent();
        inputStreamReader = new InputStreamReader(inputStream);
        in = new BufferedReader(inputStreamReader);
        StringBuffer buffer = new StringBuffer();
        String line = "";
        //循环读取请求返回信息
        while ((line = in.readLine()) != null) {
            buffer.append(line);
        }
    } catch (Exception e) {
        logger.error("PDF上传失败", e);
        throw new ServiceException(ResponseObj.CODE_FAILED, "PDF上传失败");
    } finally {
        try {
            //关闭文件流
            outputStream.close();
            in.close();
            inputStream.close();
            inputStreamReader.close();
        } catch (IOException e) {
            logger.error("数据流关闭异常", e);
            throw new ServiceException(ResponseObj.CODE_FAILED, "数据流关闭异常");
        }
    }

    return "";
}

//通过文件地址获取文件对应输出流
public ByteArrayOutputStream readUrl(String pdfUrl) {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    try {
        //通过URLConnection先读出链接的输入流，再写入输出流中
        //如果链接无法访问，会导致读取失败
        URL url = new URL(pdfUrl);
        URLConnection connection = url.openConnection();
        InputStream in = connection.getInputStream();
        byte[] b = new byte[1024];
        int n;
        while ((n = in.read(b)) != -1) {
            outputStream.write(b, 0, n);
        }
    } catch (Exception e) {
        logger.error("读取url失败", e);
        throw new ServiceException(ResponseObj.CODE_FAILED, "读取url失败");
    }
    return outputStream;

}

通过该方式就可以正常将PDF文件通过multipart/form-data方式进行上传了。