如何通过Java Http Post发送和接受文件？

Question

I just want to send a text file and a JPEG file over the network. fortunately, i have access to both the server code and the client code. Here's my (google app engine) code.

private void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    GcsService gcsService = GcsServiceFactory.createGcsService(RetryParams.getDefaultInstance());
    GcsFilename filename = new GcsFilename("my-bucket", "my-file");
    Builder fileOptionsBuilder = new GcsFileOptions.Builder();
    fileOptionsBuilder.mimeType("text/html");
    GcsFileOptions fileOptions = fileOptionsBuilder.build();
    GcsOutputChannel outputChannel = gcsService.createOrReplace(filename, fileOptions);

    byte[] buffer = new byte[1024];
    InputStream reader = req.getInputStream();
    BufferedOutputStream outStream = new BufferedOutputStream(Channels.newOutputStream(outputChannel));
    while(true) {
        int bytesRead = reader.read(buffer);
        if (bytesRead == -1) {
            break; // have a break up with the loop.
        } else if (bytesRead < 1024) {
            byte[] temp = Arrays.copyOf(buffer, bytesRead);
            outStream.write(temp);
        } else {
            outStream.write(buffer);
        }
    }

    outStream.close();
    outputChannel.close();
}

As you can see, i use a raw InputStream to get all the data that is sent over the net.

and on the client side, i send a text file over like so: (in Android)

HttpClient httpClient = new DefaultHttpClient();
HttpPost httpost = new HttpPost("http://my-hosted-url/postit");
MultipartEntity entity = new entity.addPart("myImageFile", new FileBody(someLogFile));
httpost.setEntity(entity);
HttpResponse response;
response = httpClient.execute(httpost);

This works just fine... sort of. the problem is that when i try to view the file/data that is sent, it has a header on top of it, as such:

--NNqarc4FsG0G8hUzd82A6TCjgzKH Content-Disposition: form-data; name="myString" Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit STRING_VALUE ---NNqarc4FsG0G8hUzd82A6TCjgzKH Content-Disposition: form-data; name="myImageFile"; filename="something.txt" Content-Type: application/octet-stream Content-Transfer-Encoding: binary

[Thu Aug 14 17:14:26 PDT 2014] then the real log starts here...

How do i get rid of the headers that is somehow stuck to the body?

Answer 1

What you have here is a multipart request. It is a single request where the body consists of the various parts separated by a separator string.

In your case, it's more easily viewed as:

--NNqarc4FsG0G8hUzd82A6TCjgzKH 
Content-Disposition: form-data; name="myString" 
Content-Type: text/plain; charset=US-ASCII 
Content-Transfer-Encoding: 8bit 

STRING_VALUE 
---NNqarc4FsG0G8hUzd82A6TCjgzKH 
Content-Disposition: form-data; name="myImageFile"; filename="something.txt" 
Content-Type: application/octet-stream 
Content-Transfer-Encoding: binary

[binary here]

It has two parts where each part has its corresponding headers and body. I'm guessing you're interested in the bodies. You'll need to extract them.

You can either read the HTTP specification and/or the specification about multipart requests and write your own parser, or you can use some built-in (I don't know if GAE is Servlet 3.0 ready or not) or 3rd party methods. See these

• How can my Servlet receive parameters from a multipart/form-data form?
• Convenient way to parse incoming multipart/form-data parameters in a Servlet
• How can I handle multipart/form-data POST requests in my java servlet?