Sending and receiving files in java web applications

Question

Hi I am working on web application where I need to transfer any type of file from on web app to another.

I able to transfer data as string format but I am facing problem when I need to transfer files. First I show code used to transfer data as parameter from sender to receiver.

Sender Side:

HttpClient client = new HttpClient();  
HttpMethod method = new PostMethod("http://192.168.1.108:8081/Receiver-Server/registerAction");  
List<NameValuePair> pairs = new ArrayList<NameValuePair>();  
NameValuePair nvp1= new NameValuePair("name", "Aniket");
NameValuePair nvp2= new NameValuePair("Age", "26");

method.setQueryString(new NameValuePair[]{nvp1,nvp2});  
int statusCode = client.executeMethod(method);
System.out.println(statusCode);

Now the receiver side,

String userName = request.getParameter("name");
String age = request.getParameter("Age");

Above I am successfully getting data. So now I need to transfer any type of file, but getting problem.

So can anyone help me to solve this issue, any hint or tutorial is better to be appreciated.

Answer 1

Transferring the file requires multipart HTTP request. HTTPClient recently introduced MultipartEntityBuilder to make it easy to develop. Complete project can be downloaded from GitHub

HttpClient code that uploads a file

CloseableHttpClient httpClient = HttpClients.createDefault();
try {
    FileBody bin = new FileBody(file);
    HttpEntity reqEntity = MultipartEntityBuilder.create().addPart("bin", bin).build();
    HttpPost httpPost = new HttpPost(url);
    httpPost.setEntity(reqEntity);

    CloseableHttpResponse postResponse = httpClient.execute(httpPost);
    try {
        writer.println(postResponse.getStatusLine());
        HttpEntity postResponseEntity = postResponse.getEntity();
        if (postResponseEntity != null) {
            writer.println(EntityUtils.toString(postResponseEntity));
        }
    } finally {
        postResponse.close();
    }
} finally {
    httpClient.close();
}

A Servlet that use FileUpload to receive the file

DiskFileItemFactory factory = new DiskFileItemFactory();
ServletContext servletContext = this.getServletConfig().getServletContext();
File repository = (File) servletContext.getAttribute("javax.servlet.context.tempdir");
factory.setRepository(repository);

ServletFileUpload upload = new ServletFileUpload(factory);
List<FileItem> items = upload.parseRequest(request);
for (FileItem item : items) {
    if (!item.isFormField()) {
        writer.println("fieldName = " + item.getFieldName());
        writer.println("fileName = " + item.getName());
        writer.println("contentType = " + item.getContentType());
        writer.println("size [bytes] = " + item.getSize());
        File uploadedFile = File.createTempFile("temp", ".txt");
        item.write(uploadedFile);
        writer.println("stored as  " + uploadedFile.getAbsolutePath());
    }
}

I think that the code is so easy that it does not need explanation but feel free to ask.

One important note: never ever use supplied file name as filename of created file. This is a security risk.