How to Upload Files with HttpHandler

File Upload to HttpHandler results in boundary and other MIME information being written into the request contents. As parsing this information is quite comples and error-prone, one could resort to use Commons FileUpload which is proven to work great in classic Servlet environments.

Consider this example with a custom made ContextRequest. This would handle all the parsing of boundaries added into your request body by multipart/form-data while still allowing you to keep HttpHandler interface.

The main idea consists of implementing an own version of ContextRequest to work with the data provided in HttpHandler:

   public HttpHandlerRequestContext implements RequestContext {

          private HttpExchange http;

          public HttpHandlerRequestContext(HttpExchange http) {
                this.http = http;
          }

          @Override
          public String getCharacterEncoding() {
                //Need to figure this out yet
                return "UTF-8"; 
          }

          @Override
          public int getContentLength() {
                //tested to work with 0 as return. Deprecated anyways
                return 0; 
          }

          @Override
          public String getContentType() {
                //Content-Type includes the boundary needed for parsing
                return http.getRequestHeaders().getFirst("Content-type");
          }

          @Override
          public InputStream getInputStream() throws IOException {
                 //pass on input stream
                return http.getRequestBody();
          }
 }

For reference: Here's a working example listing the received files.

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.util.List;
import java.util.Map.Entry;

import org.apache.commons.fileupload.FileItem;

import org.apache.commons.fileupload.RequestContext;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;

public class HttpServerTest {

    public static void main(String[] args) throws Exception {
        HttpServer server = HttpServer.create(new InetSocketAddress(8000), 0);
        server.createContext("/fileupload", new MyHandler());
        server.setExecutor(null); // creates a default executor
        server.start();
    }

    static class MyHandler implements HttpHandler {
        @Override
        public void handle(final HttpExchange t) throws IOException {
            for(Entry<String, List<String>> header : t.getRequestHeaders().entrySet()) {
                System.out.println(header.getKey() + ": " + header.getValue().get(0));
            }
            DiskFileItemFactory d = new DiskFileItemFactory();      

            try {
                ServletFileUpload up = new ServletFileUpload(d);
                List<FileItem> result = up.parseRequest(new RequestContext() {

                    @Override
                    public String getCharacterEncoding() {
                        return "UTF-8";
                    }

                    @Override
                    public int getContentLength() {
                        return 0; //tested to work with 0 as return
                    }

                    @Override
                    public String getContentType() {
                        return t.getRequestHeaders().getFirst("Content-type");
                    }

                    @Override
                    public InputStream getInputStream() throws IOException {
                        return t.getRequestBody();
                    }

                });
                t.getResponseHeaders().add("Content-type", "text/plain");
                t.sendResponseHeaders(200, 0);
                OutputStream os = t.getResponseBody();               
                for(FileItem fi : result) {
                    os.write(fi.getName().getBytes());
                    os.write("\r\n".getBytes());
                    System.out.println("File-Item: " + fi.getFieldName() + " = " + fi.getName());
                }
                os.close();

            } catch (Exception e) {
                e.printStackTrace();
            }            
        }
    }
}