使用HTTPURLConnection从HTTP Java客户端向Servlet发送XML数据时出现问题

Question

I have standalone java client sending xml data to http servlet using httpURLconnection class.but data appearing in non printable character format.

For simulation i have been trying to send simple string but still it was appearing in non printable format.

I have written the following client code to communicate with servlet,

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.ProtocolException;
import java.net.URL;

public class HttpClient implements IClient {

    private static IClient client = null;

    private HttpURLConnection httpConn = null;

    private OutputStream output = null;

    private InputStream input = null;

    private OutputStreamWriter out = null;

    private HttpClient() {
    }

    public static IClient getHttpClient() {
        if (client == null) {
            client = new HttpClient();
        }
        return client;
    }

    @Override
    public void connect(String urlString) throws IOException {
        URL url = new URL(urlString);
        httpConn = (HttpURLConnection) url.openConnection();
        initConnection();
        httpConn.connect();
        output = httpConn.getOutputStream();
        input = httpConn.getInputStream();
        System.out.println("Connection Response:" + httpConn.getResponseCode());
    }

    @Override
    public void sendFile(File file) throws IOException {
        // BufferedOutputStream bos = new BufferedOutputStream(output);
        // InputStream fis = new FileInputStream(file);
        // int bytesRead = 0;
        // byte[] buffer = new byte[8192];
        // while ((bytesRead = fis.read(buffer, 0, 8192)) != -1) {
        // bos.write(buffer, 0, bytesRead);
        // System.out.println("write:"+buffer);
        // }
        // bos.close();
        // fis.close();

        OutputStreamWriter out = new OutputStreamWriter(output, "UTF-16");
        out.write("test me");
    }

    @Override
    public boolean isConnected() {
        return httpConn != null ? true : false;
    }

    @Override
    public void close() {
        httpConn.disconnect();
    }

    private void initConnection() throws ProtocolException {
        httpConn.setDoOutput(true);
        httpConn.setDoInput(true);
        httpConn.setRequestMethod("POST");
        httpConn.setUseCaches(false);
        httpConn.setRequestProperty("Content-Type",
                "text/xml; charset=\"UTF-16\"");
        httpConn.setRequestProperty("Connection", "Keep-Alive");

    }

    private static byte[] getBytesFromFile(File file) throws IOException {

        InputStream is = new FileInputStream(file);
        System.out.println("\nDEBUG: FileInputStream is " + file);

        // Get the size of the file
        long length = file.length();
        System.out.println("DEBUG: Length of " + file + " is " + length + "\n");

        /*
         * You cannot create an array using a long type. It needs to be an int
         * type. Before converting to an int type, check to ensure that file is
         * not loarger than Integer.MAX_VALUE;
         */
        if (length > Integer.MAX_VALUE) {
            System.out.println("File is too large to process");
            return null;
        }

        // Create the byte array to hold the data
        byte[] bytes = new byte[(int) length];

        // Read in the bytes
        int offset = 0;
        int numRead = 0;
        while ((offset < bytes.length)
                && ((numRead = is.read(bytes, offset, bytes.length - offset)) >= 0)) {

            offset += numRead;

        }

        // Ensure all the bytes have been read in
        if (offset < bytes.length) {
            throw new IOException("Could not completely read file "
                    + file.getName());
        }

        return bytes;

    }

}

and servlet code is given below,

import java.io.BufferedInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class XMLServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        doPost(req, resp);
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("=========inside doPost=========");
//      BufferedInputStream bis = new BufferedInputStream(req.getInputStream());
//      OutputStream fos = new FileOutputStream("test.xml");
//      int bytesRead = 0;
//      byte[] buffer = new byte[8192];
//      while ((bytesRead = bis.read(buffer, 0, 8192)) != -1) {
//          System.out.println("read:"+buffer);
//          fos.write(buffer, 0, bytesRead);
//      }
//      fos.close();
//      bis.close();
//      

        req.setCharacterEncoding("UTF-16");
        InputStreamReader isr = new InputStreamReader(req.getInputStream(),"UTF-16");
        char[] data = new char[10];
        isr.read(data);
        System.out.println(data);
        for (char c : data) {
            System.out.println(c);
        }
    }

}

Please any help me to get out of this problem.

Answer 1

I think you are overcomplicating it. I JUST wrote something similar that takes any file and transfers it through HTTP to a servlet. Just remember: All data is binary (including a text file)-- period. It's up to the given application to interpret that binary data. For example, notepad.exe simply reads a binary set of data and attempts to format it using ASCII standard. So knowing that, simply read a file using a raw stream, set the mime-type of the connection to application/octet-stream and send it via "PUT" method. The servlet code should be reading the file using the raw InputStream from the request and creating the corresponding file in its space.

From the client code:

URL url = new URL(urlString);
HttpURLConnection cnx = (HttpURLConnection)url.openConnection();
cnx.setRequestMethod("PUT");
cnx.setRequestProperty("Content-Type", "application/octet-stream");
// optional request property
cnx.setRequestProperty("filename", filename);
cnx.setDoOutput(true);
cnx.connect();
BufferedInputStream fileIn = 
       new BufferedInputStream(new FileInputStream(fileName), BUFFER_SIZE);
BufferedOutputStream out = 
       new BufferedOutputStream(cnx.getOutputStream(), BUFFER_SIZE);
byte[] bytes = new byte[BUFFER_SIZE];
int bytesRead;
while((bytesRead = fileIn.read(bytes)) != -1){
   out.write(bytes, 0, bytesRead);
}

That's it.

Now the servlet code....

public void doPut(HttpServletRequest request, HttpServletResponse response){
    String filename = (String)request.getHeader("filename");
    StringBuilder fullPath = new StringBuilder(100);
    ServletContext ctxt = getServletContext();
    fullPath.append(ctxt.getRealPath(""))
      .append("uploads\\").append(filename);
    File f = new File(fullPath.toString());
    f.createNewFile();
    InputStream in = request.getInputStream();
    BufferedOutputStream fileOut = 
        new BufferedOutputStream(new FileOutputStream(f));
    byte[] bytes = new byte[BUFFER_SIZE];
    int bytesRead;
    while((bytesRead = in.read(bytes)) != -1){
       fileOut.write(bytes, 0, bytesRead);
    }
    fileOut.flush();
    fileOut.close();
    response.setStatus(HttpServletResponse.SC_CREATED);   
}

Answer 2

There are two major ways to upload a file on to server using http methods:

1. Upload a file using PUT method. This allow you to put one file at a time on to server. PUT method is easy to implement but you cannot upload a file from a html form (eg uploading form in your web browser) using PUT method.

2. Upload files using POST method. This is more complicated but most web site uses this to upload files on to server. You can do multiple file uploading per request. This is what I am going to talk about.

Note: GET is not used for file uploading unless you encode it somehow.

Uploading files using URLConnection is not straight forwards and requires you to prepare your data in " multipart form ". Of course, you shouldn't do it yourself. There are a number of libraries to deal with this for you, eg HttpClient . If you really want to use URLConnection , I shall refer to previous question on " How to use java.net.URLConnection to fire and handle HTTP requests "

Below is the code for uploading your file using HttpClient. It is simplified from HttpClient example code.

import java.io.File;


import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpStatus;
import org.apache.commons.httpclient.methods.PostMethod;
import org.apache.commons.httpclient.methods.multipart.FilePart;
import org.apache.commons.httpclient.methods.multipart.MultipartRequestEntity;
import org.apache.commons.httpclient.methods.multipart.Part;
import org.apache.commons.httpclient.params.HttpMethodParams;

public class MultipartFileUploadApp {

    public static void main(String[] args) {
        String targetURL = "http://localhost:8080/yourserver/upload";
        File targetFile = new File("/path/to/your/file.txt");

        PostMethod filePost = new PostMethod(targetURL);

        filePost.getParams().setBooleanParameter(HttpMethodParams.USE_EXPECT_CONTINUE, false);

        try {

            System.out.println("Uploading " + targetFile.getName() + " to " + targetURL);

            // add more parts you want to upload multiple files.
            Part[] parts = {new FilePart(targetFile.getName(), targetFile)};

            filePost.setRequestEntity(new MultipartRequestEntity(parts, filePost.getParams()));

            HttpClient client = new HttpClient();
            client.getHttpConnectionManager().getParams().setConnectionTimeout(5000);

            int status = client.executeMethod(filePost);

            if (status == HttpStatus.SC_OK) {
                System.out.println("Upload complete, response=" + filePost.getResponseBodyAsString());
            } else {
                System.out.println("Upload failed, response=" + HttpStatus.getStatusText(status));
            }
        } catch (Exception ex) {
            System.out.println("Error: " + ex.getMessage());
            ex.printStackTrace();
        } finally {
            filePost.releaseConnection();
        }


    }
}

For the server side, you have to parse multipart form request. Of course, there exists libraries to do that for you. Here is the snipplet I am using

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class CommonsFileUploadServlet extends HttpServlet {

    private static final String TMP_DIR_PATH = "c:\\tmp";
    private File tmpDir;
    private static final String DESTINATION_DIR_PATH = "c:\\tmp\\files";
    private File destinationDir;

    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        tmpDir = new File(TMP_DIR_PATH);
        if (!tmpDir.isDirectory()) {
            throw new ServletException(TMP_DIR_PATH + " is not a directory");
        }
        //String realPath = getServletContext().getRealPath(DESTINATION_DIR_PATH);
        destinationDir = new File(DESTINATION_DIR_PATH);
        if (!destinationDir.isDirectory()) {
            throw new ServletException(DESTINATION_DIR_PATH + " is not a directory");
        }

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        response.setContentType("text/plain");
        out.println("<h1>Servlet File Upload Example using Commons File Upload</h1>");
        out.println();

        DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();
        /*
         *Set the size threshold, above which content will be stored on disk.
         */
        fileItemFactory.setSizeThreshold(1 * 1024 * 1024); //1 MB
        /*
         * Set the temporary directory to store the uploaded files of size above threshold.
         */
        fileItemFactory.setRepository(tmpDir);

        ServletFileUpload uploadHandler = new ServletFileUpload(fileItemFactory);
        try {
            /*
             * Parse the request
             */
            List items = uploadHandler.parseRequest(request);
            out.println("Count : " + items.size());
            Iterator itr = items.iterator();
            while (itr.hasNext()) {
                FileItem item = (FileItem) itr.next();
                /*
                 * Handle Form Fields.
                 */
                if (item.isFormField()) {
                    out.println("Field = " + item.getFieldName() + ", Value = " + item.getString());
                } else {
                    //Handle Uploaded files.
                    out.println("Field Name = " + item.getFieldName()
                            + ", File Name = " + item.getName()
                            + ", Content type = " + item.getContentType()
                            + ", File Size = " + item.getSize());
                    /*
                     * Write file to the ultimate location.
                     */
                    File file = new File(destinationDir, item.getName());
                    item.write(file);
                }
            }
            out.close();
        } catch (FileUploadException ex) {
            log("Error encountered while parsing the request", ex);
        } catch (Exception ex) {
            log("Error encountered while uploading file", ex);
        }

    }
}

Answer 3

I have standalone java client sending xml data to http servlet using httpURLconnection class.but data appearing in non printable character format.

I can understand that. You're sending the data as UTF-16, but the XML file itself is likely not saved in UTF-16. You need to use the same character encoding as the XML file is saved in. That's usually UTF-8.

For simulation i have been trying to send simple string but still it was appearing in non printable format.

I don't understand that. It should work fine the way as you have in the code. Probably you didn't test it properly.