Question

I am writing a software and a part of this software involves communication between my Java desktop client app and a servlet. The servlet pulls out textual data from the database and writes it out in 1 single out.println() statement.
The problem is that whenever the textual data written by the servlet is much, parts of the text never make it to the client.This is despite setting the contentlength response.setContentLength(text.length()) in the servlet. What could be happening?
This is the servlet:

package servlets;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;'
import javax.sql.DataSource;
/**
 *
 * @author GBEMIRO
 */

public class MessageRetrieverServlet extends HttpServlet {

DataSource pool;  // Database connection pool
private HttpSession session;

@Override
public void init() throws ServletException {
    try {
        // Create a JNDI Initial context to be able to lookup the DataSource
        InitialContext ctx = new InitialContext();
        // Lookup the DataSource, which will be backed by a pool
        //   that the application server provides.
        pool = (DataSource) ctx.lookup("java:comp/env/jdbc/TestDB");
        if (pool == null) {
            throw new ServletException("Unknown DataSource 'jdbc/TestDB'");
        }
    } catch (NamingException ex) {
        ex.printStackTrace();
    }
}//end method init

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    session = request.getSession();
    Connection conn = null;
    try {

        String email = request.getParameter("email");

        conn = pool.getConnection();

        PreparedStatement pstmt = conn.prepareStatement("SELECT MSG FROM POSTS_TABLE WHERE EMAIL = ? ");

        pstmt.setString(1, email);

        ResultSet rs = pstmt.executeQuery();
        rs.next();

        //The huge text
        Clob clob = rs.getClob("MSG");

        /**
         * The text retrieved into msg is very large, but I checked with
         * System.out.println(msg) statements it is complete up to this
         * point, no part of it is lost. So the retrieval from the database
         * is always successful.
         *
         */
        String msg = clob.getSubString(0, (int) clob.length());

        out.print(msg);

    }//end try
    catch (SQLException exception) {
        String errorMsg = "error3";
        exception.printStackTrace();
        out.print(errorMsg);
    } catch (NumberFormatException numberFormatException) {
        String errorMsg = "error4";
        numberFormatException.printStackTrace();
        out.print(errorMsg);
    }


    try {
    } finally {
        out.close();
        try {
            if (conn != null) {
                conn.close();
            }  // return to pool
        } catch (SQLException ex) {
            ex.printStackTrace();
        }
    }
}//end method

// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
 * Handles the HTTP
 * <code>GET</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

/**
 * Handles the HTTP
 * <code>POST</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

/**
 * Returns a short description of the servlet.
 *
 * @return a String containing servlet description
 */
@Override
public String getServletInfo() {
    return "Short description";
}// </editor-fold>
}

Now this is the receiving method on the client where the problem arises:

public void retrieveMessages(){
    try {
        URL url = new URL("http://"+server_name_or_ip+":8080/SecureChatEngine/MessageRetrieverServlet");

            HttpURLConnection urlCon = (HttpURLConnection) url.openConnection();
        urlCon.setDoInput(true);
        urlCon.setDoOutput(true);
              urlCon.setRequestMethod("POST");        
  urlCon.setRequestProperty("Content-type",
      "application/x-www-form-urlencoded");

  PrintWriter out = new PrintWriter( new OutputStreamWriter(
      urlCon.getOutputStream(  ), "8859_1"), true );
        StringBuilder sb = new StringBuilder("");
        sb.append(URLEncoder.encode("email","UTF-8"));
        sb.append("=");
        sb.append(URLEncoder.encode("[e-mail]","UTF-8"));

           String formData = sb.toString();
           out.print(formData);
        out.flush();


   int contentLength = urlCon.getContentLength();
  byte[] raw = new byte[contentLength];
  int length = urlCon.getInputStream().read(raw);
  System.out.println("len = "+length);
  out.close();
/**
* The message retrieved here is incomplete..a truncated version of what is coming from the server, whereas 
* it should be the full version.
*/
String serverMsg = new String(raw, 0, length);    

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

}//end method

Answer 1

@EJP’s answer is correct, you aren’t guaranteed to read the input stream with one read. You need to loop as follows…

BufferedReader in = null;
    StringBuilder sb = new StringBuilder();
    try {
        in = new BufferedReader(new InputStreamReader(urlCon.getInputStream()));
        String input = null;
        while((input=in.readLine())!=null) {
            sb.append(input);
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if(in!=null) {
            try {
                in.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    String serverMsg = sb.toString();