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Java servlet neither runs nor shows any error. Just shows blank page in browser

Moin Shaikh

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posted 9 years ago

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Hello Everyone,

This is my first java servlet & jsp program. There are two pages- registration form with INSERT / doPost() method and the second one is view record page with SELECT/ doGet() method. Register page has a form that accepts and inserts record and view_record is a page that displays all records using SELECT query.

Register page works fine and adds record to SQL database but when I try to run view_record (servlet page) in browser through NetBeans, it gives me a blank screen with servlet page's directory path. No error, no warning nothing, just a blank page. see the attached screenshot.

Any idea why is this happening? I tried this on multiple computers but didn't work on any.

OS: Windows Vista 32 bit.
IDE: Netbeans
Database: MysQL (Using MySQL Workbench)

Here is my code:

index.html

<html>

<head>
  <title>Insert Employee Record</title>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>

<body>
  <form method="POST" action="register">
    <table cellpadding="5" cellspacing="5" width="70%">
      <tr>
        <td width="5%">ID:</td>
        <td>
          <input type="text" name="empId">
        </td>
      </tr>
      <tr>
        <td width="5%">Name:</td>
        <td>
          <input type="text" name="empName">
        </td>
      </tr>
      <tr>
        <td width="5%">City:</td>
        <td>
          <input type="text" name="empCity">
        </td>
      </tr>
      <tr>
        <td width="5%">Salary:</td>
        <td>
          <input type="text" name="empSalary">
        </td>
      </tr>
      <tr>
        <td colspan="2" align="left">                     
          <input type="submit" name="Submit">
        </td>
      </tr>
    </table>
  </form>
  <p><a href="table.jsp">View</a>
  </p>
</body>

</html>

Servlet code (page name: register.java)

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.DriverManager;
import java.sql.SQLException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

@
WebServlet(urlPatterns = {
  "/register"
})
public class register extends HttpServlet {

public void init(ServletConfig config) throws ServletException {
    super.init(config);
  }

/**
   * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
   * methods.
   *
   * @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 processRequest(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    try (PrintWriter out = response.getWriter()) {
      /* TODO output your page here. You may use following sample code. */
      out.println("<!DOCTYPE html>");
      out.println("<html>");
      out.println("<head>");
      out.println("<title>Servlet register</title>");
      out.println("</head>");
      out.println("<body>");
      out.println("<h1>Servlet register at " + request.getContextPath() + "</h1>");
      out.println("</body>");
      out.println("</html>");
    }
  }

/**
   * 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 req, HttpServletResponse res)
  throws ServletException, IOException {
    // String connectionURL="jdbc:odbc:empdata"; // update your db url here
    Connection con = null;
    ResultSet rs;
    res.setContentType("text/html");
    PrintWriter out = res.getWriter();
    String id = req.getParameter("empId");
    String name = req.getParameter("empName");
    String city = req.getParameter("empCity");
    String salary = req.getParameter("empSalary");

try {
      Class.forName("com.mysql.jdbc.Driver");
      con = DriverManager.getConnection("jdbc:mysql://localhost:3306/empdata", "root", "admin");

String sql = "INSERT into emptable(empId,empName, empCity, empSalary) values(?,?,?,?)";
      PreparedStatement pst = con.prepareStatement(sql);
      pst.setString(1, id);
      pst.setString(2, name);
      pst.setString(3, city);
      pst.setString(4, salary);

int numRowsChanged = pst.executeUpdate();

out.println("registered successfully!");
      pst.close();
    } catch (SQLException e) {
      out.println("SQL Exception caught: " + e.getMessage());
    } catch (Exception e) {
      out.println(e);
    } finally {
      try {
        if (con != null) {
          con.close();
        }
      } catch (SQLException ignored) {
        out.println(ignored);
      }
    }

}

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

}

Code for view_record servlet (view_record.java) - this is what not working

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
import java.io.*;
import java.sql.*;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 *
 * @author SICS
 */
public class search_record extends HttpServlet {

/**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {
            /* TODO output your page here. You may use following sample code. */
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet search_record</title>");            
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet search_record at " + request.getContextPath() + "</h1>");
            out.println("</body>");
            out.println("</html>");
        }
    }

response.setContentType("text/html");  
        PrintWriter out = response.getWriter();  
        
        String empId = request.getParameter("id");
        int id = Integer.valueOf(empId);
        
        try {
            
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/empdata", "root", "admin");
            
            PreparedStatement ps=con.prepareStatement("select * from emptable where empId=?");  
            ps.setInt(1, id);
            
            out.print("<table width=50% border=1>");  
            out.print("<caption>Result:</caption>");  
            
            ResultSet rs=ps.executeQuery();  
            
            /* Printing column names */  
            ResultSetMetaData rsmd=rs.getMetaData();  
            int total=rsmd.getColumnCount();  
            out.print("<tr>");  
            for(int i=1;i<=total;i++)  
                {  
                 out.print("<th>"+rsmd.getColumnName(i)+"</th>");  
                }
                 out.print("</tr>");  
                 
                 /* Printing result */  
  
                     while (rs.next()) {
                        String i = rs.getString("empId");
                        String nm = rs.getString("empName");
                        String ct = rs.getString("empCity");
                        int s = rs.getInt("empSalary"); 
                        out.println("<tr><td>" + i + "</td><td>" + nm + "</td><td>" + ct + "</td><td>" + s + "</td></tr>"); 
                }
            out.print("</table>");

}
        
        catch (Exception e2) {
            e2.printStackTrace();
        }  
        finally{out.close();}

}

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

}

Strange thing is I don't get any error in code or on browser and yet this does not work. It should show up the records in a tabular format but instead it only shows blank screen with Servlet's directory path on the screen.

srvlt.jpg

Dasrath Verma

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posted 9 years ago

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Welcome to Code Ranch

Please do replace line 70 of view_record servlet by

Class.forName("com.mysql.jdbc.Driver");

Tapas Chand

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posted 9 years ago

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First thing is do not create HTML in Servlet. You got JSPs for view.
If you are not getting the desired output, trace it from the query output.
Have you printed the "id" in console and run the query in MySql by replacing "?" by "id". Is it giving desired output?
Have you checked the control coming inside the while loop by putting some console outputs?

Moin Shaikh

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posted 9 years ago

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Das Verma wrote:Welcome to Code Ranch

Please do replace line 70 of view_record servlet by

Class.forName("com.mysql.jdbc.Driver");

Thank you for the warm welcome

I replaced that connection string but still the same blank screen.

Sorry but I have no idea why this is happening.

Dave Tolls

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posted 9 years ago

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Look at the source html produced.

I'm looking at the servlet code posted and you are, in the processRequest method, sending an entire page to the client.
After that you then attempt to send more stuff (after the </html>). I doubt the client will display that.

Having said that, why does the code you posted have a different title ("Servlet search_record) than that displayed in your image?

Moin Shaikh

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posted 9 years ago

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Dave Tolls wrote:Look at the source html produced.

I'm looking at the servlet code posted and you are, in the processRequest method, sending an entire page to the client.
After that you then attempt to send more stuff (after the </html>). I doubt the client will display that.

Having said that, why does the code you posted have a different title ("Servlet search_record) than that displayed in your image?

My bad

, I pasted wrong code. I actually created search_record page for testing purpose after this view_record didn't work.

The code for view_record is here:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 *
 * @author SICS
 */
@WebServlet(urlPatterns = {"/view_record"})
public class view_record extends HttpServlet {

/**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {
            /* TODO output your page here. You may use following sample code. */
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet view_record</title>");            
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet view_record at " + request.getContextPath() + "</h1>");
            out.println("</body>");
            out.println("</html>");
        }
    }

// <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 req, HttpServletResponse res)
        throws ServletException, IOException {
        processRequest(req, res);
        
         PrintWriter out = res.getWriter();
         res.setContentType("text/html");
         out.println("<html><body>");
         try {
             Class.forName("com.mysql.jdbc.Driver");  
             Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/empdata", "root", "LAB@123");
             // Here dsnname- mydsn,user id- system(for oracle 10g),password is pintu.
             Statement stmt = con.createStatement();
             ResultSet rs = stmt.executeQuery("select * from employee");
             out.println("<table border=1 width=100% height=100%>");
             out.println("<tr><th>empId</th><th>empName</th><th>empCity</th><th>empSalary</th><tr>");
             while (rs.next()) {
                 String n = rs.getString("empId");
                 String nm = rs.getString("empName");
                 String ct = rs.getString("empCity");
                 int s = rs.getInt("empSalary"); 
                 out.println("<tr><td>" + n + "</td><td>" + nm + "</td><td>" + ct + "</td><td>" + s + "</td></tr>"); 
             }
             out.println("</table>");
             out.println("</html></body>");
             con.close();
            }
             catch (Exception e) {
             out.println("error");
         }
        
        
    }

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

}

Dave Tolls

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posted 9 years ago

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Did you check the html on the client?

This is what the processRequest method will have sent, before you do any database stuff:

You then do the rest of the doGet method, and attempt to construct a table.

So check the html in your browser.
There may well be a table there.

Moin Shaikh

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posted 9 years ago

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Dave Tolls wrote:Did you check the html on the client?

This is what the processRequest method will have sent, before you do any database stuff:
<!DOCTYPE html> <html> <head> <title>Servlet view_record</title> </head> <body> <h1>Servlet view_record at (some path)</h1> </body> </html>
You then do the rest of the doGet method, and attempt to construct a table.

So check the html in your browser.
There may well be a table there.

Thank you Dave,

I got it. It should be a full html table code to display the tabular format (the code that is in the doGet() method), correct?

Dave Tolls

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posted 9 years ago

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Well, if you did as Tapas said and did the display part in a JSP then you would avoid all these problems.

The immediate fix might be to remove the </html> part from processRequest, though I expect you might find other problems.

William Brogden

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posted 9 years ago

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If you don't close the servlet response output stream, it does not flush the last buffer and you get a blank screen.

Get familiar with the "view source" capability of your browser for questions like this.

Bill

Moin Shaikh

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Thank you gentlemen for all your guidance, I am checking whole of my code and fixing it as suggested here. I need to learn so many basic Java things but this is beginning and I am confident that I will overcome this kinda mistakes.

Don't get me started about those stupid light bulbs.