Sending rows of data from Servlet to jsp

[Jeanne Pierre]

I have a html page that has a drop down menu and a submit button. Once the item in the drop down is chosen and the submit button is clicked then the html page requests some information from the servlet (which accesses a database) and then it is supposed to send/display it to a jsp. I am unsure of how to send the information that is access by the servlet, to the jsp page. I have this block of code that I know must be included in order to forward the request.

    
 if(sel.equalsIgnoreCase("OS Backups"))
                        {
                                
                                try
                                {
                                
                                        rs = myStatement.executeQuery(sql);
                                        while(rs.next())
                                        {
                                                jobId = rs.getString(1);
                                                jobType = rs.getString(2);
                                                status = rs.getString(3);
                                                masterServer = rs.getString(4);
                                                
                                        }//end of while
                                        rd = getServletContext().getRequestDispatcher("/nbu_OS.jsp");
                                        
                                        rd.forward(request, response);
                                
                                }catch(Exception ex){ex.printStackTrace();}
                        }//end of if(sel.equals......
 

The problem is that I have rows of data to send back to the jsp and I am unsure of how to do it. Thank you in advance!!
[ March 13, 2006: Message edited by: Jeanne Pierre ]

[Bimal Patel]

Hi,

Probably you can follow the ValueObject pattern. In which, create a javabean with all of the properties you need. In the servlet, traverse through the resultset and for each row, create an instance of that javabean value object class duly filled by the values you get for that row. Add such javabean instance in an arraylist object. After the traversing is done, put that object as an attribute in request object and then do the forward to the JSP. In the JSP, simple write the logic of traversing that ArrayList object to show the values for each row.

I hope this helps. I've tried to explain in detail but if you need an example on this, let me know.

[Jeanne Pierre]

Ok cool thank you so much. I will try to see if this works and let you know/see what I did and let you know the outcome....Thank you so much for your idea!!!

[Jeanne Pierre]

Ok.... sorry I think I will need an example...I was trying to do a google search of how value object works but I was not very lucky. If you could give me an example of point me to a web site that has a detailed explanation and an example I would greatly appreciate it. Thank you

[Jeanne Pierre]

Would this be legal in the servlet?....

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.sql.*;
 

public class nbu_logs extends HttpServlet
{
                String sql, url, jobId, jobType, state, status, policy, schedule, client, mediaServer, started, elapsed,
                        ended, storageUnit, Try, operation, kbytes, files, pathLastWritten, percent, jobPid,
                        owner, subtype, classtype, scheduleType, priority, groupType, masterServer, retentionUnits,
                        retentionPeriod, compression, kbytesLastWritten, filesLastWritten, streamCount, everyThingElse;
                Statement myStatement;
                Connection myConnection;
                ResultSet rs;
                RequestDispatcher rd;
 
        public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException
        {
                String sel = request.getParameter("selection");
                String but = request.getParameter("B1");
 
                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                nbu_logs nbu = new nbu_logs();
 
                if(but != null)
                {
                        sql = "SELECT jobid, jobtype, status, masterserver FROM nbu_logs WHERE schedule = 'Full'";
                        try
                        {
                                Class.forName("oracle.jdbc.driver.OracleDriver");
                                //url = "jdbc:oracle:thin:username/password@servername:portnumber:serverinstance";
                               
                                myConnection = DriverManager.getConnection(url);
                                myStatement = myConnection.createStatement();
 
                        }catch(Exception ex){ex.printStackTrace();}
 

 
                        if(sel.equalsIgnoreCase("OS Backups"))
                        {
                                //out.println("<HTML><HEAD><TITLE>GSMO NetBackup Job Reports</TITLE></HEAD><BODY>");
                                try
                                {
                                //      out.println("<P><H1>Hello Welcome to OS Backups page for </H1></P>");
                                        rs = myStatement.executeQuery(sql);
                                        while(rs.next())
                                        {
                                                /*jobId = rs.getString(1);
                                                jobType = rs.getString(2);
                                                status = rs.getString(3);
                                                masterServer = rs.getString(4);*/
 
                                                nbu.setID(rs.getString(1));
                                                nbu.setType(rs.getString(2));
 

                                //              out.println("<P>" + jobId + "</P>");
                                        }//end of while
                                        rd = getServletContext().getRequestDispatcher("/nbu_OS.jsp");
                                        request.setAttribute("item", jobId);
                                        rd.forward(request, response);
                                //      out.println("</BODY></HTML>");
 
                                }catch(Exception ex){ex.printStackTrace();}
                        }//end of if(sel.equals......
                }//end of if(but.....
 
        }//end of doGet
/**************************************************
These methods are set and get methods that will
allow the requested jsp to useBean
***************************************************/
public void setID(String id){jobId = id;}
public String getID() {return jobId;}
public void setType(String type){jobType = type;}
public String getType() {return jobType;}
}//end of public class
 

Thanks again in advance!!

[Bimal Patel]

Hi,

public class JobVO {
private String jobId;
private String jobType;
private String status;
private String masterServer;

/*
 * Setters and getters for above shown attributes...
 */
}
    

Servlet code

ArrayList dataList = null;
TempVO tempVO = null;
RequestDispatcher rd = null;
try {
if(sel.equalsIgnoreCase("OS Backups")) {
dataList = new ArrayList();
rs = myStatement.executeQuery(sql);
while(rs.next()) {
tempVO = new TempVO();
tempVO.setJobId(rs.getString(1));
tempVO.setJobType(rs.getString(2));
tempVO.setStatus(rs.getString(3));
tempVO.setMasterServer(rs.getString(4));
dataList.add(tempVO);
}//end of while
request.setAttribute("dataList", dataList);
rd = getServletContext().getRequestDispatcher("/nbu_OS.jsp");
}
} catch(Exception ex) {
rd = getServletContext().getRequestDispatcher("error_page");
ex.printStackTrace();
}
rd.forward(request, response);
    

in JSP

 
ArrayList dataList = (ArrayList)request.getAttribute("dataList");
if (dataList != null) {
for (int listCnt = 0; listCnt < dataList.size(); listCnt++) {
tempJobVO = (JobVO) dataList.get(listCnt);
/*
 * presentation logic of showing attributes of this JobVO object.
 */
}
} else {
/*
 * No data found!!!
 */
}
   

[Bear Bibeault]

Originally posted by Jeanne Pierre:
Would this be legal in the servlet?

Depends what you mean by "legal".

If you mean "best practice", then no. Anytime you import java.sql.* into a servlet, you can be sure that you are violating "separation of concerns". Database code has no place anywhere in the presentation tier.

[kwame Iwegbue]

Ben, what exactly is 'separation of concerns?' please let me know why it' s so bad to import java.sql.* into servlet. I seem to be doing that a lot.

with regards the initial question, one way I handle it is to return the ResultSet in the jsp page and basically use a loop right there. somehow i'm guessing its not the most elegant way to handle this

[Bear Bibeault]

Originally posted by kwame Iwegbue:
Ben, what exactly is 'separation of concerns?' please let me know why it' s so bad to import java.sql.* into servlet. I seem to be doing that a lot.

Look up the concept of the MVC pattern

[ak pillai]

Initially it is okay, while you are learning servlets/JSPs. Once you get the code working, refactor all your database calls to a DataAccesObject (google for DAO pattern) and move your Database connection code a another utility class called ConnectionManager. The xxxxDAO class will make use of this ConnectionManager class to get a connection and your servlet will use the xxxxDAO class to map relational data to objects (i.e value object) and return the value object to your servlet.

[Jeanne Pierre]

This is so cool....I thought I got the concept of what you were saying. For some reason I don't think the list contains anything. I am just not getting what I expect. I am trying to display one of the object to the screen but I get "cannot resolve symbol" errors. I don't even know if it the servlet that is not sending the information, and I'm pretty sure that my error occurs in the way I am accessing/handeling the objects/methods.

JSP:

    
<%@ page import= "java.util.*"%>
<HTML>
<HEAD>
<TITLE>GSMO NetBackup Job Reports</TITLE>
</HEAD>
<BODY>
        <% ArrayList listData = (ArrayList)request.getAttribute("listData"); %>
<P><H1>Hello Welcome to OS Backups page for <%= listData.getString("masterServer") %></H1></P>
        <P><SELECT size="1" name="selection">
        <OPTION></OPTION>
        <OPTION>Oracle Backups</OPTION>
        <SELECT><OPTION></OPTION>
        <OPTION>Other Jobs</OPTION></SELECT>
        </P>
<TABLE BORDER="1" WIDTH="50%">
<TR>
        <TD>Job ID</TD><TD>Job Type</TD><TD></TD><TD>Test</TD></TR>
        <!--if (listData != null) {
                for (int listCnt = 0; listCnt < listData.size(); listCnt++)
                {
                //      tempJobVO = (nbu_logs) listData.get(listCnt);
                        /*
                        * presentation logic of showing attributes of this JobVO object.
                        */
                }//end of for loop
        } else {
        /*
         * No data found!!!
         */
        } -->
</TABLE>
</BODY>
</HTML>
 

Updated Servlet code:

    
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.sql.*;
import java.util.*;
 
public class nbu_logs extends HttpServlet
{
                String sql, url, jobId, jobType, state, status, policy, schedule, client, mediaServer, started, elapsed,
                        ended, storageUnit, Try, operation, kbytes, files, pathLastWritten, percent, jobPid,
                        owner, subtype, classtype, scheduleType, priority, groupType, masterServer, retentionUnits,
                        retentionPeriod, compression, kbytesLastWritten, filesLastWritten, streamCount, everyThingElse;
                ArrayList listData = null;
                Statement myStatement;
                Connection myConnection;
                ResultSet rs;
                RequestDispatcher rd;
 
        public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException
        {
                String sel = request.getParameter("selection");
                String but = request.getParameter("B1");
 
                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                nbu_logs nbu = null;
 
                if(but != null)
                {
                        sql = "SELECT jobid, jobtype, status, masterserver FROM nbu_logs WHERE schedule = 'Full'";
                        try
                        {
                                Class.forName("oracle.jdbc.driver.OracleDriver");
                                //url = "jdbc:oracle:thin:username/password@servername:portnumber:serverinstance";
                                url = "jdbc:oracle:thin:c047647/[e-mail]:1530/dev605";
                                myConnection = DriverManager.getConnection(url);
                                myStatement = myConnection.createStatement();
 
                        }catch(Exception ex){ex.printStackTrace();}
 

 
                        if(sel.equalsIgnoreCase("OS Backups"))
                        {
                                try
                                {
                                        listData = new ArrayList();
                                        rs = myStatement.executeQuery(sql);
                                        while(rs.next())
                                        {
                                                /*jobId = rs.getString(1);
                                                jobType = rs.getString(2);
                                                status = rs.getString(3);
                                                masterServer = rs.getString(4);*/
 
                                                nbu = new nbu_logs();
                                                nbu.setID(rs.getString(1));
                                                nbu.setType(rs.getString(2));
                                                nbu.setStatus(rs.getString(3));
                                                nbu.setMasterServer(rs.getString(4));
                                                listData.add(nbu);
 

                                        }//end of while
                                        request.setAttribute("listData", listData);
                                        rd = getServletContext().getRequestDispatcher("/nbu_OS.jsp");
 
                                }catch(Exception ex){ex.printStackTrace();}
                                rd.forward(request, response);
 
                        }//end of if(sel.equals......
                }//end of if(but.....
 
        }//end of doGet
/**************************************************
These methods are set and get methods that will
allow the requested jsp to useBean
***************************************************/
public void setID(String id){jobId = id;}
public String getID() {return jobId;}
public void setType(String type){jobType = type;}
public String getType() {return jobType;}
public void setStatus(String stat){status = stat;}
public String getStatus() {return status;}
public void setMasterServer(String mServer){masterServer = mServer;}
public String getMasterServer() {return masterServer;}
}//end of public nbu_logs class
 

Error:

    
HTTP Status 500 -
 
type Exception report
 
message
 
description The server encountered an internal error () that prevented it from fulfilling this request.
 
exception
 
org.apache.jasper.JasperException: Unable to compile class for JSP
 
An error occurred at line: 17 in the jsp file: /nbu_OS.jsp
Generated servlet error:
/usr/local/jakarta-tomcat-5.0.30/work/Catalina/localhost/_/org/apache/jsp/nbu_005fOS_jsp.java:62: cannot resolve symbol
symbol  : class nbu_logs 
location: class org.apache.jsp.nbu_005fOS_jsp
      out.print( (nbu_logs) listData.getMasterServer(listCnt) );
                  ^
 

An error occurred at line: 17 in the jsp file: /nbu_OS.jsp
Generated servlet error:
/usr/local/jakarta-tomcat-5.0.30/work/Catalina/localhost/_/org/apache/jsp/nbu_005fOS_jsp.java:62: cannot resolve symbol
symbol  : method getMasterServer (int)
location: class java.util.ArrayList
      out.print( (nbu_logs) listData.getMasterServer(listCnt) );
                                    ^
2 errors
 

 
org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:84)
org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:332)
org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:437)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:497)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:476)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:464)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:511)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:295)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
nbu_logs.doGet(nbu_logs.java:69)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.catalina.servlets.InvokerServlet.serveRequest(InvokerServlet.java:419)
org.apache.catalina.servlets.InvokerServlet.doGet(InvokerServlet.java:133)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
 

[Bimal Patel]

Hi,

You need to import ArrayList and the other class for which you're getting such errors by <@ page import=...

[Jeanne Pierre]

The errors I don't think are coming from the import they are coming from the way that I access the information from the list. I don't know how to reference one particular object in the list.