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midrange.com
Ok,
I've done some reading and stuff on how to handle database records and I
think I got it now, but I want someone to verify my thoughts.
Instead of accessing my result sets and record processing through the
servlets, because they are multithreaded, I'm better off creating a DAO
class for each table and using instantiated classes of that because
instantiated classes are thread safe yes? My code follows for a simple
servlet that saves a new softwareName. Thus I shouldn't get two different
threads changing the variables in each one as it goes thru. Thanks,
package com.csj.hardwaremaintenance;
import java.io.IOException;
import java.sql.DatabaseMetaData;
import java.util.Hashtable;
import javax.naming.InitialContext;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
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;
/**
* @version 1.0
* @author
*/
public class SaveSoftwareName extends HttpServlet {
private String dsname;
private static DataSource ds = null;
private DatabaseMetaData dmd;
private ServletContext context;
private String jdbc_source;
private String softnamTable;
private static String collectionName;
/**
* @see javax.servlet.http.HttpServlet#void
(javax.servlet.http.HttpServletRequest,
javax.servlet.http.HttpServletResponse)
*/
public void doGet(HttpServletRequest req, HttpServletResponse
resp)
throws ServletException, IOException {
performTask(req, resp);
}
/**
* @see javax.servlet.http.HttpServlet#void
(javax.servlet.http.HttpServletRequest,
javax.servlet.http.HttpServletResponse)
*/
public void doPost(HttpServletRequest req, HttpServletResponse
resp)
throws ServletException, IOException {
performTask(req, resp);
}
private void getDS() {
try {
Hashtable parms = new Hashtable();
parms.put(
"java.naming.factory.initial",
"com.ibm.websphere.naming.WsnInitialContextFactory");
InitialContext cxt = new InitialContext(parms);
ds = (DataSource) cxt.lookup("jdbc/" + dsname);
} catch (Exception e) {
e.printStackTrace();
}
}
public void init(ServletConfig config) throws ServletException {
super.init(config);
try {
context = getServletContext();
collectionName =
context.getInitParameter("misc.lib");
softnamTable =
context.getInitParameter("softnam");
dsname = context.getInitParameter("ds.name");
} catch (Exception e) {
System.err.println(e);
}
}
public void performTask(HttpServletRequest req,
HttpServletResponse resp) {
try {
if (ds == null)
getDS();
HttpSession sess = req.getSession(true);
SoftwareNameDAO sd = new SoftwareNameDAO(req,
resp, ds, softnamTable, collectionName);
String url = "";
String softwareName_error = sd.insertRecord();
if (softwareName_error.equals("")){
url = "addsoftwarenameclose.jsp";
} else {
url = "addsoftwarename.jsp";
req.setAttribute("softwareName_error",
softwareName_error);
}
getServletConfig()
.getServletContext()
.getRequestDispatcher(
url).forward(
req,
resp);
} catch (Exception e) {
e.printStackTrace();
}
}
}
and my DAO
/*
* Created on May 3, 2006
*
*
*/
package com.csj.hardwaremaintenance;
import java.sql.DatabaseMetaData;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Connection;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
/**
* @author RPower
*
*
*/
public class SoftwareNameDAO {
String softwareName = null;
String softwareNotes = null;
Connection conn = null;
DataSource ds = null;
DatabaseMetaData dmd = null;
PreparedStatement insertRecord = null;
PreparedStatement checkRecord = null;
ResultSet rs = null;
String collectionName = null;
String softnamTable = null;
/**
* @param req
* @param resp
* @param ds
* @param softwareName
* @param softwareNotes
*/
public SoftwareNameDAO(HttpServletRequest req, HttpServletResponse
resp, DataSource ds, String softnamTable, String collectionName) {
super();
if (req.getParameter("softwareName") != null) {
this.softwareName = (String)
req.getParameter("softwareName").toUpperCase();
} else {
this.softwareName = "";
}
if (req.getParameter("softwareNotes") != null) {
this.softwareNotes = (String)
req.getParameter("softwareNotes").toUpperCase();
} else {
this.softwareNotes = "";
}
this.ds = ds;
this.softnamTable = softnamTable;
this.collectionName = collectionName;
}
/**
*
*/
public String insertRecord() {
String retfield = "";
try {
conn = ds.getConnection();
dmd = conn.getMetaData();
checkRecord =
conn.prepareStatement(
"SELECT * FROM "
+ collectionName
+
dmd.getCatalogSeparator()
+ softnamTable
+ " WHERE SOFTNM = '"
+ softwareName.trim()
+ "'");
rs = checkRecord.executeQuery();
if (rs.next()){
//return error that record exists
retfield = "Cannot add record, Software
Name '" + softwareName.trim() + "' already exists!";
} else {
insertRecord =
conn.prepareStatement(
"INSERT INTO "
+ collectionName
+
dmd.getCatalogSeparator()
+ softnamTable
+ " (SOFTNM,
SOFTNT) "
+ "VALUES(?,?)");
insertRecord.setString(1, softwareName);
insertRecord.setString(2, softwareNotes);
insertRecord.execute();
retfield = "";
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if(rs!=null){
try {
rs.close();
} catch (SQLException e1) {
e1.printStackTrace();
}
rs = null;
}
if(checkRecord!=null){
try {
checkRecord.close();
} catch (SQLException e1) {
e1.printStackTrace();
}
checkRecord = null;
}
if(insertRecord!=null){
try {
insertRecord.close();
} catch (SQLException e1) {
e1.printStackTrace();
}
insertRecord = null;
}
if(conn!=null){
try {
conn.close();
} catch (SQLException e1) {
e1.printStackTrace();
}
conn = null;
}
}
return retfield;
}
}
Ron Power
Programmer
Information Services
City Of St. John's, NL
P.O. Box 908
St. John's, NL
A1C 5M2
709-576-8132
rpower@xxxxxxxxxx
http://www.stjohns.ca/
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