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From Anjib Mulepati <anji...@hotmail.com>
Subject Connection between Web Application and DB
Date Mon, 23 Apr 2012 14:53:58 GMT
Hi All,

I have my DB and web application running in different machine. And 
whenever my DB machine restart my application fail since it can't 
connect to the DB. I have to restart my application every time my DB start.
I am using Struts Plug-in  to load connection information from web.xml 
file and creating the DAO factory from the information. DAO factory is 
stored in servlet context. Now this daoFactory is used by each DAO class 
to create the connection.

This problem exist in my system for long time and trying to fix it. I 
have put my most code here to make things clear. I am using tomcat 7.0.26

1. Context parameter in web.xml

<context-param>
<description>Type of DB.{ 1 = Oracle }</description>
<param-name>dbType</param-name>
<param-value>1</param-value>
</context-param>
<context-param>
<description>Resource reference for the database.</description>
<param-name>resRef</param-name>
<param-value>jdbc/mydb</param-value>
</context-param>

2. Plug-in configuration in struts-config.xml

<plug-in className="com.anjib.plugin.DBConfigPlugin">

3. My DBConfigPlugin class

     public class DBConfigPlugin implements PlugIn {

         private static Log log = 
LogFactory.getLog(DBConfigPlugin.class.getName());

         private DBConfig dbConfig;

         public void destroy() {
             //Nothing to do here
         }

         public void init(ActionServlet servlet, ModuleConfig config) 
throws ServletException {
             ServletContext servletContext = servlet.getServletContext();

             /* Create factory for database */
             String resRef = servletContext.getInitParameter("resRef");
             int dbType = 0;
             if (resRef == null || resRef.trim().length() == 0) {
                 log.fatal("Parameter resRef is null or invalid");
             }
             try {
                 dbType = 
Integer.parseInt(servletContext.getInitParameter("dbType"));
             } catch (NumberFormatException nfe) {
                 log.fatal(nfe);
                 log.error("Parameter dbType is not numeric");
             }
             if (dbType != DBConfig.ORACLE) {
                 log.fatal("Parameter dbType has to be 1 (Oracle)");
             }
             DBConfig = new DBConfig(resRef, dbType);
             DAOFactory daoFactory = DAOFactory.getDAOFactory(DBConfig);
             servletContext.setAttribute("daoFactory", daoFactory);
         }

         public DBConfig getDBConfig() {
             return DBConfig;
         }

         public void setDBConfig(DBConfig DBConfig) {
             this.DBConfig = DBConfig;
         }
     }

4. Create connection in DAOFactory class
         public abstract class DAOFactory {

             private DBConfig dbConfig;

             public static DAOFactory getDAOFactory(DBConfig dbConfig) {
                 switch (dbConfig.getDbType()) {
                     case DBConfig.ORACLE:
                         return new OracleDAOFactory(dbConfig);
                     default:
                         return null;
                 }
             }

             public DAOFactory(DBConfig dbConfig) {
                 this.dbConfig = dbConfig;
             }

            public Connection createConnection() throws DAOException {
                 try {
                     String str = "java:comp/env/" + dbConfig.getResRef();
                     DataSource dataSource = (DataSource) 
ServiceLocator.getInstance().getDataSource(str);
                     return dataSource.getConnection();
                 } catch (SQLException se) {
                     throw new DAOException(se.getMessage(), se);
                 } catch (ServiceLocatorException tase) {
                     throw new DAOException(tase.getMessage(), tase);
                 }
            }
     }

5. In my com.anjib.actions.BaseAction class

     public abstract class BaseAction extends 
org.apache.struts.action.Action {

         private static Log log = 
LogFactory.getLog(BaseAction.class.getName());

         protected DAOFactory daoFactory = null;

         private String message = null;

         private UserInfo userInfo = null;

         @Override
         public ActionForward execute(ActionMapping mapping, ActionForm 
form,
                 HttpServletRequest request, HttpServletResponse response)
                 throws IOException, ServletException {
             userInfo = new UserInfo();
             setUserInfo((UserInfo) 
request.getSession().getAttribute("userInfo"));
             ActionErrors errors = new ActionErrors();
             if (request.getSession().getAttribute("loginStatus") == 
null) {
                 errors.add("error", new 
ActionMessage("error.notloggedin"));
                 this.saveErrors(request, errors);
                 return mapping.findForward("sessionEnded");
             }
             ServletContext servletContext = servlet.getServletContext();
             try {
                 daoFactory = (DAOFactory) 
servletContext.getAttribute("daoFactory");
             } catch (NullPointerException npex) {
                 log.debug(npex);
                 log.error("Couldn't find the valid factory class.");
                 message = "Factory value is NULL.";
                 errors.add("label", new 
ActionMessage("error.null.factory"));
                 saveErrors(request, errors);
                 request.setAttribute("MYEXCEPTION", new 
DAOException(message, npex));
             }
         }

         protected abstract ActionForward executeAction(ActionMapping 
mapping,
             ActionForm form, HttpServletRequest request,
             HttpServletResponse response) throws IOException, 
ServletException;


         public UserInfo getUserInfo() {
             return userInfo;
         }

        public void setUserInfo(UserInfo userInfo) {
            this.userInfo = userInfo;
         }
}

6. Context.xml

<Resource auth="Container"
             driverClassName="oracle.jdbc.driver.OracleDriver"
             maxActive="20"
             maxIdle="10"
             maxWait="2000"
             name="jdbc/mydb"
             password="passw0rd"
             testOnBorrow="true"
             type="javax.sql.DataSource"
             url="jdbc:oracle:thin:@//localhost:5000/TESTDB"
             username="scott"
             validationQuery="SELECT 1 FROM DUAL"
              />




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