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Load database look up tables during servlet start up

Posted on 2004-09-25
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Last Modified: 2012-05-05
Hi,

I am new to JSP and Struts. I am building a web application where I have Simple "Search" button which always exists. The user will be able to search for an "application" either by its name or type ect. The "type" should be a combo box. The values in the combo box should be read from the oracle database. When and Where should I load the database lookup tables. There are atleast 5 look up tables that needs to be read at start up.

I was planning on extending "org.apache.struts.action.ActionServlet"  class and override init() method to connect to the database and load these tables and put then in application scope for use in both jsps or actions.  I am using Weblogic 8.1 app server and using its JDBC datasources and connection pool.

Please advice on how to go about this problem.

Thanks
Dasari
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Question by:DASARI_R
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5 Comments
 
LVL 21

Expert Comment

by:MogalManic
ID: 12150290
First, putting database access classes/methods in the Struts classes is not a good idea.  It makes your action class hard to test and you will repeat the same DB code in other pages that use the database.  One solution is to create a TransactionGateway:

class TransactionGateway
{
        Connection dbConn;
        public TransactionGateway(String dataSource)
        {
            //Load the connection by looking up the connection URL, username, password, ETC in Map
           //...
        }


       /**
        * Run select statement on current connection and copy the results set in
        * array of Map, where each row is a Map and each column is accessed by
        * field name as key to map
        *
        * @param selectStatement - SQL statement to execute
        * @param statementParams - List of parameters to send to statement
        */        
       public Map[] getSelect(String selectStatement, List statementParams)
       {
           //Code to build statement and copy results to map array
       }
}
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LVL 21

Expert Comment

by:MogalManic
ID: 12150319
To use the class override the ? class like this:
public class SearchAction extends Action
{
  public ActionForward execute(ActionMapping mapping,
                               ActionForm form,
                               HttpServletRequest request,
                               HttpServletResponse response)
      throws Exception
  {
    String searchStr = request.getParameter("Search");
    String keywords=searchStr.split(searchStr);
    if (keywords.length<2)
       throw new Exception("I only support exactly to word searches right now");
    ArrayList keywordList=new ArrayList();
    keyWords.add(keywords[0]);
    keyWords.add(keywords[1]);

    TransactionGateway tMgr=new TransactionGateway(SEARCH_DB);
    Map[] results=tMgr.getSelect("select * from searchDB where keyWord in (?, ?)", keyWords);
    if ((results== null)) {
      return(mapping.findForward("no-Results-Found"));
    } else {
      request.setAttribute("searchResults", results);
      return(mapping.findForward("success"));
    }
  }
}
0
 

Author Comment

by:DASARI_R
ID: 12150570
Thanks for your quick response.

I want to load the tables When the web application is loaded by the server. That was the reason I was planning to extend
"ActionServlet" not the action. I could pass in the database connection parameters as init parameters servlet in the web.xml or read them from a properties file as you suggested. My concern is that Is this the right way to load tables when no actions are called yet.

Thanks
Dasari
0
 
LVL 21

Accepted Solution

by:
MogalManic earned 2000 total points
ID: 12150820
That should work, just overload the class and be sure to call super.init() in your servlet.  Something like this

class SearchServlet extends ActionServlet
{

    public void init()
          throws javax.servlet.ServletException
    {
         super.init();
        //...My initialization stuff..
        SearchDB.getInstance().initialize();
     }
}

Then in your web.xml refer to SearchServlet instead of ActionServlet.
0
 

Author Comment

by:DASARI_R
ID: 12150840
Ok
Thank you.
0

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