thanks, I think I'm starting to understand how all this stuff is
supposed to work...
Michael
On Monday, August 26, 2002, at 05:59 PM, Michael E. Locasto wrote:
> Michael,
>
> I'm sure everyone else is gonna tell you this too, but here are some
> pointers from just glancing over the code.
>
> - set up your db connection in the init() method, not doGet().
> doGet()
> is executed every time the servlet is called with an HTTP GET. So,
> effectively, you are loading the driver and creating a connection and
> DBThing object and blah blah blah every time your servlet is called.
> That's
> a performance killer.
>
> - better yet, use a Connection Pool that's created on startup. Write
> your own, or there are many available. I'm sure others will provide
> links...
>
> - as far as your question: I'm assuming you're using an HTML form to
> POST/GET to the servlet. There are alot of ways you can go, but a
> simple one
> is to have a parameter called 'databaseaction' or whatever, and that
> indicates which operation the servlet will perform from it's doGet() or
> doPost(). Alternatvely, you can have a different HTML form/page for each
> action that calls
> the servlet (or a different servlet, although that's pretty inefficient)
> with a different parameter.
>
>>
>> This is easy enough, but how do I have the servlet update its own
>> output
>> in the web browser so that it reflects the new changes? Is there a
>> refresh command or something.
>
> You can have the servlet (or JSP) just call itself, and at the end of
> processing, just display whatever you were going to display normally.
> Servlets are based on a request/response model, so once the servlet has
> finished returning data to your browser, it is not going to attempt to
> push
> new data out. It would have to be called again after the update takes
> place.
>
>> I was thinking having a jsp page where the user inputs the changes, and
>> then POST it to the servlet.. still not sure how the page gets updated.
>> Anybody have any example sites/code??
>
> You can have the form on the JSP just call the JSP again. The JSP tests
> for
> the right combination of parameters and performs the appropriate
> actions...
>
> e.g. in 'faq.jsp' (this is basically just snippits)
>
> <html>
> <body>
> <%
> JDBCConnectionPool connectionPool =
>
> (JDBCConnectionPool)application.getAttribute("edu.tcnj.cs.cmsc446.Connection
> pool");
> %>
> <form name="myform" action="faq.jsp" method="POST">
> ...
> </form>
>
>
> <%
> /* get params, test for form submission, take appropriate action */
> String submitted=request.getParameter( "Submit" );
> String questiontext=request.getParameter( "questiontext" );
> String username=request.getParameter( "username" );
> if( submitted!=null
> && submitted.equals( "Submit Question" )
> && questiontext!=null
> && !questiontext.equals( "" )
> && username!=null
> && !username.equals( "" ) ){
>
> edu.tcnj.cs.cmsc446.SQLWorker sqlWorker = new
> edu.tcnj.cs.cmsc446.SQLWorker();
>
>
> try{
>
> sqlWorker.setConnection( connectionPool.getConnection() );
> sqlWorker.submitQuestion( questiontext, username );
> sqlWorker.logQuestionPost( username, "question",
> request.getRemoteAddr() );
>
> }catch(Exception badQues){
> application.log( "faq.jsp: error submitting new question="+badQues );
> }finally{
> if( connectionPool!=null )
> connectionPool.free( sqlWorker.getConnection() );
> }
> }else{
> out.println( "<p>No question asked at this time. Enjoy
> browsing.</p>" );
> }
> %>
>
> <!-- more html -->
> <%
> edu.tcnj.cs.cmsc446.SQLWorker sqlWorker = new
> edu.tcnj.cs.cmsc446.SQLWorker();
> try{
>
> sqlWorker.setConnection( connectionPool.getConnection() );
> Vector entries = sqlWorker.getQuestions();
>
> if( entries!=null ){
> Question ques=null;
> for( int i=0;i<entries.size();i++ ){
> ques = (Question)entries.elementAt( i );
> out.println( "<tr><td width=\"23%\"><font face=\"Arial, Helvetica,
> sans-serif\" size=\"2\"><a
> href=\"answer.jsp?refNum="+ques.getRefNum()+"\">"+ques.getRefNum()+"</a></fo
> nt></td>" );
> out.println( "<td width=\"77%\"><font face=\"Arial, Helvetica,
> sans-serif\" size=\"2\">"+ques.getQuestion()+"</font></td></tr>" );
> }
> }else{
> out.println( "<tr><td>no entries</td><td>no questions at this
> time</td></tr>" );
> }
> }catch( Exception e ){
> application.log( "faq.jsp: error getting all questions="+e );
> }finally{
> if( connectionPool!=null )
> connectionPool.free( sqlWorker.getConnection() );
> }
> %>
>
> </body>
> </html>
>
> Regards,
> Michael
>
>
>
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