Question on cache control...

[Elahe Shafie]

Hi friends,
I am trying to prevent caching of pages. i.e. any time a page is revisited,I want my servlet to be invoked for latest results, so is it right if I just add this line to stop caching and servlet bring the latest version?
response.setHeader("Cache-Control","no-cache");
Many thanks for your help,
Elahe

[David O'Meara]

There is some browser-specific behaviour here, so it is slightly more complicated.
This is the solution I tend to use:

response.setHeader("Cache-Control","no-cache"); //HTTP 1.1
response.setHeader("Pragma","no-cache"); //HTTP 1.0
response.setDateHeader ("Expires", 0); //prevents caching at the proxy server

Dave

[Elahe Shafie]

Hi david,
Thanks you so much for your answer and I tested it
response.setHeader("Cache-Control","no-
res.setHeader("Cache-Control","no-cache");//HTTP 1.1
res.setHeader("Pragma","no-cache"); //HTTP 1.0
res.setDateHeader ("Expires", 0); //prevents caching at the proxy server
and even I have this in my HTML code:
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Pragma-directive" CONTENT="no-cache">
<META HTTP-EQUIV="cache-directive" CONTENT="no-cache">
<META http-equiv="Expires" content="Tue, 01 Jan 1980 1:00:00 GMT">
but it still taking the data from cache. Do you have any clue, what might be wrong here. I will appreciate your help.
Thank you Dave
Elahe

[Elahe Shafie]

And if you like to take a look on my servlet

....
public class BugDesc extends BaseServlet {
  
  static private final boolean debug = true;
  protected String strLinkAction;
  protected String strLinkView;
  protected String strLinkUpdate;
  protected String strLinkDelete;
  
      /***************/
  public void init(ServletConfig config)
  throws ServletException
  {
    super.init(config);
    
    ServletContext sctx = config.getServletContext();
    strLinkView =   getInitParameter("linkview");
    strLinkUpdate = getInitParameter("linkupdate");
    strLinkDelete = getInitParameter("linkdelete");
  }
    /**************/
  
  
  public Template handleRequest( HttpServletRequest req,
  HttpServletResponse res,
  Context ctx )
  throws IOException, ServletException
  
  {
    Template templateRet = null;
        /* first do standard additions to context */
    handleRequestBase( req, res, ctx );
    res.setHeader("Cache-Control","no-cache"); //HTTP 1.1
    res.setHeader("Pragma","no-cache"); //HTTP 1.0
    res.setDateHeader ("Expires", 0); //prevents caching at the proxy server
    
    try
    {
/* -- 1 --------------------------------------*/
      addUserList(ctx);
      addStatusNameList(ctx);
...      

[Elahe Shafie]

Sorry here please:

package com.srs.bugtrack;
import java.io.IOException;
import java.io.FileNotFoundException;
import java.util.Properties;
import java.util.Vector;
import javax.servlet.ServletConfig;
import org.apache.velocity.Template;
import org.apache.velocity.context.Context;
import org.apache.velocity.servlet.VelocityServlet;
import org.apache.velocity.app.Velocity;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.exception.ParseErrorException;
import java.io.*;
import java.util.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.text.SimpleDateFormat;

/**
 */
public class BugDesc extends BaseServlet {
  
  static private final boolean debug = true;
  protected String strLinkAction;
  protected String strLinkView;
  protected String strLinkUpdate;
  protected String strLinkDelete;
  
      /***************/
  public void init(ServletConfig config)
  throws ServletException
  {
    super.init(config);
    
    ServletContext sctx = config.getServletContext();
    strLinkView =   getInitParameter("linkview");
    strLinkUpdate = getInitParameter("linkupdate");
    strLinkDelete = getInitParameter("linkdelete");
  }
    /**************/
  
  
  public Template handleRequest( HttpServletRequest req,
  HttpServletResponse res,
  Context ctx )
  throws IOException, ServletException
  
  {
    Template templateRet = null;
        /* first do standard additions to context */
    handleRequestBase( req, res, ctx );
    res.reset(); 
    res.setHeader("Cache-Control","no-cache"); //HTTP 1.1
    res.setHeader("Pragma","no-cache"); //HTTP 1.0
    res.setDateHeader ("Expires", 0); //prevents caching at the proxy server
    
    try
    {
           /* -- 1 --------------------------------------*/
      addUserList(ctx);
      addStatusNameList(ctx);
      
            /* This will be a link back to the servlet containing
             only the select parameters.  Any order parameters
             are removed. For example, if the request came in as
             link1?dev=ms&status=open
             this string will be
             dev=ms&status=open
             This text is placed back into the context so that
            following pages can use the same select again. */
      String strSelectParam = null;
      
          /* This will be an SQL order clause or null */
      String strOrder = null;
      
          /* This will be an SQL where clause or null */
      String strWhere = null;
      String strX;
      String strBugDesc;
      
    /* if the request has any selection parameters
       construct a sql where clause */
      
      
      strX = req.getParameter( "fldDesc" );
      templateRet = getTemplate("BugDescription.html");
      
      if ( strX != null ) {
        //     strX = "%"+ strX + "%";
        //      strWhere = "upper(b.bdesc) like'"+strX+"'";
        strWhere = " upper(b.bdesc) like '%" + strX.toUpperCase() + "%' ";
        strSelectParam = "fldDesc="+strX;
      }
      
    /* If an "order" parameter was included, use it.
       Default is by number */
      strX = req.getParameter( "order" );
      if ( strX != null ) {
        if( 0 == strX.compareToIgnoreCase( "status" ) ) {
          strOrder = "s.text";
        }
        else if( 0 == strX.compareToIgnoreCase( "desc" ) ) {
          strOrder = "bdesc";
        }
        else if( 0 == strX.compareToIgnoreCase( "sdate" ) ) {
          strOrder = "submittedDate";
        }
        else if( 0 == strX.compareToIgnoreCase( "contact" ) ) {
          strOrder = "contact";
        }
        
        else {
          strOrder = "bugNumber";
        }
      }
      else {
        strOrder = "bugNumber";
      }
      
      
       /* -- 2 --------------------------------------*/
      
      vbug = model.getBugDesc(strWhere,strOrder);
      
      /* -- 3 --------------------------------------*/
     /* Once the vector has been successfully filled with data
        add it to the context.  If we fail, before here, there will
        not be an object in the template */
      
      if (vbug.isEmpty())
      {
        ctx.put("listBugs", null );
      }
      else
      ctx.put("listBugs", vbug );
      ctx.put ( "selparam", strSelectParam );
      ctx.put ("formSelect", new Integer(1));
      ctx.put ("tool1", oTool );
      ctx.put ( "tabletitle", "Show bugs with description" );
      ctx.put ( "linkview", strLinkView );
      ctx.put ( "linkupdate", strLinkUpdate );
      ctx.put ( "linkdelete", strLinkDelete );
      
      templateRet = finishRequest();
    }
    catch ( SQLException x ) {
      ctx.put ( "errormsg", "Description is not valid Please re-enter ! " );
      ctx.put ( "errornumber", new Integer(1));
    }
    catch ( Exception x ) {
      templateRet = doErrorPage( ctx, x );
    }
    return templateRet;
  }
} // eoc