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What to do to make this web page thread safe?

Vic Hood

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posted 13 years ago

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Hi Folks,

I'm trying to write a jsp that invloves the insertion , updation etc of a set of records. Right now , I'm just trying to insert a set of records after selecting values from the dropdown and then inserting them.The thing is that I'm able to get the page to work perfectly when I use it with a single user , however when multiple users try to insert simultaneously , the values of each other.
Below, are my code snippets.

<html>
<head>
<SCRIPT TYPE="text/javascript">
	function changeCombo(Value) {
			var comboBox= document.getElementById("d-down3");
			for(i=0;i<comboBox.options.length;i++) {
				if(comboBox.options[i].value==Value) {
					comboBox.selectedIndex=i;
			}
			}
	}
	function statusChangemeterserial() {
		var objDropDown = document.getElementById("d-down1");
		var DTobjid = objDropDown.options[objDropDown.selectedIndex].value;
		document.getElementById('selectedvalmeterserial').value = DTobjid;
		document.getElementById('hdnpageState1').value = '1';
		document.getElementById('ID').submit();
	}
	function statusChangemonth() {
		var objDropDown = document.getElementById("d-down2");
		var DTobjid = objDropDown.options[objDropDown.selectedIndex].value;
		document.getElementById('selectedvalmonth').value = DTobjid;
		document.getElementById('hdnconsumptioninsert').value = 'insert';
	}
	function statusChangeyear() {
		var objDropDown = document.getElementById("d-down3");
		var DTobjid = objDropDown.options[objDropDown.selectedIndex].value;
		document.getElementById('selectedvalyear').value = DTobjid;
		document.getElementById('hdnconsumptioninsert').value = 'insert';
	}
	function pagesubmit(frm) {
		if(validate(frm)) {
		document.getElementById('hdnpageState1').value = '1';
		document.getElementById('ID').submit();
		} 
	}
	function goBack() {
     	document.getElementById('Main').submit();
	}
	function pageNext(pagenum,consumerid,meterid) {
	document.getElementById('hdnpageState1').value = '1';
	document.getElementById('hdnstart').value = pagenum;
	document.getElementById('hdnconsumptioninsert').value ='';/*if not blank then duplication message 						will be displayed each
															 	time next page is clicked after selecting value of month or year**/
		document.getElementById('ID').submit();
	}
	</SCRIPT>
</head>
<body>
<FORM METHOD="POST" ACTION="${pageContext.request.contextPath}/ConsumptionSearchServlet" NAME="crudForm1" ID="Main">
</FORM>
<FORM METHOD="POST" ACTION="${pageContext.request.contextPath}/ConsumptionServlet" NAME="form" ID="ID"  <c:out value="${consumer_id}" />

<TABLE class="MasterTable" width="100%">
	
		<TR class="even">
				<td class="FrmBodyColumnLabel" colspan="2">Consumer Name:</td>
				
				<c:forEach var="ml" items="${mList}">
					<td class="FrmBodyColumnLabel"  align="left" colspan="2" >${ml.consumer_name}</td>
				</c:forEach>
				 <td colspan="2"> </td> 
			</TR>

<TR class="odd">
				<td class="FrmBodyColumnLabel">Meter Serial:</td>
				<td class="FrmBodyMandatorySymbol">*</td>
			
				<TD><SELECT name="statusdrop1" id="d-down1"
					ONCHANGE="statusChangemeterserial()">
					<OPTION VALUE="0" label="--Select--" id="drpdwnVal1"><c:forEach
						items="${mList}" var="st">
						<OPTION VALUE="${st.nmeterID}"
							<c:if test="${st.nmeterID eq meterFlag}">
   							 selected="${st.nmeterID}" 
  							</c:if>>
						<c:out value="${st.strmeterSerial}" /></OPTION>
					</c:forEach>
				</SELECT> <INPUT TYPE="HIDDEN" NAME="selectedvalmeterserial"
					ID="selectedvalmeterserial" value="${meterFlag}"></td>
					<td colspan="2"> </td>
			</TR>

<td class="FrmBodyColumnLabel">Month of the Year:</td>
				<td class="FrmBodyMandatorySymbol">*</td>
				
				<TD><SELECT name="statusdrop2" id="d-down2"
					ONCHANGE=" statusChangemonth()">
					<OPTION VALUE="0" label="--Select--" id="drpdwnVal2"><c:forEach
						items="${dao.monthList}" var="st">
						<OPTION VALUE="${st.objid}"
							<c:if test="${st.objid eq monthFlag}">
   							 selected="${st.objid}" 
  							</c:if>>
						<c:out value="${st.description}" /></OPTION>
					</c:forEach>
				</SELECT> <INPUT TYPE="HIDDEN" NAME="selectedvalmonth" ID="selectedvalmonth"
					value="${monthFlag}"></td>
					<td colspan="2"> </td>
			</TR>

<td class="FrmBodyColumnLabel">Year:</td>
				<td class="FrmBodyMandatorySymbol">*</td>
				<TD>
				<INPUT TYPE="HIDDEN" NAME="selectedvalyear1" ID="selectedvalyear1" value="">
				<SELECT name="statusdrop3" id="d-down3"
					ONCHANGE="statusChangeyear()">
					<option value="0">--Select--</option>
					<% 
				int  nyearFlag=0;
				String stryearFlag=request.getParameter("selectedvalyear1");
				if(!"".equalsIgnoreCase(stryearFlag) && null != stryearFlag)
						 nyearFlag=Integer.parseInt(stryearFlag);
					
				int nYearDecrement=5;
				String strSelected ="";				
				 Calendar cal=Calendar.getInstance();
  					int year=cal.get(Calendar.YEAR)+1;
  					for(int i=1;i<=nYearDecrement;i++){
  						year=year-1;
  						if (year==nyearFlag)
  						{
  							strSelected ="selected";
  						}
  						else
  							strSelected ="";
  					
					%>
					<OPTION VALUE="<%=year%>" <%=strSelected%> id="drpdwnVal3"><%=year%>
					<%					
					}
					%>
					</OPTION>

</SELECT>
				
				<INPUT TYPE="HIDDEN" NAME="selectedvalyear" ID="selectedvalyear" 
				<c:choose>
				<c:when test="${hdnconsumptioninsert==update}">
         		 value="${yearFlag}" </c:when>
         		 <c:otherwise>
          		 value="${yearFlaginsert}"</c:otherwise>
  				 </c:choose>> 
				 </TD>
				 <td colspan="2"> </td>
			</TR>

<td class="FrmBodyColumnLabel">Consumption Units:</td>
				<td class="FrmBodyMandatorySymbol">*</td>
				
				<td  colspan="2"><input type="text" name="ConsumptionUnits" id="consumption_units" value="${consumerconsumption.consumption_units}">Units/Month</td>
				<td class="FrmBodyMandatoryMessage"  align="right">Fields marked with (*) are mandatory.</td>
				 
			</TR>

The usage of scriptlets at that point was unavoidable ,due to a few external circumstances. I understand that their usage is not encouraged.And below is how I process my request in the servlet
Servlet.

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		Consumer bean=new Consumer();
		Consumer bean1=new Consumer();
		ArrayList<Consumer> mList=new ArrayList<Consumer>();
		ArrayList<Consumer> consumerList=new ArrayList<Consumer>();
		ArrayList<Consumer> mList1=new ArrayList<Consumer>();
		String strctrlvar="";
		String strctrlvariable="";
		if(request.getParameter("hdnpageState1")!=null&& request.getParameter("hdnpageState1")!=""){
			hdnPageState=Integer.parseInt(request.getParameter("hdnpageState1"));
		}
		if(hdnPageState==2){// While coming in from another page.
			if(request.getParameter("hdnconsumer_id")!=null && request.getParameter("hdnconsumer_id")!=""){
				consumer_idsearchscreen=Integer.parseInt(request.getParameter("hdnconsumer_id"));
			}
			mList=dao.getmList(consumer_idsearchscreen);
			System.out.println("Size of mlist");
			System.out.println(mList.size());
			for(Consumer c:mList){
				System.out.println("Consumer name from servlet" +c.getConsumer_name());
				System.out.println("The meter serial from servlet" +c.getStrmeterSerial());
			}
			request.setAttribute("consumer_id",consumer_idsearchscreen);
			request.setAttribute("mList",mList);
		}
		
	if(hdnPageState==1){
		if(request.getParameter("selectedvalmeterserial")!=null&& request.getParameter("selectedvalmeterserial")!=""){
	
			statusmeterserial=Integer.parseInt(request.getParameter("selectedvalmeterserial"));
			System.out.println("Meter serial"+statusmeterserial);
		}
		else{
			statusmeterserial=0;
		}
		if(request.getParameter("selectedvalmonth")!=null&& request.getParameter("selectedvalmonth")!=""){

statusmonth=Integer.parseInt(request.getParameter("selectedvalmonth"));
		}
		else{
			statusmonth=0;
		}
		if(request.getParameter("selectedvalyear")!=null&& request.getParameter("selectedvalyear")!=""){

statusyear=Integer.parseInt(request.getParameter("selectedvalyear"));
		}
		else{
			statusyear=0;
		}
		if(request.getParameter("ConsumptionUnits")!=null&& request.getParameter("ConsumptionUnits")!=""){

nconsumption_units=Integer.parseInt(request.getParameter("ConsumptionUnits"));
		}

if(request.getParameter("hdnconsumer_id")!=null&& request.getParameter("hdnconsumer_id")!=""){

consumer_id=Integer.parseInt(request.getParameter("hdnconsumer_id"));
		}
		
		else{
			consumer_id=0;
		}
		if(request.getParameter("hdnconsumptionupdate")!=null&& request.getParameter("hdnconsumptionupdate")!=""){
			strctrlvar=request.getParameter("hdnconsumptionupdate");
		}
		if(request.getParameter("hdnconsumptioninsert")!=null&& request.getParameter("hdnconsumptioninsert")!=""){
			strctrlvariable=request.getParameter("hdnconsumptioninsert");
		}
	// Values extracted from request parameters and set to the bean.
		bean.setConsumer_id(consumer_id);
		bean.setNmeterID(statusmeterserial);
		bean.setConsumption_units(nconsumption_units);
		bean.setNcreated_by(nmodified_by);
		bean.setNmonth_id(statusmonth);
		bean.setNyear(statusyear);
		
		String strhdnStart1=request.getParameter("hdnstart");
		
		if (strhdnStart1!=null&&strhdnStart1!=""){
			pageoffsetValue =Integer.parseInt(strhdnStart1);
		}
		else{
			pageoffsetValue=0;
			
		}
		dao.pageLimit=pageLimit;
		dao.pageOffset=pageoffsetValue;
		if(request.getParameter("selectedvalmeterserial")!=null&& request.getParameter("selectedvalmeterserial")!="" ){
		try{
			mList=dao.getmList(consumer_id);
			consumerList=dao.getConsumerList(consumer_id,statusmeterserial);// when only drop down for meter serial is changed this should get executed
			meterFlag=bean.getNmeterID();
			System.out.println("Meter ID"+meterFlag);
			totalRows=dao.totalRows;
			if(strctrlvariable.equalsIgnoreCase("insert")&& request.getParameter("hdnconsumer_id")!=null&& request.getParameter("hdnconsumer_id")!=""){
				System.out.println("Trying to insert");
		if(dao.getDuplicateConsumptionDetails(consumer_id,statusmeterserial,statusmonth,statusyear)==0){
					dao.InsertionDB(bean);
					mList=dao.getmList(consumer_id);
					consumerList=dao.getConsumerList(consumer_id,statusmeterserial);
					strMessage=rb1.getString("message");
					request.setAttribute("strMessage",strMessage);
				}
			}
			request.setAttribute("meterFlag",meterFlag);
			request.setAttribute("consumer_id",consumer_id);	
			request.setAttribute("mList",mList);	
			request.setAttribute("perPage",pageLimit);
			System.out.println("Rows count"+totalRows);
			request.setAttribute("totalCount",totalRows);
			request.setAttribute("consumerList",consumerList);
			request.setAttribute("pageoffsetValue", pageoffsetValue);
			bean=null;
		}
			catch (Exception e){
		e.printStackTrace();
	}		}
	}
		RequestDispatcher rd = request.getRequestDispatcher("pages/ConsumptionAddEdit.jsp");
		rd.forward(request, response);
	}

I just dont seem to understand why the values are being overwritten . Any pointers would be helpful.

And Sorry for the long post!! .I really cant figure out where I 'm going wrong and hence the lengthy post!

Learning and Learning!-- Java all the way!

Rajkamal Pillai

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posted 13 years ago

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JSP's are not thread safe by default. To make them thread safe they have to implement SingleThreadModel.

Add isThreadSafe attribute to your JSPs as below.

Cheers,
Raj.

William Brogden

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posted 13 years ago

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Now THAT was really bad advice, ignore it.

JSP can be Thread safe with respect to multiple requests by careful design.

If multiple users are seeing each other's values, it suggests your servlets or jsp are using instance variables instead of good practice.

Bill

Bear Bibeault

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posted 13 years ago

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Raj Kamal wrote:
JSP's are not thread safe by default. To make them thread safe they have to implement SingleThreadModel.

Wow! Really bad Advice! Do not do this! Ever.

It is unlikely that the JSP is a source of the problems. More likely (as William pointed out) improper variable use is the likely culprit.

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Bear Bibeault

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posted 13 years ago

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And, scriptlets are always avoidable with proper structure and planning.

The use of the <%! %> style of scriptlet (which does not appear to be being used here) is also a likely culprit for introducing threading issues.

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Bear Bibeault

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posted 13 years ago

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And one more piece of advice: using uppercase in HTML makes it really hard to read and sort of went out of vogue in 1998. I'd suggest using lowercase for HTML as if you were using XHTML (even if you aren't). It looks more modern and is more readable.

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Paul Clapham

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posted 13 years ago

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You didn't say what data was being misdirected. There could be all kinds of things happening. For example somebody might have used static variables in the Consumer class. Or any number of other things. So knowing what data was the problem is an important clue for you.

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Vic Hood

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posted 13 years ago

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Sorry for all the noise folks!Bad ,bad instance variables !
Thanks for the advice !

Learning and Learning!-- Java all the way!

Rajkamal Pillai

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posted 13 years ago

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Sorry folks...

For the suggestion (if it was a bad one and there seems to be a large number of experts agreeing it was a BAD one).

I thought this was the way to make JSPs Threadsafe. Below are a few sites I found when I ran a quick google:

Webpage #1
Webpage #2
Webpage #3
Webpage #4
Webpage #5

I do not wish to argue but it was the way I was doing things till now as well...

Well one more to 'un-learn'.

Cheers,
Raj.

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