an example using js: {!REQUIRESCRIPT("/soap/ajax/22.0/connection.js")} var opportunitystage= '{!Opportunity.StageName}'; if(opportunitystage == 'prospecting') alert('stage is not prospecting'); else window.open('https://ap1.salesforce.com/80090000000PwZT/e?retURL=%2F80090000000PwZT');

80090000000PwZT is the contract id,,, put this dynamically....

Hi same thing i had doen with useing VF page and extension class as below

<apex:page standardController="Opportunity" extensions="CreateRoutineContractExtension" action="{!redirect}">
    <apex:pageMessages /> 
</apex:page>

extension calss:

public with Sharing class CreateRoutineContractExtension {
    Opportunity opp = new Opportunity();//Variable to store opportunity ids
        public CreateRoutineContractExtension(ApexPages.StandardController controller) {
    }
       public PageReference  redirect(){
        PageReference pageRef;
        id OpportuityId=ApexPages.currentPage().getParameters().get('id');

        System.debug('------------'+OpportuityId);
        opp = [Select Id,Name,StageName from Opportunity where Id =:OpportuityId];
        if(opp.StageName=='Closed Won'){
            apexpages.Message msg = new Apexpages.Message(ApexPages.Severity.Info,'Opportuity stage with Closed won user unable to create a new contract:' );
            apexpages.addmessage(msg);
        }
        else{
            pageRef = new PageReference('https://na15.salesforce.com/800/e?retURL=%2F800%2Fo');    

   }
        return pageRef;
    }
}

To make the URL as dynamic do i need to URL methods.

pls code sample.

prepare your URL as string an then use it in page reference object....

for example:

string contractID = 80090000000PwZ;

string myURL = 'https://ap1.salesforce.com/'+contractID +'/e?retURL=%2F'+contractID ;

 pageRef = new PageReference(myURL)

your myurl will depend on your contractID and hence will open the edit page for that contract....

I had doen in below way like

String dynrecordurl = URL.getSalesforceBaseUrl().toExternalForm() + '/' + opp.Id;

pageRef = new PageReference(dynrecordurl);//URL for contract edit page

but here what happens if opportunity stagename is not equal to Closed won it is redirecting to corresponding opportunity detail page.

But my requriment is it should redirect to contract edit page with prepopulated values so that user can fill contract details and save file.

Here we are createing the contract and not updateing the contract.