Avoiding "Do you want to resend information" browser messages

Avoiding "Do you want to resend information" browser messages

 This might be a minor thing but significantly improves the user experience. The problem usually happens when the update action forwards to the view action. Instead of doing a redirect. This means the user sees /editPerson.action in the address field of the browser. But he is really looking at /viewPerson.action. This means that if he presses reload he will resubmit the data. It also means the user can navigate back to the /editPerson.action by using the back and forward buttons or the browser history. 

To avoid this you can use the PRG (Post, Redirect and Get) Pattern. It can be summarized as follows: 

Never show pages in response to POST
Always load pages using GET
Navigate from POST to GET using REDIRECT

Using the PRG approach removes this possibility by never showing the /editPerson.action to the user. This means he cannot navigate back to the page in any way. In this case it means a redirect between the editPerson action (update action) and the viewPerson action (view action).

It is easily implemented in Webwork by using the redirect result type. The final mapping of editPerson and viewPerson looks like this.

< action  name ="editPerson"  class ="example.EditPersonAction" >
    < result  name ="success"  type ="redirect" >
        < param  name ="location" > /viewPerson.action?id=${userId} </ param >
        < param  name ="parse" > true </ param >
    </ result >
    < result  name ="invalid.token" > /duplicate_post.vm </ result >
    < interceptor-ref  name ="defaultStack" />
    < interceptor-ref  name ="token" />
</ action >

< action  name ="viewPerson"  class ="example.ViewPersonAction" >
    < result  name ="success" > /view_person.vm </ result >
    < interceptor-ref  name ="defaultStack" />
</ action >

One thing to notice is the OGNL expression in the location (/viewPerson.action?id=${userId}) This means Webwork will evaluate the expression at runtime and replace ${userId}. In this case it is taken directly from a request parameter.

In Struts you would have to manually code the redirect as far as I know.

方向:分布式系统设计