Web hosting isp - CHAPTER 5 PERMUTATIONS PATTERN Resources can be
CHAPTER 5 PERMUTATIONS PATTERN Resources can be assigned individual representations, meaning that multiple versions of data can coexist with each other. When URLs become resources, some developers become hesitant because it means added complexity. For example, imagine sending out an e-mail saying, Hey, buy this and you will get credited with 1000 points in your bank account. Forget for the moment that this is a famous phishing attack. Just take the sentence at face value and assume you will be sending out e-mails to people who can access their bank accounts. The question a developer has is, what URL will be sent in the e-mail? The answer is a general URL that after a login becomes specific, as illustrated in Figure 5-9. E B V N Figure 5-9. URLs used to access a bank account In Figure 5-9, the Permutations pattern is used twice, but in two different contexts. To understand the URLs, let s relate them back to the e-mail example. The bank sends out an e-mail that includes the URL /bankaccount/login. When a user receives the e-mail, the user clicks on the link. The HTTP server uses the Permutations pattern to load the appropriate content, which is HTML, and that means the URL /bankaccount/login.jsp. The URL /bankaccount/login is an interface, and the URL /bankaccount/login.jsp is its implementation. The login could be carried out by using HTTP authentication or an HTTP cookie. What you should notice is that the login is a separate process from the application itself. After being authenticated, the user is redirected to the URL /bankaccount/maryjane with an associated HTTP cookie. When the HTTP server sees the request for /bankaccount/maryjane, it checks for either HTTP authentication information or HTTP cookie information. The information is required to verify that the request can be carried out. The HTTP server sees that
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