4.8. PROCESSING NUMBERS USING SERVLETS

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((0 2 4 6 8) "even digit"))

Next we give an example of a servlet that handles many parameters:

;multiEcho.servlet

(servlet (color name age)

{

 Hi [name], so you are [age] years old!

}

)

If this servlet is accessed by visiting the  multiEcho.servlet  URL with the

following parameter string:

?name=Tim&age=46&color=lightgreen

Then the browser will return a lightgreen page with an h1 heading containing

the text

Hi Tim, so you are 46 years old!

Note that the order in which the parameters appear in the URL or in the

parameter list of the servlet does not matter.

4.8

Processing numbers using servlets

Let us now revisit and extend some of the first servlets we considered above. For

example, lets generalize the hypotenuse servlet to handle any triangle provided

we enter the lengths of the two other sides.

One way to write this servlet is the following:

; hypotenuse.servlet

(servlet (a b)

(case (a)

((#null) {Enter data by adding "?a=3&b=4" to the URL})

(else {The right triangle with sides of length [a] and [b],

has a hypotenuse of length

[(sqrt (+ (* a a) (* b b)))]})))

The servlet parameters a and b must be numbers or else the servlet will generate

an error! We will discuss methods for dealing with user input errors in a later

section on  error checking . For now, we assume that the user will follow

instructions and enter numbers when they are expected.