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3.3 MSP Functions: Expand.jsp

If  you  installed  webMathematica  as  described  

above

,  you  should  be  able  to  connect  to  this  JSP  via

http://localhost:8080/webMathematica/Examples/Expand.jsp.  (You  may  have  some  other  URL  for  accessing  your

server.)

When the submit button is pressed, the polynomial is raised to the power and expanded, and an HTML page that

contains  the result  is  returned.  The  source for this  page  is  in webMathematica/Examples/Expand.jsp.  A

section that shows the form tag is shown below.

<%@ page language="java"  %>

<%@ taglib uri="/webMathematica taglib" prefix="msp" %>

Expanding Polynomials

Enter a polynomial (e.g. x+y): 

Enter a positive integer (e.g. 4):

MSPBlock[{$$expr,$$num},

Expand[$$expr^$$num]]

secure computation with input variables  

This page contains form and input tags as described in the previous example. Additionally, the msp:evaluate

tag refers to the MSP function  

MSPBlock

.

When  the  form  is  submitted,  the  server  connects  to  a  Mathematica  kernel,  in  which  two  symbols,  $$expr  and

$$num, are assigned  to the text from the two input elements. If no text is entered the symbols will not have any

definition.

Mathematica now evaluates the contents of the msp:evaluate tag. The MSPBlock command is a programming

construct, which here inspects two input variables, $$expr and $$num. If either of these has no value, MSPBlock

returns  a  null string,  which  is  why the  first  time  you  access  the  page,  you do  not  see  a result.  The values  of both

variables  are  then  interpreted  by  Mathematica.  If  successful,  the  results  of  interpretation  are  substituted  into  the

second argument  or  body of MSPBlock.  In  this example  all instances  of $$expr  are substituted  with the parsed

value  of  $$expr,  and  the  same  is  done  for  $$num.  The  result  is  then  evaluated,  formatted,  and  placed  in  the

HTML page, which is returned to the client. 

Interpretation of the variables by Mathematica can fail in two ways: the input might not be valid Mathematica input

(for example,  f[}),  or it might be dangerous input  (such as ReadList["/etc/passwd"]). In  both cases, the

inputs are  rejected and an error message  generated. This demonstrates  some of the security  features of the system,

which  the  

Security

 section  documents  in  detail.  The  use  of  variables  is  discussed  further  in  

Tips  and  Tricks:

Variables

.

 .