Lecture7 pattern

Server-side Web Programming Lecture 7: Input Validation and Error Handling

Form Validation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

What to Validate ,[object Object],[object Object],[object Object],[object Object]

Error Prevention ,[object Object],[object Object],[object Object],[object Object]

Validating Numeric Inputs ,[object Object],[object Object],[object Object],[object Object],Validate class processRequest method Integer class class parseIntt method “ five” NumberFormatException thrown Cannot parse “five”

Validating Numeric Inputs ,[object Object],[object Object],Jump here if exception Skip if no exception Usually forward to error page

Numeric Error Prevention ,[object Object],[object Object],[object Object],[object Object]

Validating Input ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Error Prevention ,[object Object]

Regular Expressions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Regular Expressions ,[object Object],[object Object],Matches any non-digit D Matches “word” character a-z, A-Z, 0-9 w Matches any non-“word” character W Matches any “space” character ( , tab, return) s Matches any non-“space” character S Matches any digit 0-9 d Matches any character .

Regular Expressions ,[object Object],[object Object],[object Object],[object Object],[object Object],Exactly number times { number } At least once + Any number of times (including 0) *

Error Tolerance ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],digit Any number of non-digits 10 times

Calendar Dates in Java ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Error Messages ,[object Object],[object Object],[object Object],[object Object]

Error Pages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Data entry page Error page lists errors errors BACK User will have forgotten what errors were listed!

Echoing Values in Text Input ,[object Object],[object Object]

Echoing Values in Checkboxes ,[object Object],[object Object],[object Object],[object Object],[object Object]

Echoing Values in Radio Buttons ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Echoing Values in Lists ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Echoing Values in Multiple Lists ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Note: syntax of creating function in JSP

Echoing Values in Multiple Lists ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Displaying Error Messages ,[object Object],[object Object],Servlet Detects invalid Quantity in request Adds “Quantity must be number” message to request as attribute request request JSP Extracts “Quantity must be number” message from request attribute Displays message next to quantity input field

Creating Error Messages in Servlet ,[object Object]

Creating Error Messages in Servlets ,[object Object]

Displaying Error Messages in JSP ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Field where error occurred Message describing error (or nothing if no error)

Displaying Error Messages in JSP

Single Input/Error Page ,[object Object],[object Object],[object Object],JSP Form elements Displays error messages if any found by servlet Servlet Validates form Calls JSP again if errors, passing error messages request errors No errors

Single Input/Error Page ,[object Object],[object Object],[object Object],[object Object]

Last Resort Error Handling ,[object Object],[object Object],[object Object]

Last Resort Error Handling ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Default Error Pages ,[object Object],[object Object],[object Object],[object Object],[object Object]

Default Exception Handling ,[object Object],[object Object],[object Object],[object Object]

Handling Missing Pages ,[object Object],[object Object],[object Object],[object Object]

Lecture7 pattern

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Lecture7 pattern