Chapter 10: Error Handling

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Chapter 10 Error Handling
Reference Beginning JSP
2
Objectives

• Sources of Errors
• Syntax / JSP Coding Errors
• Translation-time Errors
• Request-time Errors
• Others Logical Errors, User data-entry Errors
• Handling Errors
• Using JTSL ltccatchgt action
• Using JSP Error Page Mechanism

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Syntax / JSP Coding Errors

• Reference Pages 304-309, Example 1
• Syntax errors in scripting elements will show up
  only when JSP is translated and compiled at
  request time.
• Avoid using scripting elements in new JSP
  projects to lessen complexity of debugging
• Example1\index.jsp
• Wrong use of curly bracket
• for int i0 ilt50 i
• Sample Output
• An error occurred at line 8 in the jsp file
  /example1/index.jsp Generated servlet error
  Syntax error on token "", ( expected

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Errors in JSP Directives and Actions

• Reference Pages 309-313, Example 2
• Example2\index.jsp
• Incorrect attribute for page directive caught at
  translation time
• lt_at_page lang"java" gt
• No such JSP page error for JSP action caught at
  request time
• ltjspinclude page"nosuch.jsp" /gt
• Sample Output
• org.apache.jasper.JasperException
  org.apache.jasper.runtime.JspRuntimeLibrary.intern
  alIntrospecthelper(JspRuntimeLibrary.java359)

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Handling Request-time Errors

• 1. Using JTSL ltccatch var gt action
• Catches any errors that occur in the JSP code
  residing within its body
• If optional var attribute not specified, error is
  ignored
• 2. Using JSP Error Page Mechanism
• Specify the errorPage attribute within the page
  directive
• Error-handling JSP page can be shared
• Specify the isErrorPage attribute within the page
  directive

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JTSL ltccatchgt Action

• Catching exceptions will not automatically show
  the stack trace
• Provide meaningful error message for user to act
  upon (e.g., Please call IT Support team)
• Example4\index1.jsp (Exercise 1)
• localerr variable is specified
• Specific exception class java.lang.ArithmeticExcep
  tion is handled.
• ltccatch var"localerr"gt
• errgen.divideByZero
• lt/ccatchgt
• ltcif test"localerr.rootCause.class eq 'class
  java.lang.ArithmeticException'"gt
• Do not divide by zero!
• lt/cifgt

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JSP Error Page Mechanism

• Example4\index.jsp
• lt_at_page errorPage"showerr.jsp" gt
• showerr.jsp (General error-handling JSP)
• lt_at_page isErrorPage"true" gt
• Error pageContext.exception
• URI pageContext.errorData.requestURI
• Status Code pageContext.errorData.statusCode
• Stack Trace pageContext.exception.stackTrace

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General Error-handling JSP Example
9
Next Steps

• Try It Out sections of Textbook (Chapter 10)
• Example 1, 2, 4
• Exercise 1
• You can skip Example 3 and Exercise 2