1. JSTL: The JavaServer Pages Standard Tag Library Mark A. Kolb Security Broadband, Austin, TX mak@taglib.com

2. Prerequisites  Servlet API  JavaServer Pages  Basic syntax  Implementation via Servlet API  Using resource bundles for I18N  XML

3. Related Sessions  Kimberly Bobrow’s “Introduction to JavaServer Pages (JSP)”  Bryan Basham’s “Web Application Development, A Case Study”  Noel Bergman’s “A Visitor’s Guide to Jakarta”  Mark Kolb’s “Authoring JSP Custom Tags”

4. What Is the JSTL?  A poor acronym  J = JSP?  There are actually four tag libraries in the JSP Standard Tag Library  Based on JSP 1.2/Servlet 2.3

5. What Is the JSTL?  A collection of tag libraries implementing common JSP functionality  Core functions Variables, I/O, conditionalization, iteration  Formatting/I18n Message bundles, numbers, dates  XML operations parsing, transformations  Database operations SQL

6. What Is the JSTL?  An expression language for specifying custom tag attribute values  Based on ECMAScript and Xpath  Expression language is optional  Each of the four JSTL libraries has an EL version and an RT version. EL = JSTL expression language RT = JSP request-time attribute values

7. What Is the JSTL?  A set of Java classes  Interfaces and support classes for custom tag implementors Provides for interoperability with JSTL tags  General-purpose tag library validators JSTL 1.0 validators focus on enforcing coding standards ScriptFreeTLV - prohibit scripting elements PermittedTaglibsTLV - restrict tag library usage

8. Why JSTL?  JSTL tags provide a standard implementation for typical application functionality  Reusability  Avoid reinventing the wheel  Another mechanism for avoiding the use of JSP scripting elements  EL considerably simpler than Java  Strong emphasis on “variables”  Two steps forward, one step back?

9. JSTL Expression Language  Delimiters are “ ${ ” and “ } ”  The EL can only be used for specifying attribute values in JSTL tags  Multiple expressions can be combined and mixed with static text (i.e., implicit string concatenation)

10. JSTL Expression Language  Individual expressions are combinations of identifiers, accessors, and operators  There are also identifiers for a set of JSTL implicit objects  Not the same as the JSP implicit objects (with one exception)

11. EL Identifiers  Identifiers are resolved against the four JSP scopes  Using PageContext.findAttribute(name)  Scopes are searched sequentially: page, request, session, application  Reserved identifiers for the 11 JSTL implicit objects:  pageContext, pageScope, requestScope, sessionScope, applicationScope  param, paramValues, header, headerValues  initParam, cookie

12. EL Accessors  Properties of objects are accessed via the “.” operator  user.firstName represents the value of the “firstName” property of the object referenced by the “user” identifier

13. EL Accessors  Elements of a Map, List, or array are accessed via the “[]” operator  For a map associated with the identifier users, users[”frodo”] represents the value mapped to the ”frodo” key  For a list or array associated with the identifier track, track[4] represents the fifth element of the sequence  Elements can be referenced via identifiers, as in users[username] or track[index]

14. EL Accessors  Actually, the “.” and “[]” operators are interchangeable  user.firstName and user[”firstName”] are equivalent expressions

15. EL Implicit Objects  pageContext is identical to the JSP implicit object of the same name  Provides access to the other JSP implicit objects and their properties ${pageContext.request.queryString}  The “scope” implicit objects are maps for looking up scoped attributes  pageScope, requestScope, sessionScope, and applicationScope  For example, ${sessionScope[”userProfile”]} retrieves the attribute named ”userProfile” from the user’s session, equivalent to

16. EL Implicit Objects  The param implicit object is a map for looking up the value of a request parameter  ${param[”keyword”]} is equivalent to  paramValues is also a map, which returns an array of strings containing all of the values associated with a request parameter  ${paramValues[”keyword”]} is equivalent to

17. EL Implicit Objects  The header implicit object is a map for looking up the value of a request header  ${header[”User-Agent”]} is equivalent to  headerValues is also a map, which returns an array of strings containing all of the values associated with a request header  ${headerValues[”Accept”]} is equivalent to

18. EL Implicit Objects  The initParam implicit object is a map for looking up the value of a context initialization parameter  The cookie implicit object is a map for looking up a cookie from its name

19. EL Operators  Arithmetic operators  +, -, *, / (or div ), % (or mod )  Relational operators  == (or eq ), != (or ne ), (or gt ), = (or ge )  Can be applied to both numeric and string values  Logical operators  && (or and ), || (or or ), ! (or not )  Empty operator  empty expr indicates whether expr is null or an empty String, Map, List, or array.

20. EL Operators  Logical operators will short-circuit evaluation  For example, in ${expr1 && expr2}, expr2 will not be evaluated if expr1 has a value of false.  Parentheses can be used for grouping and will override operator precedence rules  For example, ${a * (b + c)} overrides the normal precedence of multiplication over addition

21. Core Library  EL library  Dynamic attribute values specified using the JSTL expression language (i.e., ${ expr } )  RT library  Dynamic attribute values specified using the JSP expressions (i.e., )

22. Core Library Tags  General-purpose actions   Conditional actions  ,,

23. Core Library Tags  Iteration actions   URL actions ,

24. Tag  Evaluates the value attribute and outputs the result as a string  Provides equivalent functionality to JSP expressions and the action  Prints the value of the default attribute if the value attribute evaluates to null  Default result can also be specified via body content

25. Tag  The escapeXml attribute determines whether or not characters are converted to XML entities (defaults to true ) << >> && ’' ”"

26. Tag  Evaluates the value attribute and assigns the result to a scoped variable  Variable scope is either page (the default), request, session, or application  Variable value can also be specified via body content

27. Tag  Evaluates the value attribute and assigns the result to the specified JavaBeans property or map key  In the former role, provides equivalent functionality to the action  Property value can also be specified via body content

28. Tag  Removes the named variable from the indicated scope  Variable scope is either page (the default), request, session, or application

29. Tag nested actions  Catches any exception thrown by the nested actions  Caught exception is assigned to the (optional) named variable (with page scope)  If no exception is thrown, the variable is removed from page scope

30. Tag body content  Conditionally processes the body content  Body content can be omitted to just perform the variable assignment, in which case the var attribute is no longer optional

31. Tag body content … body content  Enables mutually exclusive conditionalization

32. Tag  There must be at least one action  Only the first whose test condition evaluates to true will have its body content processed  There can be at most one action, and it must be the last action within the body  The body can contain only whitespace, actions, and actions

33. ConditionalTagSupport Class  JSTL provides base class for custom tag implementors  javax.servlet.jsp.jstl.core.ConditionalTagSupport  Utility class for implementing custom tags for conditionalizing content  Custom tag works like, conditionalizing body content and optionally exposing a scoped variable  This variable can then be referenced by the test attribute of subsequent and actions

34. Tag body content  Iteratively processes the body content for a fixed number of times, like a for statement  From begin to end, by an optional step

35. Tag body content  Iteratively processes the body content for all of the items in a collection  Optionally bound by begin, end, and step

36. Tag  The items attribute supports all standard J2SE collection types  java.util.Collection, java.util.Map  java.util.Iterator, java.util.Enumeration  Arrays, including arrays of primitives  String objects which use embedded comma delimiters

37. Tag  The variable named by the var attribute references the current item of the iteration  Primitives (from an array) are wrapped  For maps, the variable references an instance of java.util.Map.Entry ( inner class of Map ) Entry has two properties, key and value  This variable has nested visibility

38. Tag  The variable named by the varStatus attribute references an instance of the LoopTagStatus class from the javax.servlet.jsp.jstl.core package  Properties indicate the current iteration status  This variable has nested visibility

39. LoopTagStatus Class  The LoopTagStatus properties are defined by eight getter methods  getCurrent() returns the current item  getIndex() returns the current index (0-based, initialized via the begin attribute)  getCount() returns the current count (1-based, independent of the begin attribute)  isFirst(), isLast()  getBegin(), getEnd(), getStep()

40. LoopTag Interface  JSTL provides an interface and a corresponding base class for custom tag implementors  javax.servlet.jsp.jstl.core.LoopTag interface  javax.servlet.jsp.jstl.core.LoopTagSupport class  Allows developers to leverage the functionality of in their own custom tags

41. Tag body content  JSTL version of java.util.StringTokenizer  Iteratively processes the body content for all of the tokens in a String  String is tokenized using the specified delimiters

42. Tag  URL re-writing  Appends session id (if appropriate)  Prepends context to relative URLs (defaulting to current context)  Request parameters can be specified via body content

43. Tag  Used to add request parameters to a URL  Nested in the body content of a,, or tag  The values of the name and value will be URL encoded when added to the URL

44. Tag  Sends an HTTP redirect response  Aborts processing of remainder of page  Request parameters can be specified via body content

45. Tag  Fetches the content of a URL  If a variable is specified, content is assigned to variable as a String  If no variable is specified, content is inserted into current page (like action)  Request parameters can be specified via body content

46. Tag body content  Fetches the content of a URL  URL content is exposed via a variable referencing a java.io.Reader  The varReader variable has nested scope  Request parameters cannot be specified via body content  Can use with var attribute to build URL with request parameters, then pass variable to

47. Formatting Library  EL library  Dynamic attribute values specified using the JSTL expression language (i.e., ${ expr } )  RT library  Dynamic attribute values specified using the JSP expressions (i.e., )

48. Formatting Library Tags  Internationalization actions , 

49. Formatting Library Tags  Data formatting actions 

50. Tag  Displays a message fetched from a resource bundle  The bundle attribute specifies an instance of javax.servlet.jsp.jstl.fmt.LocalizationContext  Message key can also be specified in body content  Message parameters can be specified via body content (after the key value, if present)

51. Tag  Supplies a single value for parametric replacement within a message  Each parameter in a message requires a corresponding tag  Nested within a action

52. Tag body content  Specifies a localization context for nested formatting actions (e.g., )  Required basename attribute identifies the resource bundle (subject to localization)  Optional prefix attribute specifies a prefix to be prepended to all message keys appearing in the body content

53. Other I18N Tags  assigns a localization context to a variable, or assigns the default localization context for a scope  sets the current locale across a JSP scope (overrides browser-based locale)  JSTL also provides a configuration variable for specifying a fallback locale  set the character encoding for a request so that request parameter values can be correctly decoded  Compensates for browser misbehavior with respect to the Content-Type header

54. Tag  Displays a formatted number, or assigns the formatted result to a variable

55. Tag  The value to be formatted can also be specified via body content.  Formatting type is either number, currency, or percentage  The pattern attribute takes precedence over the type attribute, and must follow the pattern conventions of the java.text.DecimalFormat class  Formatting is influenced by localization context

56. Tag  Displays a formatted date and/or time, or assigns the formatted result to a variable

57. Tag  Formatting type is either time, date, or both  Permitted values for the dateStyle and timeStyle attributes are default, short, medium, long, and full  Values follow java.text.DateFormat conventions  The pattern attribute takes precedence over the type, dateStyle, and timeStyle attributes, and must follow the pattern conventions of the java.text.SimpleDateFormat class  Formatting is influenced by localization context

58. Parsing Tags  parses a String into a numeric value  Resulting value can be assigned to a variable or output to page  parses a String into a numeric value  Resulting value can be assigned to a variable or output to page  Both parsing tags are locale-sensitive

59. Tag body content  Specifies the timezone in which to format or parse any nested or tags  The timezone value can be either a String identifying a timezone or an instance of java.util.TimeZone  assigns a time zone to a variable, or assigns the default time zone

60. Tag  Assigns a time zone to a variable, or assigns the default time zone for a scope

61. XML Library  EL library  Dynamic attribute values specified using the JSTL expression language (i.e., ${ expr } )  RT library  Dynamic attribute values specified using the JSP expressions (i.e., )

62. XML Library Tags  Core actions   Flow control actions  ,, 

63. XML Library Tags  Transform actions ,

64. Tag  Parses an XML document via a String or Reader specified via the xml attribute  Interoperable with action

65. Tag body content  Parses an XML document provided as body content

66. Tag  Result is stored in a variable  Variable specified by either var and optional scope, or by varDom and optional scopeDom  When var is used, the type of the result is implementation-specific  When varDom is used, the result will implement the org.w3c.dom.Document interface  The filter attribute can specify an instance of org.xml.sax.XMLFilter for filtering the XML document during parsing

67. Tag  Displays data from a parsed XML document  The select attribute employs a syntax based on XPath to identify the data to be displayed  References variable created by  Analogous to action

68. Tag  Assigns data from a parsed XML document  The select attribute employs a syntax based on XPath to identify the data to be displayed  References variable created by  Analogous to action

69. XML Flow Control Tags  Three sets of flow control actions  ,,   Analogous to like-named JSTL core actions  Conditionalization or iteration driven by XPath expression values ( select attribute), rather than EL or RT values

70. Tag  Transforms an XML document specified via the xml attribute  String, Reader, javax.xml.transform.Source, org.w3c.dom.Document, or implementation-specific class  Transformation parameters can be supplied via nested actions

71. Tag body content  Transforms an XML document provided as body content, via a nested document,, or  XML document can be followed by actions for setting transformation parameters

72. Tag  Stylesheet specified via the xslt attribute  String, Reader, or javax.xml.transform.Source  The result attribute specifies an instance of javax.xml.transform.Result for capturing the transformation result  If the var attribute is specified, the named variable will be assigned an instance of org.w3c.dom.Document representing the transformation result  If neither var nor result is specified, the transformation result is written to the JSP page.

73. Tag  Supplies a value for the named transformation parameter  Parameter value can also be specified via body content

74. SQL Library  EL library  Dynamic attribute values specified using the JSTL expression language (i.e., ${ expr } )  RT library  Dynamic attribute values specified using the JSP expressions (i.e., )

75. SQL Library Tags  Database actions ,,   Useful for debugging and quick one-offs  Heinous violation of MVC design pattern: DB code (i.e., raw SQL) doesn’t belong in the presentation layer!

76. JSTL Resources  URLs  JSP home page http://java.sun.com/products/jsp  Reference implementation http://jakarta.apache.org/taglibs/index.html  Books  “JSTL in Action” by Shawn Bayern  “Core JSTL” by David Geary  “JSTL: JSP Standard Tag Library Kick Start” by Jeff Heaton