Custom Tags Organization of the platform Your

Organization of the platform Your web pages Your application JSTL Java. Server Pages (JSP)

What’s irritating about Custom Tags? The tag-extension protocol is too complicated do. Start. Tag()

What’s irritating about JSP? Also, tags don’t support certain kinds of code reuse. <font

What’s bad about JSP? ( ) The general consensus says… Scriplets They complicate abstraction

JSP 2. 0 Sun introduced the solution to these problems in JSP 2. 0.

JSP Expression Language JSP became beautiful after this The motivation is to lose scriplets

EL syntax Expressions appear between ${ and }. Note that ${ and } may

EL syntax EL searches each scope area if a scope isn’t specified Specific scope

EL Operators Arithmetic +, -, *, / (or div), % (or mod) – note

EL Operators (Examples) Arithmetic ${age + 3} Comparisons ${age > 21} Equality checks ${age

Implicit objects in EL Param and paramvalues Access HTTP request parameters Example: ${param. password}

EL: Uses JSTL 1. 0 introduced the EL, but it could be used only

JSTL JSP Standard Tag Library Set of tags that should be available in all

Why JSTL? A big reason is that writing your own custom actions, or tags,

JSTL: Features Control flow Iteration, conditions URL management Retrieve data, add session IDs Text

JSTL: Libraries Library features Recommended prefix Core (control flow, URLs, variable access) Text formatting

Managing variables Outputting values with EL <c: out value=”${user. IQ}” /> Storing data <c:

Iteration A loop with a start, end, and step (typical for statement) <c: for.

${x} ${x *" src="https://present5.com/presentation/fa244b3973a43d8b504029e054b42fb7/image-20.jpg" alt="Example

Value

Square

${x}

${x *" />

Conditional logic Conditional evaluation <c: if test=”${a == b}”> a equals b </c: if>

This is an" src="https://present5.com/presentation/fa244b3973a43d8b504029e054b42fb7/image-22.jpg" alt="Example This is an" />

URL management Retrieving data <c: import var=”cnn” url=”http: //www. cnn. com/cnn. rss”/> Data exposed

Text formatting Locale-sensitive formatting and parsing <fmt: format. Number type=“currency” Numbers value=“${salary}” /> Dates

database manipulation Queries (and Result. Set caching) <sql: query sql=“SELECT * FROM USERS” var=“result”

XML manipulation Use of XPath to access, display pieces of XML documents <c: import

Why Not XSLT JSTL integrates XPath with convenient, standard access to Java/JSP code. E.

Adding New Tag There are two ways to add news tags Extend the JSTL

Tag Files Solve difficulty of reusing text/HTML within a tag. And makes it much

Tag Files <%@ tag name=”table. Tag” %> <%@ attribute name=”items” %> <table width=”…” bgcolor=”…”>

Using new Tag. . Your shopping cart: <my: table. Tag items=”${cart}” /> Your wish

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Custom Tags

Organization of the platform Your web pages Your application JSTL Java. Server Pages (JSP) Java Servlet API Java language

What’s irritating about Custom Tags? The tag-extension protocol is too complicated do. Start. Tag() or d f en? har , ev o To ling s Go do. Init. Body() do. Catch() do. End. Tag() release() Tag handler do. After. Body() do. Finally()

What’s irritating about JSP? Also, tags don’t support certain kinds of code reuse. ”> <% for (…) { %> <%= customer %>: <%= hat. Size %> <% } %> out. println(…); for(…) { out. println(…); … }

What’s bad about JSP? ( ) The general consensus says… Scriplets They complicate abstraction and code reuse. They make it harder for nonprogrammers to maintain pages

JSP 2. 0 Sun introduced the solution to these problems in JSP 2. 0. It addresses theses issues by introducing Expression language Tag files Simplified Tag API (Simple. Tag versus Tag) Improved XML syntax JSTL, although it is not part of JSP specificiation.

JSP Expression Language JSP became beautiful after this The motivation is to lose scriplets whatsoever. Also non java programmers should be able to use it easily, because it is just an expression language. It was inspired by xpath and java script except it is much easier than any of them

EL syntax Expressions appear between ${ and }. Note that ${ and } may contain whole expressions, not just variable names E. g. , ${my. Expression + 2} Access Java. Bean properties using. (dot) ${book. title} translates to book. get. Title() Access to Array and Collection elements using collection[] Access to a Map value by key using map[“key”]

EL syntax EL searches each scope area if a scope isn’t specified Specific scope areas can be used: ${page. Scope. title} ${request. Scope. title} ${session. Scope. title} ${application. Scope. title} ${duck. beak. Color} can resolve to ((Duck) page. Context. get. Attribute(”duck”)). get. Beak. Color() Automatic Casting, wow

EL Operators Arithmetic +, -, *, / (or div), % (or mod) – note on XPath Relational == (or eq), != (or ne), < (or lt) > (or gt), <= (or le), >= (or ge) Logical && (or and), || (or or), ! (or not) Validation empty null values Collections or Arrays that are empty Strings that evaluate to “”

EL Operators (Examples) Arithmetic ${age + 3} Comparisons ${age > 21} Equality checks ${age = 55} Logical operations ${young or beautiful} Emptiness detection ${empty a} ‘a’ is empty String (“”), empty List, null, etc. Useful for ${empty param. x}

Implicit objects in EL Param and paramvalues Access HTTP request parameters Example: ${param. password} Header and headervalues Request header information Example: ${header[“User-Agent”]} Initparam (for the context init parameters of the webapp) Example: ${page. Context. request. remote. User} Cookies Example: ${cookie. crumb}

EL: Uses JSTL 1. 0 introduced the EL, but it could be used only within tags. In JSP 2. 0, it can be used almost anywhere Hi, ${user}. You are years old.

JSTL JSP Standard Tag Library Set of tags that should be available in all compliant JSP containers Promotes rapid application development at the web page layer

Why JSTL? A big reason is that writing your own custom actions, or tags, can be a pain There was lots of reinventing the wheel going on, for tasks like displaying a date in a special format Many open source libraries sprung up, but there was still no standard This fueled the fire behind JSTL

JSTL: Features Control flow Iteration, conditions URL management Retrieve data, add session IDs Text formatting and internationalization Dates and numbers Localized messages XML manipulation XPath, XSLT Database access Queries, updates (you do not need to write java any more )

JSTL: Libraries Library features Recommended prefix Core (control flow, URLs, variable access) Text formatting c XML manipulation x Database access sql fmt

Managing variables Outputting values with EL Storing data // arbitrary text Note the use of “var” and “scope”: a JSTL convention

Iteration A loop with a start, end, and step (typical for statement) body content A loop using an Iterator for a collection body content

Example <table> <tr><th>Value</th><th>Square</th></tr> <c: for. Each var=

${x}

${x *" src="https://present5.com/presentation/fa244b3973a43d8b504029e054b42fb7/image-20.jpg" alt="Example

Value

Square

${x}

${x *" /> Example

Value	Square
${x}	${x * x}

Conditional logic Conditional evaluation a equals b Mutually exclusive conditionals a equals b a equals c I don’t know what ’a’ equals.

Example <c: choose> <c: when test= This is an" src="https://present5.com/presentation/fa244b3973a43d8b504029e054b42fb7/image-22.jpg" alt="Example This is an" /> Example This is an insecure Web session. This is a secure Web session. You are using an unrecognized Web protocol. How did this happen? !

URL management Retrieving data Data exposed as String or Reader All core URLs supported (HTTP, FTP, HTTPS with JSSE) Local, cross-context imports supported Printing URLs Redirection

Text formatting Locale-sensitive formatting and parsing Dates Internationalization Message bundles Message argument substitution “Hi {0}. I would like to {1} your money today. I will use it to buy myself a big {2}. ”

Example <table> <fmt: time. Zone value= Example

${blog. Entry. title}

${blog. Entry. text} [Posted ]

database manipulation Queries (and Result. Set caching) … Updates / inserts Transactions () Parametric (Prepared. Statement) argument substitution () Data. Source-based connection management

XML manipulation Use of XPath to access, display pieces of XML documents Chaining XSLT transformations

Why Not XSLT JSTL integrates XPath with convenient, standard access to Java/JSP code. E. g. , parse an article URL out of a document, then follow the URL and parse its contents. JSP/JSTL may be more familiar and convenient for simple tasks. Functional versus imperative programming

Adding New Tag There are two ways to add news tags Extend the JSTL and override methods Define Tag files (This is much easier, so we gone study this )

Tag Files Solve difficulty of reusing text/HTML within a tag. And makes it much easier to write simple tags, since you can do so in JSP instead of Java. Stand-alone file with <%@ tag %> directive instead of traditional <%@ page %> directive.

Tag Files <%@ tag name=”table. Tag” %> <%@ attribute name=”items” %>

	Name	IQ
${i. full. Name}	${i. IQ}

Using new Tag. . Your shopping cart: Your wish list: Things we want you to buy: