session7 custom tags

8/13/2019 Session7 Custom Tags

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JAD Session 14 - Custom Tags 1/14

Session 14 - Custom Tags

(chapter 8+9)


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Objectives

Tag Libraries The Custom Tag Development Process Hunting the Tag

Custom Tag Example JSTL (read at home)- JSP Standard Tag Library Tag Interfaces and Classes in javax.servlet.jsp.tagext

The Classic Custom Tag Event Model

Tags and Implicit Variables


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Tag Extension Mechanism

Enables creation of custom tags Java code can be avoided using custom tags

The different terminologies related to tagextension mechanism are: Tag library

TLD Custom action Custom


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Tag extension mechanism..

Tag library is acollection of customactions and tags

Custom tagencapsulates complexrecurring code.

Custom tag invokes acustom action


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Custom Tags

Separates the work profiles of Web designersand developers

Custom tags can be reused Written using XML syntax The different types of custom tags are:

Empty tag Tag with attributes Body tags


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Custom Tags

The function of the tag can be customizedusing the attributes in the custom tags

TLD file contains the details of the tagattributes

Custom tag body can include static text,HTML, and JSP elements like scriptlets,between the start and the end tag.


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The Custom Tag Development Process

There are four essential steps to writing acustom tag for use in your JavaServer Pages: Writing a Java class called a tag handler Defining the tag within a tag library definition

(TLD) file. Providing details of where to find the TLD file in

the deployment descriptor, web.xml Referencing the TLD file in your JSP page source

and using the tags from it.


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Hunting the Tag

JSP Document

Web Deployment Descriptor

test_taglib

/WEB-INF/myown-taglib.tld

Tag Library Descriptor

showDateexamples.ShowDateTagEMPTY

Tag Handler Class1000001000000010101010000010101010000001001010000111111110000000001000001000000010101010

00001010101000000100101000011111111000000000

START HERE: tag used in JSP page.

taglib uri declaration inJSP page maps to in deployment descriptor.

indeployment descriptor maps to

the real tag library descriptor file.

Finally: in the TLD maps toa tag handler class.


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Custom Tag Example

Demo\CusTags


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Tag Interfaces and Classes in javax.servlet.jsp.tagext

Tag Interfaces and Classes in javax.servlet.jsp.tagext


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The Classic Custom Tag Event Model

JSP container processing one occurrence of a tag implementing the TagInterface in one JSP page.


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Taglib step by step cc thnhphn c bn


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Taglib step by step -Custom tagn gin

T o file TLD (Tag Library Descriptor) Khi t o file TLD ch ng ta cn h nh dung tag c a ch ng ta c bao nhiuproperty.

Trong v d ny ch ng ta s c 2property l tn ng i cn ch o m ngv ki u th hi n ng y th ng nm

bd welcome taglib.customWelcome empty

ten

kieuNgay


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Taglib step by step -Custom tagn gin

S du ng Tag Library Descriptor: s d ng file TLD ch ng ta d ng 1 trong 2 c ch sau:- Khai b o tr c tip thng qua th nh phn directive taglig c atrang JSP:-

Ho c khai b o trong web.xml :< jsp-config > < taglib >

< taglib-uri >http://bodua.com < taglib-location > /WEB-

INF/tlds/mySimpleTag.tld


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Taglib step by step -Custom tagwith body

Khi ch ng ta t o custom tag c n i dung, java class taghandler x ly tag cn c th c hi n kh c nhau t y thu c v on i dung c a th cn c thi h nh m t ln hay nhi u ln:Thi ha nh m t ln : nu n i dung ch cn thi h nh m t ln th tag

handler nn implement interface Tag ho c extends abstractclass TagSupport. H m doStartTag c a tag handler cn returngi tr EVAL_BODY_INCLUDE trong tr ng h p ch ng ta cnthi h nh n i dung c a th hay return gi tri BODY_SKIP trongtr ng h p ng c l i.Thi ha nh nhi u ln : nu n i dung c a th cn thi h nh nhi uln, ch ng ta nn implements BodyTag interface l m tinterface extends t interface Tag c thm m t s h m h tr(setBodyContent, doInitBody va doAfterBody ) cho phep taghandler ki m tra v thay i n i dung th


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Taglib step by step -Custom tagwith body

Ngo i ra tng t nh TagSupport class, b n c th ch cnvit tag handler extend t BodyTagSupport implement tinterface BodyTag . V c b n ch cn vit code choh m doInitBody v doAfterBody .

H m doInitBody c g i ra thi h nh sau khi n i dung th c c nhng tr c khi n i dung th thi h nhH m doAfterBody c g i ra sau khi n i dung th thi h nh.


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Summary

Tag Libraries The Custom Tag Development Process Hunting the Tag

Custom Tag Example JSTL (read at home) Tag Interfaces and Classes in javax.servlet.jsp.tagext The Classic Custom Tag Event Model


Q&A

session7 custom tags

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