Use JSP custom tags

JSP custom tags are actually quite useful. For example, you can insert a few simple sentences on a complicated page.

To avoid a large amount of redundant code. For example, you can create a custom tag for playing a magic lamp on a news website. The following is a general example of custom tags:

Public class slidenewstag extends simpletagsupport {

/** TAG body Processing */

Public void dotag () throws jspexception, ioexception {

.......

// Use the webapplicationcontextutils tool class to obtain the DaO instance in the Spring IoC container

Dao = (basedaoimpl) webapplicationcontextutils. getrequiredwebapplicationcontext (pagecontext) getjspcontext (). getservletcontext (). getbean ("Dao ");

Stringbuffer sb = new stringbuffer ();

List list = Dao. Query (hql, 1, number );

If (list = NULL | list. Size () = 0 ){

// Output the processing result to the page

Getjspcontext (). getout (). println ("");

Return;

}

Iterator it = List. iterator ();

SB. append ("<script language = JavaScript> \ n ");

SB. append ("Var focus_width" + slideno + "=" + width + ";/* slide news Image Width */\ n ");

SB. append ("Var focus_height" + slideno + "=" + height + ";/* slide news Image Height */\ n ");

SB. append ("Var text_height" + slideno + "= 20;/* slide News Text title height */\ n ");

SB. append ("Var swf_height" + slideno + "= focus_height" + slideno + "+ text_height" + slideno + "; \ n ");

SB. append ("Var pics" + slideno + "=''; \ n ");

SB. append ("Var links" + slideno + "=''; \ n ");

SB. append ("Var texts" + slideno + "=''; \ n ");

SB. append ("function ATI" + slideno + "(URL, IMG, title) \ n ");

SB. append ("{\ n ");

SB. append ("If (pics" + slideno + "! = '') \ N ");

SB. append ("{\ n ");

SB. append ("pics" + slideno + "= \" | \ "+ pics" + slideno + "; \ n ");

SB. append ("Links" + slideno + "= \" | \ "+ Links" + slideno + "; \ n ");

SB. append ("texts" + slideno + "= \" | \ "+ texts" + slideno + "; \ n ");

SB. append ("}");

SB. append ("pics" + slideno + "= escape (IMG) + pics" + slideno + "; \ n ");

SB. append ("Links" + slideno + "= escape (URL) + Links" + slideno + "; \ n ");

SB. append ("texts" + slideno + "= title + texts" + slideno + "; \ n ");

SB. append ("} \ n ");

SB. append ("</SCRIPT> \ n ");

SB. append ("<script language = JavaScript> \ n ");

While (it. hasnext ()){

OBJ = (News) it. Next ();

If (obj. gettitle (). Length ()> titlelen ){

SB. append ("ATI" + slideno + "('" + baseurl + obj. gethtmlpath () + "','" + baseurl + "/" + obj. getpicture (). trim () + "','" + tools. cutstring (obj. gettitle (), titlelen * 2) + "'); \ n ");

} Else {

SB. append ("ATI" + slideno + "('" + baseurl + obj. gethtmlpath () + "','" + baseurl + "/" + obj. getpicture (). trim () + "','" + obj. gettitle () + "'); \ n ");

}

}

SB. append ("document. write ('<embed src = \ "" + baseurl + "/JS/pixviewer.swf \" wmode = \ "Opaque \" flashvars = \ "pics =' + pics" + slideno + "+ '& links =' + Links" + slideno + "+ '& texts =' + texts" + slideno + "+ '& borderwidth =' + focus_width" + slideno +" + '& borderheight =' + focus_height "+ slideno +" + '& textheight =' + text_height "+ slideno +" + '\ "menu = \" false \ "bgcolor = \ "# dadada \" Quality = \ "High \" width = \ "'+ focus_width" + slideno + "+' \" Height = \ "'+ swf_height" + slideno +" + '\ "allowScriptAccess = \" samedomain \ "type = \" application/X-Shockwave-Flash \ "/> '); \ n ");

SB. append ("</SCRIPT> \ n ");

// Output the processing result to the page

Getjspcontext (). getout (). println (SB );

}

As you can see, it is actually a constant assembly of HTML, nothing complicated and special.

2. Create a XXX. TLD File

<Taglib xmlns = "http://java.sun.com/xml/ns/j2ee"

Xmlns: xsi = "http://www.w3.org/2001/XMLSchema-instance"

Xsi: schemalocation = "http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"

Version = "2.0">

<! -- Tag library version -->

<Tlib-version> 1.0 </tlib-version>

<! -- Default prefix of the tag library -->

<Short-Name> eportal </short-Name>

<! -- Default URI of the tag library -->

<URI>/eportal </uri>

<Tag>

<Description> slide News list tag </description>

<Name> slidenews </Name>

<Tag-class> com. eportal. TLD. slidenewstag </Tag-class>

<! -- The TAG body is empty -->

<Body-content> Empty </body-content>

<Attribute>

<Description> topic number. Multiple topic numbers are separated by numbers, for example, I _001 and I _002 </description>

<Name> section </Name>

<Required> true </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

<Attribute>

<Description> News Type: 0-Latest news 1-headlines 2-hot news 3-excellent recommendations 4-all types </description>

<Name> newstype </Name>

<Required> false </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

<Attribute>

<Description> Number of news entries </description>

<Name> Number </Name>

<Required> true </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

<Attribute>

<Description> slide width </description>

<Name> width </Name>

<Required> true </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

<Attribute>

<Description> slide height </description>

<Name> height </Name>

<Required> true </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

<Attribute>

<Description> title words </description>

<Name> titlelen </Name>

<Required> true </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

<Attribute>

<Description> basic URL </description>

<Name> baseurl </Name>

<Required> false </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

<Attribute>

<Description> serial number of the current slide on this page </description>

<Name> slideno </Name>

<Required> true </required>

<Rtexprvalue> true </rtexprvalue>

</Attribute>

</Tag>

Note that all <attribute> must set getter and Setter in Java.

3 call

<% @ Taglib prefix = "E" uri = "/eportal" %>

<! -- Use a custom magic lamp News Tag -->

<E: slidenews section = "001" number = "5" titlelen = "30" width = "440" Height = "260" baseurl = "<% = basepath %>" slideno = "1 "/>

Do not place the TLD under Web-INF.