JSP2.0 Custom Label __jsp

JSP1.0 can be implemented by inheriting TagSupport or Bodytagsupport to implement a custom tag processing method.

JSP2.0 also supports a simpler way to customize the tag, which is to simply store the JSP code as a *.tag or *.tagx tag definition file. Tag and TAGX files support not only classic JSP code, various tag template codes, but also XML-style JSP instruction code.

By convention, tag and TAGX files need to be placed in the Web-inf/tags directory.

Here are some simple examples:

1. Simply Show time Time.tag

<%@ tag import= "java.util.*" import= "java.text.*"%> <% dateformat
  df = dateformat.getdateinstance ( Dateformat.long);
  Date d = new Date (System.currenttimemillis ());
  Out.println (Df.format (d));
%>

<%@ taglib prefix= "util" tagdir= "/web-inf/tags"%>
2. Copy string how many times Repeater.tag


<%@ attribute Name= "Count" type= "Java.lang.Integer" required= "true"%>
<%@ attribute name= "value" type= " Java.lang.String "required=" true "%>
<%!
  Private String Repeater (Integer count, String s) {
    int n = count.intvalue ();
    StringBuffer sb = new StringBuffer ();
    for (int i = 0; i < n; i++) {
      sb.append (s);
    }
    return sb.tostring ();
  }
%>
<%
  out.println (Repeater (count, value));
%>
 
<%@ taglib prefix= "util" tagdir= "/web-inf/tags"%>
3. Find the province Lookup.tag


<%@ tag import= "java.util.*"%> <%@ attribute name= "CityName" required= "true"%> <%@
Variable name-given= "province"%> <%@ variable name-given= "Population" variable-class= "Java.lang.Integer"%>
    <% if ("Toronto". Equals (CityName)) {Jspcontext.setattribute ("province", "Ontario");
  Jspcontext.setattribute ("Population", new Integer (2553400));
    else if ("Montreal". Equals (CityName)) {Jspcontext.setattribute ("province", "Quebec");
  Jspcontext.setattribute ("Population", new Integer (2195800));
    else {jspcontext.setattribute ("province", "Unknown");
  Jspcontext.setattribute ("Population", new Integer (-1)); }%> <jsp:dobody/> 
 
<%@ taglib prefix= "util" tagdir= "/web-inf/tags"%>
The above are all classic JSP code used, and the 3rd example is implemented using a different code:

* Use Tags:


<%@ tag import= "java.util.*"%> <%@ taglib prefix= "C" uri= "http://java.sun.com/jsp/jstl/" Core "%> <%@ attribute name=" CityName "required=" true "%>" <%@ variable name-given= "province"%> <%@ Vari Able name-given= "Population"%> <c:choose> <c:when test= "cityname eq ' Toronto ' > <c:set var=" Provin  Ce "value=" Ontario "/> <c:set var=" Population "value=" 2553400 "/> </c:when> <c:when test=" CityName
  eq ' Montreal ' > <c:set var= "Province" value= "Quebec"/> "<c:set" var= "Population" value= "2195800"/> </c:when> <c:otherwise> <c:set var= "province" value= "Unknown"/> <c:set "var=" Val Ue= "-1"/> </c:otherwise> </c:choose>%> <jsp:dobody/> 
 
<%@ taglib prefix= "util" tagdir= "/web-inf/tags"%> <%@ taglib prefix=
"C" uri= "http://java.sun.com/jsp/" Jstl/core "%>
* Use JSP directives, which usually generate XML-formatted files in this way


<?xml version= ' 1.0 '?> <jsp:root ' xmlns:jsp= http://java.sun.com/JSP/Page ' > <jsp: Directive.tag import= "java.util.*"/> <jsp:directive.taglib prefix= "C" uri= "Http://java.sun.com/jsp/jstl/core" "/> <jsp:directive.attribute name=" CityName "required=" true "/> <jsp:directive.variable"  Province "/> <jsp:directive.variable name-given=" Population "/> <c:choose> <c:when test=" CityName eq
	  ' Toronto ' > <c:set var= "Province" value= "Ontario"/> "<c:set" var= "Population" value= "2553400"/> </c:when> <c:when test= "cityname eq ' Montreal ' > <c:set var=" Province "value=" Quebec "/> < C:set var= "Population" value= "2195800"/> </c:when> <c:otherwise> <c:set var= "province" value= "Unknown"/> <c:set var= "Population" value= "-1"/> </c:otherwise> </c:choose> </jsp:root> ;
 
<?xml version= ' 1.0 '?>
<jsp:root
          version= ' 2.0 ' xmlns:jsp= ' http://java.sun.com/JSP/Page ' Xmlns:util= "Urn:jsptagdir:/web-inf/tags"
          xmlns:c= "Http://java.sun.com/jsp/jstl/core" >
  <jsp: Directive.page contenttype= "text/html"/>          
	
 


Appendix:

Commonly used directives in the label file:



     
 
 
      
 
       
 
        
Tag
 
        
Similar to the JSP page directive, can be used to import common Java class libraries, etc.
 
       
 
       
 
        
Include
 
        
Import other label definition files
 
       
 
       
 
        
Taglib
 
        
Use other tags, such as jstl, spring tag, struts tag, etc.
 
       
 
       
 
        
Attribute
 
        
Define a property
 
       
 
       
 
        
Variable
 
        
Defines a variable that is visible in a JSP page, and the default range is nested, which indicates that the label is valid. Available options are at_begin and At_end
 
       
 
      
 

     
 

Optional attributes for these directives


     
 
 
      
 
       
 
        
Body-content
 
        
Label body handling mode, Optional: ' Empty ', ' tagdependent ' or ' scriptless '
 
       
 
       
 
        
Import
 
        
Java class libraries used for import
 
       
 
       
 
        
Pageencoding
 
        
Set page encoding
 
       
 
       
 
        
Iselignored
 
        
Whether to ignore El expressions
 
       
 
       
 
        
Dynamic-attributes
 
        
A map for storing custom attributes, which is called a custom attribute: an implicitly-declared variable
 
       
 
       
 
        
Language
 
        
The scripting language used, must now be Java
 
       
 
       
 
        
Display-name
 
        
Label Signature
 
       
 
       
 
        
Small-icon
 
        
For tools
 
       
 
       
 
        
Large-icon
 
        
For tools
 
       
 
       
 
        
Description
 
        
Label function description
 
       
 
       
 
        
Example
 
        
Informal description of how the ' tag is used
 
       
 
      
 

     
Optional properties for <jsp:directive:attribute>


     
 
 
      
 
       
 
        
Name
 
        
Property name
 
       
 
       
 
        
Required
 
        
True or False
 
       
 
       
 
        
Rtexprvalue
 
        
True or false-Specifies whether Run-time expressions are supported
 
       
 
       
 
        
Type
 
        
Value type-default is Java.lang.String
 
       
 
       
 
        
Fragment
 
        
True or false-values are passed first to the container (false) and passed directly to the label processing method (True)
 
       
 
       
 
        
Description
 
        
Attribute description
 
       
 
      
 

     
 

Optional properties for <jsp:directive:variable>


     
 
 
      
 
       
 
        
Name-given
 
        
Variable name (variable name when label is used)
 
       
 
       
 
        
Name-from-attribute
 
        
Specifies the name of an attribute, whose value are the name of the variable that would be available the calling JSP page . Exactly one of Name-given or name-from-attribute must be supplied.
 
       
 
       
 
        
Alias
 
        
A locally scoped variable which'll store the variable ' s value. Used only with Name-from-attribute.
 
       
 
       
 
        
Variable-class
 
        
Variable class. The default is java.lang.String.
 
       
 
       
 
        
Declare
 
        
Indicates whether the variable is declared in the calling JSP page or tag file. The Default is true. Not entirely clear what this means!
 
       
 
       
 
        
Scope
 
        
Variable range, optional at_begin (valid after tag in JSP page), At_end (valid in JSP page after tag) and NESTED. NESTED (default, valid in label)
 
       
 
       
 
        
Description
 
        
Variable description