Java Development jsp custom tag

This article aims to correct some incorrect articles on the Internet!

Development steps:

First, create a class:

Inherit BodyTagSupport

Then set the field generation set Method

Class:

[Java] package org. pan. tags;
 
Import java. io. IOException;
Import java. io. PrintWriter;
 
Import javax. servlet. http. HttpServletRequest;
Import javax. servlet. http. HttpServletResponse;
Import javax. servlet. http. HttpSession;
Import javax. servlet. jsp. JspException;
Import javax. servlet. jsp. tagext. BodyTagSupport;
 
Public class SessionProperty extends BodyTagSupport {
 
Private static final long serialVersionUID = 1L;

Private String value; // The attribute to be obtained.

Public void setValue (String value ){
This. value = value;
}

Public String getValue (){
Return value;
}
 
@ Override
Public int doEndTag () throws JspException {
// TODO Auto-generated method stub
Return super. doEndTag ();
}
 
@ Override
Public int doStartTag () throws JspException {

System. out. println ("OK ");
HttpServletRequest request = (HttpServletRequest) pageContext. getRequest ();
HttpSession session = request. getSession ();

Object object = session. getAttribute (value );
If (object = null) return EVAL_PAGE;

If (object instanceof String ){

Try {
PageContext. getOut (). write (object. toString ());
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
}

Return super. doStartTag ();
}
 
}

Package org. pan. tags;

Import java. io. IOException;
Import java. io. PrintWriter;

Import javax. servlet. http. HttpServletRequest;
Import javax. servlet. http. HttpServletResponse;
Import javax. servlet. http. HttpSession;
Import javax. servlet. jsp. JspException;
Import javax. servlet. jsp. tagext. BodyTagSupport;

Public class SessionProperty extends BodyTagSupport {

Private static final long serialVersionUID = 1L;
 
Private String value; // The attribute to be obtained.
 
Public void setValue (String value ){
This. value = value;
}
 
Public String getValue (){
Return value;
}

@ Override
Public int doEndTag () throws JspException {
// TODO Auto-generated method stub
Return super. doEndTag ();
}

@ Override
Public int doStartTag () throws JspException {
 
System. out. println ("OK ");
HttpServletRequest request = (HttpServletRequest) pageContext. getRequest ();
HttpSession session = request. getSession ();

Object object = session. getAttribute (value );
If (object = null) return EVAL_PAGE;

If (object instanceof String ){

Try {
PageContext. getOut (). write (object. toString ());
} Catch (IOException e ){
// TODO Auto-generated catch block
E. printStackTrace ();
}
}

Return super. doStartTag ();
}

}
Note:

The output content must be:

[Java] pageContext. getOut (). write (object. toString ());

PageContext. getOut (). write (object. toString ());

Tld Configuration:

Create a tld file that needs to be placed in the WEB-INF

 

 

[Html] <? Xml version = "1.0" encoding = "UTF-8"?>
 
<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">
 
<Description> JSTL 1.1 core library </description>
<Display-name> JSTL core </display-name>
<Tlib-version> 1.1 </tlib-version>
<Short-name> w </short-name>
<Uri> http:/winter.baletu.com/</uri>
<Tag>
<Description> Obtained from the session attribute </description>
<Name> property </name>
<Tag-class> org. pan. tags. SessionProperty </tag-class>
<Body-content> JSP </body-content>
<Attribute>
<Name> value </name>
<Required> true </required>
<Rtexprvalue> false </rtexprvalue>
</Attribute>
</Tag>
</Taglib>