Role: Custom tags are primarily used to remove Java code from JSP pages.
Implementation: You need to complete the following two steps:
Code: Create a new Day11 project, create a new Cn.itcast.web.tag package in the SRC directory, viewiptag java file
PackageCn.itcast.web.tag;Importjava.io.IOException;Importjavax.servlet.http.HttpServletRequest;Importjavax.servlet.jsp.JspException;ImportJavax.servlet.jsp.JspWriter;ImportJavax.servlet.jsp.tagext.TagSupport; Public classViewiptagextendsTagSupport {@Override Public intdoStartTag ()throwsjspexception {httpservletrequest request= (HttpServletRequest) This. Pagecontext.getrequest (); JspWriter out= This. Pagecontext.getout (); String IP=request.getremoteaddr (); Try{out.print (IP); } Catch(IOException e) {Throw NewRuntimeException (e); } return Super. doStartTag (); }}
Then create a new itcast.tld in the Webroot\web-inf directory
<?XML version= "1.0" encoding= "UTF-8"?><!--part of this code is from: X:\apache-tomcat-7.0.77-src\webapps\examples\WEB-INF\jsp2\jsp2-example-taglib.tld Licensed to the Apache software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); You are not a use of this file except in compliance with the License. Obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 unless required by applicable or agreed to writing, software distributed under the License are distributed on a "as is" BASIS, without warranties or CONDITIONS of any KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. -<taglibxmlns= "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>A Tag Library exercising simpletag handlers.</Description> <tlib-version>1.0</tlib-version> <Short-name>Itcast</Short-name> <URI>http://www.itcast.cn</URI> <Tag> <Description>Output Client IP</Description> <name>Viewip</name> <Tag-class>Cn.itcast.web.tag.ViewIPTag</Tag-class> <body-content>Empty</body-content> </Tag> </taglib>
This tag can be used in any JSP file.
<%@ Page Language="Java"Import="java.util.*"pageencoding="UTF-8"%><%@ taglib URI="http://www.itcast.cn"prefix="Itcast" %><!DOCTYPE HTML><HTML> <Head> <title>Starting page</title> </Head> <Body>This is my JSP page.<BR>the IP from the client is:<Itcast:viewip/> </Body></HTML>
Label Invocation Process:
1. Browser sends JSP page request to WEB server
2. The WEB server begins to interpret the JSP page
3. When you encounter a custom label, first instantiate the label processor class for the label
4. Call the Setpagecontext method to pass the page's PageContext object to the label processor class
5. See if the label has a parent tag, if there is a parent tag, the parent tag as an object, call the SetParent method to pass to the label processor class, if not, pass a null
6. After the initialization of the above tag is completed, the server starts to execute the tag. When you encounter the label's start tag, call the doStartTag method
7. If the label has a label body, then the server will generally execute the label body
8. When the server encounters a JSP page end tag, call the Doendtag method of the Label processor class
9. After the entire label is executed, the server typically calls the release method to release the resources that the label is working on
Method Summary = setpagecontext (PageContext pc) GetParent () setParent () doStartTag () Doendtag () release ()
In the Viewiptag.java class, the doStartTag method defaults to return Super.dostarttag ();
Output label body if rewritten as return Tag.eval_body_include
If rewritten as return tag.skip_body does not output the label body
The Doendtag method defaults to return Super.doendtag ();
Output if rewritten as return tag.eval_page
Stop output if rewritten as return tag.skip_page
If the label body needs to be executed 5 times, write in the Doafterbody method:
@Override Public intdoStartTag ()throwsjspexception {returnTag.eval_body_include;} @Override Public intDoafterbody ()throwsjspexception {intX=5; X--; if(x>0){ returnIterationtag.eval_body_again; }Else{ returnIterationtag.skip_body; }}
//Modify the label body Public classTagDemo4extendsBodytagsupport {@Override Public intdoStartTag ()throwsjspexception {returnbodytag.eval_body_buffered; } @Override Public intDoendtag ()throwsjspexception {bodycontent BC= This. Getbodycontent (); String content=bc.getstring (); Content=content.touppercase (); Try { This. Pagecontext.getout (). write (content); } Catch(IOException e) {Throw NewRuntimeException (e); } returnTag.eval_page; }}
Go Introduction to [Java] custom tags
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