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JSP tag

2022-07-24 06:27:00 【zsm030616】

Catalog

One , Language characteristics of labels
Two , The development and use of custom labels
3、 ... and , Tag life cycle
Four ,z:if label
5、 ... and ,z:set label z:out label

One , Language characteristics of labels

（1） form ：< The start tag attribute =“ Property value ”> Tagging body </ End tag >

（2） classification

Empty label for example ：br,hr

ui label for example ：input,table

Control tags for example ：if.foreach

Data labels for example ：out label

Two , The development and use of custom labels

（1） step ： Helper （ Inherit BodyTagSupport）

package com.zsm.tag;
 
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
 
/**
 *  Helper   Must inherit bodytagSupport
 * @author zjjt
 */
public class DemoTag1 extends BodyTagSupport {
 
	@Override
	public int doStartTag() throws JspException {
		System.out.println("=================================doStartTag=======================");
		// skip 
		//return SKIP_BODY;
		//return super.doStartTag();
		return EVAL_BODY_INCLUDE;
	}
	
	@Override
	public int doAfterBody() throws JspException {
	System.out.println("=================================doAfterBody=======================");
		return super.doAfterBody();
		// loop 
		//return EVAL_BODY_AGAIN;
	}
	
	@Override
	public int doEndTag() throws JspException {
		System.out.println("=================================doEndTag=======================");
		return super.doEndTag();
		// Only read the previous content 
		//return SKIP_PAGE;
	}
}

（2） Label library description file （tld）
Be careful ：tld The file must be kept in WEB-INF Directory or its subdirectories
（3）jsp adopt taglib Instruction import label Library

 <%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

（4） example ： take c:if Label to z:if
1. The custom tag library is related to tld Document related , Also with tag Element is related to the corresponding helper class

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    <%@ taglib uri="http://jsp.veryedu.cn" prefix="z" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 
<z:if test="true">true</z:if>
<z:if test="false">false</z:if>
<z:set value="zsm" var="name"></z:set>
<z:out value="${name}"></z:out>
</body>
</html>

. 2. Tags in tag library and tld Medium Tag The elements are related to （ When there is no if Number of tags ）
error Insert picture description here

3、 ... and , Tag life cycle

Insert picture description here

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    <%@ taglib uri="http://jsp.veryedu.cn" prefix="z" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<z:dome1>xxxx</z:dome1>
	<z:if test="true">true</z:if>
	<z:if test="false">false</z:if>
	<z:set var="name" value="laoliu"></z:set>
	<z:out value="${name }"></z:out>
</body>
</html>

package com.zsm.tag;
 
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
 
/**
 *  Helper   Must inherit bodytagSupport
 * @author zjjt
 */
public class DemoTag1 extends BodyTagSupport {
 
	@Override
	public int doStartTag() throws JspException {
		System.out.println("=================================doStartTag=======================");
		// skip 
		//return SKIP_BODY;
		//return super.doStartTag();
		return EVAL_BODY_INCLUDE;
	}
	
	@Override
	public int doAfterBody() throws JspException {
	System.out.println("=================================doAfterBody=======================");
		return super.doAfterBody();
		// loop 
		//return EVAL_BODY_AGAIN;
	}
	
	@Override
	public int doEndTag() throws JspException {
		System.out.println("=================================doEndTag=======================");
		return super.doEndTag();
		// Only read the previous content 
		//return SKIP_PAGE;
	}
}

Read only the front part

@Override
	public int doEndTag() throws JspException {
		System.out.println("=================================doEndTag=======================");
		return super.doEndTag();
		// Only read the previous content 
		//return SKIP_PAGE;
	}

design sketch
Insert picture description here
1. With label body , By default, the helper class will be called dostarttag.doafterbody,doendtag Method

	@Override
	public int doStartTag() throws JspException {
		System.out.println("=================================doStartTag=======================");
	    return super.doStartTag();
	
	}

2. If you will dostarttag The return value of is changed to skip_body, that doafterbody There will be no call to execute （ Line one ）

Popular point ：（ Change the return value of the method to skip , In the case of a label body, it is also worth calling two methods ）

@Override
	public int doStartTag() throws JspException {
		System.out.println("=================================doStartTag=======================");
		// skip 
		return SKIP_BODY;
	}

3. If you will dostarttag The return value of is changed to EVAL_BODY_INCLUDE, that doafterbody Will call to execute （ line 2）

	@Override
	public int doStartTag() throws JspException {
		System.out.println("=================================doStartTag=======================");
		return EVAL_BODY_INCLUDE;
	}

4. If you will doafterbody The return value of is changed to EVAL_BODY_again, Then call consistently doafterbody, Into the loop （ Route 3）

@Override
	public int doAfterBody() throws JspException {
	System.out.println("=================================doAfterBody=======================");
		return super.doAfterBody();
		// loop 
		//return EVAL_BODY_AGAIN;
	}

Four ,z:if label

Case study

package com.zsm.tag;
/**
 * if label 
 *  If the conditions are met , Just print the label body ---》dostatag The return value of eval_body_include
 *  If you don't do that , The label body is not output ---》dostarttag The return value of skip_body
 *  You need to obtain the value of whether the conditions are met , Then the attribute value of the tag boolean
 * 
 * @author zjjt
 */
 
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
 
public class ifTag extends BodyTagSupport {
 
	private boolean test;
	
	public boolean isTest() {
		return test;
	}
 
	public void setTest(boolean test) {
		this.test = test;
	}
 
	
	
	@Override
	public int doStartTag() throws JspException {
		 //  If the conditions are met , Just print the label body ---》dostatag The return value of eval_body_include
		return test ? EVAL_BODY_INCLUDE : SKIP_BODY;
	}
	
}

5、 ... and ,z:set label z:out label

1.z:set Label helper class
Case study

package com.zsm.tag;
 
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
 
/**
 *  Data labels ： Store the data 
 * 
 *  To store data, store it in the form of key value pairs ： The tag has two properties 
 * @author zjjt
 */
public class SetTag extends BodyTagSupport {
 
	private String var;
	private Object value;
	
	
	public String getVar() {
		return var;
	}
 
 
	public void setVar(String var) {
		this.var = var;
	}
 
 
	public Object getValue() {
		return value;
	}
 
 
	public void setValue(Object value) {
		this.value = value;
	}
 
 
	@Override
	public int doStartTag() throws JspException {
		// To store data, store it in the form of key value pairs ： The tag has two properties 
		pageContext.setAttribute(var, value);
		return super.doStartTag();
	}
	
	
}

2.z:out Label helper class
servlet Background code foreground output content ：out.print
Send the data to the front desk ： First get the output stream
Case study

package com.zsm.tag;
 
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * servlet Background code foreground output content   ：out.print
 *  Send the data to the front desk ： First get the output stream 
 * @author zjjt
 */
public class Outtag extends BodyTagSupport {
 
	private Object value;
 
	public Object getValue() {
		return value;
	}
 
	public void setValue(Object value) {
		this.value = value;
	}
	
	@Override
		public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
			out.print(value);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return super.doStartTag();
		}
}

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