JSP custom tag

JSP Custom tag ：

1. Tag language features
< The start tag attribute =“ Property value ”> Tagging body </ End tag >

Empty label

---

< The start tag ></ End tag >
< The start tag />

2. Development and use steps of custom labels
2.1 Create a label helper class ( Inherit BodyTagSupport)
The tag property must correspond to the property of the helper class 、 And corresponding information shall be provided get/set Method
rtexprvalue

2.2 Create a label library description file (tld), Add custom label configuration
notes ：tld The file must be saved to WEB-INF Directory or its subdirectories
jstl Tag library

2.3 stay JSP adopt taglib Instruction import label Library , And access custom tags by specifying suffixes

3. Tag life cycle

technological process A：
SKIP_BODY
3.1 Instantiate the tag helper class ->doStartTag()------------->doEndTag()
// Mainly used to develop simple labels

technological process B：
EVAL_BODY_INCLUDE SKIP_BODY
3.2 Instantiate the tag helper class ->doStartTag()------------->doAfterBody---------------->doEndTag()…
EVAL_BODY_AGAIN

3.3 …

jrebal Thermal loading

SKIP_BODY： Skip body
EVAL_BODY_INCLUDE： Calculate the main content of the label and [ Output ]
EVAL_PAGE: Calculate subsequent parts of the page
SKIP_PAGE: Skip the rest of the page
EVAL_BODY_AGAIN: Calculate the subject again

jsp Customize the life cycle of the tag :

Custom label profile ：

<!DOCTYPE taglib
  PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
   "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<!--  Tag library descriptor  -->
<taglib xmlns="http://java.sun.com/JSP/TagLibraryDescriptor">
	<!--  Represents the version number of the tag library  -->
	<tlib-version>1.0</tlib-version>
	<!--  representative jsp Version of  -->
	<jsp-version>1.2</jsp-version>
	<!--  The abbreviation of your tag library  -->
	<short-name>z</short-name>
	<!--  Reference to your tag library uri -->
	<uri>/zking</uri>

	<tag>
		<!--  Tag name  -->
		<name>if</name>
		<!--  Label tool class  -->
		<tag-class>com.king.text.IfTag</tag-class>
		<!--  The content type of the tag ：empty Represents an empty label ,jsp It can be any legal JSP Elements  -->
		<body-content>JSP</body-content>
		<!--  Custom label attribute definitions , Please note that the corresponding... Must be provided in the tag class get/set Method  -->
		<attribute>
			<!--  The attribute name of the custom tag  -->
			<name>test</name>
			<!-- true It means required  -->
			<required>true</required>
			<!-- true Support dynamic values , You can fill in the value jsp expression 、EL expression ,false Do not support  -->
			<rtexprvalue>true</rtexprvalue>
		</attribute>
	</tag>
	<tag>
		<!--  Tag name  -->
		<name>out</name>
		<!--  Label tool class  -->
		<tag-class>com.king.text.outTag</tag-class>
		<!--  The content type of the tag ：empty Represents an empty label ,jsp It can be any legal JSP Elements  -->
		<body-content>JSP</body-content>
		<!--  Custom label attribute definitions , Please note that the corresponding... Must be provided in the tag class get/set Method  -->
		<attribute>
			<!--  The attribute name of the custom tag  -->
			<name>value</name>
			<!-- true It means required  -->
			<required>true</required>
			<!-- true Support dynamic values , You can fill in the value jsp expression 、EL expression ,false Do not support  -->
			<rtexprvalue>false</rtexprvalue>
		</attribute>
	</tag>
	<tag>
		<!--  Tag name  -->
		<name>foreach</name>
		<!--  Label tool class  -->
		<tag-class>com.king.text.foreachTag</tag-class>
		<!--  The content type of the tag ：empty Represents an empty label ,jsp It can be any legal JSP Elements  -->
		<body-content>JSP</body-content>
		<!--  Custom label attribute definitions , Please note that the corresponding... Must be provided in the tag class get/set Method  -->
		<attribute>
			<!--  The attribute name of the custom tag  -->
			<name>items</name>
			<!-- true It means required  -->
			<required>true</required>
			<!-- true Support dynamic values , You can fill in the value jsp expression 、EL expression ,false Do not support  -->
			<rtexprvalue>true</rtexprvalue>
		</attribute>
		<attribute>
			<!--  The attribute name of the custom tag  -->
			<name>var</name>
			<!-- true It means required  -->
			<required>true</required>
			<!-- true Support dynamic values , You can fill in the value jsp expression 、EL expression ,false Do not support  -->
			<rtexprvalue>false</rtexprvalue>
		</attribute>
		<attribute>
			<!--  The attribute name of the custom tag  -->
			<name>varStudent</name>
			<!-- true It means required  -->
			<required>false</required>
			<!-- true Support dynamic values , You can fill in the value jsp expression 、EL expression ,false Do not support  -->
			<rtexprvalue>false</rtexprvalue>
		</attribute>
	</tag>
</taglib>

Custom label method ：

package com.king.text;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
import java.util.Iterator;
import java.util.List;

public class foreachTag extends BodyTagSupport {
    
    private List items; // aggregate 
    private String var;
    private varStudent varstu;
    private String varstudent;

    //getset Method 
    public String getVarstudent() {
    
        return varstudent;
    }

    public void setVarstudent(String varstudent) {
    
        this.varstudent = varstudent;
    }

    public List getItems() {
    
        return items;
    }

    public void setItems(List items) {
    
        this.items = items;
    }

    public String getVar() {
    

        return var;
    }

    public void setVar(String var) {
    
        this.var = var;
    }

    public varStudent getVarstu() {
    
        return varstu;
    }

    public void setVarstu(varStudent varstu) {
    
        this.varstu = varstu;
    }


    @Override
    public int doStartTag() throws JspException {
    
        // Determines if the set is empty 

        // Get the iterator 
        Iterator its =(Iterator) pageContext.getAttribute("it");
        // Determine whether a set or iterator has a value 
        if(items.size() > 0 || its!=null){
    
            Iterator it = items.iterator();
            if(its != null){
    // Judge iterators 
                it=its;
            }
            if(it.hasNext()){
    // Judge whether there is next 
                ne(it);// If there is a next one, call the method 
                return  super.doAfterBody();// call doAfterBody
            }else{
    
                return EVAL_PAGE;
            }


        }else{
    
            return EVAL_PAGE;
        }

    }

    private void ne(Iterator it) {
    
        // Get the iterator and move the subscript down one bit 
        Object next = it.next();
        // Save the object to the scope 
        pageContext.setAttribute(var,next);
        // Save the iterator to the scope 
        pageContext.setAttribute("it",it);
        // Assign default 
        int index=0;
        int count=1;
        // Save to scope 
        varStudent v =(varStudent) pageContext.getAttribute("varstu");

        if(v!=null){
    // If varStudent If not empty, give index,count assignment 
        index = v.getIndex()+1;
        count = v.getCount()+1;
        }
        // to varStudent assignment 
        varstu.setCount(count);
        varstu.setCount(index);
        // hold varstudent Save to scope 
        pageContext.setAttribute(varstudent,varstu);
    }

    @Override
    public int doAfterBody() throws JspException {
    
        // Get the iterator 
        Iterator it =(Iterator) pageContext.getAttribute("it");
        if(it.hasNext()){
    // Judge whether there is next 
            ne(it);// If there is a next one, call the method 
            return super.doStartTag();
        }else{
    
            return EVAL_PAGE;
        }
    }
}