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JSP tag 02

2022-07-24 06:27:00 【zsm030616】

Catalog

One 、z:foreach label
Two 、z:select label

One 、z:foreach label

attribute ：
①var
var:String
②items
items There are collections in it, so the data type is list
Analyze the circuit ：
Article 1 with a ：eval_body_include
Second ：eval_body_again
< Code demonstration >

package com.zsm.tag;
/**
 * @author zjjt
 */
 
import java.util.Iterator;
import java.util.List;
 
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
 
public class ForeachTag extends BodyTagSupport {
	
	private String var;
	private List<Object> items;
	public String getVar() {
		return var;
	}
	public void setVar(String var) {
		this.var = var;
	}
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	public ForeachTag() {
		// TODO Auto-generated constructor stub
	}
	public ForeachTag(String var, List<Object> items) {
		super();
		this.var = var;
		this.items = items;
	}
	
	@Override
		public int doStartTag() throws JspException {
		Iterator<Object> it = items.iterator();
		//var = c,it.next() Is an object in the collection 
		//pageContext.setAttribute("c", items.get(0));
		pageContext.setAttribute(var,it.next());
		pageContext.setAttribute("it",it);// For the existing position of the pointer during iteration 
		return EVAL_BODY_INCLUDE;
		}
	
		@Override
		public int doAfterBody() throws JspException {
			Iterator<Object> it = (Iterator<Object>)pageContext.getAttribute("it");
			// Determine whether there is another one in the iterator , If there is, it will enter the cycle , If not, stop the cycle 
			if(it.hasNext()) {
				pageContext.setAttribute(var, it.next());
				pageContext.setAttribute("it", it);// To preserve the existing position of the pointer during iteration 
				return EVAL_BODY_AGAIN;
			}
			else {
				return EVAL_PAGE;
			}
		}
}

Create an entity class

package com.zsm.entity;
 
import java.io.Serializable;
 
/**
 *  Entity class ： Teachers 
 * @author zjjt
 */
public class Teacher implements Serializable{
	
	
	private static final long serialVersionUID = 1L;
	private String tid;
	private String name;
	public String getTid() {
		return tid;
	}
	public void setTid(String tid) {
		this.tid = tid;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Teacher() {
		// TODO Auto-generated constructor stub
	}
	public Teacher(String tid, String name) {
		super();
		this.tid = tid;
		this.name = name;
	}
	
	
}

tld Customized in the file for label

<tag>
    <name>for</name>
    <tag-class>com.zsm.tag.ForeachTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>items</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

jsp Interface

<%@page import="java.util.ArrayList"%>
<%@page import="com.zsm.entity.Teacher"%>
<%@page import="java.util.List"%>
<%@ 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>
 <%
 	List<Teacher> ls = new ArrayList<Teacher>();
 	ls.add(new Teacher("t001","zs"));
 	ls.add(new Teacher("t002","ls"));
 	ls.add(new Teacher("t003","ww"));
	request.setAttribute("ls", ls);
 %>
<z:for items="${ls}" var="t">
	${t.tid }:${t.name}
</z:for>
</body>
</html>

Put the defined attributes into jsp In the set in the interface （ Add attribute values in the process of adding to the set ） Then save the collection
design sketch
Insert picture description here

Two 、z:select label

attribute
（1）id

（2）name

（3）items

（4）textKey

（5）textVal

（6）headerTextKey

（7）headerTextVal

（8）selectedVal
Code thinking ：
1. Background to traverse —> data source –>items
2. You need an object attribute to represent the corresponding display content of the drop-down box –>textval
3. You need an object attribute to represent the corresponding... Of the drop-down box value value —>textKey
4. The default header option shows the content —>headerTextVal
5. The default header option is selected –>headTextVal
6. Values stored in data , To facilitate data echo –>selectedVal
*

The following three conditions can be omitted
7.id
8.name
9.cssStyle
PropertyUtils.getProperty(obj, textVal) For tool class , One code makes three codes , namely （Field textKeyFild = obj.getClass().getDeclaredField(textKey);
textKeyFild.setAccessible(true);
Object value = textKeyFild.get(obj); These three codes
The above codes are from commons-beanutils-1.8.0jar package

tld file

<tag>
    <name>select</name>
    <tag-class>com.zsm.tag.SelectTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>items</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <name>textVal</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>textKey</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>headTextVal</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>headTextKey</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>selectedVal</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <name>id</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>name</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

jsp Interface

<%@page import="java.util.ArrayList"%>
<%@page import="com.dengxiyan.entity.Teacher"%>
<%@page import="java.util.List"%>
<%@ 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>
<style type="text/css">
#mySel{
	color:blue;
}
 
</style>
</head>
<body>
 
 <%
 	List<Teacher> ls = new ArrayList<Teacher>();
 	ls.add(new Teacher("t001","zs"));
 	ls.add(new Teacher("t002","ls"));
 	ls.add(new Teacher("t003","ww"));
	request.setAttribute("ls", ls);
 %>
<z:for items="${ls}" var="t">
	${t.tid }:${t.name}
</z:for> 
 
 <select>
	<option value="1">zs</option>
	<option value="2">ls</option>
</select>
<z:select selectedVal="t002" id="mySel" headTextKey="-1" headTextVal="=== Please select ==" textVal="name" items="${ls}" textKey="tid"></z:select>
</body>
</html>

SelectTag Entity class

package com.zsm.tag;
 
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.List;
 
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
 
import org.apache.commons.beanutils.PropertyUtils;
 
/**
 *  The goal is ：
 * 1. Omit the process of traversal 
 * <z:select></selcet>
 * 2. When the data is echoed , Disorder increases if Judge , No need to add new code 
 * 
 * @author zjjt
 */
public class SelectTag extends BodyTagSupport{
 
	private List<Object> items;
	private String textVal;// Equivalent to name 
	private String textKey;
	private String headTextVal;
	private String headTextKey;
	private String selectedVal;
	private String id;
	private String name;
	
	
	@Override
	public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
			out.print(toHTML());
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.doStartTag();
	}
	
	
	private String toHTML() throws Exception {
		StringBuffer sb = new StringBuffer();
		sb.append("<select id='"+id+"' name='"+name+"'>");
        // Judge when headTextVal Not equal to null and not an empty string 
		if(headTextVal!=null && !"".equals(headTextVal)) {
			sb.append("<option value='"+headTextKey+"'>"+headTextVal+"</option>");
		}
		for (Object obj : items) {
			Field textKeyFild = obj.getClass().getDeclaredField(textKey);
			textKeyFild.setAccessible(true);
			Object value = textKeyFild.get(obj);// The value really displayed 
			
			if(selectedVal !=null && !"".equals(selectedVal) && selectedVal.equals(value)) {
        // When the value matches, add selected You can achieve the rollback effect 
				sb.append("<option selected value='"+value+"'>"+PropertyUtils.getProperty(obj, textVal)+"</option>");
 
			}else {
				sb.append("<option value='"+value+"'>"+PropertyUtils.getProperty(obj, textVal)+"</option>");
			}
		}
		sb.append("</select>");
		return sb.toString();
	}
 
 
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	public String getTextVal() {
		return textVal;
	}
	public void setTextVal(String textVal) {
		this.textVal = textVal;
	}
	public String getTextKey() {
		return textKey;
	}
	public void setTextKey(String textKey) {
		this.textKey = textKey;
	}
	public String getHeadTextVal() {
		return headTextVal;
	}
	public void setHeadTextVal(String headTextVal) {
		this.headTextVal = headTextVal;
	}
	public String getHeadTextKey() {
		return headTextKey;
	}
	public void setHeadTextKey(String headTextKey) {
		this.headTextKey = headTextKey;
	}
	public String getSelectedVal() {
		return selectedVal;
	}
	public void setSelectedVal(String selectedVal) {
		this.selectedVal = selectedVal;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	
	
	
}

design sketch
Insert picture description here