自定义标签

一.自定义标签语言的特点

<开始标签属性="属性值">标签体</结束标签>

空标签

<开始标签></结束标签>

<开始标签/>

ui标签控制标签数据标签（数据标签就是用来存储数据的）

z:out 1 m:if 2 m:set 4
m:select 5 m:forEach 3

二.JSP自定义标签生命周期图

SKIP_BODY：跳过主体 EVAL_BODY_INCLUDE：计算标签主体内容并[输出] EVAL_BODY_BUFFERED：计算标签主体内容并[缓存]

EVAL_PAGE:计算页面的后续部分 SKIP_PAGE:跳过页面的后续部分 EVAL_BODY_AGAIN:再计算主体一次

三. 自定义标签的开发及使用步骤

1.创建标签库类（继承BodyTagSupport）
标签属性必须与助手类的属性对应、并且要提供对应get/set方法
2.创建标签库文件（在WEB-INF）下面，以tld为后缀，添加自定义标签的配置
3.页面引入 在JSP通过taglib指令导入标签库，并通过指定后缀自定义标签


四.自定义标签案例

ui标签控制标签数据标签（数据标签就是用来存储数据的）

z:out 1 m:if 2 m:set 4
m:select 5 m:forEach 3

助手类（set out if ）

SetTag

 1 package com.JavaCustomLabel.day;
 2 
 3 import javax.servlet.jsp.JspException;
 4 import javax.servlet.jsp.tagext.BodyTagSupport;
 5 
 6 public class SetTag extends BodyTagSupport{
 7 
 8     /**
 9      * 
10      */
11     private static final long serialVersionUID = 4392633628405470426L;
12 
13     private String var;
14     private String value;
15     public String getVar() {
16         return var;
17     }
18     public void setVar(String var) {
19         this.var = var;
20     }
21     public String getValue() {
22         return value;
23     }
24     public void setValue(String value) {
25         this.value = value;
26     }
27     @Override
28     public int doStartTag() throws JspException {
29         // TODO Auto-generated method stub
30         pageContext.setAttribute(var, value);
31         
32         return SKIP_BODY;
33     }
34 }

OutTag

package com.JavaCustomLabel.day;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;

public class OutTag extends BodyTagSupport{

/**
*
*/
private static final long serialVersionUID = 3372012340573875946L;

private String value;

public String getValue() {
return value;
}

public void setValue(String value) {
this.value = value;
}
@Override
public int doStartTag() throws JspException {
// TODO Auto-generated method stub
JspWriter out = pageContext.getOut();
try {
out.print(value);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return SKIP_BODY;
}
}

IfTag

package com.JavaCustomLabel.day;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;

public class IfTag extends BodyTagSupport{

    /**
     * 
     */
    private static final long serialVersionUID = -1792746228632351099L;

    private Boolean test;

    public Boolean getTest() {
        return test;
    }

    public void setTest(Boolean test) {
        this.test = test;
    }
    @Override
    public int doStartTag() throws JspException {
        // TODO Auto-generated method stub
        return test ? EVAL_BODY_INCLUDE :SKIP_BODY;
    }
}

x.tld文件

<?xml version="1.0" encoding="UTF-8"?>
<taglib xmlns="http://java.sun.com/JSP/TagLibraryDescriptor">


<tlib-version>1.0</tlib-version>
<jsp-version>1.2</jsp-version>
  <short-name>Simple Tags</short-name>
  <uri>/XuFanQi</uri>

 
<!-- set标签 --> 
  <tag>
    <!-- 标签库中的标签  (类似c:set c:out的定义) -->
    <name>set</name>
    <!-- 是标签运行具体代码，也就是助手类，下面填写的助手类的全路径名 -->
    <tag-class>com.JavaCustomLabel.day.SetTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <!-- 该标签的属性 -->
        <name>var</name>
        <!-- 该属性是否必填 -->
        <required>true</required>
        <!-- 是否支持表达式 -->
        <rtexprvalue>false</rtexprvalue>
    </attribute>
     <attribute>
        <!-- 该标签的属性 -->
        <name>value</name>
        <!-- 该属性是否必填 -->
        <required>true</required>
        <!-- 是否支持表达式 -->
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>

<!-- out标签 --> 
  <tag>
    <name>out</name>
    <tag-class>com.JavaCustomLabel.day.OutTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
 <!-- IF标签 -->
  <tag>
    <name>if</name>
    <tag-class>com.JavaCustomLabel.day.IfTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>test</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
</taglib>

jsp页面引入

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    <%@taglib uri="/XuFanQi" prefix="x" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<x:Set var="name" value="李四"></x:Set>
<x:Out value="${name }"></x:Out>
<br>
---------------------
<br>
<x:if test="true">张三</x:if>
<x:if test="false">王五</x:if>
</body>
</html>

页面引入显示

 

Foreach标签
ForeachTag（助手类）

 1 package com.JavaCustomLabel.day;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Iterator;
 5 import java.util.List;
 6 
 7 import javax.servlet.jsp.JspException;
 8 import javax.servlet.jsp.tagext.BodyTagSupport;
 9 
10 /**
11  * c:forech
12  * 
13  * var 指针
14  * items  指的是需要遍历的集合对象
15  * <c:forech var="stu" items="stus">
16  *  ${stu.sid}
17  *  ......
18  * </c:forech>
19  * @author Administrator
20  *
21  */
22 public class ForeachTag extends BodyTagSupport {
23 
24     
25     private static final long serialVersionUID = 3755053789995595493L;26 
27     private String var;
28     private List<Object> items = new  ArrayList<>();
29     public String getVar() {
30         return var;
31     }
32     public void setVar(String var) {
33         this.var = var;
34     }
35     public List<Object> getItems() {
36         return items;
37     }
38     public void setItems(List<Object> items) {
39         this.items = items;
40     }
41     
42     @Override
43     public int doStartTag() throws JspException {
44         
45         Iterator it = items.iterator();
46 //        默认指针存放的位置是没有指向对象的，现在需要指向对象。那么需要指针下移
47         pageContext.setAttribute(var, it.next());
48 //        英文集合中元素较多，那么指针需要循环的向下移动，那么需要我们将迭代器保存，用于下一次指针下移所用
49         pageContext.setAttribute("it", it);
50         return EVAL_BODY_INCLUDE;
51     }
52     
53     @Override
54     public int doAfterBody() throws JspException {
55 //        获取以保存的迭代器
56         Iterator it = (Iterator) pageContext.getAttribute("it");
57         if(it.hasNext()) {
58 //            指针下移指向新的元素
59             pageContext.setAttribute(var, it.next());
60 //            再保存正在使用的迭代器
61             pageContext.setAttribute("it", it);
62             return EVAL_BODY_AGAIN;
63         }else {
64             return EVAL_PAGE;
65         }
66     }
67 }

x.tld文件

 1 <!-- Foreach标签 -->
 2 <tag>
 3     <name>foreach</name>
 4     <tag-class>com.JavaCustomLabel.day.ForeachTag</tag-class>
 5     <body-content>JSP</body-content>
 6     <attribute>
 7         <name>var</name>
 8         <required>true</required>
 9         <rtexprvalue>false</rtexprvalue>
10     </attribute>
11      <attribute>
12         <name>items</name>
13         <required>true</required>
14         <rtexprvalue>true</rtexprvalue>
15     </attribute>
16   </tag>

jsp页面引入

 1 <%
 2       List<Student> list = new ArrayList<Student>();
 3       list.add(new Student("s001","zs"));
 4       list.add(new Student("s002","li"));
 5       list.add(new Student("s003","zz"));
 6       request.setAttribute("stus", list);
 7    %>
 8    <br>
 9    <ul>
10    <x:foreach items="${stus }" var="s">
11        ${s.sid }
12        ${s.sname }<br>
13    </z:foreach>
14    </ul>
15    <br>

select标签
SelectTag（助手类）

  1 package com.JavaCustomLabel.day;
  2 
  3 import java.io.IOException;
  4 import java.lang.reflect.Field;
  5 import java.lang.reflect.InvocationTargetException;
  6 import java.util.ArrayList;
  7 import java.util.List;
  8 
  9 import javax.servlet.jsp.JspException;
 10 import javax.servlet.jsp.JspWriter;
 11 import javax.servlet.jsp.tagext.BodyTagSupport;
 12 
 13 import org.apache.commons.beanutils.BeanUtils;
 14 
 15 /**
 16  * <select id='' name=''>
 17  *    <option value='-1' selected >---请选择---</option>
 18  * </select>
 19  * 
 20  * 
 21  * --->
 22  *    <z:select ....></select>
 23  *    查询维度：  下拉列表
 24  *    修改页面：   下拉列表        数据回显
 25  *    
 26  *    1.id name
 27  *    2.数据源，存入数据库中的值 textKey、展示列textVal
 28  *    3.加入属性（默认的头部属性值headTextKey、默认的展示列值headTextVal）
 29  *    4.加入属性，能够实现数据回显的功能selectedVal
 30  *    
 31  * @author Administrator
 32  *
 33  */
 34 public class SelectTag extends BodyTagSupport {
 35 
 36     
 37     private static final long serialVersionUID = -8499199884457216397L; 38 
 39     private String id;
 40     private String name;
 41     private List<Object> items = new ArrayList<>();
 42     private String textKey;
 43     private String textVal;
 44     private String headTextKey;
 45     private String headTextVal;
 46     private String selectedVal;
 47     public String getId() {
 48         return id;
 49     }
 50     public void setId(String id) {
 51         this.id = id;
 52     }
 53     public String getName() {
 54         return name;
 55     }
 56     public void setName(String name) {
 57         this.name = name;
 58     }
 59     public List<Object> getItems() {
 60         return items;
 61     }
 62     public void setItems(List<Object> items) {
 63         this.items = items;
 64     }
 65     public String getTextKey() {
 66         return textKey;
 67     }
 68     public void setTextKey(String textKey) {
 69         this.textKey = textKey;
 70     }
 71     public String getTextVal() {
 72         return textVal;
 73     }
 74     public void setTextVal(String textVal) {
 75         this.textVal = textVal;
 76     }
 77     public String getHeadTextKey() {
 78         return headTextKey;
 79     }
 80     public void setHeadTextKey(String headTextKey) {
 81         this.headTextKey = headTextKey;
 82     }
 83     public String getHeadTextVal() {
 84         return headTextVal;
 85     }
 86     public void setHeadTextVal(String headTextVal) {
 87         this.headTextVal = headTextVal;
 88     }
 89     public String getSelectedVal() {
 90         return selectedVal;
 91     }
 92     public void setSelectedVal(String selectedVal) {
 93         this.selectedVal = selectedVal;
 94     }
 95     
 96     @Override
 97     public int doStartTag() throws JspException {
 98         JspWriter out = pageContext.getOut();
 99         try {
100             out.write(toHTML());
101         } catch (IOException | NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
102             // TODO Auto-generated catch block
103             e.printStackTrace();
104         }
105         
106         return super.doStartTag();
107     }
108     
109     /**
110      * 拼接出下拉 列表所对应的selecte的HTML代码
111      * <select id='' name=''>
112             <option value='-1' selected >---请选择---</option>
113        </select>
114      * @return
115      * @throws SecurityException 
116      * @throws NoSuchFieldException 
117      * @throws IllegalAccessException 
118      * @throws IllegalArgumentException 
119      * @throws NoSuchMethodException 
120      * @throws InvocationTargetException 
121      */
122     private String toHTML() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, NoSuchMethodException {
123         StringBuilder sb = new StringBuilder();
124         sb.append("<select id='"+id+"' name='"+name+"' >");
125         if(!(headTextKey == null || "".equals(headTextKey) || headTextVal == null || "".equals(headTextVal))) {
126             sb.append("<option value='"+headTextKey+"' selected >"+headTextVal+"</option>");
127         }
128         String val;
129         String html;
130         for (Object obj : items) {
131 //            让学生的id存入数据库，让学生的名字展示在jsp页面
132 //            <option value='s001'>zs</option>
133 //            obj sid sname
134 //            第一种方式
135             Field textKeyField = obj.getClass().getDeclaredField(textKey);
136             textKeyField.setAccessible(true);
137             val = (String) textKeyField.get(obj);
138 //            第二种方式(需要架包) 
139             html = BeanUtils.getProperty(obj, textVal);
140             if(val.equals(selectedVal)) {
141                 sb.append("<option value='"+val+"' selected>"+html+"</option>");
142             }else {
143                 sb.append("<option value='"+val+"' >"+html+"</option>");
144             }
145         }
146         sb.append("</select>");
147         return sb.toString();
148     }
149 }

x.tld文件

 1 <tag>
 2     <name>select</name>
 3     <tag-class>com.JavaCustomLabel.day.SelectTag</tag-class>
 4     <body-content>JSP</body-content>
 5     <attribute>
 6         <name>id</name>
 7         <required>false</required>
 8         <rtexprvalue>false</rtexprvalue>
 9     </attribute>
10      <attribute>
11         <name>name</name>
12         <required>false</required>
13         <rtexprvalue>false</rtexprvalue>
14     </attribute>
15     <attribute>
16         <name>items</name>
17         <required>true</required>
18         <rtexprvalue>true</rtexprvalue>
19     </attribute>
20     <attribute>
21         <name>textKey</name>
22         <required>true</required>
23         <rtexprvalue>false</rtexprvalue>
24     </attribute>
25     <attribute>
26         <name>textVal</name>
27         <required>true</required>
28         <rtexprvalue>false</rtexprvalue>
29     </attribute>
30     <attribute>
31         <name>headTextKey</name>
32         <required>false</required>
33         <rtexprvalue>false</rtexprvalue>
34     </attribute>
35     <attribute>
36         <name>headTextVal</name>
37         <required>false</required>
38         <rtexprvalue>false</rtexprvalue>
39     </attribute>
40     <attribute>
41         <name>selectedVal</name>
42         <required>false</required>
43         <rtexprvalue>true</rtexprvalue>
44     </attribute>
45   </tag>

jsp页面引入

 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3     <%@taglib uri="/XuFanQi" prefix="x" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>Insert title here</title>
 9 </head>
10 <body>
11 
12 <x:select headTextKey="-1" headTextVal="---请选择---" selectedVal="s003" textVal="sname" items="${stus }" textKey="sid"></z:select>
13 
14 </body>
15 </html>

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原文地址：https://www.cnblogs.com/xcn123/p/11042328.html