欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识！
您现在的位置是： 首页

jsp自定义标签

程序员文章站 2022-03-11 11:06:13
...

1. 标签语言特点

<开始标签 属性=“属性值”>标签体</结束标签>

2.三大类标签

2.1 ui标签 c:out
特点是显示数据，并且数据不是来源于标签体的，而是来源于jsp标签本身
2.2 控制标签 if /foreach/c
特点是控制的对象是标签体
2.3 数据标签 set
特点是存储数据，没有任何的页面效果

3.了解标签的生命周期图

jsp自定义标签

4.自定义标签的开发及使用步骤

创建一个标签助手类(继承BodyTagSupport)标签属性必须助手类的属性对应、且要提供对应get/set方法和doStartTag()、doAfterBody()、doEndTag()方法，并了解

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

2 创建标签库描述文件(tld)，添加自定义标签的配置
注：tld文件必须保存到WEB-INF目录或其子目录

3 在JSP通过taglib指令导入标签库，并通过指定后缀
访问自定义标签

下面代码演示：

SatTag:

package com.pyc;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * 数据标签（不需要展示类容）
 * 作用：
 * 是将value值赋予变量var
 * @author 96345
 *
 */
public class SetTag extends BodyTagSupport{

	private static final long serialVersionUID = -6063398854261197972L;
	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 {
		pageContext.setAttribute(var, value);
		return SKIP_BODY;
	}
}

OutTag:

package com.pyc;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * out 属于UI标签（需要展示效果，是依靠标签属性展示页面效果）
 * JspWriter
 *  * @author 96345
 *
 */
public class OutTag extends BodyTagSupport{

	private static final long serialVersionUID = 900890541735512755L;
    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 (IOException e) {
			e.printStackTrace();
		}
		return super.doStartTag();
	}
}

IfTag:

package com.pyc;

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

public class IfTag extends BodyTagSupport{

	private static final long serialVersionUID = 3665095875292237752L;
    private boolean flag;
	public boolean isFlag() {
		return flag;
	}
	public void setFlag(boolean flag) {
		this.flag = flag;
	}
    @Override
    public int doStartTag() throws JspException {
    	return flag ? EVAL_BODY_INCLUDE : SKIP_BODY;
    }
}

ForeachTag:

package com.pyc;

import java.util.ArrayList;
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 static final long serialVersionUID = -2364828486746117631L;

	private List<Object> items = new ArrayList<>();
	
	private String var;

	public List<Object> getItems() {
		return items;
	}

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

	public String getVar() {
		return var;
	}

	public void setVar(String var) {
		this.var = var;
	}
	
	public int doStartTag() throws JspException {
		Iterator<Object> it = items.iterator();
		pageContext.setAttribute(var, it.next());
		pageContext.setAttribute("it",it);
		
		return EVAL_BODY_INCLUDE;
		
	}
	
	public int doAfterBody() throws JspException {
//		获取原来状态的迭代器，而非新创建一个迭代器
		Iterator<Object> it = (Iterator<Object>) pageContext.getAttribute("it");
		if(it.hasNext()) {
			pageContext.setAttribute(var, it.next());
			pageContext.setAttribute("it",it);
			return EVAL_BODY_AGAIN;
		}else {
			return EVAL_PAGE;
		}
		
		
	}
	
}

selectTag:

package com.pyc;

import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
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;

/**
 * 自定义select标签应具备的功能
 * 1。新增查询页面，只要通过一个标签就可以完成数据的绑定，而并非使用c:foreach绑定
 * 2。修改页面，同样通过一个自定义标签完成数据的遍历的展示，以及默认选择指定项
 * 
 * 思考：
 *  1。要往后台传值 id，name
 *  2.定义数据库存储的对于的标签属性，前台页面展示的标签属性 textKey,textVal
 *  3.定义下拉框的默认值headerTextKey,headTextVal
 *  4.下拉框需要加载数据 items
 *  5.属性值接受数据库中保存的value值 selectedVal
 *  
 *  需要UI标签
 * @author 96345
 *
 */
public class SelectTag extends BodyTagSupport{

	private static final long serialVersionUID = 4863443457992720507L;
    
	private String id;
	private String name;
	private List<Object> items=new ArrayList<>();
	private String textKey;
	private String textVal;
	private String headerTextKey;
	private String headerTextVal;
	private String selectedVal;
	 @Override
	    public int doStartTag() throws JspException {
	    	JspWriter out = pageContext.getOut();
	    	try {
//	    		之所以能够在页面上看到select下拉框的效果，原因在于后台做了html代码的拼接
				out.print(toHTML());
			} catch (IOException | NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e){
				e.printStackTrace();
			}
	    	return super.doStartTag();
	    }
	    
		private String toHTML() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, NoSuchMethodException {
			StringBuilder sb = new StringBuilder();
			String value = "";
			String html = ""; 
			sb.append("<select id='"+id+"' name='"+name+"'>");
	        if(!(headerTextKey == null || "".equals(headerTextKey) || headerTextVal == null || "".equals(headerTextVal))) {
	        	sb.append("<option selected value='"+headerTextKey+"'>"+headerTextVal+"</option>");	
	        }
//			items=data,textKey=sid,textVal=sname
			for (Object obj : items) {
//	        底层代码
				Field f = obj.getClass().getDeclaredField(textKey);
				f.setAccessible(true);
				value = (String) f.get(obj);
//			第三方工具包方法
				html = (String) PropertyUtils.getProperty(obj, textVal);
				
//				考虑如果是修改页面需要下拉框回选数据库存储的值
				if(value.equals(selectedVal)) {
					sb.append("<option selected value='"+value+"'>"+html+"</option>");
				}
				else {
					sb.append("<option value='"+value+"'>"+html+"</option>");
				}
				
			}
			sb.append("</select>");
			
			return sb.toString();
		}




	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;
	}
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	public String getTextKey() {
		return textKey;
	}
	public void setTextKey(String textKey) {
		this.textKey = textKey;
	}
	public String getTextVal() {
		return textVal;
	}
	public void setTextVal(String textVal) {
		this.textVal = textVal;
	}
	public String getHeaderTextKey() {
		return headerTextKey;
	}
	public void setHeaderTextKey(String headerTextKey) {
		this.headerTextKey = headerTextKey;
	}
	public String getHeaderTextVal() {
		return headerTextVal;
	}
	public void setHeaderTextVal(String headerTextVal) {
		this.headerTextVal = headerTextVal;
	}
	public String getSelectedVal() {
		return selectedVal;
	}
	public void setSelectedVal(String selectedVal) {
		this.selectedVal = selectedVal;
	}
	
}

tid文件

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="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>pro_qx 1.1 core library</description>
  <display-name>pro_qx core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>c</short-name>
  <uri>/pro_qx</uri>

  <tag>
  <!-- 填写的是标签库中的标签 -->
    <name>demo</name>
    <!-- 标签对应的后台助手类(每在页面上写标签都会去访问后台代码) -->
    <tag-class>com.pyc.DemoTag</tag-class>
   <!-- 标签类别 -->
    <body-content>JSP</body-content>
    <attribute>
    <!-- 自定义标签中的属性 -->
        <name>test</name>
        <!-- 属性值是否必填 -->
        <required>true</required>
        <!-- 是否支持表达式EL表达式/ognl表达式 -->
        <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>
  
   <!-- set标签 -->
  <tag>
    <name>set</name>
    <tag-class>com.pyc.SetTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
  
  <!-- out标签 -->
  <tag>
    <name>out</name>
    <tag-class>com.pyc.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.pyc.IfTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>flag</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
 
 <!-- foreach标签 -->
  <tag>
    <name>foreach</name>
    <tag-class>com.pyc.ForeachTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
     <attribute>
        <name>items</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
   <!-- select标签 -->
  <tag>
    <name>select</name>
    <tag-class>com.pyc.SelectTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>id</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>name</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>items</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <name>textKey</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>textVal</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>headerTextKey</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>headerTextVal</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>selectedVal</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
</taglib>

demo2.jsp

<%@page import="com.pyc.Teacher"%>
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ taglib prefix="m" uri="/pro_qx" %>
<!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>jsp自定义标签</title>
</head>
<body>
<!-- set,out -->
<m:set var="name" value="pyc"></m:set>
<m:out value="${name}"></m:out>
<hr>
<!-- if -->
<m:if flag="true">xiaopan</m:if>

<hr>

<!-- foreach -->
<%
/* 模拟查过来的集合 */
  List list = new ArrayList();
  list.add(new Teacher("1","春"));
  list.add(new Teacher("2","秋"));
  list.add(new Teacher("3","冬"));
  pageContext.setAttribute("data", list);
%>
 <m:foreach items="${data}" var="t">
  ${t.id},${t.name}<br>
</m:foreach> 
<hr>

<!-- select -->
  <h2>新增查询页面下拉框</h2>
  <m:select textVal="name" items="${data }" textKey="id"></m:select>
<hr>
<m:select headerTextKey="-1" headerTextVal="--请选择--" textVal="name" items="${data }" textKey="id"></m:select>
<hr>
 <h2>修改页面下拉框</h2>
 <m:select headerTextKey="-1" headerTextVal="--请选择--" textVal="name" items="${data }" textKey="id" selectedVal="2"></m:select>
 
</body>
</html>

运行结果：
jsp自定义标签

相关标签： 自定义标签

上一篇： 自定义控件 - 流式布局（FlowLayout）

下一篇： 解决HTML5对手机页面长按会粘贴复制禁用的方法

推荐阅读