jsp自定义标签库

it2022-05-05 157

标签的概念：

标签：标签是一种XML元素，通过标签可以使JSP网页变得简洁并且易于维护，还可以方便地实现同一个JSP文件支持多种语言版本。由于标签是XML元素，所以它的名称和属性都是大小写敏感的

标签处理类：标签处理类似是Java类，这个类继承了TagSupport或者扩展了SimpleTag接口，通过这个类可以实现自定义JSP标签的具体功能

标签语言特点： <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 if /foreach 数据标签 set

自定义标签的开发及使用步骤 1 . 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 rtexprvalue

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

4 . 使用标签库的时候需要导入jar包

// 序列号的作用是方便对象序列化，序列化实际上就是将对象按照特定的规则持久化到硬盘 private static final long serialVersionUID = 2102051784152825544L;

代码： SetTag:

package com.xhh.jsp.tag; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.BodyTagSupport; /** * * 数据标签(不需要展示内容) * 作用： * 是将value值赋给var * @author linyaodong * */ public class SetTag extends BodyTagSupport { private static final long serialVersionUID = 7076852223410589098L; 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.xhh.jsp.tag; import java.io.IOException; import javax.servlet.jsp.JspException; import javax.servlet.jsp.JspWriter; import javax.servlet.jsp.tagext.BodyTagSupport; /** * out属性UI（标签效果，是依靠标签属性展现页面效果） * @author linyaodong * */ public class OutTag extends BodyTagSupport { private static final long serialVersionUID = -244786502784959729L; 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) { // TODO Auto-generated catch block e.printStackTrace(); } return super.doStartTag(); } }

IfTag:

package com.xhh.jsp.tag; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.BodyTagSupport; /** * if属于控制标签(页面展示效果依赖的是标签体) * @author linyaodong * */ public class IfTag extends BodyTagSupport { private static final long serialVersionUID = 2102051784152825544L; private boolean test; public boolean isTest() { return test; } public void setTest(boolean test) { this.test = test; } @Override public int doStartTag() throws JspException { return test ? EVAL_BODY_INCLUDE : SKIP_BODY; } }

z.tld:

<?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>xhh 1.1 core library</description> <display-name>xhh core</display-name> <tlib-version>1.1</tlib-version> <short-name>c</short-name> <uri>/xhh</uri>  <tag>  <name>set</name>  <tag-class>com.xhh.jsp.tag.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>  <tag> <name>out</name> <tag-class>com.xhh.jsp.tag.OutTag</tag-class> <body-content>JSP</body-content> <attribute> <name>value</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag>  <tag> <name>if</name> <tag-class>com.xhh.jsp.tag.IfTag</tag-class> <body-content>JSP</body-content> <attribute> <name>test</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag> </taglib>

jsp页面：

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@taglib prefix="z" uri="/xhh"%> <!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>2</title> </head> <body> <z:set var="name" value="xhh"></z:set> <z:out value="${name}"></z:out> <z:if test="true">linyaodong</z:if> <z:if test="false">sb</z:if> </body> </html>

运行结果： ForEachTag:

package com.xhh.jsp.tag; 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 = 1L; private String var; private List<Object> items=new ArrayList<>(); 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; } @Override public int doStartTag() throws JspException { Iterator<Object> it=items.iterator(); pageContext.setAttribute(var, it.next()); pageContext.setAttribute("it", it); return EVAL_BODY_INCLUDE; } @Override 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; } return EVAL_PAGE; } }

z.tld

<tag> <name>foreach</name> <tag-class>com.xhh.jsp.tag.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>

jsp页面：

<%@page import="com.xhh.entity.Student"%> <%@page import="java.util.ArrayList"%> <%@page import="java.util.List"%> <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@taglib prefix="z" uri="/xhh"%> <!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>2</title> </head> <body> <z:set var="name" value="xhh"></z:set> <z:out value="${name}"></z:out> <z:if test="true">linyaodong</z:if> <z:if test="false">sb</z:if> <br> <% List <Student> list = new ArrayList<Student>(); list.add(new Student("1","林")); list.add(new Student("2","耀")); list.add(new Student("3","东")); request.setAttribute("data", list); %> <z:foreach items="${data}" var="t"> ${t.tid} ${t.tname}<br> </z:foreach> </body> </html>

运行结果： SelectTag: 第三方工具包需要导入jar架包

package com.xhh.jsp.tag; 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.BeanUtils; import org.apache.commons.beanutils.PropertyUtils; 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，以及默认选中指定项 * * 思考： * 1.要往后台传值 id,name * 2.定义数据库存储的对应的标签属性，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 * * 属于UI标签 * @author linyaodong * */ public class SelectTag extends BodyTagSupport{ private static final long serialVersionUID = 6885147458102952045L; private String id; private String name; private List<Object> items = new ArrayList<>(); private String textkey; private String textval; private String headkey; private String headval; private String 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; } 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 getHeadkey() { return headkey; } public void setHeadkey(String headkey) { this.headkey = headkey; } public String getHeadval() { return headval; } public void setHeadval(String headval) { this.headval = headval; } public String getSelectedval() { return selectedval; } public void setSelectedval(String selectedval) { this.selectedval = selectedval; } @Override public int doStartTag() throws JspException { JspWriter out = pageContext.getOut(); try { //对你想展现在页面上的html代码进行拼接 out.print(toHTML()); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } return super.doStartTag(); } //拼接标签代码 private String toHTML() throws Exception, Exception { StringBuilder sb = new StringBuilder();//更快 sb.append("<select id='"+id+"' name='"+name+"'>"); //加载类似于下拉框默认显示的请选择 //判定是否有值 if(!(headkey == null || "".equals(headkey) || headval == null || "".equals(headval))) { sb.append("<option selected value='"+headkey+"'>"+headval+"</option>"); } String val = "";//写option value 的 String html = "";//写在option标签体的展示看 //循环打印数据 items = value for (Object obj : items) { Field f = obj.getClass().getDeclaredField(textkey); f.setAccessible(true); val = (String) f.get(obj); f = obj.getClass().getDeclaredField(textval); f.setAccessible(true); html = (String) f.get(obj); //考虑如果是修改页面时，下拉框回选数据库所存储的值也就是默认选中数据库所存储的值 if(val.equals(selectedval)) { sb.append("<option selected value='"+val+"'>"+html+"</option>"); }else { sb.append("<option value='"+val+"'>"+html+"</option>"); } } sb.append("</select>"); return sb.toString();//返回拼接的值 } }

z.tld:

<tag> <name>select</name> <tag-class>com.xhh.jsp.tag.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>headkey</name> <required>false</required> <rtexprvalue>false</rtexprvalue> </attribute><attribute> <name>headval</name> <required>false</required> <rtexprvalue>false</rtexprvalue> </attribute> <attribute> <name>selectedval</name> <required>false</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag>

jsp页面

<h2>新增查询页面下拉框</h2> <z:select textval="tname" items="${data}" textkey="tid"></z:select> <hr> <z:select headkey="-1" headval="--请选择--" textval="tname" items="${data }" textkey="tid"></z:select> <hr> <h2>修改页面下拉框</h2> <z:select headkey="-1" headval="--请选择--" textval="tname" items="${data}" textkey="tid" selectedval="2"></z:select>

运行结果：

专利

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