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jsp中自定义标签用法实例分析

来源:互联网 作者:佚名 时间:2015-09-29 01:45
这篇文章主要介绍了jsp中自定义标签用法,以实例形式较为详细的分析了jsp自定义标签的功能、定义及具体实现技巧,具有一定参考借鉴价值,需要的朋友可以参考下

本文实例讲述了jsp中自定义标签用法。分享给大家供大家参考。具体如下:

这里简单的写了一个自定义标签,自己定义标签的好处就是在jsp页面中可以使用自己定义的功能,完全与Java代码分离

1. tld文件如下:

首先是要写×.tld文件,当项目随着服务器启动的时候,会检查项目中有没有*tld文件。
写的tld文件

<?xml version="1.0" encoding="UTF-8" ?> <taglib xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee " version="2.1"> <!-- 定义版本 --> <tlib-version>1.0</tlib-version> <!-- 定义名字 --> <short-name>apsliyuan</short-name> <!-- 定义uri --> <uri></uri> <!-- 定义自己的类 --> <tag> <!-- name 就是在jsp中显示的标签名字,<aps:hellowTag/> --> <name>hellowTag</name> <!-- 自己写的标签类的完整路径 --> <tag-class>cn.itcast.apsliyuan.tag.HellowtTag</tag-class> <!-- jsp中主题中是不是要显示内容,有四个属性, 如果为empty的话。在jsp页面中标签就不能定义自己的内容了,否则会报 Servlet.service() for servlet jsp threw exception org.apache.jasper.JasperException: /index.jsp(12,8) According to TLD, tag aps:hellowTag must be empty, but is not 异常 --> <body-content>JSP</body-content> </tag> <!-- 这里没有写属性,有时间补上 --> <tag> <name>ApsliyuanTag</name> <tag-class>cn.itcast.apsliyuan.tag.ApsliyuanTag</tag-class> <body-content>JSP</body-content> </tag> </taglib>

2. 自定义标签类java代码如下:

//自定义标签的类 package cn.itcast.apsliyuan.tag; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; import javax.servlet.jsp.JspException; import javax.servlet.jsp.JspWriter; import javax.servlet.jsp.tagext.TagSupport; public class HellowtTag extends TagSupport{ /** * */ private static final long serialVersionUID = 1781703371130382609L; @Override public int doStartTag() throws JspException { // TODO Auto-generated method stub JspWriter out = pageContext.getOut(); SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); try { out.print(format.format(new Date())); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } return EVAL_BODY_INCLUDE; } @Override public int doEndTag() throws JspException { // TODO Auto-generated method stub JspWriter out = pageContext.getOut(); try { out.print("<br/> <hr/>标签执行完毕了"); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } return EVAL_PAGE; } }

3. jsp引入自己定义标签代码如下:

//jsp中引入自己定义的标签 <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@taglib uri="http://my.oschina.net/aps" prefix="aps" %> <%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%> <!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>index.jsp</title> </head> <body> 现在的时间是:<aps:hellowTag> </aps:hellowTag><br/> <hr/> 我爱的人是: <aps:ApsliyuanTag/> </body> </html>

4. TagSupport代码如下:

//看看TagSupport中的源代码,, 这个是适配器模式 public class TagSupport implements IterationTag, Serializable { public static final Tag findAncestorWithClass(Tag from, // TCK signature test fails with generics @SuppressWarnings("unchecked") Class klass) { boolean isInterface = false; if (from == null || klass == null || (!Tag.class.isAssignableFrom(klass) && !(isInterface = klass.isInterface()))) { return null; } for (;;) { Tag tag = from.getParent(); if (tag == null) { return null; } if ((isInterface && klass.isInstance(tag)) || klass.isAssignableFrom(tag.getClass())) return tag; else from = tag; } } /** * Default constructor, all subclasses are required to define only * a public constructor with the same signature, and to call the * superclass constructor. * * This constructor is called by the code generated by the JSP * translator. */ public TagSupport() { } /** * Default processing of the start tag, returning SKIP_BODY. * * @return SKIP_BODY * @throws JspException if an error occurs while processing this tag * * @see Tag#doStartTag() */ public int doStartTag() throws JspException { return SKIP_BODY; } /** * Default processing of the end tag returning EVAL_PAGE. * * @return EVAL_PAGE * @throws JspException if an error occurs while processing this tag * * @see Tag#doEndTag() */ public int doEndTag() throws JspException { return EVAL_PAGE; } /** * Default processing for a body. * * @return SKIP_BODY * @throws JspException if an error occurs while processing this tag * * @see IterationTag#doAfterBody() */ public int doAfterBody() throws JspException { return SKIP_BODY; } // Actions related to body evaluation /** * Release state. * * @see Tag#release() */ public void release() { parent = null; id = null; if( values != null ) { values.clear(); } values = null; } /** * Set the nesting tag of this tag. * * @param t The parent Tag. * @see Tag#setParent(Tag) */ public void setParent(Tag t) { parent = t; } /** * The Tag instance most closely enclosing this tag instance. * @see Tag#getParent() * * @return the parent tag instance or null */ public Tag getParent() { return parent; } /** * Set the id attribute for this tag. * * @param id The String for the id. */ public void setId(String id) { this.id = id; } /** * The value of the id attribute of this tag; or null. * * @return the value of the id attribute, or null */ public String getId() { return id; } /** * Set the page context. * * @param pageContext The PageContext. * @see Tag#setPageContext */ public void setPageContext(PageContext pageContext) { this.pageContext = pageContext; } /** * Associate a value with a String key. * * @param k The key String. * @param o The value to associate. */ public void setValue(String k, Object o) { if (values == null) { values = new Hashtable<String, Object>(); } values.put(k, o); } /** * Get a the value associated with a key. * * @param k The string key. * @return The value associated with the key, or null. */ public Object getValue(String k) { if (values == null) { return null; } else { return values.get(k); } } /** * Remove a value associated with a key. * * @param k The string key. */ public void removeValue(String k) { if (values != null) { values.remove(k); } } /** * Enumerate the keys for the values kept by this tag handler. * * @return An enumeration of all the keys for the values set, * or null or an empty Enumeration if no values have been set. */ public Enumeration<String> getValues() { if (values == null) { return null; } return values.keys(); } // private fields private Tag parent; private Hashtable<String, Object> values; /** * The value of the id attribute of this tag; or null. */ protected String id; // protected fields /** * The PageContext. */ protected PageContext pageContext; }

doStartTag的返回值

在doStartTag返回的值决定的body部分的数据如何显示。

两个返回值:

0 – SKIP_BODY – 常量。不显示body。
1-EVAN_BODY_INCLUDE ;包含body部分的数据,正常显示。
3:在doEndTag也有两个返回值

决定后面的页面部分是否显示:

SKIP_PAGE : 不再显示后面的页面部分。

EVAL_PAGE : 显示后面的page部分。

希望本文所述对大家的JSP程序设计有所帮助。

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