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jsp中自定义标签用法实例分析

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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

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./xml/ns/javaee" xmlns:xsi="http://.w3./2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun./xml/ns/javaee 
  http://java.sun./xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
  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>http://my.oschina./aps</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>.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 .apache.jasper.JasperException: /index.jsp(12,8) 
      Aording 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>.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 .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./aps" prefix="aps" %>
  <%@taglib uri="http://java.sun./jsp/jstl/core" prefix="c"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://.w3./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 ours 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 ours 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 ours 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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