jsp中自定义标签用法实例分析

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

  
  1.0
  
  apsliyuan
  
  http://my.oschina.net/aps
  
  
    
    hellowTag
    
    cn.itcast.apsliyuan.tag.HellowtTag
    
    JSP
  

  
    ApsliyuanTag
    cn.itcast.apsliyuan.tag.ApsliyuanTag
    JSP
  

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("
 
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"%>







  现在的时间是： 

  

  我爱的人是： 

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();
  }
  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 getValues() {
  if (values == null) {
    return null;
  }
  return values.keys();
  }
  // private fields
  private  Tag     parent;
  private  Hashtable  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。