withcollectiontag.java

J2EE独立开发制作

package diegoyun;

import java.util.Collection;
import java.util.Iterator;

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

import org.apache.commons.beanutils.PropertyUtils;

public class WithCollectionTag extends BodyTagSupport {
 private Object element = null;
 private String property=null;
 private Collection list = null;

 private Iterator iterator = null;

 public Object getElement() {
  return element;
 }

 public void setProperty(String property) throws JspException {
 //取得父Tag对象,并且得到Collection
  WithObjectTag parent = (WithObjectTag) getParent();
  if (parent == null)
   throw new JspException("parent tag is null");
  try {
   Object propertyValue = PropertyUtils.getProperty(parent.getValue(),
     property);
   this.list = (Collection) propertyValue;
   if (list == null)
    throw new JspException("Collection is null");
  } catch (Exception e) {
   throw new JspException(e);
  }
 }

 public int doStartTag() throws JspException {
 //设置第一个元素,然后执行子Tag
  iterator = list.iterator();
  if (iterator.hasNext())
   element = iterator.next();

  return EVAL_BODY_INCLUDE;
 }

 public int doAfterBody() {
  if (iterator.hasNext()) {
  //如果还存在子元素,设置子元素,并且再次执行子Tag
  //循环由此而来
  //否则不再执行子Tag
   element = iterator.next();
   return EVAL_BODY_AGAIN;
  }
  else
   return EVAL_PAGE;
 }
}