第四篇 支持循环的Tag
1。问题:在request里的 People 对象,有个属性叫 men ,men 是一个Collection ,有许多个man 。现在,把 collection里的man的名字都显示出来
显然,这是一个嵌套Tag的问题。有三个Tag互相作用:最外层的Tag找到People对象,中间的Tag取得Collection,子Tag负责打印。
例如:
<diego:withObject value="${people}">
<diego:withCollection property="men">
<diego:elementout property="name"/>
</diego:withCollection>
</diego:withObject>
思路如下:
1.编写WithObjectTag,负责从El表达式中取得对象
2.编写WithCollectionTag,负责从对象中取得 Collection ,遍历 Collection ,每遍历一次 Collection ,执行一次body
3.编写ElementoutTag ,把 Collection 中每个men对象的 name 打印出来
2. 完整程序如下:
在上例的diegoyun.vo包内,编写 People 类
package diegoyun.vo;
import Java.util.Collection;
public class People
{
private Collection men = null;
public Collection getMen()
{
return men;
}
public void setMen(Collection men)
{
this.men = men;
}
}
编写 withObject ,这是从request里取得People对象的最外层Tag
package diegoyun;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
import org.apache.taglibs.standard.lang.support.EXPressionEvaluatorManager;
public class WithObjectTag extends BodyTagSupport
{
private Object value = null;
public Object getValue()
{
return value;
}
public void setValue(Object value)throws JspException
{
this.value = ExpressionEvaluatorManager.evaluate(
"value", value.toString(), Object.class, this, pageContext);
}
public int doStartTag()
{
return EVAL_BODY_INCLUDE;
}
public int doEndTag()throws JspException
{
return EVAL_PAGE;
}
}
编写WithCollectionTag,该Tag负责取得Collection,并遍历执行子Tag
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 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