下载本文示例代码
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 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; }} 编写 ElementOutputTag
package diegoyun;import java.io.IOException;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.TagSupport;import org.apache.commons.beanutils.PropertyUtils;public class ElementOutputTag extends TagSupport{ private Object propertyValue = null; public void setProperty(String property)throws JspException { WithCollectionTag parent = (WithCollectionTag)getParent(); if(parent == null) throw new JspException("parent tag is null"); try { //判断上层tag中是否存在该属性名称,如果存在,取得属性值,否则报错 propertyValue = PropertyUtils.getProperty(parent.getElement(), property); } catch (Exception e) { throw new JspException(e); } } public int doEndTag()throws JspException { try { //简单的把值打印到jsp页面 pageContext.getOut().print(propertyValue); } catch (IOException e) { throw new JspException(e); } return EVAL_PAGE; }} 编写tld
＜!--WithObjectTag--＞＜tag＞ ＜name＞withObject＜/name＞ ＜tag-class＞diegoyun.WithObjectTag＜/tag-class＞ ＜body-content＞JSP＜/body-content＞ ＜attribute＞ ＜name＞value＜/name＞ ＜required＞false＜/required＞ ＜rtexprvalue＞true＜/rtexprvalue＞ ＜/attribute＞＜/tag＞＜!--WithCollectionTag--＞＜tag＞ ＜name＞withCollection＜/name＞ ＜tag-class＞diegoyun.WithCollectionTag＜/tag-class＞ ＜body-content＞JSP＜/body-content＞ ＜attribute＞ ＜name＞property＜/name＞ ＜required＞false＜/required＞ ＜rtexprvalue＞true＜/rtexprvalue＞ ＜/attribute＞＜/tag＞＜!--ElementOutputTag--＞＜tag＞ ＜name＞elementout＜/name＞ ＜tag-class＞diegoyun.ElementOutputTag＜/tag-class＞ ＜body-content＞empty＜/body-content＞ ＜attribute＞ ＜name＞property＜/name＞ ＜required＞false＜/required＞ ＜rtexprvalue＞true＜/rtexprvalue＞ ＜/attribute＞＜/tag＞ 编写jsp
＜%@ page language="java" %＞＜%@ page import="diegoyun.vo.*"%＞＜%@ page import="java.util.*"%＞＜%@ taglib uri="/WEB-INF/tlds/diego.tld" prefix="diego"%＞＜html＞＜body bgcolor="#FFFFFF"＞＜% Collection c = new ArrayList(); Man man1 = new Man(); man1.setName("diego"); c.add(man1); Man man2 = new Man(); man2.setName("Zidane"); c.add(man2); Man man3 = new Man(); man3.setName("Rui"); c.add(man3); People p =new People(); p.setMen(c); request.setAttribute("people",p);%＞Test loop tag:＜br＞＜diego:withObject value="${people}"＞＜diego:withCollection property="men"＞＜diego:elementout property="name"/＞＜br＞＜/diego:withCollection＞＜/diego:withObject＞＜/body＞＜/html＞ 运行,则可以看到:
Test loop tag: diego Zidane Rui
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 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; }} 编写 ElementOutputTag
package diegoyun;import java.io.IOException;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.TagSupport;import org.apache.commons.beanutils.PropertyUtils;public class ElementOutputTag extends TagSupport{ private Object propertyValue = null; public void setProperty(String property)throws JspException { WithCollectionTag parent = (WithCollectionTag)getParent(); if(parent == null) throw new JspException("parent tag is null"); try { //判断上层tag中是否存在该属性名称,如果存在,取得属性值,否则报错 propertyValue = PropertyUtils.getProperty(parent.getElement(), property); } catch (Exception e) { throw new JspException(e); } } public int doEndTag()throws JspException { try { //简单的把值打印到jsp页面 pageContext.getOut().print(propertyValue); } catch (IOException e) { throw new JspException(e); } return EVAL_PAGE; }} 编写tld
＜!--WithObjectTag--＞＜tag＞ ＜name＞withObject＜/name＞ ＜tag-class＞diegoyun.WithObjectTag＜/tag-class＞ ＜body-content＞JSP＜/body-content＞ ＜attribute＞ ＜name＞value＜/name＞ ＜required＞false＜/required＞ ＜rtexprvalue＞true＜/rtexprvalue＞ ＜/attribute＞＜/tag＞＜!--WithCollectionTag--＞＜tag＞ ＜name＞withCollection＜/name＞ ＜tag-class＞diegoyun.WithCollectionTag＜/tag-class＞ ＜body-content＞JSP＜/body-content＞ ＜attribute＞ ＜name＞property＜/name＞ ＜required＞false＜/required＞ ＜rtexprvalue＞true＜/rtexprvalue＞ ＜/attribute＞＜/tag＞＜!--ElementOutputTag--＞＜tag＞ ＜name＞elementout＜/name＞ ＜tag-class＞diegoyun.ElementOutputTag＜/tag-class＞ ＜body-content＞empty＜/body-content＞ ＜attribute＞ ＜name＞property＜/name＞ ＜required＞false＜/required＞ ＜rtexprvalue＞true＜/rtexprvalue＞ ＜/attribute＞＜/tag＞ 编写jsp
＜%@ page language="java" %＞＜%@ page import="diegoyun.vo.*"%＞＜%@ page import="java.util.*"%＞＜%@ taglib uri="/WEB-INF/tlds/diego.tld" prefix="diego"%＞＜html＞＜body bgcolor="#FFFFFF"＞＜% Collection c = new ArrayList(); Man man1 = new Man(); man1.setName("diego"); c.add(man1); Man man2 = new Man(); man2.setName("Zidane"); c.add(man2); Man man3 = new Man(); man3.setName("Rui"); c.add(man3); People p =new People(); p.setMen(c); request.setAttribute("people",p);%＞Test loop tag:＜br＞＜diego:withObject value="${people}"＞＜diego:withCollection property="men"＞＜diego:elementout property="name"/＞＜br＞＜/diego:withCollection＞＜/diego:withObject＞＜/body＞＜/html＞ 运行,则可以看到:
Test loop tag: diego Zidane Rui
下载本文示例代码
Taglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的TagTaglib原理和实现之循环的Tag
