jsp tag实例

 

　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=$＞

＜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..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

 

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=$＞

＜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