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