Struts2 的UITag原理:
Struts2 UITag分三部份组成,一部份用于定义Tag的内容与逻辑的UIBean,一部份用于定义JSP Tag,也就是平时我们定义的那种,最后就是Template,它存放在你的theme目录之下,是一个FreeMarker模板文件。
我现在辑写一份MMTag,它主要是用于输出带链接的文字,比如像这样:
<cur:mm message="'I am a boy.'" />
就会输出:
<a href="http://www.blogjava.net/natlive">I am boy.</a>
我们先写UIBean部份:我们把它定义为MM,它继承于org.apache.struts2.components.UIBean:
package
limitstudy.corestruts2.tag;
import org.apache.struts2.components.UIBean;
import org.apache.struts2.views.annotations.StrutsTag;
import org.apache.struts2.views.annotations.StrutsTagAttribute;
import com.opensymphony.xwork2.util.ValueStack;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@StrutsTag(name = " mm " , tldTagClass = " limitstudy.corestruts2.tag.MMTag " , description = " MM " )
public class MM extends UIBean {
private String message;
public MM(ValueStack stack, HttpServletRequest request, HttpServletResponse response) {
super (stack, request, response);
}
@Override
protected String getDefaultTemplate() {
return " mm " ;
}
@StrutsTagAttribute(description = " set message " , type = " String " )
public void setMessage(String message) {
this .message = message;
}
@Override
protected void evaluateExtraParams() {
super .evaluateExtraParams();
if ( null != message) {
addParameter( " message " , findString(message));
}
}
}
import org.apache.struts2.components.UIBean;
import org.apache.struts2.views.annotations.StrutsTag;
import org.apache.struts2.views.annotations.StrutsTagAttribute;
import com.opensymphony.xwork2.util.ValueStack;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@StrutsTag(name = " mm " , tldTagClass = " limitstudy.corestruts2.tag.MMTag " , description = " MM " )
public class MM extends UIBean {
private String message;
public MM(ValueStack stack, HttpServletRequest request, HttpServletResponse response) {
super (stack, request, response);
}
@Override
protected String getDefaultTemplate() {
return " mm " ;
}
@StrutsTagAttribute(description = " set message " , type = " String " )
public void setMessage(String message) {
this .message = message;
}
@Override
protected void evaluateExtraParams() {
super .evaluateExtraParams();
if ( null != message) {
addParameter( " message " , findString(message));
}
}
}
* strutsTag注解指明了该UIBean的名字和Tag类的类名。
* getDefaultTemplate()方法用于返回模板的名字,Struts2会自动在后面加入.ftl扩展名以找到特定的模板文件。
* setXXX,设置UIBean的属性,一般Tag中有几个这样的属性,这里就有几个。 @StrutsTagAttribute(description = " set message " , type = " String " )注解,说明该属性是字符串(也可以是其它),这一步很重要。
* 覆写 evaluateExtraParams()方法,在UIBean初始化后会调用这个方法来初始化设定参数,如addParameter方法,会在freemarker里的parameters里加入一个key value。这里要注意findString,还有相关的findxxxx方法,它们是已经封装好了的解释ognl语法的工具,具体是怎么样的,大家可以查看一下UIBean的api doc。
然后是Tag部份:
package
limitstudy.corestruts2.tag;
import org.apache.struts2.views.jsp.ui.AbstractUITag;
import org.apache.struts2.components.Component;
import com.opensymphony.xwork2.util.ValueStack;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class MMTag extends AbstractUITag {
private String message;
@Override
public Component getBean(ValueStack stack, HttpServletRequest request, HttpServletResponse response) {
return new MM(stack, request, response);
}
@Override
protected void populateParams() {
super .populateParams();
MM mm = (MM)component;
mm.setMessage(message);
}
public void setMessage(String message) {
this .message = message;
}
}
import org.apache.struts2.views.jsp.ui.AbstractUITag;
import org.apache.struts2.components.Component;
import com.opensymphony.xwork2.util.ValueStack;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class MMTag extends AbstractUITag {
private String message;
@Override
public Component getBean(ValueStack stack, HttpServletRequest request, HttpServletResponse response) {
return new MM(stack, request, response);
}
@Override
protected void populateParams() {
super .populateParams();
MM mm = (MM)component;
mm.setMessage(message);
}
public void setMessage(String message) {
this .message = message;
}
}
* getBean()返回该Tag中的UIBean。
* populateParams()初始化参数,一般用来初始化UIBean(Component)。
* setXXXX设置属性,和jsp tag是一样的。
在/WEB-INF/tlds/下建立current.tld文件(文名随你喜欢):
<?
xml version="1.0" encoding="UTF-8"
?>
< taglib xmlns ="http://java.sun.com/xml/ns/j2ee" xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance" version ="2.0"
xsi:schemaLocation ="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd" >
< description > test </ description >
< tlib-version > 2.0 </ tlib-version >
< short-name > cur </ short-name >
< uri > /cur </ uri >
< tag >
< name > mm </ name >
< tag-class > limitstudy.corestruts2.tag.MMTag </ tag-class >
< body-content > JSP </ body-content >
< attribute >
< name > message </ name >
< required > true </ required >
</ attribute >
</ tag >
</ taglib >
< taglib xmlns ="http://java.sun.com/xml/ns/j2ee" xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance" version ="2.0"
xsi:schemaLocation ="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd" >
< description > test </ description >
< tlib-version > 2.0 </ tlib-version >
< short-name > cur </ short-name >
< uri > /cur </ uri >
< tag >
< name > mm </ name >
< tag-class > limitstudy.corestruts2.tag.MMTag </ tag-class >
< body-content > JSP </ body-content >
< attribute >
< name > message </ name >
< required > true </ required >
</ attribute >
</ tag >
</ taglib >
在源代码目录中建立template/simple目录(这个目录名和你的theme有关),然后在里面建一个mm.ftl文件:
<
a
href
="http://www.yinsha.com"
>
${parameters.message?html}
</
a
>
建一个action测试一下,视图文件:
<%
@ page contentType
=
"
text/html;charset=UTF-8
"
language
=
"
java
"
%>
<% @ taglib prefix = " s " uri = " /struts-tags " %>
<% @ taglib prefix = " cur " uri = " /cur " %>
< html >
< head >
< title >< s:property value ="message" /></ title >
</ head >
< body >
< cur:mm message ="haoahahhahaha" />
</ body >
</ html >
<% @ taglib prefix = " s " uri = " /struts-tags " %>
<% @ taglib prefix = " cur " uri = " /cur " %>
< html >
< head >
< title >< s:property value ="message" /></ title >
</ head >
< body >
< cur:mm message ="haoahahhahaha" />
</ body >
</ html >
完。