Struts通过加载插件的形式初始化系统常量以及其他信息

一：通过插件的形式加载系统中定义的常量：

思路：首先定义一个常量类存放系统常量，或者定义一个xml或properties文件中然后进行读取，

然后把相应的常量放入map中

最后编写插件类，加载map类

最后把插件类放入struts-config.xml中启动的时候进行加载

这样在其他页面中就可以随意访问了。

1：首先定义在常量类中定义一些常量：

package com.topwqp.common.constants;public class Globals {   public static  final  String  AUTHOR = "topwqp";   public static  final  String  PLUGINTEST = "puginTest";}

2：把常量放在map中，

package com.topwqp.common.constants;import java.util.HashMap;import java.util.Map;public class Constants {private Map  globals;public Constants(){globals = new HashMap();globals.put("AUTHOR", Globals.AUTHOR);globals.put("PLUGINTEST", Globals.PLUGINTEST);}public Map getGlobals() {return globals;}public void setGlobals(Map globals) {this.globals = globals;}}

3：编写对应的插件类：

插件类需要实现PlugIn接口关于这个接口的介绍在下面

package com.topwqp.plugin;import javax.servlet.ServletException;import org.apache.struts.action.ActionServlet;import org.apache.struts.action.PlugIn;import org.apache.struts.config.ModuleConfig;import com.topwqp.common.constants.Constants;public class ConstantsPlugin implements PlugIn{@Overridepublic void destroy() {// TODO Auto-generated method stub}@Overridepublic void init(ActionServlet servlet, ModuleConfig config)throws ServletException {System.out.println("load constans success. then you  can access constans.......");// TODO Auto-generated method stubConstants  constants = new Constants();servlet.getServletContext().setAttribute("Constants", constants);}}

关于PlugIn接口的源码如下：意思就是需要实现init(） 其中init方法用于系统启动的一些设置在这个方法中进行编写，

deploy方法是系统关闭时候的一些操作在这个方法中进行设置。

源码如下：

/* * $Id: PlugIn.java 471754 2006-11-06 14:55:09Z husted $ * * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements.  See the NOTICE file * distributed with this work for additional information * regarding copyright ownership.  The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License.  You may obtain a copy of the License at * *  http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied.  See the License for the * specific language governing permissions and limitations * under the License. */package org.apache.struts.action;import org.apache.struts.config.ModuleConfig;import javax.servlet.ServletException;/** * <p>A <strong>PlugIn</strong> is a configuration wrapper for a * module-specific resource or service that needs to be notified about * application startup and application shutdown events (corresponding to when * the container calls <code>init</code> and <code>destroy</code> on the * corresponding {@link ActionServlet} instance). <code>PlugIn</code> objects * can be configured in the <code>struts-config.xml</code> file, without the * need to subclass {@link ActionServlet} simply to perform application * lifecycle activities.</p> * * <p>Implementations of this interface must supply a zero-argument * constructor for use by {@link ActionServlet}. Configuration can be * accomplished by providing standard JavaBeans property setter methods, which * will all have been called before the <code>init()</code> method is * invoked.</p> * * <p>This interface can be applied to any class, including an Action * subclass. </p> * * @version $Rev: 471754 $ $Date: 2005-05-14 01:09:32 -0400 (Sat, 14 May 2005) *          $ * @since Struts 1.1 */public interface PlugIn {    /**     * <p>Receive notification that our owning module is being shut down.</p>     */    void destroy();    /**     * <p>Receive notification that the specified module is being started     * up.</p>     *     * @param servlet ActionServlet that is managing all the modules in this     *                web application     * @param config  ModuleConfig for the module with which this plug-in is     *                associated     * @throws ServletException if this <code>PlugIn</code> cannot be     *                          successfully initialized     */    void init(ActionServlet servlet, ModuleConfig config)        throws ServletException;}

然后把编写的插件类在struts-config.xml中进行配置即可，当application在tomcat中启动 时候，首先加载web.xml的文件，web.xml中有相应的初始化设置加载指定的文件：

及struts-config.xml文件：

当然struts允许同时加载多个文件如下我的web.xml的配置如下：

<servlet>    <servlet-name>action</servlet-name>    <servlet-class>        org.apache.struts.action.ActionServlet    </servlet-class>    <init-param>        <param-name>config</param-name>        <param-value>         /WEB-INF/struts-config.xml, /WEB-INF/struts-config-1.xml, /WEB-INF/struts-config-2.xml        </param-value>    </init-param>        <init-param>        <param-name>config/admin</param-name>        <param-value>         /WEB-INF/struts-config-admin.xml        </param-value>    </init-param>    <init-param>        <param-name>config/common</param-name>        <param-value>         /WEB-INF/struts-config-common.xml        </param-value>    </init-param>        <load-on-startup>1</load-on-startup>  </servlet>      <servlet-mapping>       <servlet-name>action</servlet-name>       <url-pattern>*.do</url-pattern>  </servlet-mapping>

把编写的插件配置在struts-config.xml中即可：

 <plug-in className="com.topwqp.plugin.ConstantsPlugin"></plug-in>

在对应的jsp页面中访问：

<p>Field name: AUTHOR<br />Field value: <bean:write name="Constants" property="globals(AUTHOR)"/><br /></p><p>Field name: PluginTest<br />Field value: <c:out value="${Constants.globals.PLUGINTEST}"/><br /></p>

2：创建一个插件记录应用的启动时间以及已经运行了多久

思路：定义时间追踪类，该类中有应用的启动时间，以及方法获取距离启动时间多久，然后在插件中放入这个类的实例，最后在jsp页面中进行显示即可。

1：定义时间类：

package com.topwqp.plugin;import java.util.Date;public class TimeTracker {private long  startUpTimeMillis;private Date startupOn;public TimeTracker (){startUpTimeMillis = System.currentTimeMillis();startupOn = new Date();}//  how long the application  have started up;public  long getUptime(){return System.currentTimeMillis() - startUpTimeMillis;}// get  the  application  startup timepublic  Date getStartupOn(){return startupOn;}}

这个类中有个默认的构造方法，当对象创建的时候对应的启动时间就产生了，

有一个getUptime方法，用去动态生成距离启动时间的毫秒数。

2：创建对应的插件类：

package com.topwqp.plugin;import javax.servlet.ServletException;import org.apache.struts.action.ActionServlet;import org.apache.struts.action.PlugIn;import org.apache.struts.config.ModuleConfig;public class TimeTrackerPlugin implements PlugIn{private String contextKey ;public void  setContextKey(String contextKey){this.contextKey = contextKey;}@Overridepublic void destroy() {// TODO Auto-generated method stubSystem.out.println("do nothing............");}@Overridepublic void init(ActionServlet servlet, ModuleConfig config)throws ServletException {// TODO Auto-generated method stubservlet.getServletContext().setAttribute(contextKey, new TimeTracker());}}

3：在struts-config.xml中配置插件：

 <plug-in className="com.topwqp.plugin.TimeTrackerPlugin">      <set-property property="contextKey" value="timeTracker"/>    </plug-in>

4：在jsp页面中获取对应的时间：

<h4> 系统启动日期： since <bean:write name="timeTracker" property="startupOn" format="MM/dd/yyyy HH:mm"/><br> 已经运行时间：for<bean:write name="timeTracker" property="uptime"/> milliseconds!</h4>

然后启动应用访问即可：

两个插件的访问页面显示效果：