Spring容器启动后自动执行Servlet进行预处理

通常做法是定义一个Servlet，并在web.xml中配置Servlet的启动顺序<load-on-startup>的值在DispatcherServlet之后。但这样做的缺点是在Servlet中无法使用Spring的依赖注入功能，只能使用WebApplicationContext的getBean()方法获取bean。

找到的解决办法如下：

1、自定义一个用于代理启动Servlet的类DelegatingServletProxy：

package cn.edu.swu.oa.common.util;



import java.io.IOException;



import javax.servlet.GenericServlet;

import javax.servlet.Servlet;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;



import org.springframework.web.context.WebApplicationContext;

import org.springframework.web.context.support.WebApplicationContextUtils;



public class DelegatingServletProxy extends GenericServlet {



	private String targetBean;

	private Servlet proxy;

	

	@Override

	public void service(ServletRequest arg0, ServletResponse arg1)

			throws ServletException, IOException {

		proxy.service(arg0, arg1);

	}



	@Override

	public void init() throws ServletException {

		this.targetBean = getServletName();

		getServletBean();

		proxy.init(getServletConfig());

	}

	

	private void getServletBean() {

		WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());

		this.proxy = (Servlet)wac.getBean(targetBean);

	}



}

2、编写启动Servlet：

package cn.edu.swu.oa.common.util;



import java.io.IOException;

import java.util.List;



import javax.annotation.Resource;

import javax.servlet.ServletConfig;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import org.springframework.stereotype.Component;



import cn.edu.swu.oa.agency.model.Department;

import cn.edu.swu.oa.agency.model.Group;

import cn.edu.swu.oa.agency.service.DepService;

import cn.edu.swu.oa.agency.service.GroService;

import cn.edu.swu.oa.common.model.SysCode;

import cn.edu.swu.oa.safe.model.User;

import cn.edu.swu.oa.safe.service.UserService;



/**

 * 

 * 工程：WebOA

 * 类型解释：Spring启动完成后执行初始化操作

 * 类型表述：预读某些实体的Key-Value，放入map，方便以后使用

 * @author ChenGuanwei

 * @version 创建时间：2010-3-25 下午10:55:44

 *

 */

@Component("initialServlet")

public class InitialServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	

	@Resource

	private UserService userService;

	

	@Resource

	private DepService depService;

       

	@Resource

	private GroService groService;

	

    /**

     * @see HttpServlet#HttpServlet()

     */

    public InitialServlet() {

        super();

    }



	/**

	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

	 */

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		

	}



	/**

	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

	 */

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		// TODO Auto-generated method stub

	}



	@Override

	public void init(ServletConfig config) throws ServletException {

		//初始化eserMap

		List<User> users = userService.getUsers();

		for(int i = 0; i < users.size(); i++) {

			User user = users.get(i);

			Integer userId = user.getUserId();

			String userName = user.getUserName();

			SysCode.userMap.put(userId, userName);

		}

		//初始化depMap

		List<Department> deps = depService.getAllDeps();

		for(int i = 0; i < deps.size(); i++) {

			Department dep = deps.get(i);

			Integer depId = dep.getDepId();

			String depName = dep.getDepName();

			SysCode.depMap.put(depId, depName);

		}

		//初始化groMap

		List<Group> gros = groService.getAllGroups();

		for(int i = 0; i < gros.size(); i++) {

			Group gro = gros.get(i);

			Integer groId = gro.getGroId();

			String groName = gro.getGroName();

			SysCode.groMap.put(groId, groName);

		}

	}



}

在web.xml文件中配置InitialServlet ：

<servlet>

    <description></description>

    <display-name>InitialServlet</display-name>

    <servlet-name>initialServlet</servlet-name>

    <servlet-class>cn.edu.swu.oa.common.util.

DelegatingServletProxy

</servlet-class>

    <load-on-startup>2</load-on-startup>

  </servlet>

  <servlet-mapping>

    <servlet-name>initialServlet</servlet-name>

    <url-pattern>/InitialServlet</url-pattern>

  </servlet-mapping>

完成这些操作后，就可以在Spring容器启动后执行自定义的Servlet，并且在自定义Servlet中可以使用Spring Annotation的自动注入功能。