Servlet有init(ServletConfig config)方法，那这个方可以在初始化的时候通过getInitParameter 方法获取初始化参数，通过<param-name>得到value的值。

ex：获取每页默认显示条数

web.xml配置

<servlet>
    <description></description>
    <servlet-class>com.wawa.login.servlet.VisitorServlet</servlet-class>
    <init-param>
    <param-name>perPage</param-name>
    <!-- 每页显示的行数 -->
    <param-value>12</param-value>
    </init-param>
  </servlet>

代码：

public class VisitorServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
    private int perPage = 12;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public VisitorServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
	public void init(ServletConfig config) throws ServletException {
		// TODO Auto-generated method stub
		// 初始化的时候通过getInitParameter 获取初始化参数  通过 <param-name> 得到value值
		String str = config.getInitParameter("perPage");
		if(str!=null&!str.equals("")){
			perPage = Integer.parseInt(str);
		}
	}
    
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		String flag = request.getParameter("flag");
		String nowPageStr = request.getParameter("nowPage");
		 // 当前的页数
		 int nowPage = 1;
		 if(nowPageStr!=null&&!nowPageStr.equals("")){
			 nowPage = Integer.parseInt(nowPageStr);
		 }
		 System.out.println(nowPage);
		VisitorService visitorService = new VisitorService();
		if(flag.equals("selectall")){
			 
			 // 分多少页
			 int totalPage = 0;
			
			// 查询所有
			 List<User> list = visitorService.selectVisitor();

			// 分多少页  总页数取余12 
			 int countPage = list.size();
			
			 // 整除   --一共分多少页
			 if(countPage%perPage==0){
				 totalPage = countPage/perPage;
			 }else{
				 // 不能整除
				 totalPage = countPage/perPage+1;
			 }
			 // 根据页数查询要显示的内容
			 List<User> listVisitor = visitorService.selectVisitor(perPage,nowPage);
			 
			 request.setAttribute("countPage", countPage);
			 request.setAttribute("totalPage", totalPage);
			 request.setAttribute("listVisitor", listVisitor);
			 request.getRequestDispatcher("visitorManager.jsp").forward(request, response);		
		}
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws Servlet