Servlet学习

public   class  ValidatorPlugIn
     implements  PlugIn
{
.

     public  String getPathnames()
     {
         return  pathnames;
    }

     public   void  setPathnames(String pathnames)
     {
         this .pathnames  =  pathnames;
    }


     public   void  init(ActionServlet servlet, ModuleConfig config)
         throws  ServletException
     {
         this .config  =  config;
         this .servlet  =  servlet;
         try
         {
            initResources();
         catch (Exception e)
         {
            log.error(e.getMessage(), e);
             throw   new  UnavailableException( " Cannot load a validator resource from ' "   +  pathnames  +   " ' " );
        }
    }

     protected   void  initResources()
         throws  IOException, ServletException
     {
         if (pathnames  ==   null   ||  pathnames.length()  <=   0 )
             return ;
        StringTokenizer st  =   new  StringTokenizer(pathnames,  " , " );
        List streamList  =   new  ArrayList();
         try
         {
             while (st.hasMoreTokens()) 
             {
                String validatorRules  =  st.nextToken().trim();
                 if (log.isInfoEnabled())

.

}

学习Java Web 技术，首先必须先把Servlet搞明白。没有Servlet基础，别的都是扯淡！

主要就是掌握Servlet的生命周期，所关联到的类，以及他们的方法。

我简要回顾一下

打开Servlet-API

Servlet接口，三个关乎生命周期的重要方法签名

                  ServletConfig，是一个较重要的对象。

                                          功能:1，获得初始化参数
                                                   2，获得Servlet上下文对象。public ServletContextgetServletContext()

GeneralServlet抽象类，等待你去重写service方法。

                  功能主要就是，为程序员编写Servlet提供一些方便
                                          方便:1，直接覆盖public void init() throws ServletException 
                                                   2，直接调用getInitParameter(java.lang.String name) 
                                                         直接调用public ServletContextgetServletContext()
                                                         直接调用public void log(java.lang.String msg)

                                                         因为GeneralServlet是个懒家伙，都委托给相应ServletConfig/ServletContext完成功能


HttpServlet没什么，自己看API吧

ServletRequest能做什么，几件事

                                             事情1: public java.lang.Object getAttribute(java.lang.String name)/////还有set
                                             事情2: public java.lang.String getParameter(java.lang.String name)
                                                                                        两方面参数,
                                                                                                      方面1:html表单中，有name属性的值.
                                                                                                                  eg. <input type="text" name="userid" size="20" maxlength="20" />
                                                                                                                         request.getParameter("userid");
                                                                                                      方面2:地址栏参数，eg. http://www.infogo.com.cn/action.do?name=admin
                                                                                                                          request.getParameter("name");
                                                           
                                                          由于参数的值有时会是一组，那么就要用public java.lang.String[] getParameterValues(java.lang.String name)
 eg.
   ====================================================
   <c:forEach items="${cart.cartItem}" var="item">
  <TR align=middle>
    <TD height=30><INPUT type=checkbox value="${item.value.product.id}" name=item></TD>
    <TD height=30>${item.value.product.name}&nbsp;</TD>
    <TD height=30>${item.value.product.price}&nbsp;</TD>
    <TD height=30><INPUT maxLength=10 size=10 value="${item.value.number}" name=itemnum></TD>
    <TD height=30>${item.value.cost}&nbsp;</TD>
  </TR>
  </c:forEach>
    ====================================================

//获得页面,checkbox组的信息,可以知道用户选择的商品
  String[] itemkeystr = request.getParameterValues("item");
  System.out.println(itemkeystr);
                Integer[] itemkeyigr = new Integer[itemkeystr.length];
                for(int i = 0; i < itemkeystr.length; i++)
                {
                        itemkeyigr[i] = Integer.valueOf(itemkeystr[i]);
                }
================================================

                                                                                  事情3:public RequestDispatchergetRequestDispatcher(java.lang.String path)
                                                                                  事情4:public void setCharacterEncoding(java.lang.String env)
                          throws java.io.UnsupportedEncodingException
eg.主要防止用户在表单中输入了中文。

过滤器实例:

public   final   class  CharacterEncodingFilter  implements  Filter
{
     private  String  encoding  =   " gb2312 " ;

     private   boolean  ignore    =   false ;

     public   void  init(FilterConfig config)
     {
         if  (config.getInitParameter( " encoding " )  !=   null )
         {
            encoding  =  config.getInitParameter( " encoding " );
        }

         if  (config.getInitParameter( " ignore " )  !=   null )
         {
            ignore  =   new  Boolean(config.getInitParameter( " ignore " )).booleanValue();
        }

    }

     public   void  doFilter(ServletRequest request, ServletResponse response, FilterChain chain)  throws  IOException,
            ServletException
     {
        HttpServletRequest req  =  (HttpServletRequest) request;
        HttpServletResponse res  =  (HttpServletResponse) response;

         if  ( ! ignore)
         {
            req.setCharacterEncoding(encoding);
            res.setCharacterEncoding(encoding);
        }

        chain.doFilter(request, response);
    }

     public   void  destroy()
     {

    }
}

ServletResponse，就是负责输出呗。

                                                                              负责1:  public void setContentType(java.lang.String type) 
                                                                                            eg. response.setContentType(text/html;charse=gbk)
                                                                              负责2:  public java.io.PrintWriter getWriter() throws java.io.IOException
                                                                              这里注意：
                                                                            1 必须先设置setContextType或者setCharacterEncoding，再获得输出。否则设置编码无效！
                                                                            2不得在ResquestDispatcher.forward()调用前，进行向客户端的输出。有风险。
                                                                              


ServletContext整个应用只有一个实例，可以为应用放置一些只读的共享数据。

责任1:public java.lang.String getInitParameter(java.lang.String name)
责任2:public RequestDispatchergetRequestDispatcher(java.lang.String path)绝对路径
责任3:public void log(java.lang.String msg)


Filter接口，实现对于某一个url匹配的过滤。是一个责任链模式的应用

package  ljl.shop.common;

import  java.io.IOException;
                                                                                                               
import  javax.servlet.Filter;
import  javax.servlet.FilterChain;
import  javax.servlet.FilterConfig;
import  javax.servlet.ServletException;
import  javax.servlet.ServletRequest;
import  javax.servlet.ServletResponse;
import  javax.servlet.http.HttpServletRequest;
import  javax.servlet.http.HttpServletResponse;


/** */ /**
 * 权限过滤器 通过配置web.xml中的filter初始化参数，实现动态判别
 * 
 *  <filter-mapping>
 *       <filter-name>CharacterEncodingFilter</filter-name>
 *       <url-pattern>/*</url-pattern>
 *   </filter-mapping>                                                                            
 *
 *   <filter>
 *       <filter-name>PermissionFilter</filter-name>
 *       <filter-class>ljl.shop.common.PermissionFilter</filter-class>
 *       <init-param>
 *               <param-name>checkpage</param-name>
 *               <param-value>checkout.jsp#order_created.jsp#postLogin.jsp</param-value>
 *       </init-param>
 *   </filter>
 * 
 *  @author  lujl
  */
public   class  PermissionFilter  implements  Filter
{
     private  String checkpage  =   null ;

     private  FilterConfig config  =   null ;

     public