Servlet笔记(二)

一、ServletContext(非常重要)

1、作用：每一个JavaWeb应用都会有唯一的ServletContext对象。

在Tomcat加载应用时，就创建该对象的实例。（ServletContext是一个接口，它的实例类由服务器提供）

实现servlet之间数据共享

     public   
     class   ServletContextDemo1Servlet   
     extends  HttpServlet {
     
      
     public   
     void  doGet(HttpServletRequest request, HttpServletResponse response)
     
              
     throws  ServletException, IOException {
     
         ServletConfig config 
     = getServletConfig();
     //只为当前 Servlet 服务
     
         ServletContext sc 
     = config.getServletContext();
     
         sc.setAttribute( 
     "p" ,  
     "ppp" );     }
    

      public   
      class   ServletContextDemo2Servlet   
      extends  HttpServlet {
      
      public   
      void  doGet(HttpServletRequest request, HttpServletResponse response)
      
      throws  ServletException, IOException {
      
      //只为当前 Servlet 服务
      
         ServletConfig config 
      = getServletConfig();
      
      //只要是当前应用，不论是谁，得到的ServletContext都是同一个对象
      
         ServletContext sc 
      = config.getServletContext();
      
         Object  obj  
      = sc.getAttribute( 
       "p" );     }

2、得到ServletContext的实例：

ServletConfig getServletContext()

        
   public   
   void  doGet(HttpServletRequest req, HttpServletResponse resp)
   
   throws  ServletException, IOException {
   
   //获取当前服务的 config ,只为当前 Servlet 服务
   
         ServletConfig config 
   = getServletConfig();
   
   //获取ServletContext对象,就可以对ServletContext进行操作了.
   
   //只要是当前应用，不论是谁，得到的ServletContext都是同一个对象
   
   //就是说ServletContext的范围比 Servlet 还要大
   
         ServletContext sc 
   = config.getServletContext();
   
   // 此句是另一个 Servlet 上设置数据sc.setAttribute("q"," qqq ");
   
   //读取并打印数据
   
         resp.getOutputStream().write(((String)sc.getAttribute( 
    "q" )).getBytes());
   
   //如果先运行Demo2,则会报错,空指针异常,必须先向ServletContext存值,才可以取出             }

3、读取应用级的参数

web.xml中：

           <context-param>
   <!-- 配置的是应用全局参数，读取应该使用ServletContext -->
   
             <param-name>
   encoding</param-name>
   
             <param-value>
   UTF-8</param-value>   
   
       </context-param>
  

        
   public   
   void  doGet(HttpServletRequest request, HttpServletResponse response)
   
   throws  ServletException, IOException {
   
   //实际开发需要删掉this.因为这是多余的.在这里写出来是为了明确HttpServlet里面有这个方法
   
         ServletContext sc 
   =  
   this .getServletContext();
   
   //读取对象,打印到控制台上
   
         String str 
   = sc.getInitParameter( 
    "encoding" );
   
         System. out .println(str);     }

4、实现Servlet的转发。

    public   
    class   ServletContextDemo4Servlet   
    extends  HttpServlet {
    
    //演示转发：ServletContext转发的。源，转发到Demo5，最后显示的是Demo5的信息
    
    public   
    void  doGet(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException {
    
         response.getOutputStream().write( 
    "I am 4" .getBytes());
    
         ServletContext sc 
    = getServletContext();
    
    //请求分发器  path，目标路径，该路径必须以"/"开头。斜线代表的是当前应用/day04_00_servletContext
    
         RequestDispatcher rd 
    = sc.getRequestDispatcher(
    "/servlet/ServletContextDemo5Servlet" );
    
    //必须forward一下，否则不会转发
    
         rd.forward(request, response);     }

5、读取配置文件（*.properties *.xml）

方式一：利用ServletContext

特点：用于Web环境下。可以读取应用任何目录下的任何文件

         
    //利用ServletContext读取cfg3.properties
    
    private   
    void   test3(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException  {
    
         String realPath 
    = getServletContext().getRealPath(
    "/WEB-INF/classes/com/itheima/servlet/cfg3.properties" );
    
    //创建Properties类来读取文件内容。
    
         Properties props 
    =  
    new  Properties();
    
    //用FileInputStream流来关联 。
    
         props.load( 
    new   FileInputStream (realPath));
    
         String value 
    = props.getProperty( 
     "hello" );
    
         response.getOutputStream().write(value.getBytes());
    
     }
    
    //利用ServletContext读取cfg2.properties
    
    private   
    void   test2(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException  {
    
         String realPath 
    = getServletContext().getRealPath(
    "/WEB-INF/classes/cfg2.properties" );
    
         Properties props 
    =  
    new  Properties();
    
         props.load( 
    new  FileInputStream(realPath));
    
         String value 
    = props.getProperty( 
     "hello" );
    
         response.getOutputStream().write(value.getBytes());
    
     }
    
    //利用ServletContext读取cfg1.properties
    
    private   
    void   test1(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException  {
    
         String realPath 
    = getServletContext().getRealPath(
    "/WEB-INF/cfg1.properties" );
    
         Properties props 
    =  
    new  Properties();
    
         props.load( 
    new  FileInputStream(realPath));
    
         String value 
    = props.getProperty( 
     "hello" );
    
         response.getOutputStream().write(value.getBytes());     }

方式二：利用ResourceBundle

特点：可以用在非web环境和Web环境下。专门读取properties文件的，只能读取类路径中的properties文件

         
    //利用ResourceBundle(国际化)读取cfg3.properties
    
    private   
    void   test5(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException  {
    
    //注意使用的是基名
    
         ResourceBundle rb 
    = ResourceBundle. getBundle (
    "com.itheima.servlet.cfg3" );
    
         response.getOutputStream().write(rb.getString( 
     "hello" ).getBytes());
    
     }    
    
    //利用ResourceBundle(国际化)读取cfg2.properties
    
    private   
    void   test4(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException  {
    
         ResourceBundle rb 
    = ResourceBundle. getBundle (
    "cfg2" ); 
    //基名
    
         response.getOutputStream().write(rb.getString( 
     "hello" ).getBytes());     }

方式三：利用类加载器（更加专业）

特点：可以用在非web环境和Web环境下，可以读取类路径中的任何配置文件，不适合读取特别大的文件

         
    //利用类加载器读取cfg3.properties的真实路径
    
    private   
    void  test8(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException {
    
    //获得类加载器，用类加载器获得指定资源路径
    
         ClassLoader cl 
    = ServletContextDemo7Servlet.
    class .getClassLoader();
    
         URL url 
    = cl.getResource( 
     "com/itheima/servlet/cfg3.properties" );
    
    //得到真实的绝对路径。如果该路径有空格或有中文，构建流时报错
    
         String realPath 
    = url.getPath();
    
         InputStream in 
    =  
    new  FileInputStream(realPath);
    
         Properties props 
    =  
    new  Properties();
    
         props.load(in);
    
         String value 
    = props.getProperty( 
     "hello" );
    
         response.getOutputStream().write(value.getBytes());
    
     }    
    
    //利用类加载器读取cfg3.properties，注意资源路径
    
    private   
    void   test7(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException  {
    
    //获得类加载器，再用类加载器获得指定资源的输入流
    
         ClassLoader cl 
    = ServletContextDemo7Servlet.
    class .getClassLoader();
    
         InputStream in 
    = cl.getResourceAsStream(
    "com/itheima/servlet/cfg3.properties" );
    
         Properties props 
    =  
    new  Properties();
    
         props.load(in);
    
         String value 
    = props.getProperty( 
     "hello" );
    
         response.getOutputStream().write(value.getBytes());
    
     }
    
    //利用类加载器读取cfg2.properties，注意资源路径
    
    private   
    void   test6(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException  {
    
         ClassLoader cl 
    = ServletContextDemo7Servlet.
    class .getClassLoader();
    
         InputStream in 
    = cl.getResourceAsStream(
    "cfg2.properties" );
    
         Properties props 
    =  
    new  Properties();
    
         props.load(in);
    
         String value 
    = props.getProperty( 
     "hello" );
    
         response.getOutputStream().write(value.getBytes());     }

二、Servlet规范中的核心接口类图(非常重要)

javax.servlet.Servlet

javax.servlet.GenericServlet

javax.servlet.http.HttpServlet

javax.servlet.ServletContext

javax.servlet.RequestDispatcher

javax.servlet.ServletConfig

javax.servlet.ServletRequest

javax.servlet.ServletResponse

三、响应对象HttpServletResponse(非常重要)

1、输出数据中文编码

        
   //利用字节流输出中文数据
   
   private   
   void  test3(HttpServletResponse response)  
   throws  IOException {
   
   int  data 
    = 
   97;
   
         ServletOutputStream out 
   = response.getOutputStream();
   
   //如果不加转成字符串，会输出a
   
         out.write((data
   + 
    "" ).getBytes());
   
     }
   
   private   
   void   test2(HttpServletResponse response)  
   throws  IOException  {
   
         String data 
   =  
   "陈冠希爱阿娇" ;
   
         ServletOutputStream out 
   = response.getOutputStream();
   
   //通知浏览器，服务端使用的编码
   
         response.setContentType( 
   "text/html;charset=UTF-8" );
   //记住
   
   byte  b[] 
    = data.getBytes( 
   "UTF-8" );
   
         out.write(b);
   
     }
   
   //用本地平台默认编码输出：没有乱码
   
   private   
   void   test1(HttpServletResponse response)  
   throws  IOException  {
   
         String data 
   =  
   "中国" ;
   
         ServletOutputStream out 
   = response.getOutputStream();
   
   byte  b[] 
    = data.getBytes();
   
         out.write(b);
   
     }

         
    //日后使用
    
    private   
    void   test1(HttpServletResponse response)  
    throws  IOException  {
    
         String data 
    =  
    "李宗瑞李宗盛" ;
    
    //更改字符流默认查询的码表 只对post提交有效
    
         response.setCharacterEncoding( 
    "UTF-8" );
    
    //通知浏览器解码用什么编码
    
         response.setContentType( 
    "text/html;charset=UTF-8" );
    
         PrintWriter out 
    = response.getWriter();
    
         out.write(data); 
    //默认查ISO-8859-1 规范要求     }

2、一些应用案例（响应头的应用）

下载中文文件名的文件

         
    public   
    void  doGet(HttpServletRequest request, HttpServletResponse response)
    
              
    throws  ServletException, IOException {
    
              
    //得到输入流:路径该怎么获取，斜线就代表当前应用
    
             String path 
    =  
    "/WEB-INF/阿娇.jpg" ;
    
              
    //截取文件名，包含头，所以要+1，把/排出
    
             String filename 
    = path.substring(path.lastIndexOf(
    "/" )
    +
    1);
    
              
    //告知客户端以下载的方式打开
    
             response.setHeader( 
    "Content-Disposition" ,  
    "attachment;filename="
    +URLEncoder. encode (filename,  
    "UTF-8" ));
    
             response.setHeader( 
    "Content-Type" ,  
    "application/octet-stream" );
    
              
    //根据相对于当前应用的路径，得到绝对路径
    
             String realPath 
    = getServletContext().getRealPath(path);
    
              
    //下面打印：C:\ apache - tomcat -6.0.35\ webapps \day04_01_response\WEB-INF\阿娇. jpg
    
             System. out .println(realPath);
    
             InputStream in 
    =  
    new  FileInputStream(realPath);
    
             OutputStream out 
    = response.getOutputStream();
    
              
    int  len 
     = 
    -
    1;
    
              
    byte  b[] 
     =  
    new   
    byte [
    1024];
    
              
    while ((len
    =in.read(b))
    !=
    -
    1){
    
                 out.write(b, 
    0, len);
    
             }
    
             in.close();
    
             out.close();     }
   

输出CAPTCHA图像，就是验证图片

        
   public   
   void  doGet(HttpServletRequest request, HttpServletResponse response)
   
              
   throws  ServletException, IOException {
   
          
   //通知浏览器，图片不要缓存
   
         response.setHeader( 
   "Expires" ,  
   "-1" );
   
         response.setHeader( 
   "Cache-Control" ,  
   "no-cache" );
   
         response.setHeader( 
   "Pragma" ,  
   "no-cache" );
   
         
   
          
   int  width 
    = 
   120;
   
          
   int  height 
    = 
   25;
   
          
   //搞出代表内存图片的对象BufferedImage，然后取画笔：开始画
   
         BufferedImage image 
   =  
   new  BufferedImage(width,height,BufferedImage. TYPE_INT_RGB );
   
         Graphics g 
   = image.getGraphics();
   
          
   //填充背景
   
         g.setColor(Color. YELLOW );
   
         g.fillRect(
   0, 
    0, width, height);
   
          
   //画边框
   
         g.setColor(Color. BLUE );
   
         g.drawRect(
   1, 
    1, width
   -
   2, height
   -
   2);
   
          
   //画干扰线
   
         g.setColor(Color. GRAY );
   
         Random r 
   =  
   new  Random();
   
          
   for ( 
    int  i
   =
   0;i
   <
   30;i
   ++)
   
             g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));
   
          
   //写随机验证码
   
         g.setColor(Color. RED );
   
         g.setFont( 
   new  Font(
   "宋体" ,Font. BOLD 
   |Font. ITALIC ,
   18));
   
          
   //数字
   
 
   //        for( int  i=1;i<5;i++){
   
 
   //            g.drawString(r.nextInt(10)+"", x*22, 20);
   
 
   //            x+=20;
   
 
   //        }
   
          
   // 汉字的，随意添加即可
   
         String base 
   =  
   "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728" ;
   
          
   int  x 
    = 
   22;
   
          
   for ( 
    int  i
   =
   1;i
   <
   5;i
   ++){
   
             g.drawString(base.charAt(r.nextInt(base.length()))
   +
   "" , x
   *
   22,
   20);
   
             x
   +=
   20;
   
         }
   
          
   //输出到页面上：ImageIO
   
         ImageIO. write (image,  
   "jpg" , response.getOutputStream());     }
  

控制浏览器定时刷新

         
    //定时刷新到别处
    
      
    private   
    void  test2(HttpServletResponse response)  
    throws  IOException {
    
         response.setContentType( 
    "text/html;charset=UTF-8" );
    
         response.setHeader( 
    "Refresh" ,  
    "2;url=http://www.itheima.com" );
    
         response.getWriter().write( 
    "注册成功！2秒后自动转向主页" );
    
     }
    
      
    //定时2秒就刷新自己
    
      
    private   
    void   test1(HttpServletResponse response)  
    throws  IOException  {
    
         response.setIntHeader( 
    "Refresh" , 
     2);     }
   

控制缓存的有效期

         
    public   
    void  doGet(HttpServletRequest request, HttpServletResponse response)
    
              
    throws  ServletException, IOException {
    
          
    //相对于当前时间的。如果值比当前时间的毫秒值小，倒退1小时。
    
         response.setDateHeader( 
    "Expires" , System. currentTimeMillis ()
    +
    1
    *
    60
    *
    60
    *
    1000);     }
   

3、一些细节

a，字节流和字符流不能同时使用

b，服务器会自动关闭流

c，Servlet向ServletOutputStream或PrintWriter对象中写入的数据，将被Tomcat从response里面获取，Tomcat将这些数据当作响应消息的正文，

然后再与响应状态行和各响应头组合后输出到客户端。

四、请求对象HttpServletRequest(非常重要)

1、常用方法

         
    public   
    void  doGet(HttpServletRequest request, HttpServletResponse response)
    
    throws  ServletException, IOException {
    
    //打印客户端的 url 地址
    
         String url
    = request.getRequestURL().toString();
    
    //打印客户端的 uri 地址
    
          String  uri
    = request.getRequestURI();
    
    //打印客户端的GET返回值
    
         String queryString 
    = request.getQueryString();
    
    //打印客户端的访问IP地址
    
         String remoteAddr 
    = request.getRemoteAddr();
    
    //打印客户端的访问port
    
    int  remotePort 
     = request.getRemotePort();
    
    //打印客户端的提交数据方式
    
         String method 
    = request.getMethod();     }

2、获取请求消息头

        
   public   
   void  doGet(HttpServletRequest request, HttpServletResponse response)
   
   throws  ServletException, IOException {
   
         System. out .println( 
   "----------------" );
   
   //获取所有的请求消息头和值
   
          Enumeration  e 
   = request.getHeaderNames();
   
   //用while循环.这个类的方法不多,hasMoreElements判断里面是否还有
   
   while (e.hasMoreElements()){
   
             String headerName 
   = (String)e.nextElement();
   
             System. out .println(headerName
   + 
    ":::::" 
   +request.getHeader(headerName));
   
         }
   
     }

3、获取请求参数

         
    //获取所有的请求参数值
    
    private   
    void   test4(HttpServletRequest request, PrintWriter out)  {
    
    //key: String请求参数名字   value:String[]  请求参数值
    
         Map
    <String,String[]
    > map
    =  request.getParameterMap() ;
    
    for (Map.Entry
    <String, String[]
    > me
    :map.entrySet()){
    
             System. out .println(me.getKey()
    + 
     "=" 
    +Arrays. asList (me.getValue()));
    
         }
    
     }
    
    //获取所有的请求参数值
    
    private   
    void   test3(HttpServletRequest request, PrintWriter out)  {
    
          Enumeration  e 
    = request.getParameterNames();
    //所有的请求参数名
    
    while (e.hasMoreElements()){
    
             String  paramName  
    = (String)e.nextElement();
    
             System. out .println( paramName 
    + 
     "=" 
    +Arrays. asList (request.getParameterValues( paramName )));
    
         }
    
     }
    
    //获取重名的请求参数值
    
    private   
    void   test2(HttpServletRequest request, PrintWriter out)  {
    
    //同样的key可能会有多个value，所以取回的value是数组
    
         String[]  passwords  
    = request.getParameterValues(
    "password" );
    
     }
    
    //获取单一的请求参数值
    
    private   
    void   test1(HttpServletRequest request, PrintWriter out)  {
    
    //用户所有的界面输入都是String类型，如果表单的输入域没有name属性，浏览器根本不传递数据
    
         String  username  
    = request.getParameter(
    "username" ); 
    //
    
         String  password  
    = request.getParameter(
    "password" );     }

4、常用表单及数据的获取

         
    //**封装数据到JavaBean中:遵循了一个约定，表单字段名和User中的属性(getter setter)一致
    
    private   
    void  test10(HttpServletRequest request, PrintWriter out) {
    
    try  {
    
             User user 
    =  
    new  User();
    
             System. out .println( 
    "封装前：" 
     +user);
    
    //String-->基本类型：自动转换。
    
    //日期的不会：注册类型转换器
    
    //            ConvertUtils.register(new Converter() {
    
    //                public Object convert(Class type, Object value) {
    
    //                    DateFormat  df  = new SimpleDateFormat(" yyyy -MM- dd ");
    
    //                    if(type==Date.class){
    
    //                        //要把String转成Date
    
    //                        String s = (String)value;
    
    //                        try {
    
    //                            return df.parse(s);
    
    //                        } catch (ParseException e) {
    
    //                            throw new RuntimeException(e);
    
    //                        }
    
    //                    }else if(type==String.class){
    
    //                        //把Date转成String
    
    //                        Date date = (Date)value;
    
    //                        return df.format(date);
    
    //                    }
    
    //                    return null;
    
    //                }
    
    //            }, Date.class);
    
             ConvertUtils. register ( 
    new  DateLocaleConverter(), Date.
    class ); 
    //请看上面注释
    
             BeanUtils. populate (user, request.getParameterMap()); 
     //原理看test7
    
             System. out .println( 
    "封装后：" 
     +user);
    
         }  
    catch  (Exception e) {
    
             e.printStackTrace();
    
         }
    
     }
    
    //**封装数据到JavaBean中:遵循了一个约定，表单字段名和User中的属性(getter setter)一致
    
    private   
    void   test8(HttpServletRequest request, PrintWriter out)  {
    
    try  {
    
             User user 
    =  
    new  User();
    
             System. out .println( 
    "封装前：" 
     +user);
    
             BeanUtils. populate (user, request.getParameterMap()); 
     //原理看test7
    
             System. out .println( 
    "封装后：" 
     +user);
    
         }  
    catch  (Exception e) {
    
             e.printStackTrace();
    
         }     }

（反射及内省）

         
    //封装数据到JavaBean中:遵循了一个约定，表单字段名和User中的属性(getter setter)一致
    
      
    private   
    void   test6(HttpServletRequest request, PrintWriter out)  {
    
          
    try  {
    
             Map
    <String, String[]
    > map
    =  request.getParameterMap() ;
    
             User user 
    =  
    new  User();
    
             System. out .println( 
    "封装前：" 
     +user);
    
              
    //封装
    
              
    for (Map.Entry
    <String, String[]
    > me
    :map.entrySet()){
    
                 String paramName 
    = me.getKey();
    //请求参数名   和User中的属性(getter setter)一致
    
                 String[] paramValue 
    = me.getValue();
    //请求参数值                 
    
                  
    //属性描述其
    
                 PropertyDescriptor pd 
    =  
    new  PropertyDescriptor(paramName, User.
    class );
    
                  
    //调用其中的setter方法
    
                 Method method 
    = pd.getWriteMethod();
    
                  
    if (paramValue
    != null
    &mValue. length 
    >
    1){
    //看如何反射main方法
    
                     method.invoke(user, (Object)paramValue);
    
                 } 
    else {
    
                      method.invoke(user,paramValue) ;
    
                 }
    
             }
    
             System. out .println( 
    "封装后：" 
     +user);
    
         }  
    catch  (Exception e) {
    
             e.printStackTrace();
    
         }              }
   

以流的形式获取请求正文内容

         
    private   
    void   test9(HttpServletRequest request, PrintWriter out)  
    throws  IOException  {
    
         ServletInputStream in 
    = request.getInputStream();
    
          
    int  len 
     = 
    -
    1;
    
          
    byte  b[] 
     =  
    new   
    byte [
    1024];
    
          
    while ((len
    =in.read(b))
    !=
    -
    1){
    
             System. out .println( 
    new  String(b,
    0,len));
    
         }
    
         in.close();     }
   

5、请求转发和重定向

6、请求范围的域对象