Request 和 Response

区别

1. 要取得客户端为服务端提交过来的数据，需要找Request。
2. 要从服务端向客户端传送数据，需要找Response。

服务器端设置编码

@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1)
            throws ServletException, IOException {
    response.setCharacterEncoding("UTF-8");//更改服务器发送数据的默认编码
    response.setHeader("Content-Type","text/html;charset=UTF-8");//还要通知客户端解码方式
//字节流
    String data = "你好,中国";  
    OutputStream out = response.getOutputStream();  
    response.setContentType("text/html;charset=UTF-8");  
    out.write(data.getBytes("UTF-8"));//以UTF-8进行编码

或者
//字符流
    PrintWriter writer = response.getWriter();//默认编码是iso-8859-1 创建该对象前必须设置好编码方式
    writer.write(data);
}

指定数据以下载的方式打开

通过设置response的响应头就可以实现，content-disposition服务器通过这个响应头告诉浏览器通过下载方式打开文件。

@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1)
            throws ServletException, IOException {
    String path = "C:\\Users\\wwhhf\\Pictures\\Camera Roll\\QQ图片20160210090519.jpg";  
    String filename = path.substring(path.lastIndexOf("\\") + 1);  

    arg1.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(filename, "UTF-8"));  

    InputStream in = null;  
    OutputStream out = null;  

    try {  
        in = new FileInputStream(path);  
        int len = 0;  
        byte[] buffer = new byte[1024];  
        out = arg1.getOutputStream();  
        while((len = in.read(buffer)) > 0) {  
            out.write(buffer,0,len);  
        }  
    }catch(Exception e) {  
        throw new RuntimeException(e);  
    }finally {  
        if(in != null) {  
            try {  
                in.close();  
            }catch(Exception e) {  
                throw new RuntimeException(e);  
            }  
        }  
    }  
}

生成验证码图片

@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1)
        throws ServletException, IOException {
    // TODO Auto-generated method stub
    //      super.service(arg0, arg1);
    arg1.addHeader("Pragma", "no-cache"); 
    arg1.setHeader("Cache-Control", "no-cache"); 
    arg1.setHeader("Expires", "0"); 

    //1.内存图像 BufferedImage  
    BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB); 

    //2.创建画笔  
    Graphics g = image.getGraphics(); 

    //2.1画边框  
    g.setColor(Color.GRAY);//设置边框颜色 
    g.drawRect(0, 0, WIDTH, HEIGHT);//画矩形边框 
    //2.2填充边框  
    g.fillRect(1, 1, WIDTH-1, HEIGHT-1); 

    //2.3输出验证随机数字4个  
    Random r = new Random(); 
    g.setColor(Color.BLUE); 
    int x = 5; 
    for(int i=0;i<4;i++) 
    {  
        g.setFont(new Font("宋体",Font.BOLD,20)); 
        g.drawString(r.nextInt(10)+"", x, 20); 
        x+=30; 
    }  

    //2.4画干扰线  
    g.setColor(Color.YELLOW); 
    for(int i = 0;i<9;i++) 
    {                  
        g.drawLine(r.nextInt(WIDTH),r.nextInt(HEIGHT),r.nextInt(WIDTH), r.nextInt(HEIGHT)); 
    }  

    //3 利用response输出流输出image  
    ImageIO.write(image,"jpeg",arg1.getOutputStream());
    arg1.setDateHeader("Expires",System.currentTimeMillis()+10*24*1000*60*60);
}

在后台生成验证码的一般处理程序中除了在session写入验证码的内容，在cookie中也写一个验证码的内容

控制url跳转(延迟跳转)

@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1)
            throws ServletException, IOException {
    // TODO Auto-generated method stub
    // super.service(arg0, arg1);
    arg1.setHeader("Refresh", "5;URL=http://www.qq.com/");//5秒后跳转，url是跳转的链接 
}

缓存作用：Expires实体报头域给出响应过期的日期和时间。为了让代理服务器或浏览器在一段时间以后更新缓存中（再次访问曾访问过的页面时，直接从缓存中加载，缩短响应时间和降低服务器负载）的页面，我们可以使用Expires实体报头域指定页面过期时间

用response实现请求重定向（状态码302重定向）

response.sendRedirect("login.jsp") ->http://localhost:8080/xxxSearch/login.jsp
需用绝对路径，因为重定向是发生在客户端的

[重定向]http://blog.chinaunix.net/uid-11121450-id-3221825.html)

获取客户端请求的信息

String locale = request.getLocalName();//传输协议 
String url = request.getRequestURL().toString();//请求的地址 
String uri = request.getRequestURI();//没有主机名的地址 
String protocol = request.getProtocol();//获取协议 
String add = request.getRemoteAddr();//客户端IP 
String host = request.getRemoteHost();//客户端主机名 
String port = request.getRemotePort()+"";//客户端端口号 
String method = request.getMethod();//客户端的请求方式 
String localAddr = request.getLocalAddr();//获取服务器地址 
String username = request.getParameter("username");//地址后面?请求的参数 
String serverPort = request.getServerPort()+"";//服务器端口号 
String serverName = request.getServerName();//服务器名

获取请求参数的值

@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1)
        throws ServletException, IOException {
    // TODO Auto-generated method stub
    // super.service(arg0, arg1);
    Enumeration names = arg0.getParameterNames();  
    while(names.hasMoreElements())  {  //根据参数名得到值 
          String name = (String)names.nextElement();  
          System.out.println(name+"------->"+arg0.getParameter(name));  
    }
}

显示图片在html上

private static final String PNG  = "image/png;charset=utf-8";// 设定输出的类型 
private static final String JPG = "image/jpeg;charset=utf-8";  

@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1)
        throws ServletException, IOException {

    String imagePath = "C:\\Users\\wwhhf\\Pictures\\Camera Roll\\zen-icons.png";  

    Image img=ImageIO.read(new File(imagePath));
    BufferedImage bi = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
    bi.getGraphics().drawImage(img.getScaledInstance(WIDTH, HEIGHT, Image.SCALE_SMOOTH), 0, 0, null); 

    arg1.reset();  
    if (imagePath.toLowerCase().endsWith(".jpg"))// 使用编码处理文件流的情况： 
    {  
        arg1.setContentType(JPG);// 设定输出的类型 
        ImageIO.write(bi,"jpeg",arg1.getOutputStream());
     arg1.setDateHeader("Expires",System.currentTimeMillis()+10*24*1000*60*60);
    }  
    if (imagePath.toLowerCase().endsWith(".png"))// 使用编码处理文件流的情况： 
    {  
        arg1.setContentType(PNG);// 设定输出的类型 
        ImageIO.write(bi,"png",arg1.getOutputStream());
            arg1.setDateHeader("Expires",System.currentTimeMillis()+10*24*1000*60*60);
    }  
}

Header知识