Filter-过虑器应用之2-设置页面缓存

设置某些页面缓存或是不缓存

要想让所有浏览器不缓存页面：

<%  response.setHeader("expires","-1");  response.setHeader("pragma","no-cache");  response.setHeader("cache-control","no-cache");  %>

分析：通过一个过虑器，对所有*.jsp过虑，设置三个头，全部不缓存。

第一步：实现过虑器接口

public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {//转换HttpServletResponse resp = (HttpServletResponse) response;resp.setHeader("expires","-1");  resp.setHeader("pragma","no-cache");  resp.setHeader("cache-control","no-cache");//都放行chain.doFilter(request, response);}

第二步：配置过虑器，url-pattern=*.jsp

<!-- 配置控制缓存的filter --><filter><filter-name>cache</filter-name><filter-class>cn.itcast.filter.CacheFilter</filter-class></filter><filter-mapping><filter-name>cache</filter-name><url-pattern>*.jsp</url-pattern></filter-mapping>

第三步：设置对某些页面缓存N天

HttpServletResponse resp = (HttpServletResponse) response;//计算2天以后的毫秒值//日历Calendar cl = Calendar.getInstance();//日历上加2天cl.add(Calendar.DATE, 2);long time = cl.getTimeInMillis();resp.setDateHeader("expires", time);//resp.setHeader("expires",""+time);//  resp.setHeader("pragma","no-cache");//  resp.setHeader("cache-control","no-cache");//都放行chain.doFilter(request,resp);

生成验证码的：

public void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {//设置响应类型resp.setContentType("image/jpeg");int width=60;int height=30;BufferedImage img = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);Graphics g = img.getGraphics();g.setColor(Color.WHITE);g.fillRect(0,0, width, height);g.setFont(new Font("宋体", Font.BOLD,18));Random r = new Random();for(int i=0;i<4;i++){Color c = new Color(r.nextInt(256),r.nextInt(256),r.nextInt(256));int code = r.nextInt(10);g.setColor(c);g.drawString(""+code,i*15,10+r.nextInt(20));}for(int i=0;i<10;i++){Color c = new Color(r.nextInt(256),r.nextInt(256),r.nextInt(256));g.setColor(c);g.drawLine(r.nextInt(60),r.nextInt(30),r.nextInt(60),r.nextInt(30));}//图片生效g.dispose();//写到ImageIO.write(img, "JPEG",resp.getOutputStream());}