过虑器基础3—页面缓存和生成验证码(48)

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);[W2]

//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：

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());

}