我要评论向response中写数据的两种方法：getOutputStream()，getWriter()
文件下载：
图片认证：
public class VerificationServlet extends HttpServlet {
private static final int WIDTH = 120;
private static final int HEIGHT = 25;
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
Graphics g =image.getGraphics();
setBackGround(g); //设置背景色
setBorder(g); //设置边框
drawRandomLine(g); //画干扰线
drawRandomNum((Graphics2D)g); //写随机数
//图形写给浏览器
response.setContentType("image/jpeg");
//发头控制浏览器不要缓存
response.setDateHeader("expries",-1);
response.setHeader("Cache-Control","no-cache");
response.setHeader("Pragma","no-cache");
ImageIO.write(image,"jpg",response.getOutputStream() );
}
private void setBackGround(Graphics g)
{
g.setColor(Color.WHITE);
g.fillRect(0,0,WIDTH,HEIGHT); //填充指定的矩形
}
private void setBorder(Graphics g)
{
g.setColor(Color.BLUE);
g.drawRect(1,1,WIDTH-2,HEIGHT-2); //绘制指定矩形的边框
}
private void drawRandomLine(Graphics g)
{
g.setColor(Color.GREEN);
for(int i=0;i<5;i++)
{
int x1=new Random().nextInt(WIDTH); //起始
int y1=new Random().nextInt(HEIGHT);
int x2=new Random().nextInt(WIDTH); //终点
int y2=new Random().nextInt(HEIGHT);
g.drawLine(x1,y1,x2,y2); //画一条线
}
}
private void drawRandomNum(Graphics2D g)
{
g.setColor(Color.RED);
g.setFont(new Font("宋体",Font.BOLD,20));
String base=" ";
int x=10;
for(int i=0;i<4;i++)
{
int degree =new Random().nextInt()%30; //随机生成-30到30之间的数
String ch=base.charAt(new Random().nextInt(base.length() ) )+"";
g.rotate(degree*Math.PI/180,x,20); //设置旋转弧度
g.drawString(ch,x,20);
x=+30;
}
}
控制浏览器缓存时间：
response.setDateHeader("expires",System.currentTimeMillis()+1000*3600)
//控制浏览器缓存，并设置缓存过期时间。System.currentTimeMillis()返回以毫秒为单位的当前时间，1000*3600指一小时
本文地址：https://blog.csdn.net/weixin_45647970/article/details/107367147
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