Servlet中的response

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