response应用案例
案例一：定时刷新网页
应用场景：登陆、注销、提示xxx秒后，将会跳转xxx页面。网页数据，定时更新
package cn.itcast.day06.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ResponseServlet2 extends HttpServlet
{
//定时刷新网页
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
//http响应头信息 refresh
//5秒后自动跳转到welcome.html 格式：时间（秒）;url=跳转地址
response.setHeader("refresh", "5;url=/myday06/welcome.html");//这个是设置刷新5秒后自动跳转到另一个页面
response.setContentType("text/html;charset=utf-8");//这个是设置浏览器的显示编码，固定的，一定得记得
PrintWriter out=response.getWriter();
out.println("5秒后自动跳转到欢迎页面");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doGet(request, response);
}
}
------------------------------------------------------------------------
在这里还有一个重点是：
html网页里面的meta头信息也可以实现自动跳转的功能
下面是一个html的头文件信息
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" >
<!-- meta设置头信息 -->
<meta http-equiv="refresh" content="5;url=/day6/welcome.html" >这个也可以实现页面的自动刷新功能
<title>Insert title here</title>
-------------------------------------------------------------
java里面实现不了动态的时间跳转效果，一般的时间跳转效果都是javascript做出来的
下面用javascript来做一个时间倒计时的动态效果：
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" >
<!-- meta设置头信息 -->
<!--<meta http-equiv="refresh" content="5;url=/day6/welcome.html" >-->
<title>Insert title here</title>
<script type="text/javascript">
var i =5;
function init(){
document.getElementById("content").innerHTML = i; // 更新标签内的 内容
if(i>0){
i--;
setTimeout("init();", 1000); // 间隔1秒后 执行 init方法
}else{
location.href="/day6/welcome.html"; // 跳转到 xxx页面
}
}
</script>
</head>
<body onload="init();"> <!-- onload网页 加载完成调用 方法 -->
<span id="content"></span>秒后 自动跳转到 欢迎页面!
</body>
</html>
案例二：对网页请求重定向
package cn.itcast.servlet.response;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ResponseServlet2 extends HttpServlet {
// 通过 状态码和头信息 完成 重定向
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setStatus(302);
response.setHeader("Location", "/day6/index.jsp");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
案例三、设置缓存过期时间
package cn.itcast.day06.servlet;
import java.io.IOException;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ResponseServlet3 extends HttpServlet
{
//缓存这个servlet生产页面
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
// 过期时间需要用http协议头信息expires来设置
//java描述时间 毫秒描述
//当前时间毫秒
long time1=new Date().getTime();//第一种方法获取当前时间
long time2=System.currentTimeMillis();//第二种获取当前时间的方法
response.setDateHeader("expires", time1+1000*60*60);//设置缓存过期时间一个小时
response.getWriter().println("web content!!");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doGet(request, response);
}
}
案例四：servlet中文件下载的实现功能
package cn.itcast.day06.web.servlet;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DownloadServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 实现防盗链功能
// 获得 referer 头 用于说明来访者来自哪里
String referer = request.getHeader("referer");
if(referer==null || !referer.startsWith("http://localhost")) {
// 是盗链者
response.sendRedirect("/day06/index.jsp");//这是图片的存放地址
return ;
}
// 解决response中文乱码问题
response.setContentType("text/html;charset=utf-8"); // 设置消息体的编码
// 通过 http 协议 发送的http响应消息头 不能出现中文 中文必须要经过url编码
String filename = URLEncoder.encode("美女.jpg", "utf-8");
// 通知浏览器以下载的方式读取资源***
response.setHeader("content-disposition", "attachment;filename="+filename);
// 使用流读取图片数据 发给ie浏览器
String webPath = "/download/美女.jpg"; // 相当于当前web应用的path
ServletContext servletContext = super.getServletContext();
InputStream in = servletContext.getResourceAsStream(webPath);
OutputStream out = response.getOutputStream();
int len;
byte[] buffer = new byte[1024];
while((len=in.read(buffer))!=-1)
out.write(buffer, 0, len);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
案例五、生成图片验证码功能
package cn.itcast.day06.servlet;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ResponseServlet1 extends HttpServlet
{
// 用java生成一张图片
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
// 使用java技术图像界面绘制一张图片
int charNum = 4;// 数量，四个字。
int width = 30 * 4;
int height = 40;
// 1 创建一张内存图片
BufferedImage bufferedImage = new BufferedImage(width, height,
BufferedImage.TYPE_INT_BGR);
// 2获得绘图对象
Graphics graphics = bufferedImage.getGraphics();
// 3绘制背景颜色
graphics.setColor(Color.YELLOW);
// 4.绘制矩形。
graphics.fillRect(0, 0, width, height);
// 5.绘制图片边框
graphics.setColor(Color.BLUE);
graphics.drawRect(0, 0, width - 1, height - 1);
// 6.输出验证码内容
graphics.setColor(Color.RED);
graphics.setFont(new Font("宋体", Font.BOLD, 30));
// 7，随机输出4个字母,graphics2D来选择字母
Graphics2D graphics2d=(Graphics2D)graphics;
String s = "ABCDEFGHIJKLMN";
//常用的简体中文汉字
// String base = "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728\u4eba\u4eec\u6709\u6765\u4ed6\u8fd9\u4e0a\u7740\u4e2a\u5730\u5230\u5927\u91cc\u8bf4\u5c31\u53bb\u5b50\u5f97\u4e5f\u548c\u90a3\u8981\u4e0b\u770b\u5929\u65f6\u8fc7\u51fa\u5c0f\u4e48\u8d77\u4f60\u90fd\u628a\u597d\u8fd8\u591a\u6ca1\u4e3a\u53c8\u53ef\u5bb6\u5b66\u53ea\u4ee5\u4e3b\u4f1a\u6837\u5e74\u60f3\u751f\u540c\u8001\u4e2d\u5341\u4ece\u81ea\u9762\u524d\u5934\u9053\u5b83\u540e\u7136\u8d70\u5f88\u50cf\u89c1\u4e24\u7528\u5979\u56fd\u52a8\u8fdb\u6210\u56de\u4ec0\u8fb9\u4f5c\u5bf9\u5f00\u800c\u5df1\u4e9b\u73b0\u5c71\u6c11\u5019\u7ecf\u53d1\u5de5\u5411\u4e8b\u547d\u7ed9\u957f\u6c34\u51e0\u4e49\u4e09\u58f0\u4e8e\u9ad8\u624b\u77e5\u7406\u773c\u5fd7\u70b9\u5fc3\u6218\u4e8c\u95ee\u4f46\u8eab\u65b9\u5b9e\u5403\u505a\u53eb\u5f53\u4f4f\u542c\u9769\u6253\u5462\u771f\u5168\u624d\u56db\u5df2\u6240\u654c\u4e4b\u6700\u5149\u4ea7\u60c5\u8def\u5206\u603b\u6761\u767d\u8bdd\u4e1c\u5e2d\u6b21\u4eb2\u5982\u88ab\u82b1\u53e3\u653e\u513f\u5e38\u6c14\u4e94\u7b2c\u4f7f\u5199\u519b\u5427\u6587\u8fd0\u518d\u679c\u600e\u5b9a\u8bb8\u5feb\u660e\u884c\u56e0\u522b\u98de\u5916\u6811\u7269\u6d3b\u90e8\u95e8\u65e0\u5f80\u8239\u671b\u65b0\u5e26\u961f\u5148\u529b\u5b8c\u5374\u7ad9\u4ee3\u5458\u673a\u66f4\u4e5d\u60a8\u6bcf\u98ce\u7ea7\u8ddf\u7b11\u554a\u5b69\u4e07\u5c11\u76f4\u610f\u591c\u6bd4\u9636\u8fde\u8f66\u91cd\u4fbf\u6597\u9a6c\u54ea\u5316\u592a\u6307\u53d8\u793e\u4f3c\u58eb\u8005\u5e72\u77f3\u6ee1\u65e5\u51b3\u767e\u539f\u62ff\u7fa4\u7a76\u5404\u516d\u672c\u601d\u89e3\u7acb\u6cb3\u6751\u516b\u96be\u65e9\u8bba\u5417\u6839\u5171\u8ba9\u76f8\u7814\u4eca\u5176\u4e66\u5750\u63a5\u5e94\u5173\u4fe1\u89c9\u6b65\u53cd\u5904\u8bb0\u5c06\u5343\u627e\u4e89\u9886\u6216\u5e08\u7ed3\u5757\u8dd1\u8c01\u8349\u8d8a\u5b57\u52a0\u811a\u7d27\u7231\u7b49\u4e60\u9635\u6015\u6708\u9752\u534a\u706b\u6cd5\u9898\u5efa\u8d76\u4f4d\u5531\u6d77\u4e03\u5973\u4efb\u4ef6\u611f\u51c6\u5f20\u56e2\u5c4b\u79bb\u8272\u8138\u7247\u79d1\u5012\u775b\u5229\u4e16\u521a\u4e14\u7531\u9001\u5207\u661f\u5bfc\u665a\u8868\u591f\u6574\u8ba4\u54cd\u96ea\u6d41\u672a\u573a\u8be5\u5e76\u5e95\u6df1\u523b\u5e73\u4f1f\u5fd9\u63d0\u786e\u8fd1\u4eae\u8f7b\u8bb2\u519c\u53e4\u9ed1\u544a\u754c\u62c9\u540d\u5440\u571f\u6e05\u9633\u7167\u529e\u53f2\u6539\u5386\u8f6c\u753b\u9020\u5634\u6b64\u6cbb\u5317\u5fc5\u670d\u96e8\u7a7f\u5185\u8bc6\u9a8c\u4f20\u4e1a\u83dc\u722c\u7761\u5174\u5f62\u91cf\u54b1\u89c2\u82e6\u4f53\u4f17\u901a\u51b2\u5408\u7834\u53cb\u5ea6\u672f\u996d\u516c\u65c1\u623f\u6781\u5357\u67aa\u8bfb\u6c99\u5c81\u7ebf\u91ce\u575a\u7a7a\u6536\u7b97\u81f3\u653f\u57ce\u52b3\u843d\u94b1\u7279\u56f4\u5f1f\u80dc\u6559\u70ed\u5c55\u5305\u6b4c\u7c7b\u6e10\u5f3a\u6570\u4e61\u547c\u6027\u97f3\u7b54\u54e5\u9645\u65e7\u795e\u5ea7\u7ae0\u5e2e\u5566\u53d7\u7cfb\u4ee4\u8df3\u975e\u4f55\u725b\u53d6\u5165\u5cb8\u6562\u6389\u5ffd\u79cd\u88c5\u9876\u6025\u6797\u505c\u606f\u53e5\u533a\u8863\u822c\u62a5\u53f6\u538b\u6162\u53d4\u80cc\u7ec6";
Random random = new Random();
int x = 5;
for (int i = 0; i < 4; i++)
{
int index = random.nextInt(14);
String content = String.valueOf(s.charAt(index));
double theta=random.nextInt(35)*Math.PI/180;//这个是得到一个角度,转换成弧度的公式
graphics2d.rotate(theta, x, 28);
graphics2d.drawString(content, x, 28);
graphics2d.rotate(-theta, x, 28);//转过去后再转回来
x+=30;
}
// 8,生成干扰线
graphics.setColor(Color.GRAY);
for (int i = 0; i < 50; i++)
{
int x1=random.nextInt(width);
int x2=random.nextInt(width);
int y1=random.nextInt(height);
int y2=random.nextInt(height);
graphics.drawLine(x1, y1, x2, y2);
}
//释放一下内存资源
graphics.dispose();
// 图片输出imageIo
graphics.setColor(Color.YELLOW);
ImageIO.write(bufferedImage, "jpg", response.getOutputStream());
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doGet(request, response);
}
}
为了实现点击图片自动刷新功能，需要写一个js代码，代码如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
function refreshImage(){
var img=document.getElementById("myimg");
//刷新验证码图片，要想刷新地址，必须不一样，
img.src="/myday06/response1?time="+new Date().getTime();
}
</script>
</head>
<body>
请输入验证码：<input type="text" name="checkCode"/><img src="/myday06/response" id="myimg" onclick="refreshImage()">
</body>
</html>
实现的效果如下：
