Java WEB中的HttpServletResponse数据传递

1.什么是HttpServletResponse

2.使用HttpServletResponse向浏览器发送数据及相关实例。

　　实例1：实现文件下载功能

　　实例2：实现验证码注册

　　实例3:实现页面3秒后跳转

　　实例4:实现页面缓存

　　实例5：重定向技术

什么是HttpServletResponse

HttpServletResponse：以在发送一个响应消息时提供 指定的HTTP功能性。例如它有访问HTTP 头和cookies的方法.servlet容器创建一个 HttpServletRequest 对象并将之作为一个参数传递给 servlet的 service方法 (如doGet, doPost等）.

使用HttpServletResponse向浏览器发送数据

public void test(HttpServletResponse response) throws IOException {
		String date = "hello！";
		//设置response使用的码表，以控制response以什么码表向浏览器写数据
		response.setCharacterEncoding("UTF-8");
		//指定浏览器以什么码表去读取传输过来的数据，
		response.setHeader("Content-type", "text/html;charset=UTF-8");
                //response.setContentType("text/html;charset=UTF-8");//开发中不建议这样使用
		PrintWriter pr=response.getWriter();
		pr.write(date);
	}

 在这里要注意一个乱码问题：以什么样的码表向浏览器写数据，浏览器就要用什么样的码表去读取传输过来是数据。如果两者分别使用的码表不一致，则会导致乱码问题。

我这里是用字节流向浏览器写数据，数据的读写分为两大板块：字节流，字符流，根据实际情况使用，当数据中全是字符类型的话可以使用字符流，否则的话使用字节流：比如读取一部影片就要使用字节流。

最保险的方法就是：无论读写什么样的数据都使用字节流。

实例：实现文件下载功能：

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Response1 extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String path = this.getServletContext().getRealPath("/download/斗地主.png");
		String filename = path.substring(path.lastIndexOf("\") + 1);
		// 如果下载文件是中文文件，则文件名需要经过URI编码
		response.setContentType("text/html;charset=UTF-8");//开发中不建议这样使用
                //Content-Disposition:浏览器弹出下载对话框
		response.setHeader("content-disposition", "attachment;filename="+ URLEncoder.encode(filename, "UTF-8"));
		ServletOutputStream out = response.getOutputStream();
		download(out, path);

	}

//文件下载方法，通用
	private void download(ServletOutputStream responseout, String path) {
		InputStream in = null;
		OutputStream out = null;
		try {
			try {
				in = new FileInputStream(path);
				int len = 0;
				byte buffer[] = new byte[1204];
				out = responseout;
				while ((len = in.read(buffer)) > 0) {
					out.write(buffer, 0, len);
				}
			} catch (Exception e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}

		} finally {
			if (in != null) {
				try {
					in.close();
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
			if (out != null) {
				try {
					out.close();
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}

	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

	}

}

 实例：实现验证码注册

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.io.PrintWriter;
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 Response2 extends HttpServlet {
	public static final int HEIGHT = 30;
	public static final int WHITH = 120;
	public  static String context="";

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		

		BufferedImage image = new BufferedImage(WHITH, HEIGHT,
				BufferedImage.TYPE_INT_RGB);
		Graphics g = image.getGraphics();

		// 设置背景色
		setBackground(g);
		// 设置边框
		setBorder(g);
		// 设置干扰线
		setRandomLine(g);
		// 写随机数
		setRandomNum((Graphics2D) g);
		// 图形给浏览器
		response.setContentType("image/jpeg");
		// 发头，控制浏览器不要缓存
		response.setHeader("Cache-Control", "no-cache");
		response.setHeader("Pragma", "no-cache");
		ImageIO.write(image, "jpg", response.getOutputStream());
		
//		 String password =request.getParameter("userpassword"); 
//		 System.out.println("网页验证码为："+request.getAttribute(password));
//		 System.out.println("验证码为："+context);
//		 if(!context.equals(password)){
//			 System.out.println("验证码输入错误！");
//		 }else{
//			 System.out.println("验证码输入正确！");
//		 }

	}

	private void setBackground(Graphics g) {
		g.setColor(Color.WHITE);
		g.fillRect(0, 0, WHITH, HEIGHT);

	}

	private void setBorder(Graphics g) {
		g.setColor(Color.BLUE);
		g.drawRect(1, 1, WHITH - 2, HEIGHT - 2);

	}

	private void setRandomLine(Graphics g) {
		g.setColor(Color.GREEN);
		for (int i = 0; i < 5; i++) {
			int x1 = new Random().nextInt(WHITH);
			int y1 = new Random().nextInt(HEIGHT);
			int x2 = new Random().nextInt(WHITH);
			int y2 = new Random().nextInt(HEIGHT);
			g.drawLine(x1, y1, x2, y2);
		}

	}

	private void setRandomNum(Graphics2D g) {
		g.setColor(Color.RED);
		g.setFont(new Font("微软雅黑", Font.BOLD, 15));
		// 准备常用汉字集
		String base = "u7684u4e00u4e86u662fu6211u4e0du5728u4ebau4eecu6709u6765u4ed6u8fd9u4e0au7740u4e2au5730u5230u5927u91ccu8bf4u5c31u53bbu5b50u5f97u4e5fu548cu90a3u8981
u4e0bu770bu5929u65f6u8fc7u51fau5c0fu4e48u8d77u4f60u90fdu628au597du8fd8u591au6ca1u4e3au53c8u53efu5bb6u5b66u53eau4ee5u4e3bu4f1au6837u5e74u60f3u751fu540cu8001u4e2du5341u4ece
u81eau9762u524du5934u9053u5b83u540eu7136u8d70u5f88u50cfu89c1u4e24u7528u5979u56fdu52a8u8fdbu6210u56deu4ec0u8fb9u4f5cu5bf9u5f00u800cu5df1u4e9bu73b0u5c71u6c11u5019u7ecfu53d1
u5de5u5411u4e8bu547du7ed9u957fu6c34u51e0u4e49u4e09u58f0u4e8eu9ad8u624bu77e5u7406u773cu5fd7u70b9u5fc3u6218u4e8cu95eeu4f46u8eabu65b9u5b9eu5403u505au53ebu5f53u4f4fu542cu9769
u6253u5462u771fu5168u624du56dbu5df2u6240u654cu4e4bu6700u5149u4ea7u60c5u8defu5206u603bu6761u767du8bddu4e1cu5e2du6b21u4eb2u5982u88abu82b1u53e3u653eu513fu5e38u6c14u4e94u7b2c
u4f7fu5199u519bu5427u6587u8fd0u518du679cu600eu5b9au8bb8u5febu660eu884cu56e0u522bu98deu5916u6811u7269u6d3bu90e8u95e8u65e0u5f80u8239u671bu65b0u5e26u961fu5148u529bu5b8cu5374
u7ad9u4ee3u5458u673au66f4u4e5du60a8u6bcfu98ceu7ea7u8ddfu7b11u554au5b69u4e07u5c11u76f4u610fu591cu6bd4u9636u8fdeu8f66u91cdu4fbfu6597u9a6cu54eau5316u592au6307u53d8u793eu4f3c
u58ebu8005u5e72u77f3u6ee1u65e5u51b3u767eu539fu62ffu7fa4u7a76u5404u516du672cu601du89e3u7acbu6cb3u6751u516bu96beu65e9u8bbau5417u6839u5171u8ba9u76f8u7814u4ecau5176u4e66u5750
u63a5u5e94u5173u4fe1u89c9u6b65u53cdu5904u8bb0u5c06u5343u627eu4e89u9886u6216u5e08u7ed3u5757u8dd1u8c01u8349u8d8au5b57u52a0u811au7d27u7231u7b49u4e60u9635u6015u6708u9752u534a
u706bu6cd5u9898u5efau8d76u4f4du5531u6d77u4e03u5973u4efbu4ef6u611fu51c6u5f20u56e2u5c4bu79bbu8272u8138u7247u79d1u5012u775bu5229u4e16u521au4e14u7531u9001u5207u661fu5bfcu665a
u8868u591fu6574u8ba4u54cdu96eau6d41u672au573au8be5u5e76u5e95u6df1u523bu5e73u4f1fu5fd9u63d0u786eu8fd1u4eaeu8f7bu8bb2u519cu53e4u9ed1u544au754cu62c9u540du5440u571fu6e05u9633
u7167u529eu53f2u6539u5386u8f6cu753bu9020u5634u6b64u6cbbu5317u5fc5u670du96e8u7a7fu5185u8bc6u9a8cu4f20u4e1au83dcu722cu7761u5174u5f62u91cfu54b1u89c2u82e6u4f53u4f17u901au51b2
u5408u7834u53cbu5ea6u672fu996du516cu65c1u623fu6781u5357u67aau8bfbu6c99u5c81u7ebfu91ceu575au7a7au6536u7b97u81f3u653fu57ceu52b3u843du94b1u7279u56f4u5f1fu80dcu6559u70edu5c55
u5305u6b4cu7c7bu6e10u5f3au6570u4e61u547cu6027u97f3u7b54u54e5u9645u65e7u795eu5ea7u7ae0u5e2eu5566u53d7u7cfbu4ee4u8df3u975eu4f55u725bu53d6u5165u5cb8u6562u6389u5ffdu79cdu88c5
u9876u6025u6797u505cu606fu53e5u533au8863u822cu62a5u53f6u538bu6162u53d4u80ccu7ec6";
		int x = 10;
		
		for (int i = 0; i < 4; i++) {
			int degree = new Random().nextInt() % 30;// -30 +30
			String ch = base.charAt(new Random().nextInt(base.length())) + "";
			context += ch;
			g.rotate(degree * Math.PI / 180, x, 15);
			g.drawString(ch, x, 20);
			g.rotate(-degree * Math.PI / 180, x, 15);
			x += 25;
		}

		
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

	}

}

 html显示代码：

<!DOCTYPE html>
<html>
<head>
<title>index</title>

<meta name="keywords" content="keyword1,keyword2,keyword3">
<meta name="description" content="this is my page">
<meta name="content-type" content="text/html; charset=gb2312">

<!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
<script type="text/javascript">
	function changerImage(img) {
		img.src = img.src + "?" + new Date().getTime();
	}
</script>

</head>

<body>
	<form action="">
		用户名：<input type="text" /><br> 密码：<input type="password" name="userpassword"><br>
		认证码：<input type="text" name="checkcode"><img src="/day-02/Response2" onclick="changerImage(this)" style="cursor:pointer;"><br>
		<input type="button" value="注册">

	</form>
</body>
</html>

 实现效果：

 实例:实现页面3秒后跳转

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Response3 extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		test2(request, response);

	}
	//自动跳转技术
	public void test2(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//在开发中最实用的
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=UTF-8");// 开发中不建议这样使用
		String message="<meta http-equiv='refresh' content='3;url=/day-02/index.jsp'>恭喜你 ！登录成功！本浏览器将在3秒后跳转到首页，如果没有跳，请点<a href=''>请继续</a>";
		this.getServletContext().setAttribute("message", message);
		//页面跳转
		this.getServletContext().getRequestDispatcher("/message.jsp").forward(request, response);
	}

	public void test1(HttpServletResponse response) throws IOException {
		// 假设这是一个用于处理登录的Servlet
		// 假设程序用运行到此，用户登录成功！
		response.setContentType("text/html;charset=UTF-8");// 开发中不建议这样使用
		response.setHeader("refresh", "3;url='/day-02/index.html'");
		response.getWriter().write("恭喜你 ！登录成功！本浏览器将在3秒后跳转到首页，如果没有跳，请点<a href=''>请继续</a>");
	}

	public void test(HttpServletResponse response) throws IOException {
		// 浏览器每过一秒刷新一次
		response.setHeader("refresh", "1");
		String date = new Random().nextInt(10000) + "";
		response.getWriter().write(date);
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

	}

}

 实例:实现页面缓存

 为什么要使用页面缓存：在实际开发中，为了实现二次加载速度，通常把一些固定的数据缓存起来，入图片，字等等，当浏览器二次访问时，直接从内存中获取缓存数据，不需要再次访问服务器进行数据传递。

具体实现代码：

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 Response4 extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		/*Expires实体报头域给出响应过期的日期和时间。为了让代理服务器或浏览器在一段时间以后更新缓存中(再次访问曾访问过的页面时，
		 * 直接从缓存中加载，缩短响应时间和降低服务器负载)的页面，我们可以使用Expires实体报头域指定页面过期的时间。
		 * eg：Expires：Thu，15 Sep 2006 16:23:12 GMT
		HTTP1.1的客户端和缓存必须将其他非法的日期格式（包括0）看作已经过期。eg：为了让浏览器不要缓存页面，
		我们也可以利用Expires实体报头域，设置为0，jsp中程序如下：response.setDateHeader("Expires","0");
		*/
		response.setDateHeader("expires", System.currentTimeMillis()+1000*3600);//指定一小时后再向服务器在发送请求
		String date="aaaaaaa";
		response.getWriter().write(date);

	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

	}

}

 实例：重定向技术

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 Response5 extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//1.浏览器会向服务器发送两次请求，意味着有两个request，response
		//2.用重定向技术，浏览器地址栏会发生变化
		//请求重定向，登录情况和购物车、下必须要用请求重定向
		/*response.setStatus(302);
		response.setHeader("location", "/day-02/index.jsp");*///同下面代码功能相同
		response.sendRedirect("/day-02/index.jsp");

	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

	}

}