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web服务器会收到客户端的http请求，会对每一次的请求，分别创建一个用于代表请求的request和代表响应的response对象，获取客户机提交的数据，只需要找request对象；向客户机输出数据，只需找response对象。
response常见的应用：向客户端输出中文数据：分别以OutputStream和PrintWriter输出
//OutputStream
public class Demo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
test1(response);
}
private void test4(HttpServletResponse response) throws IOException,
UnsupportedEncodingException {
// 这里把数据写给response，再由response写到浏览器。
OutputStream out = response.getOutputStream();
out.write(1); //编码不一样，去找国标的1代表的字符
out.write((1 + "").getBytes()); //看到正常的1
}
private void test3(HttpServletResponse response) throws IOException,
UnsupportedEncodingException {
response.setHeader("Content-type", "text/html,charset=utf-8");
String data = "中国";
// 这里把数据写给response，再由response写到浏览器。
OutputStream out = response.getOutputStream();
out.write(data.getBytes("utf-8"));
}
private void test2(HttpServletResponse response) throws IOException,
UnsupportedEncodingException {
// 用html技术中的meta标签模拟一个http响应头，控制浏览器的行为
String data = "中国";
// 这里把数据写给response，再由response写到浏览器。
OutputStream out = response.getOutputStream();
out.write("<meta http-equiv=‘content-type‘ content=‘text/html;charset=utf-8‘>"
.getBytes());
out.write(data.getBytes("utf-8")); // 写成字节流,指定以何种编码写给客户机
}
private void test1(HttpServletResponse response) throws IOException,
UnsupportedEncodingException {
// 设定浏览器以何种编码打开
response.setHeader("Content-type", "text/html;charset=utf-8");
String data = "中国";
// 这里把数据写给response，再由response写到浏览器。
OutputStream out = response.getOutputStream();
out.write(data.getBytes("utf-8")); // 写成字节流,指定以何种编码写给客户机
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
}
PrintWriter---writer流只能写，字符或字符串
public class Demo2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置PrintWrite写给response的码表为utf-8,默认的码表示iso
response.setCharacterEncoding("UTF-8");
//设置浏览器的码表
response.setHeader("Content-Type", "text/html;charset=utf-8");
String data = "中国";
PrintWriter out = response.getWriter();
out.write(data);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
}
文件下载：
public class Demo3 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//在servlet里读取资源
//得到资源的绝对地址
String path = this.getServletContext().getRealPath("/download/1.jpg");
//截取文件地址，最后一个斜杠后面的文件名
String filename = path.substring(path.lastIndexOf("\\") + 1);
//设置以何种方式打开文件
//下载的图片名为中文的，修改编码
response.setHeader("content-disposition", "attachement;filename =" + URLEncoder.encode(filename, "utf-8"));
response.setHeader("content-disposition", "attachement;filename" + filename);
InputStream in = null;
OutputStream out = null;
try{
in = new FileInputStream(path);
int len = 0;
byte buffer[] = new byte[1024];
out = response.getOutputStream();
while((len = in.read(buffer)) > 0){
out.write(buffer, 0, len);
}
}finally{
if(in != null){
try{
in.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
}
输出随机图片：
产生图片：
public class Demo4 extends HttpServlet {
//输出随机图片
public static final int WIDTH = 120;
public static final int HEIGHT = 35;
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//内存中构建一幅图像
BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
//得到这副图像
Graphics g = image.getGraphics();
//设置背景色
setBackGround(g);
//设置边框
setBorder(g);
//画干扰线
drawRoundomLine(g);
//写随机数
drawRoundomNum((Graphics2D)g);
//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("Pragme", "no-cache");
ImageIO.write(image, "jpg", response.getOutputStream());
}
private void drawRoundomNum(Graphics2D g) {
// TODO Auto-generated method stub
g.setColor(Color.RED);
g.setFont(new Font("宋体", Font.BOLD, 20));
//汉字的取值区间是 [\u4e00--\u9fa5]
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";
int x = 10;
for(int i = 0; i < 5; i ++){
int degree = new Random().nextInt() % 30; //-30~30
String ch = base.charAt(new Random().nextInt(base.length())) + "";
g.rotate(degree * Math.PI/180, x, 20);//设置旋转角度
g.drawString(ch, x, 20);
g.rotate(-degree * Math.PI/180, x, 20);
x += 30;
}
}
private void drawRoundomLine(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.CYAN);
for(int i = 0; i < 7; i ++){
int x1= new Random().nextInt(WIDTH);
int y1= new Random().nextInt(HEIGHT);
int x2= new Random().nextInt(WIDTH);
int y2= new Random().nextInt(HEIGHT);
g.drawLine(x1, y1, x2, y2);
}
}
private void setBorder(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.BLUE);
g.drawRect(1, 1, WIDTH - 2, HEIGHT - 2);
}
private void setBackGround(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.WHITE);
g.fillRect(0, 0, WIDTH, HEIGHT);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
}
在html文件获取此文件，再输出来。
<html>
<head>
<title>sign.html</title>
<script type="text/javascript">
function changeImage(img){
img.src = img.src + "?" + new Date().getTime();
}
</script>
</head>
<body>
<form>
用户名：<input type="text" name="username"><br/>
密 码：<input type="password" name="password"><br/>
认证码：<input type="text" name="checkcode">
<img src="/day6/servlet/Demo4" onclick="changeImage(this)" alt="换一张" style="cursor:handle">
<input type="submit" value="注册">
</form>
</body>
</html>
控制浏览器定时刷新：
public class Demo5 extends HttpServlet {
//控制浏览器定时刷新
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
test3(request, response);
}
//实用的跳转
private void test3(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
//假设这是一个处理登录的servlet
//假设程序运行到此，用户登录成功
String message = "<meta http-equiv=‘refresh‘ content=‘3;url=/day6/index.jsp‘>等待跳转中，不成功<a href=‘‘>请点击</a>";
this.getServletContext().setAttribute("message", message);
this.getServletContext().getRequestDispatcher("/message.jsp").forward(request, response);
}
/*private void test2(HttpServletResponse response) throws IOException {
//假设这是一个处理登录的servlet
//假设程序运行到此，用户登录成功
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
response.setHeader("refresh", "3;url=‘/day6/index.jsp‘");
response.getWriter().write("等待跳转中，不成功<a href=‘‘>请点击</a>");
}*/
//定时产生随机数
private void test1(HttpServletResponse response) throws IOException {
response.setHeader("refresh", "3");
String data = new Random().nextInt(100000) + "";
response.getWriter().write(data);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
}
message.jsp--显示页面。
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP ‘message.jsp‘ starting page</title>
</head>
<body>
<%
String message = (String)application.getAttribute("message");
out.write(message);
%>
</body>
</html>
//控制缓存时间
public class Demo6 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setDateHeader("expires", System.currentTimeMillis() + 1000 * 3600);
String data = "aaaaaaaaa";
response.getWriter().write(data);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
}
请求重定向：--地址栏发生变化/浏览器会向服务器发送两次意味着有两个response，request
在用户登录和显示购物车时，通常会用到重定向技术
response细节：getOutputStream和getWriter方法分别用于得到输出二进制数据，输出文本数据的ServletOutPutStream，Printwriter对象
getOutputStream和getWriter方法是互斥的，调用其中任何一个方法后，就不能再调用您一个方法。（如果是重定向，就可以在重定向的网页使用与之互斥的方法。否则不可以，因为重定向是重新发起第二次访问）
Servlet程序向ServletOutStream或PrintWriter对象中写入的数据将被Servlet引擎从response里面获取，Sservlet引擎将这些数据当作响应信息的正文。然后再与响应头组合后发送到客户端。
Servlet的service方法结束后，Servlet引擎将检查getWriter或getOutputStream方法返回的输出流对象是否已经调用过close方法，如果没有，Servlet引擎调用close方法关闭输出流对象
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原文地址：http://www.cnblogs.com/lcpholdon/p/4340591.html
