一、响应对象 Response（重点：HTTP协议响应部分）

查看 HttpServletResponse

set是 有这个头 修改 没有添加一个新的 和 add 有点小区别

案例：

1. 字节流向客户端输出中文数据 ServletOutputStream

//字节流向客户端输出中文数据
public class ResponseDemo1 extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {test2(response);}//解决方案一：更改浏览器的码表（不建议）//解决方案二(不建议)：向客户端输出一个<meta>标签,模拟了响应消息头：<meta http-equiv='Content-Type' content='text/html;charset=UTF-8'>//out.write("<meta http-equiv='Content-Type' content='text/html;charset=UTF-8'>".getBytes());//解决方案三（建议）:向客户端输出响应消息头：response.setHeader("Content-Type", "text/html;charset=UTF-8");//解决方案四（建议）：向客户端输出响应消息头response.setContentType("text/html;charset=UTF-8");//字节流输出数据查UTF-8private void test2(HttpServletResponse response) throws IOException {String data = "不见了远处的青山";response.setContentType("text/html;charset=UTF-8");ServletOutputStream out = response.getOutputStream();out.write(data.getBytes("UTF-8"));//默认情况下：浏览器是乱码的（他默认查GBK）}//字节流输出数据查本地码表private void test1(HttpServletResponse response) throws IOException {String data = "不见了远处的青山";ServletOutputStream out = response.getOutputStream();out.write(data.getBytes());//String:  getBytes()查本地默认的码表GBK getBytes(String charset)查指定码表}

2. 字符流输出中文数据 PrintWriter

//字符流输出中文数据
public class ResponseDemo2 extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String data = "幸福是什么呢";//改变字符流查的码表，还能告知客户端用UTF-8进行解码response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();//HttpServletResponse的实例由Tomcat服务器提供，默认查ISO-8859-1的。//Tomcat8.X ,默认编码就变为了UTF-8out.write(data);}private void test1(HttpServletResponse response) throws IOException {String data = "幸福是什么";//改变字符流查的码表response.setCharacterEncoding("UTF-8");//告知客户端用UTF-8进行解码response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();//HttpServletResponse的实例由Tomcat服务器提供，默认查ISO-8859-1的。//Tomcat8.X ,默认编码就变为了UTF-8out.write(data);}

3.输出随机验证码图片：CAPTCHA图像

//输出随机验证码图片：CAPTCHA图像
public class ResponseDemo3 extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {int width = 120;int height = 25;//创建一副内存图像BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);//得到画笔Graphics g = image.getGraphics();//开始画//边线g.setColor(Color.BLUE);g.drawRect(0, 0, width, height);//填充背景色g.setColor(Color.YELLOW);g.fillRect(1, 1, width-2, height-2);//话干扰线g.setColor(Color.GRAY);Random r = new Random();for(int i=0;i<9;i++)g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));//验证码g.setColor(Color.RED);g.setFont(new Font("宋体", Font.ITALIC|Font.BOLD, 19));
//          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";int x = 20;for(int i=0;i<4;i++){g.drawString(r.nextInt(10)+"", x,20 );
//              g.drawString(base.charAt(r.nextInt(base.length()))+"", x, 20);x+=18;}//输出response.setHeader("Expires", "-1");response.setHeader("Cache-Control", "no-cache");response.setHeader("Pragma", "no-cache");ImageIO.write(image, "jpg", response.getOutputStream());}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

html

<body><form action="" method="post">用户名：<input type="text" name="username"/><br/>密码：<input type="password" name="password"/><br/><input type="text" size="3" name="code"/><img id="img1" src="/day08_00_response/servlet/ResponseDemo3"/><a href="javascript:change()">看不清</a><br/><input type="submit" value="登录"/></form><script type="text/javascript">function change(){var imgObj = document.getElementById("img1");imgObj.src="/day08_00_response/servlet/ResponseDemo3?time="+new Date().getTime();//浏览器发现地址没有变化，根本不发请求}</script></body>

4.定时刷新  登陆跳转等待

//控制客户端定时刷新
public class ResponseDemo4 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {test2(response);}//定时刷新到别处private void test2(HttpServletResponse response) throws IOException {response.setContentType("text/htm;charset=UTF-8");response.setHeader("Refresh", "2;URL=http://www.huyifan.cn");response.getWriter().write("登录成功，2秒后跳转到主页");}//定时刷新自己private void test1(HttpServletResponse response) throws IOException {Random r = new Random();
//      response.setHeader("Refresh", "1");response.setIntHeader("Refresh", 1);response.getWriter().write(r.nextInt()+"");}

5.控制缓存时间

//控制缓存的时间
//静态资源需要控制缓存时间
//动态资源一般不要缓存
public class ResponseDemo5 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String data = "不见了远处的青山";//让他缓存1个小时response.setDateHeader("Expires", System.currentTimeMillis()+1*60*60*1000);response.setContentType("text/html;charset=UTF-8");response.getWriter().write(data);}

6.请求重定向

//演示请求重定向:可以重定向到任何地址上//发出2次请求//地址栏会发生变化
public class ResponseDemo6 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.sendRedirect("http://www.huyifan.com");}//重定向到应用内的资源private void test1(HttpServletResponse response) throws IOException {//      response.setStatus(302);
//      response.setHeader("Location", "/day08_00_response/servlet/ResponseDemo7");response.sendRedirect("/day08_00_response/servlet/ResponseDemo7");}

public class ResponseDemo7 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.getWriter().write("I am yif");
//      response.getOutputStream().write("a".getBytes());}

细节：

1、字节流和字符流互斥，只能用其中一个。

2、response的流用完之后自动关（服务器关）

二、请求对象 Request（重点：HTTP协议请求部分）

1、HttpServletRequest对象的生命周期

诞生：请求来了

死亡：响应结束

2、也是一个域（范围）对象：请求范围

request

Map

setAttribute

getAttribute

removeAttribute‘

3、开发中尽量用绝对路径

绝对路径：要不要加应用名称

地址给服务器用的：/就代表当前应用

地址给客户端用的：/day08

1. HttpServletRequest中的常用方法

public class RequestDemo1 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String method = request.getMethod();//请求方式String uri = request.getRequestURI();//    /day08_01_request/servlet/RequestDemo1String url = request.getRequestURL().toString();//  http://localhost:8080/day08_01_request/servlet/RequestDemo1String protocal = request.getProtocol();//客户端使用的协议String remoteIp = request.getRemoteAddr();//来访者的ipint port = request.getRemotePort();// 随机的String queryString = request.getQueryString();//GET方式：/day08_01_request/servlet/RequestDemo1?username=abc&password=123//username=abc&password=123System.out.println(method);System.out.println(uri);System.out.println(url);System.out.println(protocal);System.out.println(remoteIp);System.out.println(port);System.out.println(queryString);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

2. 获取请求消息头

public class RequestDemo2 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {test3(request);}//得到所有的消息头private void test3(HttpServletRequest request) {Enumeration<String> e = request.getHeaderNames();while(e.hasMoreElements()){String headerName = e.nextElement();//透明称Enumeration<String> headerValues = request.getHeaders(headerName);while(headerValues.hasMoreElements()){System.out.println(headerName+":"+headerValues.nextElement());}}}//http协议是允许头有重复的情况，多个重名的头private void test2(HttpServletRequest request) {Enumeration<String> e = request.getHeaders("Accept-Encoding");//得到的头值while(e.hasMoreElements()){String headerValue = e.nextElement();System.out.println(headerValue);}}//得到指定请求消息头的值。如果没有该头，返回nullprivate void test1(HttpServletRequest request) {String supportEncoding = request.getHeader("Accept-Encoding");if(supportEncoding.contains("gzip")){System.out.println("支持gzip压缩");}else{System.out.println("不支持gzip压缩");}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

3.//获取请求参数

public class RequestDemo3 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {test8(request, response);}//终极解决方案：借助BeanUtil框架      jar包直接放在 web-inf 的 ；lib 文件夹里就okprivate void test8(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {User user = new User();System.out.println("封装前："+user);try {BeanUtils.populate(user, request.getParameterMap());} catch (Exception e) {e.printStackTrace();}System.out.println("封装后："+user);}//getParameterMap获取参数:封装到JavaBean中private void test7(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//key:请求参数名 value:请求参数值数组Map<String,String[]> map = request.getParameterMap();User user = new User();System.out.println("封装前："+user);for(Map.Entry<String, String[]> me:map.entrySet()){String paramName = me.getKey();//参数名称String paramValues[] = me.getValue();//参数值try {PropertyDescriptor pd = new PropertyDescriptor(paramName, User.class);Method m = pd.getWriteMethod();//setter方法if(paramValues.length>1){m.invoke(user, (Object)paramValues);//参考补充视频：反射main方法}else{m.invoke(user, paramValues);}} catch (Exception e1) {e1.printStackTrace();}}System.out.println("封装后："+user);}//getParameterMap获取参数private void test6(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//key:请求参数名 value:请求参数值数组Map<String,String[]> map = request.getParameterMap();for(Map.Entry<String, String[]> me:map.entrySet()){System.out.println(me.getKey()+"="+Arrays.asList(me.getValue()));}}//把请求参数的值封装到JavaBean中//约定优于编码：表单的输入域的name取值和JavaBean中的属性（getter和setter方法）保持一致private void test5(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {Enumeration<String> e = request.getParameterNames();//参数名User user = new User();System.out.println("封装前："+user);while(e.hasMoreElements()){String paramName = e.nextElement();//即是JavaBean中的属性名称String paramValue = request.getParameter(paramName);
//          setUsername(paramValue); setPassword(paramValue);//JavaBean的内省try {PropertyDescriptor pd = new PropertyDescriptor(paramName, User.class);Method m = pd.getWriteMethod();//setter方法m.invoke(user, paramValue);} catch (Exception e1) {e1.printStackTrace();}}System.out.println("封装后："+user);}
//  private void test4(HttpServletRequest request, HttpServletResponse response)
//          throws ServletException, IOException {
//      User user = new User();
//      System.out.println("封装前："+user);
//      String username = request.getParameter("username");
//      String password = request.getParameter("password");
//      String gender = request.getParameter("gender");
//      user.setUsername(username);
//      user.setPassword(password);
//      user.setGender(gender);
//      System.out.println("封装后："+user);
//  }  //以下内容只用简单的程序开发//获取所有的请求参数名和值private void test3(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {Enumeration<String> e = request.getParameterNames();//参数名while(e.hasMoreElements()){String paramName = e.nextElement();String values [] = request.getParameterValues(paramName);System.out.println(paramName+"="+Arrays.asList(values));}}//获取重名请求参数的值private void test2(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String username = request.getParameter("username");//不区分get还是post的String passwords[] = request.getParameterValues("password");//获取重名的请求参数值System.out.println(username+":"+Arrays.asList(passwords));}//获取单一的请求参数的值(用户所有的输入都是String)private void test1(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String username = request.getParameter("username");//不区分get还是post的String password = request.getParameter("password");System.out.println(username+":"+password);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

domain

public class User {private String username;private String password[];private String gender;public String getUsername() {//读属性，属性名称usernamereturn username;}public void setUsername(String username) {//写属性，属性名usernamethis.username = username;}public String[] getPassword() {return password;}public void setPassword(String[] password) {this.password = password;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}@Overridepublic String toString() {return "User [username=" + username + ", password="+ Arrays.toString(password) + ", gender=" + gender + "]";}}

public class Student {private int id;//BeanUtil对于基本类型自动转换private String name;private String password;private String gender;private boolean married;private String[] hobby;private String province;private String description;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public boolean isMarried() {return married;}public void setMarried(boolean married) {this.married = married;}public String[] getHobby() {return hobby;}public void setHobby(String[] hobby) {this.hobby = hobby;}public String getProvince() {return province;}public void setProvince(String province) {this.province = province;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}@Overridepublic String toString() {return "Student [id=" + id + ", name=" + name + ", password="+ password + ", gender=" + gender + ", married=" + married+ ", hobby=" + Arrays.toString(hobby) + ", province="+ province + ", description=" + description + "]";}}

<form action="/day08_01_request/servlet/RequestDemo4" method="post">用户名：<input type="text" name="username"/><br/>密码：<input type="password" name="password"/><br/>确认密码：<input type="password" name="password"/><br/>性别：<input type="text" name="gender" value="male"/><input type="submit" value="注册"/></form>

4.  以输入流的形式接收请求正文：POST
　　一般情况下用不着，文件上传时使用。

public class RequestDemo4 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {ServletInputStream in = request.getInputStream();int len = -1;byte b[] = new byte[1024];while((len=in.read(b))!=-1){System.out.println(new String(b,0,len));}in.close();}

5.获取常用表单输入域的值
　type:radio checkbox   ,如果用户一个都没有选，客户端是根本不会传参数到服务器的。

public class RequestDemo5 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {test3(request,response);}//请求编码和响应编码没有关系private void test3(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("UTF-8");//设置请求正文的编码。只对POST有效Student s = new Student();System.out.println("封装前："+s);try {BeanUtils.populate(s, request.getParameterMap());} catch (Exception e) {e.printStackTrace();}response.setContentType("text/html;charset=UTF-8");response.getWriter().write(s.toString());}//get请求方式的编码问题private void test2(HttpServletRequest request)throws UnsupportedEncodingException {String username = request.getParameter("name");//是二进制数据  %E6%9D%8E%E5%9B%9Bbyte b[] = username.getBytes("ISO-8859-1");username = new String(b,"UTF-8");System.out.println(username);//二进制转为字符，用ISO-8859-1的}//获取请求正文的参数乱码问题private void test1(HttpServletRequest request)throws UnsupportedEncodingException {request.setCharacterEncoding("UTF-8");//设置请求正文的编码。只对POST有效Student s = new Student();System.out.println("封装前："+s);try {BeanUtils.populate(s, request.getParameterMap());} catch (Exception e) {e.printStackTrace();}System.out.println("封装后："+s);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

<form action="/day08_01_request/servlet/RequestDemo5" method="post"><input type="hidden" value="438" name="id"/><table border="1" width="438"><tr><td>姓名</td><td><input type="text" name="name"/></td></tr><tr><td>密码</td><td><input type="password" name="password"/></td></tr><tr><td>性别</td><td><input type="radio" name="gender" value="male" checked="checked"/>男性<input type="radio" name="gender" value="female"/>女性</td></tr><tr><td>婚否</td><td><input type="checkbox" name="married"/></td></tr><tr><td>爱好</td><td><input type="checkbox" name="hobby" value="eat"/>吃饭<input type="checkbox" name="hobby" value="sleep"/>睡觉<input type="checkbox" name="hobby" value="java"/>学Java</td></tr><tr><td>籍贯</td><td><select name="province"><option value="BJ">北京</option><option value="SD">山东</option><option value="HB">湖北</option></select></td></tr><!--<tr><td>靓照</td><td><input type="file" name="image"/></td></tr>--><tr><td>简介</td><td><textarea rows="3" cols="38" name="description"></textarea></td></tr><tr><td colspan="2">
<!--                     <input type="submit" value="注册"/> -->
<!--                     <input type="image" src="an-0333.gif"/> --><input type="button" value="注册" onclick="toSubmit()"/></td></tr></table><script type="text/javascript">function toSubmit(){//验证用户的输入document.forms[0].submit();}</script></form>

编码：

6.请求转发

//转发：源
//源和目标：共享请求范围中的数据
public class RequestDemo6 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setAttribute("p", "ppp");//ServletContext:地址的写法。必须以"/"，代表当前应用。（应用开头的绝对路径）
//      RequestDispatcher rd = getServletContext().getRequestDispatcher("/servlet/RequestDemo7");//绝对路径
//      RequestDispatcher rd = request.getRequestDispatcher("/servlet/RequestDemo7");//相对路径RequestDispatcher rd = request.getRequestDispatcher("RequestDemo7");rd.forward(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//转发：目标
public class RequestDemo7 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String s = (String)request.getAttribute("p");//注意和getParameter没有关系response.getWriter().write(s);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

请求与重定向区别

7.//包含：源  服务器端行为

public class RequestDemo8 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");response.getWriter().write("我喜欢");RequestDispatcher rd = request.getRequestDispatcher("/servlet/RequestDemo9");rd.include(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

public class RequestDemo9 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");response.getWriter().write("成都");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

8.请求 和 包含 的小细节

//转发前后，源输出的任何响应正文无效
public class Forward1 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setHeader("Refresh", "1");System.out.println("转发前");response.getWriter().write("forward before");//转发前会清空响应对象中的正文内容request.getRequestDispatcher("/servlet/Forward2").forward(request, response);//转发System.out.println("转发后");response.getWriter().write("forward after");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//转发：目标
public class Forward2 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.getWriter().write("222222");//响应结束}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//包含：源
//只会包含目标的正文，头部信息包含前清空
public class IncludeDemo1 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.getWriter().write("11111");request.getRequestDispatcher("/servlet/IncludeDemo2").include(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//包含：目标
public class IncludeDemo2 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setIntHeader("Refresh", 1);response.getWriter().write("22222");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}