HttpServletResponse

Web服务器接收到客户端的Http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表相应的一个HttpServletResponse；

如果要获取客户端请求过来的参数：找HttpServletRequest如果要给客户端相应一些信息：找HttpServletResponse

1.简单分类

负责向浏览器发送数据的方法

servletOutputStream getoutputstream() throws IOException; PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法

void setCharacterEncoding(java.lang.String s); void setContentLength(int i); void setContentLengthLong(long l); void setContentType(java.lang.String s); void setDateHeader(java.lang.String s, long l); void addDateHeader(java.lang.String s, long l); void setHeader(java.lang.String s, java.lang.String s1); void addHeader(java.lang.String s, java.lang.String s1); void setIntHeader(java.lang.String s, int i); void addIntHeader(java.lang.String s, int i);

响应的状态码

int SC_CONTINUE = 100; int SC_SWITCHING_PROTOCOLS = 101; int SC_OK = 200; int SC_CREATED = 201; int SC_ACCEPTED = 202; int SC_NON_AUTHORITATIVE_INFORMATION = 203; int SC_NO_CONTENT = 204; int SC_RESET_CONTENT = 205; int SC_PARTIAL_CONTENT = 206; int SC_MULTIPLE_CHOICES = 300; int SC_MOVED_PERMANENTLY = 301; int SC_MOVED_TEMPORARILY = 302; int SC_FOUND = 302; int SC_SEE_OTHER = 303; int SC_NOT_MODIFIED = 304; int SC_USE_PROXY = 305; int SC_TEMPORARY_REDIRECT = 307; int SC_BAD_REQUEST = 400; int SC_UNAUTHORIZED = 401; int SC_PAYMENT_REQUIRED = 402; int SC_FORBIDDEN = 403; int SC_NOT_FOUND = 404; int SC_METHOD_NOT_ALLOWED = 405; int SC_NOT_ACCEPTABLE = 406; int SC_PROXY_AUTHENTICATION_REQUIRED = 407; int SC_REQUEST_TIMEOUT = 408; int SC_CONFLICT = 409; int SC_GONE = 410; int SC_LENGTH_REQUIRED = 411; int SC_PRECONDITION_FAILED = 412; int SC_REQUEST_ENTITY_TOO_LARGE = 413; int SC_REQUEST_URI_TOO_LONG = 414; int SC_UNSUPPORTED_MEDIA_TYPE = 415; int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416; int SC_EXPECTATION_FAILED = 417; int SC_INTERNAL_SERVER_ERROR = 500; int SC_NOT_IMPLEMENTED = 501; int SC_BAD_GATEWAY = 502; int SC_SERVICE_UNAVAILABLE = 503; int SC_GATEWAY_TIMEOUT = 504; int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

2.常见应用

向浏览器输出消息

下载文件

要获取下载文件的路径下载的文件名称设置让浏览器支持下载所需获取下载文件的输入流创建缓冲区获取OutputStream对象将FileOutputStream流写入buffer缓冲区使用OutputStream将缓冲区中的数据输出到客户端 public class FileServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //1．要获取下载文件的路径 String realPath = "C:\\Users\\wswck\\IdeaProjects\\javaweb-02-servlet\\response\\src\\main\\resources\\姜子牙.png"; System.out.println("下载文件的路径:"+realPath); //2.下载的文件名称 String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1); //3.设置让浏览器支持(Content-Disposition)下载所需,中文文件名URLEncoder.encode编码，否则可能乱码 resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8")); //4．获取下载文件的输入流 FileInputStream in = new FileInputStream(realPath); //5．创建缓冲区 int len = 0; byte[] buffer = new byte[1024]; //6．获取OutputStream对象 ServletOutputStream out = resp.getOutputStream(); //7．将FileOutputStream流写入buffer缓冲区,使用OutputStream将缓冲区中的数据输出到客户端 while((len=in.read(buffer))>0){ out.write(buffer,0,len); } in.close(); out.close(); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }

验证码功能

前端实现后端实现，需要用到Java的图片类 public class ImageServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //如何让浏览器5秒刷新一次 resp.setHeader("refresh","3"); //在内存中创建一个图片 BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB); //得到图片 Graphics2D g = (Graphics2D) image.getGraphics();//笔 //设置图片的背景颜色 g.setColor(Color.white); g.fillRect(0,0,80,20); //给图片写数据 g.setColor(Color.BLUE); g.setFont(new Font(null,Font.ITALIC,20)); g.drawString(makeNum(),00,20); //告诉浏览器，这个请求用图片的方式打开 resp.setContentType("image//jpeg"); //网站存在缓存，不让浏览器缓存 resp.setDateHeader("expires",-1); resp.setHeader("Cache-Control","no-cache"); resp.setHeader("Pragma","no-cache"); //把图片写给浏览器 ImageIO.write(image,"jpg", resp.getOutputStream()); } //生成随机数 private String makeNum(){ Random random = new Random(); String num = random.nextInt(9999999) + ""; StringBuffer sb = new StringBuffer(); for(int i = 0; i < 7-num.length() ; i++){ sb.append("0"); } num = sb.toString() + num; return num; } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }

实现重定向

B一个web资源收到客户端A请求后，B他会通知A客户端去访问另外一个web资源C，这个过程叫重定向

常见场景：用户登录

void sendRedirect(String var1) throws IOException;

测试：

public class RedirectServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { /* resp.setHeader("Location","/r/img"); resp.setStatus(302); */ resp.sendRedirect("/response_war/img");//重定向 } }

面试题：请你聊聊重定向和转发的区别？

​ 相同点

页面都会实现跳转

​ 不同点

请求转发的时候，url不会产生变化重定向时候，url地址栏会发生变化

简单实现登录重定向

public class RedirectServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { /* resp.setHeader("Location","/r/img"); resp.setStatus(302); */ resp.sendRedirect("/response_war/img");//重定向 } } public class RequestTest extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //处理请求 String username = req.getParameter("username"); String password = req.getParameter("password"); System.out.println(username+":"+password); //重定向时候一定要注意，路径问题，否则404； resp.sendRedirect("/response_war/success.jsp"); } }

前端代码

<html> <body> <h2>Hello World!</h2> <%--这里提交的路径，需要寻找到项目的路径--%> <%--${pageContext.request.contextPath}代表当前的项目--%> <form action="${pageContext.request.contextPath}/login" method="get"> 用户名：<input type="text" name="username"> <br> 密码：<input type="password" name="password"> <br> <input type="submit"> </form> </body> </html> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <h1>Success</h1> </body> </html>