1. HttpServletResponse
注:响应可以设置前端说有东西
web服务器接收到客户端的http请求,这对这个请求,分别创建一个代表请求的HttpServletRequest对象,代表响应的一个HttpServletResponse;
如果要获取客户端请求过来的参数:找HttpServletRequest
如果要给客户端响应一些信息:找HttpServletResponse
1.1简单分类
负责向浏览器发送数据的方法
1.ServletOutputStream getOutputStream() throws IOException; 2.PrintWriter getWriter() throws IOException;
负责向浏览器发送响应头的方法
void setCharacterEncoding(String var1); void setContentLength(int var1); void setContentLengthLong(long var1); void setContentType(String var1); void setDateHeader(String var1, long var2); void addDateHeader(String var1, long var2); void setHeader(String var1, String var2); void addHeader(String var1, String var2); void setIntHeader(String var1, int var2); void addIntHeader(String var1, int var2);
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;
1.2常见应用
1.向浏览器输出信息
2.下载文件(步骤)
2.1 获取下载文件路径
2.2 下载文件的名是什么
2.3 设置让浏览器能够支持下载我们需要的东西
2.4 获取下载文件的输入流
2.5 创建缓冲区
2.6 获取OutpuitStream对象
2.7 将FileOutputstream流写入到buffer缓冲区
2.8 使用OutputStream将缓冲区中的数据输出的客户端
利用响应(Response)下载文件
package com.king.servlet; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.FileInputStream; import java.io.IOException; import java.net.URLEncoder; public class FileServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //2.1 获取下载文件路径 //String realPath = this.getServletContext().getRealPath("/1.png"); String realPath="D:\JavaWebStudy\javaweb-02-maven\response\target\classes\1.png"; System.out.println("下载文件的路径:"+realPath); //2.2 下载文件的名是什么 //利用substring分割路径:截取路径最后一个(有两个“”是因为有一个转义字符)的后一位,这样就达到获取当前文件的目的 String filename = realPath.substring(realPath.lastIndexOf("\") + 1); //2.3 设置让浏览器能够支持下载我们需要的东西,使用URLEncoder.encode(filename,"UTF-8"),中文文件名编码,目的是为了让文件的中文名能被识别 resp.setHeader("Content-disposition","attachment;filename+"+ URLEncoder.encode(filename,"UTF-8")); //2.4 获取下载文件的输入流 FileInputStream in = new FileInputStream(realPath); //2.5 创建缓冲区 int len=0; byte[] buffer = new byte[1024]; //2.6 获取OutpuitStream对象 ServletOutputStream out= resp.getOutputStream(); //2.7 将FileOutputstream流写入到buffer缓冲区 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); } } 注:最后别忘了配置web.xml,因为很简单我就不说了,不知道的可以翻翻我以前的有
实现验证码功能
1.前端实现
2.后端实现,需要用到的java的图片类,生成一个图片
package com.king.servlet; import javax.imageio.ImageIO; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.awt.*; import java.awt.image.BufferedImage; import java.io.IOException; import java.util.Random; public class ImageServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //如何让浏览器每秒刷新一次; resp.setHeader("refresh", "3");//键值对的形式 //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();//把他看成一支笔 //设置图片背景颜色 g.setColor(Color.white); g.fillRect(0, 0, 80, 20);//设置矩形 //给图片写数据 g.setColor(Color.BLUE); g.setFont(new Font(null,Font.BOLD,20)); g.drawString(makeUnm(),0,20); //告诉浏览器,这个请求用图片方式打开 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 boolean write = ImageIO.write(image, "jpeg", resp.getOutputStream()); } //生成随机数 private String makeUnm() { Random random = new Random(); String num = random.nextInt(99999999) + ""; StringBuffer sb = new StringBuffer(); for (int i=0;i<7-num.length();i++){ sb.append("0");//当小于时,用0填充 } num=sb.toString()+ num; return num; } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }