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1. HTTP协议:响应消息2. Response对象3. ServletContext对象
请求消息详解在文章谈到,这里主要介绍响应消息
1. 请求消息:客户端发送给服务器端的数据 * 数据格式: 1. 请求行 2. 请求头 3. 请求空行 4. 请求体2. 响应消息:服务器端发送给客户端的数据 * 数据格式: 1. 响应行 1. 组成:协议/版本 响应状态码 状态码描述 2. 响应状态码:服务器告诉客户端浏览器本次请求和响应的一个状态。 1. 状态码都是3位数字 2. 分类: 1. 1xx:服务器就收客户端消息,但没有接受完成,等待一段时间后,发送1xx多状态码 2. 2xx:成功。代表:200 3. 3xx:重定向。代表:302(重定向),304(访问缓存) 4. 4xx:客户端错误。 * 代表: * 404(请求路径没有对应的资源) * 405:请求方式没有对应的doXxx方法 5. 5xx:服务器端错误。代表:500(服务器内部出现异常) 2. 响应头: 1. 格式:头名称: 值 2. 常见的响应头: 1. Content-Type:服务器告诉客户端本次响应体数据格式以及编码格式 2. Content-disposition:服务器告诉客户端以什么格式打开响应体数据 * 值: * in-line:默认值,在当前页面内打开 * attachment;filename=xxx:以附件形式打开响应体。文件下载 3. 响应空行 4. 响应体:传输的数据 * 响应字符串格式 HTTP/1.1 200 OK Content-Type: text/html;charset=UTF-8 Content-Length: 101 Date: Wed, 06 Jun 2018 07:08:42 GMT$Title$ hello , response
* 功能:设置响应消息 1. 设置响应行 1. 格式:HTTP/1.1 200 ok 2. 设置状态码:setStatus(int sc) 2. 设置响应头:setHeader(String name, String value) 3. 设置响应体: * 使用步骤: 1. 获取输出流 * 字符输出流:PrintWriter getWriter() * 字节输出流:ServletOutputStream getOutputStream() 2. 使用输出流,将数据输出到客户端浏览器
案例1:完成重定向
* 案例: 1. 完成重定向 * 重定向:资源跳转的方式 * 代码实现: //1. 设置状态码为302 response.setStatus(302); //2.设置响应头location response.setHeader("location","/day15/responseDemo2"); //简单的重定向方法 response.sendRedirect("/day15/responseDemo2"); * 重定向的特点:redirect 1. 地址栏发生变化 2. 重定向可以访问其他站点(服务器)的资源 3. 重定向是两次请求。不能使用request对象来共享数据 * 转发的特点:forward 1. 转发地址栏路径不变 2. 转发只能访问当前服务器下的资源 3. 转发是一次请求,可以使用request对象来共享数据 * forward 和 redirect 区别 * 路径写法: 1. 路径分类 1. 相对路径:通过相对路径不可以确定唯一资源 * 如:./index.html * 不以/开头,以.开头路径 * 规则:找到当前资源和目标资源之间的相对位置关系 * ./:当前目录 * ../:后退一级目录 2. 绝对路径:通过绝对路径可以确定唯一资源 * 如:http://localhost/day15/responseDemo2 /day15/responseDemo2 * 以/开头的路径 * 规则:判断定义的路径是给谁用的?判断请求将来从哪儿发出 * 给客户端浏览器使用:需要加虚拟目录(项目的访问路径) * 建议虚拟目录动态获取:request.getContextPath() * ,
重定向示例代码,重定向因为是两次请求, request因为是域对象,对同一个请求有效,所以setAttribute方法使用无效
package cn.itcast.web.servlet;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/** * 重定向 */@WebServlet("/responseDemo1")public class ResponseDemo1 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("demo1........"); //访问/responseDemo1,会自动跳转到/responseDemo2资源 /* //1. 设置状态码为302 response.setStatus(302); //2.设置响应头location response.setHeader("location","/day15/responseDemo2");*/ request.setAttribute("msg","response"); //动态获取虚拟目录 String contextPath = request.getContextPath(); //简单的重定向方法 response.sendRedirect(contextPath+"/responseDemo2"); //response.sendRedirect("http://www.itcast.cn"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
重定向的servlet
package cn.itcast.web.servlet;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/responseDemo2")public class ResponseDemo2 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("demo2222222........"); Object msg = request.getAttribute("msg"); System.out.println(msg); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
转发的servlet
package cn.itcast.web.servlet;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/responseDemo3")public class ResponseDemo3 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //转发 request.getRequestDispatcher("/responseDemo2").forward(request,response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
绝对路径和相对路径前端写法,对于JAVA EE的web项目,如果是直接在web目录下,如location.html,代码如下:
Title 相对路径
找到当前资源和目标资源之间的相对位置关系
当前资源:location.html http://localhost/day15/location.html
目标资源: http://localhost/day15/responseDemo2
responseDemo2 responseDemo2
绝对路径
responseDemo2
如果有嵌套自己建的文件夹,页面location2.html,相对路径的写法如下
Title 找到当前资源和目标资源之间的相对位置关系
当前资源:location.html http://localhost/day15/htmls/location2.html
目标资源: http://localhost/day15/responseDemo2
responseDemo2
案例2 服务器输出字符数据到浏览器
2. 服务器输出字符数据到浏览器 * 步骤: 1. 获取字符输出流 2. 输出数据 * 注意: * 乱码问题: 1. PrintWriter pw = response.getWriter();获取的流的默认编码是ISO-8859-1 2. 设置该流的默认编码 3. 告诉浏览器响应体使用的编码 //简单的形式,设置编码,是在获取流之前设置 response.setContentType("text/html;charset=utf-8");
示例代码
package cn.itcast.web.servlet;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.io.PrintWriter;@WebServlet("/responseDemo4")public class ResponseDemo4 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //获取流对象之前,设置流的默认编码:ISO-8859-1 设置为:GBK // response.setCharacterEncoding("utf-8"); //告诉浏览器,服务器发送的消息体数据的编码。建议浏览器使用该编码解码 //response.setHeader("content-type","text/html;charset=utf-8"); //简单的形式,设置编码 response.setContentType("text/html;charset=utf-8"); //1.获取字符输出流 PrintWriter pw = response.getWriter(); //2.输出数据 //pw.write("hello response
"); pw.write("你好啊啊啊 response"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
案例3 服务器输出字节数据到浏览器
3. 服务器输出字节数据到浏览器 * 步骤: 1. 获取字节输出流 2. 输出数据
package cn.itcast.web.servlet;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/responseDemo5")public class ResponseDemo5 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=utf-8"); //1.获取字节输出流 ServletOutputStream sos = response.getOutputStream(); //2.输出数据 sos.write("你好".getBytes("utf-8")); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
案例4 验证码
4. 验证码 1. 本质:图片 2. 目的:防止恶意表单注册
package cn.itcast.web.servlet;import javax.imageio.ImageIO;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.annotation.WebServlet;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;@WebServlet("/checkCodeServlet")public class CheckCodeServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { int width = 100; int height = 50; //1.创建一对象,在内存中图片(验证码图片对象) BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); //2.美化图片 //2.1 填充背景色 Graphics g = image.getGraphics();//画笔对象 g.setColor(Color.PINK);//设置画笔颜色 g.fillRect(0,0,width,height); //2.2画边框 g.setColor(Color.BLUE); g.drawRect(0,0,width - 1,height - 1); String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789"; //生成随机角标 Random ran = new Random(); for (int i = 1; i <= 4; i++) { int index = ran.nextInt(str.length()); //获取字符 char ch = str.charAt(index);//随机字符 //2.3写验证码 g.drawString(ch+"",width/5*i,height/2); } //2.4画干扰线 g.setColor(Color.GREEN); //随机生成坐标点 for (int i = 0; i < 10; i++) { int x1 = ran.nextInt(width); int x2 = ran.nextInt(width); int y1 = ran.nextInt(height); int y2 = ran.nextInt(height); g.drawLine(x1,y1,x2,y2); } //3.将图片输出到页面展示 ImageIO.write(image,"jpg",response.getOutputStream()); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
验证码案例的前端代码,用?后面跟参数,参数是时间戳。这样做的目的是让每次请求的参数不同,因为请求相同,浏览器有缓存机制,就不会发送相同的请求,无法正常更换验证码图片
Title 看不清换一张?
1. 通过request对象获取 request.getServletContext(); 2. 通过HttpServlet获取 this.getServletContext();
package cn.itcast.web.servletcontext;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/servletContextDemo1")public class ServletContextDemo1 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /* ServletContext对象获取: 1. 通过request对象获取 request.getServletContext(); 2. 通过HttpServlet获取 this.getServletContext(); */ //1. 通过request对象获取 ServletContext context1 = request.getServletContext(); //2. 通过HttpServlet获取 ServletContext context2 = this.getServletContext(); System.out.println(context1); System.out.println(context2); System.out.println(context1 == context2);//true,说明两者生成getServletContext等效 } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
* MIME类型:在互联网通信过程中定义的一种文件数据类型 * 格式: 大类型/小类型 text/html image/jpeg* 获取:String getMimeType(String file)
package cn.itcast.web.servletcontext;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/servletContextDemo2")public class ServletContextDemo2 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /* ServletContext功能: 1. 获取MIME类型: * MIME类型:在互联网通信过程中定义的一种文件数据类型 * 格式: 大类型/小类型 text/html image/jpeg * 获取:String getMimeType(String file) 2. 域对象:共享数据 3. 获取文件的真实(服务器)路径 */ //2. 通过HttpServlet获取 ServletContext context = this.getServletContext(); //3. 定义文件名称 String filename = "a.jpg";//image/jpeg //4.获取MIME类型 String mimeType = context.getMimeType(filename); System.out.println(mimeType); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
1. setAttribute(String name,Object value)2. getAttribute(String name)3. removeAttribute(String name)* ServletContext对象范围:所有用户所有请求的数据
测试ServletContext对象范围,对demo3使用setAttribute方法,看demo4可以接受到不,如果可以接收说明,范围是所有用户所有请求的数据
package cn.itcast.web.servletcontext;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/servletContextDemo3")public class ServletContextDemo3 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /* ServletContext功能: 1. 获取MIME类型: 2. 域对象:共享数据 3. 获取文件的真实(服务器)路径 */ //2. 通过HttpServlet获取 ServletContext context = this.getServletContext(); //设置数据 context.setAttribute("msg","haha"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
demo4调用getServletContext方法
package cn.itcast.web.servletcontext;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/servletContextDemo4")public class ServletContextDemo4 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /* ServletContext功能: 1. 获取MIME类型: 2. 域对象:共享数据 3. 获取文件的真实(服务器)路径 */ //2. 通过HttpServlet获取 ServletContext context = this.getServletContext(); //获取数据 Object msg = context.getAttribute("msg"); System.out.println(msg); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
1. 方法:String getRealPath(String path) String b = context.getRealPath("/b.txt");//web目录下资源访问 System.out.println(b); String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问 System.out.println(c); String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问 System.out.println(a);
package cn.itcast.web.servletcontext;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.File;import java.io.IOException;@WebServlet("/servletContextDemo5")public class ServletContextDemo5 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /* ServletContext功能: 1. 获取MIME类型: 2. 域对象:共享数据 3. 获取文件的真实(服务器)路径 */ // 通过HttpServlet获取 ServletContext context = this.getServletContext(); // 获取文件的服务器路径 String b = context.getRealPath("/b.txt");//web目录下资源访问 System.out.println(b); // File file = new File(realPath); String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问 System.out.println(c); String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问 System.out.println(a); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
* 文件下载需求: 1. 页面显示超链接 2. 点击超链接后弹出下载提示框 3. 完成图片文件下载
* 分析: 1. 超链接指向的资源如果能够被浏览器解析,则在浏览器中展示,如果不能解析,则弹出下载提示框。不满足需求 2. 任何资源都必须弹出下载提示框 3. 使用响应头设置资源的打开方式: * content-disposition:attachment;filename=xxx
Title 图片1 视频
图片1 视频
package cn.itcast.web.download;import cn.itcast.web.utils.DownLoadUtils;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.FileInputStream;import java.io.IOException;@WebServlet("/downloadServlet")public class DownloadServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1.获取请求参数,文件名称 String filename = request.getParameter("filename"); //2.使用字节输入流加载文件进内存 //2.1找到文件服务器路径 ServletContext servletContext = this.getServletContext(); String realPath = servletContext.getRealPath("/img/" + filename); //2.2用字节流关联 FileInputStream fis = new FileInputStream(realPath); //3.设置response的响应头 //3.1设置响应头类型:content-type String mimeType = servletContext.getMimeType(filename);//获取文件的mime类型 response.setHeader("content-type",mimeType); //3.2设置响应头打开方式:content-disposition //解决中文文件名问题 //1.获取user-agent请求头、 String agent = request.getHeader("user-agent"); //2.使用工具类方法编码文件名即可,工具类的定义在下面 filename = DownLoadUtils.getFileName(agent, filename); response.setHeader("content-disposition","attachment;filename="+filename); //4.将输入流的数据写出到输出流中 ServletOutputStream sos = response.getOutputStream(); byte[] buff = new byte[1024 * 8]; int len = 0; while((len = fis.read(buff)) != -1){ sos.write(buff,0,len); } fis.close(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); }}
import sun.misc.BASE64Encoder注意导入这个包在jdk8里面有效,高版本的jdk不适用
package cn.itcast.web.utils;import sun.misc.BASE64Encoder;import java.io.UnsupportedEncodingException;import java.net.URLEncoder;public class DownLoadUtils { public static String getFileName(String agent, String filename) throws UnsupportedEncodingException { if (agent.contains("MSIE")) { // IE浏览器 filename = URLEncoder.encode(filename, "utf-8"); filename = filename.replace("+", " "); } else if (agent.contains("Firefox")) { // 火狐浏览器 BASE64Encoder base64Encoder = new BASE64Encoder(); filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?="; } else { // 其它浏览器 filename = URLEncoder.encode(filename, "utf-8"); } return filename; }}
案例的结构
转载地址:http://xcvgi.baihongyu.com/