8web入门回顾/ Http

Posted 2020-08-17 梦之魂_JG

1 web入门回顾

 web入门

                     1）web服务软件作用: 把本地资源共享给外部访问

                     2）tomcat服务器基本操作      ：

                                          启动:  %tomcat%/bin/startup.bat

                                          关闭： %tomcat%/bin/shutdown.bat

 

                                          访问tomcat主页：

                                                               http://localhost:8080

                     3）web应用目录结构

                                          |- WebRoot   根目录

                                                     |-静态资源（html+css+javascript+images+xml）  可以直接被浏览器访问到的

                                                     |-WEB-INF                                  不可以直接被浏览器访问到

                                                               |-classes     存放class字节码文件

                                                               |-lib         存放jar包文件

                                                               web.xml      web应用的配置文件，配置servlet

                                         

                     4）Servlet技术： 用java语言开发动态资源的技术

                                          开发一个Servlet程序的步骤：

                                                               1）创建一个java类，继承HttpServlet类

                                                               2）重写HttpServlet类的doGet方法

                                                               3）把写好的servlet程序交给tomcat服务器运行！！！！

                                                                          3.1 把编译好的servlet的class文件拷贝到tomcat的一个web应用中。（web应用                                                                                                   的WEB-INF/classes目录下）                  
                                                                          3.2 在当前web应用的web.xml文件中配置servlet

                                                                                               <!-- servlet配置 -->

                                                                                               <servlet>

                                                                                                         <servlet-name>HelloServlet</servlet-name>

                                                                                                         <servlet-class>gz.itcast.HelloServlet</servlet-class>

                                                                                               </servlet>

                                                                                               <!--  servlet的映射配置 -->

                                                                                               <servlet-mapping>

                                                                                                         <servlet-name> HelloServlet </servlet-name>

                                                                                                          <url-pattern>/hello</url-pattern>

                                                                                               </servlet-mapping>

                                                               4）访问servlet

                                                                                    http://localhost:8080/myweb/hello

 

2 Http协议入门

                     2.1 什么是http协议

                                          http协议： 对浏览器客户端 和  服务器端 之间数据传输的格式规范

 

                     2.2 查看http协议的工具

                                          1）使用火狐的firebug插件（右键->firebug->网络）

                                          2）使用谷歌的“审查元素”

                                          3）使用系统自带的telnet工具（远程访问工具）                                        

                                                               a）telnet localhost 8080      访问tomcat服务器

                                                               b）ctrl+]     回车          可以看到回显

                                                               c）输入请求内容

                                                                         

GET /day09/hello HTTP/1.1 Host: localhost:8080

                                                               d）回车，即可查看到服务器响应信息。

 

                     2.3 http协议内容

                               

请求（浏览器-》服务器） GET /day09/hello HTTP/1.1 Host: localhost:8080 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: zh-cn,en-us;q=0.8,zh;q=0.5,en;q=0.3 Accept-Encoding: gzip, deflate Connection: keep-alive

 

          

响应（服务器-》浏览器） HTTP/1.1 200 OK Server: Apache-Coyote/1.1 Content-Length: 24 Date: Fri, 30 Jan 2015 01:54:57 GMT   this is hello servlet!!!

 

3 Http请求

GET /day09/hello HTTP/1.1               -请求行 Host: localhost:8080                    --请求头（多个key-value对象） User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: zh-cn,en-us;q=0.8,zh;q=0.5,en;q=0.3 Accept-Encoding: gzip, deflate Connection: keep-alive                                     --一个空行 name=eric&password=123456             --（可选）实体内容

 

              3.1 请求行

                                GET /day09/hello HTTP/1.1    

              #http协议版本

                     http1.0：当前浏览器客户端与服务器端建立连接之后，只能发送一次请求，一次请求之后连接关闭。

                     http1.1：当前浏览器客户端与服务器端建立连接之后，可以在一次连接中发送多次请求。（基本都使用1.1）

 

              #请求资源

                                          URL:  统一资源定位符。http://localhost:8080/day09/testImg.html。只能定位互联网资源。是URI                                                                  的子集。

                                          URI： 统一资源标记符。/day09/hello。用于标记任何资源。可以是本地文件系统，局域网的资源（//192.168.14.10/myweb/index.html），                                                             可以是互联网。

              #请求方式

                                常见的请求方式： GET 、 POST、 HEAD、 TRACE、 PUT、 CONNECT 、DELETE  

 

                                常用的请求方式： GET  和 POST         

 

                                表单提交：

                                          <form action="提交地址" method="GET/POST">      

 

                                          <form>

 

                                GET   vs  POST 区别

 

                                1）GET方式提交

                                                     a）地址栏（URI）会跟上参数数据。以？开头，多个参数之间以&分割。

GET /day09/testMethod.html?name=eric&password=123456 HTTP/1.1 Host: localhost:8080 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: zh-cn,en-us;q=0.8,zh;q=0.5,en;q=0.3 Accept-Encoding: gzip, deflate Referer: http://localhost:8080/day09/testMethod.html Connection: keep-alive

 

                                                     b）GET提交参数数据有限制，不超过1KB。

                                                     c）GET方式不适合提交敏感密码。

                                                     d）注意： 浏览器直接访问的请求，默认提交方式是GET方式

                                2）POST方式提交

                                          a）参数不会跟着URI后面。参数而是跟在请求的实体内容中。没有？开头，多个参数之间以&分割。

POST /day09/testMethod.html HTTP/1.1 Host: localhost:8080 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:35.0) Gecko/20100101 Firefox/35.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: zh-cn,en-us;q=0.8,zh;q=0.5,en;q=0.3 Accept-Encoding: gzip, deflate Referer: http://localhost:8080/day09/testMethod.html Connection: keep-alive   name=eric&password=123456

 

                                                     b）POST提交的参数数据没有限制。

                                                     c）POST方式提交敏感数据。

              3.2 请求头

Accept: text/html,image/*      -- 浏览器接受的数据类型 Accept-Charset: ISO-8859-1     -- 浏览器接受的编码格式 Accept-Encoding: gzip,compress  --浏览器接受的数据压缩格式 Accept-Language: en-us,zh-       --浏览器接受的语言 Host: www.it315.org:80          --（必须的）当前请求访问的目标地址（主机:端口） If-Modified-Since: Tue, 11 Jul 2000 18:23:51 GMT  --浏览器最后的缓存时间 Referer: http://www.it315.org/index.jsp      -- 当前请求来自于哪里 User-Agent: Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0)  --浏览器类型 Cookie:name=eric                     -- 浏览器保存的cookie信息 Connection: close/Keep-Alive            -- 浏览器跟服务器连接状态。close: 连接关闭  keep-alive：保存连接。 Date: Tue, 11 Jul 2000 18:23:51 GMT      -- 请求发出的时间

 

              3.3 实体内容

                                          只有POST提交的参数会放到实体内容中

 

              3.4 HttpServletRequest对象

                                HttpServletRequest对象作用是用于获取请求数据。

 

                                             核心的API：

                                                     请求行：

                                                               request.getMethod();   请求方式

                                                               request.getRequetURI()   / request.getRequetURL()   请求资源

                                                               request.getProtocol()   请求http协议版本

                                                    

                                                     请求头：

                                                               request.getHeader("名称")   根据请求头获取请求值

                                                               request.getHeaderNames()    获取所有的请求头名称

 

                                                     实体内容:

                                                               request.getInputStream()   获取实体内容数据

              3.5 service 和 doXX方法区别

HttpSevlet类的源码： protected void service(HttpServletRequest req, HttpServletResponse resp)         throws ServletException, IOException {        //得到请求方式         String method = req.getMethod();           if (method.equals(METHOD_GET)) {             long lastModified = getLastModified(req);             if (lastModified == -1) {                 // servlet doesn‘t support if-modified-since, no reason                 // to go through further expensive logic                 doGet(req, resp);             } else {                 long ifModifiedSince;                 try {                     ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);                 } catch (IllegalArgumentException iae) {                     // Invalid date header - proceed as if none was set                     ifModifiedSince = -1;                 }                 if (ifModifiedSince < (lastModified / 1000 * 1000)) {                     // If the servlet mod time is later, call doGet()                     // Round down to the nearest second for a proper compare                     // A ifModifiedSince of -1 will always be less                     maybeSetLastModified(resp, lastModified);                     doGet(req, resp);                 } else {                     resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);                 }             }           } else if (method.equals(METHOD_HEAD)) {             long lastModified = getLastModified(req);             maybeSetLastModified(resp, lastModified);             doHead(req, resp);           } else if (method.equals(METHOD_POST)) {             doPost(req, resp);                     } else if (method.equals(METHOD_PUT)) {             doPut(req, resp);                            } else if (method.equals(METHOD_DELETE)) {             doDelete(req, resp);                     } else if (method.equals(METHOD_OPTIONS)) {             doOptions(req,resp);                     } else if (method.equals(METHOD_TRACE)) {             doTrace(req,resp);                     } else {             //             // Note that this means NO servlet supports whatever             // method was requested, anywhere on this server.             //               String errMsg = lStrings.getString("http.method_not_implemented");             Object[] errArgs = new Object[1];             errArgs[0] = method;             errMsg = MessageFormat.format(errMsg, errArgs);                         resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);         }     }

 

              3.6 案例-获取浏览器的类型（user-agent）

              3.7 案例- 防止非法链接(referer)

第1次        CSDN/51CTO    ->   页面(点击下载)   -> 弹出广告页面（点击此处下载） -> 开始下载 

第2次         直接点击此处下载  ->  转回广告页面  ->  开始下载

 

                                          非法链接：                                                                     

                                                               1）直接访问下载的资源

                                                               2）不是从广告页面过来的链接

 

                                          referer： 当前请求来自于哪里。

              3.8 传递的请求参数如何获取       

                                 GET方式： 参数放在URI后面

                                 POST方式： 参数放在实体内容中

 

                                获取GET方式参数：

                                                     request.getQueryString();

                                获取POST方式参数：

                                                     request.getInputStream();

 

                                问题：但是以上两种不通用，而且获取到的参数还需要进一步地解析。

                                所以可以使用统一方便的获取参数的方式：

                                         

                                         核心的API：

                                          request.getParameter("参数名");  根据参数名获取参数值（注意，只能获取一个值的参数）

                                          request.getParameterValue("参数名“)；根据参数名获取参数值（可以获取多个值的参数）

 

                                          request.getParameterNames();   获取所有参数名称列表  

              3.9 请求参数编码问题

                                          修改POST方式参数编码：

                                                               request.setCharacterEncoding("utf-8");

                                          修改GET方式参数编码：

                                                               手动解码：String name = new String(name.getBytes("iso-8859-1"),"utf-8");

4 Http响应

HTTP/1.1 200 OK                --响应行 Server: Apache-Coyote/1.1         --响应头（key-vaule） Content-Length: 24 Date: Fri, 30 Jan 2015 01:54:57 GMT                                    --一个空行 this is hello servlet!!!                  --实体内容

 

                     4.1 响应行

                   #http协议版本

                      #状态码: 服务器处理请求的结果（状态）

                                                     常见的状态：

                                                               200 ：  表示请求处理完成并完美返回

                                                               302：   表示请求需要进一步细化。
                                                               404：   表示客户访问的资源找不到。

                                                               500：   表示服务器的资源发送错误。（服务器内部错误）

                     #状态描述        

      4.2 常见的响应头

Location: http://www.it315.org/index.jsp   -表示重定向的地址，该头和302的状态码一起使用。 Server:apache tomcat                 ---表示服务器的类型 Content-Encoding: gzip                 -- 表示服务器发送给浏览器的数据压缩类型 Content-Length: 80                    --表示服务器发送给浏览器的数据长度 Content-Language: zh-cn               --表示服务器支持的语言 Content-Type: text/html; charset=GB2312   --表示服务器发送给浏览器的数据类型及内容编码 Last-Modified: Tue, 11 Jul 2000 18:23:51 GMT  --表示服务器资源的最后修改时间 Refresh: 1;url=http://www.it315.org     --表示定时刷新 Content-Disposition: attachment; filename=aaa.zip --表示告诉浏览器以下载方式打开资源（下载文件时用到） Transfer-Encoding: chunked Set-Cookie:SS=Q0=5Lb_nQ; path=/search   --表示服务器发送给浏览器的cookie信息（会话管理用到） Expires: -1                           --表示通知浏览器不进行缓存 Cache-Control: no-cache Pragma: no-cache Connection: close/Keep-Alive           --表示服务器和浏览器的连接状态。close：关闭连接 keep-alive:保存连接

 

                     4.3 HttpServletResponse对象

                                HttpServletResponse对象修改响应信息：

 

                                                     响应行：

                                                                          response.setStatus()  设置状态码

                                                     响应头：

                                                                          response.setHeader("name","value")  设置响应头

                                                     实体内容：

                                                                          response.getWriter().writer();   发送字符实体内容

                                                                          response.getOutputStream().writer()  发送字节实体内容

 

                     4.4 案例- 请求重定向（Location）

                     4.5 案例- 定时刷新(refresh)

                     4.6 案例-content-Type作用

 

                     总结：

                                          http协议： 浏览器和服务器之间数据传输的格式规范

 

                                          1）http请求：

                                                               格式：

                                                                                    请求行

                                                                                    请求头

                                                                                    空行

                                                                                    实体内容（POST提交的数据在实体内容中）

                                                               重点：

                                                                          使用HttpServletRequest对象： 获取请求数据

 

                                2）http响应;

                                                     格式：

                                                                          响应行

                                                                          响应头

                                                                          空行

                                                                          实体内容（浏览器看到的内容）

                                                     重点：

                                                                使用HttpServletResponse对象： 设置响应数据