笔记 - http协议

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Http协议入门

                     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 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。

 

                     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!!!

 

一、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

 

              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(安全)

                                     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。

              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 实体内容

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

 

              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

             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);

        }

    }

 

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

              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。

             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  

              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");

二、 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

 

       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        

      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

 

      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 案例- 请求重定向(Location)

      5 案例- 定时刷新(refresh)

      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

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