<!doctype html>02 - JavaEE - Servlet&HTTP&Request

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Web开发-Servlet&HTTP&Request：

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1. Servlet

2. HTTP协议

3. Request

Servlet：

xxxxxxxxxx

1. 概念

2. 步骤

3. 执行原理

4. 生命周期

5. Servlet3.0 注解配置

6. Servlet的体系结构

Servlet -- 接口

GenericServlet -- 抽象类

HttpServlet  -- 抽象类

* GenericServlet：将Servlet接口中其他的方法做了默认空实现，只将service()方法作为抽象

* 将来定义Servlet类时，可以继承GenericServlet，实现service()方法即可

* HttpServlet：对http协议的一种封装，简化操作

1. 定义类继承HttpServlet

2. 复写doGet/doPost方法

7. Servlet相关配置

1. urlpartten:Servlet访问路径

1. 一个Servlet可以定义多个访问路径 ： @WebServlet({"/xxx","/xxxx","/xxxxx"})

2. 路径定义规则：

1. /xxx：路径匹配

2. /xxx/xxx:多层路径，目录结构

3. *.do：扩展名匹配

HTTP：

xxxxxxxxxx

* 概念：Hyper Text Transfer Protocol 超文本传输协议

* 传输协议：定义了，客户端和服务器端通信时，发送数据的格式

* 特点：

1. 基于TCP/IP的高级协议

2. 默认端口号:80

3. 基于请求/响应模型的:一次请求对应一次响应

4. 无状态的：每次请求之间相互独立，不能交互数据

* 历史版本：

* 1.0：每一次请求响应都会建立新的连接

* 1.1：复用连接

* 请求消息数据格式

1. 请求行

请求方式 请求url 请求协议/版本

GET /login.htmlHTTP/1.1

* 请求方式：

* HTTP协议有7中请求方式，常用的有2种

* GET：

1. 请求参数在请求行中，在url后。

2. 请求的url长度有限制的

3. 不太安全

* POST：

1. 请求参数在请求体中

2. 请求的url长度没有限制的

3. 相对安全

2. 请求头：客户端浏览器告诉服务器一些信息

请求头名称: 请求头值

* 常见的请求头：

1. User-Agent：浏览器告诉服务器，我访问你使用的浏览器版本信息

* 可以在服务器端获取该头的信息，解决浏览器的兼容性问题

2. Referer：http://localhost/login.html

* 告诉服务器，我(当前请求)从哪里来？

* 作用：

1. 防盗链：

2. 统计工作：

3. 请求空行

空行，就是用于分割POST请求的请求头，和请求体的。

4. 请求体(正文)：

* 封装POST请求消息的请求参数的

* 字符串格式：

POST /login.htmlHTTP/1.1

Host: localhost

User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:60.0) Gecko/20100101 Firefox/60.0

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2

Accept-Encoding: gzip, deflate

Referer: http://localhost/login.html

Connection: keep-alive

Upgrade-Insecure-Requests: 1

username=zhangsan

xxxxxxxxxx

* 响应消息数据格式

Request：

1. request对象和response对象的原理

1. request和response对象是由服务器创建的。我们来使用它们

2. request对象是来获取请求消息，response对象是来设置响应消息

2. request对象继承体系结构：

ServletRequest--接口

|继承

HttpServletRequest-- 接口

|实现

org.apache.catalina.connector.RequestFacade 类(tomcat)

3. request功能：

1. 获取请求消息数据

1. 获取请求行数据

* GET /test/demo1?name=zhangsan HTTP/1.1

* 方法：

1. 获取请求方式 ：GET

* String getMethod()

2. (*)获取虚拟目录：/test

* String getContextPath()

3. 获取Servlet路径: /demo1

* String getServletPath()

4. 获取get方式请求参数：name=zhangsan

* String getQueryString()

5. (*)获取请求URI：/test/demo1

* String getRequestURI():/test/demo1

* StringBuffer getRequestURL()  :http://localhost/test/demo1

* URL:统一资源定位符 ： http://localhost/test/demo1中华人民共和国

* URI：统一资源标识符 : /test/demo1共和国

6. 获取协议及版本：HTTP/1.1

* String getProtocol()

7. 获取客户机的IP地址：

* String getRemoteAddr()

2. 获取请求头数据

* 方法：

* (*)String getHeader(String name):通过请求头的名称获取请求头的值

* Enumeration<String> getHeaderNames():获取所有的请求头名称

3. 获取请求体数据:

* 请求体：只有POST请求方式，才有请求体，在请求体中封装了POST请求的请求参数

* 步骤：

1. 获取流对象

*  BufferedReader getReader()：获取字符输入流，只能操作字符数据

*  ServletInputStream getInputStream()：获取字节输入流，可以操作所有类型数据

* 在文件上传知识点后讲解

2. 再从流对象中拿数据

其他功能：
1. 获取请求参数通用方式：不论get还是post请求方式都可以使用下列方法来获取请求参数
  1. String getParameter(String name):根据参数名称获取参数值 username=zs&password=123
    1. String[] getParameterValues(String name):根据参数名称获取参数值的数组 hobby=xx&hobby=game
      1. Enumeration getParameterNames():获取所有请求的参数名称
      2. Map<String,String[]> getParameterMap():获取所有参数的map集合

* 中文乱码问题：

* get方式：tomcat 8 已经将get方式乱码问题解决了

* post方式：会乱码

* 解决：在获取参数前，设置request的编码request.setCharacterEncoding("utf-8");

请求转发：一种在服务器内部的资源跳转方式
1. 步骤：
  1. 通过request对象获取请求转发器对象：RequestDispatcher getRequestDispatcher(String path)
    1. 使用RequestDispatcher对象来进行转发：forward(ServletRequest request, ServletResponse response)

2. 特点：

1. 浏览器地址栏路径不发生变化

2. 只能转发到当前服务器内部资源中。

3. 转发是一次请求

3. 共享数据：

* 域对象：一个有作用范围的对象，可以在范围内共享数据

* request域：代表一次请求的范围，一般用于请求转发的多个资源中共享数据

* 方法：

1. void setAttribute(String name,Object obj):存储数据

2. Object getAttitude(String name):通过键获取值

3. void removeAttribute(String name):通过键移除键值对

4. 获取ServletContext：

* ServletContext getServletContext()