HTTP

概念

HTTP协议（HyperText Transfer Protocol，超文本传输协议）是因特网上应用最为广泛的一种网络传输协议，所有的WWW文件都必须遵守这个标准

传输协议：定义了客户端和服务端通信时，发送数据的格式

HTTP是一个基于TCP/IP通信协议来传递数据

HTTP的默认端口为80

基于请求/响应模型：一次请求对应一次响应

HTTP是一种无状态协议，每次请求之间相互独立，无法交互数据

请求消息数据格式

请求行

请求方式 请求URL 请求协议/版本

○ 请求方式

HTTP标准有9种请求方式

GET与POST请求的区别

GET：请求参数在==请求行==中（拼接在URL之后），请求的URL长度有限制

POST：请求参数在==请求体==中，请求的URL长度没有限制

请求头

请求头名称：请求头值

○ 常见的请求头

1. User-Agent：访问服务器使用的浏览器版本信息，可获取该头信息来解决浏览器兼容问题
2. Accept：浏览器可接收的文件类型
3. Accept-Language：浏览器可接收的语言
4. Accept-Encoding：浏览器可支持的编码类型
5. Referer：告知服务器请求的来源URL，可用来做统计工作和防止盗链

请求空行

空行，分隔请求头和请求体

请求体

封装POST请求消息的请求参数

Request

继承体系结构

功能

获取请求消息数据

(1). 获取请求行数据

@WebServlet("/requestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取请求方式
        String method = request.getMethod();
        System.out.println(method);
        // 获取虚拟目录
        String contextPath = request.getContextPath();
        System.out.println(contextPath);
        // 获取Servlet路径
        String servletPath = request.getServletPath();
        System.out.println(servletPath);
        // 获取get请求方式参数
        String queryString = request.getQueryString();
        System.out.println(queryString);
        // 获取请求URI
        String requestURI = request.getRequestURI();
        StringBuffer requestURL = request.getRequestURL();
        System.out.println(requestURI);
        System.out.println(requestURL);
        // 获取协议及版本
        String protocol = request.getProtocol();
        System.out.println(protocol);
        // 获取客户机IP地址
        String remoteAddr = request.getRemoteAddr();
        System.out.println(remoteAddr);
    }
}

(2). 获取请求头数据

@WebServlet("/requestDemo")
public class requestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取所有请求头名称
        Enumeration<String> headerNames = request.getHeaderNames();
        // 遍历
        while (headerNames.hasMoreElements()){
            String name = headerNames.nextElement();
            // 获取请求头的值
            String value = request.getHeader(name);
            System.out.println(name + "===" + value);
        }
    }
}

(3). 获取请求体数据

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

@WebServlet("/RequestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取字符流
        BufferedReader reader = request.getReader();
        // 读取数据
        String line = null;
        while ((line = reader.readLine()) != null){
            System.out.println(line);
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

获取请求参数通用方式

无论是get还是post请求方式都可以使用以下方法获取请求参数，由于方式通用，所以不必在doGet和doPost中重复写相同的代码

 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    	// 通用方式代码
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		this.doPost(request,response);
    }

方法

① String getParameter(String name)：根据参数名称获取参数值

String name = request.getParameter("name");
System.out.println(name);

② String[] getParameterValues(String name)：根据参数名称获取参数值的数组

String[] checks = request.getParameterValues("check");
for (String check : checks) {
	System.out.println(check);
}

③ Enumeration< String > getParameterNames()：获取所有的请求参数名称

Enumeration<String> parameterNames = request.getParameterNames();
while (parameterNames.hasMoreElements()){
	String s = parameterNames.nextElement();
	System.out.println(s);
}

④ Map< String,String[] > getParameterMap()：获取所有参数的Map集合

Map<String, String[]> parameterMap = request.getParameterMap();
Set<String> keySet = parameterMap.keySet();
for (String key : keySet) {
	// 根据key获取value
	String[] values = parameterMap.get(key);
	for (String v : values) {
	System.out.println(v);
	}
}

完整代码

@WebServlet("/RequestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("post");
        System.out.println("------------");

        // 根据参数名获取参数值
        String name = request.getParameter("name");
        System.out.println(name);

        // 根据参数名获取多选参数值
        String[] checks = request.getParameterValues("check");
        for (String check : checks) {
            System.out.println(check);
        }

        // 获取所有请求的参数名称
        Enumeration<String> parameterNames = request.getParameterNames();
        while (parameterNames.hasMoreElements()){
            String s = parameterNames.nextElement();
            System.out.println(s);
        }

        // 获取所有参数的Map集合
        Map<String, String[]> parameterMap = request.getParameterMap();
        Set<String> keySet = parameterMap.keySet();
        for (String key : keySet) {
            // 根据key获取value
            String[] values = parameterMap.get(key);
            for (String v : values) {
                System.out.println(v);
            }
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("get");
        System.out.println("------------");
        this.doPost(request,response);
    }
}

获取请求参数中的中文乱码问题

tomcat8 已经解决了get方式的中文乱码问题，但post方式仍会出现乱码问题

可以通过setCharacterEncoding()方法在==获取参数之前==将Request编码更改为 utf-8

request.setCharacterEncoding("utf-8");

请求转发

一种在服务器内部的资源跳转方式

请求转发步骤

1. 通过Request对象获取请求转发器对象

RequestDispatcher getRequestDispatcher(String path)

2. 使用RequestDispatcher对象的forward()方法来进行转发

void forward(ServletRequest request, ServletResponse response)

示例

demo4代码

@WebServlet("/RequestDemo4")
public class RequestDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("this is demo 4");
        // 转发到demo5
        request.getRequestDispatcher("RequestDemo5").forward(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

demo5代码

@WebServlet("/RequestDemo5")
public class RequestDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("this is demo 5");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

访问RequestDemo4控制台输出为

this is demo 4
this is demo 5

请求转发特点

1. 浏览器地址栏路径不会发生变化
2. 只能转发到当前服务器内部资源中，不能转发到外部资源
3. 转发是一次请求

共享数据

域对象

一个具有作用范围的对象，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

demo4代码

@WebServlet("/RequestDemo4")
public class RequestDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("this is demo 4");
        // 存储数据到Request域中
        request.setAttribute("name","name1");
        // 转发到demo5
        request.getRequestDispatcher("RequestDemo5").forward(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

demo5代码

@WebServlet("/RequestDemo5")
public class RequestDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取并输出Request域中的数据
        Object name = request.getAttribute("name");
        System.out.println(name);
        System.out.println("this is demo 5");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

访问RequestDemo4后控制台输出

this is demo 4
name1
this is demo 5

获取ServletContext

○ ServletContext getServletContext()

@WebServlet("/RequestDemo")
public class RequestDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = request.getServletContext();
        System.out.println(servletContext);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

输出结果

org.apache.catalina.core.ApplicationContextFacade@158ac881