Overview of ttpServletRequest object
In the Servlet API, an HttpServletRequest interface is defined, which inherits from the ServletReauest interface and is specially used to encapsulate HTTP request messages. Since the HTTP request message is divided into three parts: request line, request header and request message body, the relevant methods to obtain the request line, request header and request message body are defined in the HttpServletRequest interface.
When creating a Servlet, we will override the service() method or doGet()/doPost(). These methods have two parameters, one is the request representing the request and the other is the response representing the response.
The type of request in the service method is ServletRequest, while the type of request in the doGet/doPost method is HttpServletRequest. HttpServletRequest is a sub interface of ServletRequest. Its functions and methods are more powerful. Today we learn HttpServletRequest.
Operation process of request

Grab HTTP requests through the packet capture tool

Obtain request line information through request
When accessing a Servlet, the request line of the request message contains information such as the request method, request resource name, request path, etc. in order to obtain these information, a series of methods for obtaining the request line are defined in the HTTPServletRequest interface, as shown in the following table:

Example:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        //Get information about the request line
        out.println("getMethod:" + request.getMethod() + "<br/>");
        out.println("getQueryString:" + request.getQueryString() + "<br/>");
        out.println("getProtocol:" + request.getProtocol() + "<br/>");
        out.println("getContextPath" + request.getContextPath() + "<br/>");
        out.println("getPathInfo:" + request.getPathInfo() + "<br/>");
        out.println("getPathTranslated:" + request.getPathTranslated() + "<br/>");
        out.println("getServletPath:" + request.getServletPath() + "<br/>");
        out.println("getRemoteAddr:" + request.getRemoteAddr() + "<br/>");
        out.println("getRemoteHost:" + request.getRemoteHost() + "<br/>");
        out.println("getRemotePort:" + request.getRemotePort() + "<br/>");
        out.println("getLocalAddr:" + request.getLocalAddr() + "<br/>");
        out.println("getLocalName:" + request.getLocalName() + "<br/>");
        out.println("getLocalPort:" + request.getLocalPort() + "<br/>");
        out.println("getServerName:" + request.getServerName() + "<br/>");
        out.println("getServerPort:" + request.getServerPort() + "<br/>");
        out.println("getScheme:" + request.getScheme() + "<br/>");
        out.println("getRequestURL:" + request.getRequestURL() + "<br/>");
    }

Accessed through the browser, the page displays:

Get the request header through request
When requesting a Servlet, you need to pass additional information to the server through the request header, such as the data type, compression mode, language, etc. that the client can receive. To this end, a series of methods for obtaining HTTP request header fields are defined in the HttpServletRequest interface, as shown in the following table:

Example:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        //Get request header information
        Enumeration headerNames = request.getHeaderNames();
        //Use the loop to traverse the request header and get a header field with the specified name through the getHeader() method
        while (headerNames.hasMoreElements()){
            String headerName = (String) headerNames.nextElement();
            out.println(headerName + " : " + request.getHeader(headerName) + "<br/>");
        }
    }

Accessed through the browser, the page displays:

Get the request body (request parameters) through request
In actual development, it is often necessary to obtain the form data submitted by the user, such as user name, password, e-mail, etc. in order to facilitate the acquisition of request parameters in the form, some columns of methods to obtain request parameters are defined in the HttpServletRequest interface, as shown in the following table:

Example:
Create a jsp page with a form:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>form </title>
</head>
<body>
    <form action="/JavaEEDemo/request" method="post">
        user name:<input type="text" name="username"><br/>
        dense&nbsp;&nbsp;code:<input type="password" name="password"><br/>
        love&nbsp;&nbsp;Good:
        <input type="checkbox" name="hobby" value="sing">sing
        <input type="checkbox" name="hobby" value="dance">dance
        <input type="checkbox" name="hobby" value="football">Football
        <input type="submit" value="Submit">

    </form>
</body>
</html>

Write the doPost method of the Servlet:

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        System.out.println("user name:" + username);
        System.out.println("password:" + password);

        //Gets the value of the parameter named hobby
        String[] hobbys = request.getParameterValues("hobby");
        System.out.println("Hobbies:");
        for (int i = 0; i < hobbys.length; i++) {
            System.out.println(hobbys[i] + ", ");
        }
    }

To access a jsp page through a browser:

I'm in bold
I'm Microsoft YaHei
I'm Chinese Caiyun
color=#0099ff size=72 face = "bold"
color=#00ffff
color=gray