How to use HttpServletRequest in Java?

In Java, you can retrieve information about an HTTP request using the HttpServletRequest object.

Firstly, make sure to import the HttpServletRequest class in your code.

import javax.servlet.http.HttpServletRequest;

Then, in the `doGet()` or `doPost()` method of the Servlet, you can use the `HttpServletRequest` object to obtain information about the request, such as the request method, request URL, request parameters, and so on. Here are some examples of commonly used methods:

protected void doGet(HttpServletRequest request, HttpServletResponse response) {
    // 获取请求方法
    String method = request.getMethod();
    System.out.println("请求方法：" + method);
    
    // 获取请求URL
    String url = request.getRequestURL().toString();
    System.out.println("请求URL：" + url);
    
    // 获取请求参数
    String paramValue = request.getParameter("paramName");
    System.out.println("请求参数值：" + paramValue);
    
    // 获取请求头信息
    String userAgent = request.getHeader("User-Agent");
    System.out.println("User-Agent：" + userAgent);
    
    // 获取请求的IP地址
    String ipAddress = request.getRemoteAddr();
    System.out.println("请求IP地址：" + ipAddress);
    
    // 获取Session对象
    HttpSession session = request.getSession();
}

These methods are just a part of the HttpServletRequest class, you can use other methods as needed to obtain more request information.

Before using the HttpServletRequest object, make sure you have created a Servlet class and overridden the doGet() or doPost() method.