HttpServletRequest深度解析：Java Web开发的核心组件

引言

在Java Web开发中，HttpServletRequest是处理HTTP请求的核心接口。它封装了客户端发送给服务器的所有请求信息，是Servlet API中最重要的组件之一。无论您是初学者还是有经验的开发者，深入理解HttpServletRequest都是构建健壮Web应用的基础。

什么是HttpServletRequest？

HttpServletRequest是javax.servlet.http包中的一个接口，它继承自ServletRequest接口。当客户端（通常是浏览器）向服务器发送HTTP请求时，Web容器（如Tomcat、Jetty等）会创建一个HttpServletRequest对象，将所有请求信息封装在其中。

核心特性

• 封装HTTP请求的所有信息（请求行、请求头、请求体）
• 提供访问请求参数、属性和会话的方法
• 支持国际化和本地化
• 提供安全相关的方法
• 线程安全（每个请求都有独立的实例）

HttpServletRequest的主要功能

1. 请求基本信息获取

@WebServlet("/info")
public class RequestInfoServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 获取请求方法
        String method = request.getMethod();
        
        // 获取请求URI和URL
        String requestURI = request.getRequestURI();
        StringBuffer requestURL = request.getRequestURL();
        
        // 获取协议信息
        String protocol = request.getProtocol();
        String scheme = request.getScheme();
        
        // 获取服务器信息
        String serverName = request.getServerName();
        int serverPort = request.getServerPort();
        
        // 获取客户端信息
        String remoteAddr = request.getRemoteAddr();
        String remoteHost = request.getRemoteHost();
        
        // 构造响应
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("<h2>请求信息详情</h2>");
        out.println("<p>请求方法: " + method + "</p>");
        out.println("<p>请求URI: " + requestURI + "</p>");
        out.println("<p>请求URL: " + requestURL + "</p>");
        out.println("<p>协议: " + protocol + "</p>");
        out.println("<p>客户端地址: " + remoteAddr + "</p>");
    }
}

2. 请求参数处理

HttpServletRequest提供了多种方式来获取请求参数：

@WebServlet("/params")
public class ParameterServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 设置请求编码，防止中文乱码
        request.setCharacterEncoding("UTF-8");
        
        // 获取单个参数
        String username = request.getParameter("username");
        String age = request.getParameter("age");
        
        // 获取多值参数（如复选框）
        String[] hobbies = request.getParameterValues("hobbies");
        
        // 获取所有参数名
        Enumeration<String> paramNames = request.getParameterNames();
        
        // 获取参数映射
        Map<String, String[]> paramMap = request.getParameterMap();
        
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        
        out.println("<h2>参数处理结果</h2>");
        out.println("<p>用户名: " + username + "</p>");
        out.println("<p>年龄: " + age + "</p>");
        
        if (hobbies != null) {
            out.println("<p>爱好: " + String.join(", ", hobbies) + "</p>");
        }
        
        // 遍历所有参数
        out.println("<h3>所有参数:</h3>");
        for (Map.Entry<String, String[]> entry : paramMap.entrySet()) {
            out.println("<p>" + entry.getKey() + ": " + 
                       Arrays.toString(entry.getValue()) + "</p>");
        }
    }
}

3. 请求头操作

@WebServlet("/headers")
public class HeaderServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 获取特定请求头
        String userAgent = request.getHeader("User-Agent");
        String accept = request.getHeader("Accept");
        String host = request.getHeader("Host");
        
        // 获取所有请求头名称
        Enumeration<String> headerNames = request.getHeaderNames();
        
        // 获取多值请求头
        Enumeration<String> acceptEncodings = request.getHeaders("Accept-Encoding");
        
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        
        out.println("<h2>请求头信息</h2>");
        out.println("<p>User-Agent: " + userAgent + "</p>");
        out.println("<p>Accept: " + accept + "</p>");
        out.println("<p>Host: " + host + "</p>");
        
        out.println("<h3>所有请求头:</h3>");
        while (headerNames.hasMoreElements()) {
            String headerName = headerNames.nextElement();
            String headerValue = request.getHeader(headerName);
            out.println("<p>" + headerName + ": " + headerValue + "</p>");
        }
    }
}

4. 会话管理

@WebServlet("/session")
public class SessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 获取当前会话，如果不存在则创建新会话
        HttpSession session = request.getSession();
        
        // 获取会话，但不创建新会话
        HttpSession existingSession = request.getSession(false);
        
        // 会话操作
        String sessionId = session.getId();
        long creationTime = session.getCreationTime();
        long lastAccessedTime = session.getLastAccessedTime();
        int maxInactiveInterval = session.getMaxInactiveInterval();
        
        // 存储和获取会话属性
        Integer visitCount = (Integer) session.getAttribute("visitCount");
        if (visitCount == null) {
            visitCount = 0;
        }
        visitCount++;
        session.setAttribute("visitCount", visitCount);
        
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        
        out.println("<h2>会话信息</h2>");
        out.println("<p>会话ID: " + sessionId + "</p>");
        out.println("<p>创建时间: " + new Date(creationTime) + "</p>");
        out.println("<p>最后访问时间: " + new Date(lastAccessedTime) + "</p>");
        out.println("<p>访问次数: " + visitCount + "</p>");
    }
}

5. 请求属性管理

@WebServlet("/attributes")
public class AttributeServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 设置请求属性
        request.setAttribute("currentTime", new Date());
        request.setAttribute("userRole", "admin");
        
        // 获取请求属性
        Date currentTime = (Date) request.getAttribute("currentTime");
        String userRole = (String) request.getAttribute("userRole");
        
        // 获取所有属性名
        Enumeration<String> attributeNames = request.getAttributeNames();
        
        // 移除属性
        // request.removeAttribute("userRole");
        
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        
        out.println("<h2>请求属性</h2>");
        out.println("<p>当前时间: " + currentTime + "</p>");
        out.println("<p>用户角色: " + userRole + "</p>");
        
        out.println("<h3>所有属性:</h3>");
        while (attributeNames.hasMoreElements()) {
            String attrName = attributeNames.nextElement();
            Object attrValue = request.getAttribute(attrName);
            out.println("<p>" + attrName + ": " + attrValue + "</p>");
        }
    }
}

高级特性和实践

1. 请求转发和包含

@WebServlet("/forward")
public class ForwardServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 设置转发数据
        request.setAttribute("message", "这是转发的数据");
        
        // 请求转发
        RequestDispatcher dispatcher = request.getRequestDispatcher("/target");
        dispatcher.forward(request, response);
        
        // 或者包含其他资源
        // dispatcher.include(request, response);
    }
}

2. 文件上传处理

@WebServlet("/upload")
@MultipartConfig(
    maxFileSize = 1024 * 1024 * 10,      // 10MB
    maxRequestSize = 1024 * 1024 * 50,   // 50MB
    fileSizeThreshold = 1024 * 1024       // 1MB
)
public class FileUploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 获取上传的文件
        Part filePart = request.getPart("file");
        
        if (filePart != null) {
            String fileName = getFileName(filePart);
            String uploadPath = getServletContext().getRealPath("/uploads");
            
            // 确保上传目录存在
            File uploadDir = new File(uploadPath);
            if (!uploadDir.exists()) {
                uploadDir.mkdirs();
            }
            
            // 保存文件
            String filePath = uploadPath + File.separator + fileName;
            filePart.write(filePath);
            
            response.getWriter().println("文件上传成功: " + fileName);
        }
    }
    
    private String getFileName(Part part) {
        String contentDisposition = part.getHeader("content-disposition");
        String[] tokens = contentDisposition.split(";");
        for (String token : tokens) {
            if (token.trim().startsWith("filename")) {
                return token.substring(token.indexOf('=') + 2, token.length() - 1);
            }
        }
        return "";
    }
}

3. 安全性考虑

@WebServlet("/secure")
public class SecurityServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        // 检查是否为HTTPS连接
        boolean isSecure = request.isSecure();
        
        // 获取认证信息
        String authType = request.getAuthType();
        String remoteUser = request.getRemoteUser();
        Principal userPrincipal = request.getUserPrincipal();
        
        // 角色检查
        boolean isAdmin = request.isUserInRole("admin");
        boolean isUser = request.isUserInRole("user");
        
        // 输入验证和清理
        String userInput = request.getParameter("input");
        if (userInput != null) {
            // 防止XSS攻击
            userInput = escapeHtml(userInput);
        }
        
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        
        out.println("<h2>安全信息</h2>");
        out.println("<p>安全连接: " + isSecure + "</p>");
        out.println("<p>认证类型: " + authType + "</p>");
        out.println("<p>远程用户: " + remoteUser + "</p>");
        out.println("<p>是否为管理员: " + isAdmin + "</p>");
    }
    
    private String escapeHtml(String input) {
        return input.replace("&", "&amp;")
                   .replace("<", "&lt;")
                   .replace(">", "&gt;")
                   .replace("\"", "&quot;")
                   .replace("'", "&#x27;");
    }
}

常见问题和解决方案

1. 中文乱码问题

// 在Servlet开始处理之前设置编码
request.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");

// 或者使用过滤器统一处理
@WebFilter("/*")
public class EncodingFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
                        FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        chain.doFilter(request, response);
    }
}

2. 获取真实IP地址

public String getRealIpAddress(HttpServletRequest request) {
    String ip = request.getHeader("X-Forwarded-For");
    
    if (ip == null || ip.isEmpty() || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getHeader("Proxy-Client-IP");
    }
    if (ip == null || ip.isEmpty() || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getHeader("WL-Proxy-Client-IP");
    }
    if (ip == null || ip.isEmpty() || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getHeader("HTTP_CLIENT_IP");
    }
    if (ip == null || ip.isEmpty() || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getHeader("HTTP_X_FORWARDED_FOR");
    }
    if (ip == null || ip.isEmpty() || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getRemoteAddr();
    }
    
    return ip;
}

3. 参数验证工具类

public class RequestValidator {
    
    public static boolean isValidEmail(String email) {
        String emailRegex = "^[A-Za-z0-9+_.-]+@(.+)$";
        Pattern pattern = Pattern.compile(emailRegex);
        return email != null && pattern.matcher(email).matches();
    }
    
    public static boolean isValidPhoneNumber(String phone) {
        String phoneRegex = "^[1][3-9]\\d{9}$";
        Pattern pattern = Pattern.compile(phoneRegex);
        return phone != null && pattern.matcher(phone).matches();
    }
    
    public static String sanitizeInput(String input) {
        if (input == null) return null;
        
        return input.trim()
                   .replaceAll("<script[^>]*>.*?</script>", "")
                   .replaceAll("<[^>]+>", "");
    }
    
    public static Integer parseIntParameter(HttpServletRequest request, 
                                          String paramName, Integer defaultValue) {
        String paramValue = request.getParameter(paramName);
        if (paramValue == null || paramValue.trim().isEmpty()) {
            return defaultValue;
        }
        
        try {
            return Integer.parseInt(paramValue.trim());
        } catch (NumberFormatException e) {
            return defaultValue;
        }
    }
}

性能优化建议

1. 减少对象创建

// 避免在循环中创建不必要的对象
Map<String, String[]> paramMap = request.getParameterMap();
StringBuilder result = new StringBuilder();

for (Map.Entry<String, String[]> entry : paramMap.entrySet()) {
    result.append(entry.getKey()).append("=")
          .append(Arrays.toString(entry.getValue())).append("\n");
}

2. 合理使用请求属性

// 将计算结果存储在请求属性中，避免重复计算
String expensiveResult = (String) request.getAttribute("expensiveResult");
if (expensiveResult == null) {
    expensiveResult = performExpensiveOperation();
    request.setAttribute("expensiveResult", expensiveResult);
}

与Spring框架的集成

在Spring MVC中，HttpServletRequest的使用更加便捷：

@Controller
@RequestMapping("/spring")
public class SpringController {
    
    @RequestMapping("/info")
    public String getRequestInfo(HttpServletRequest request, Model model) {
        // 直接注入HttpServletRequest
        String userAgent = request.getHeader("User-Agent");
        model.addAttribute("userAgent", userAgent);
        return "info";
    }
    
    @RequestMapping("/param")
    @ResponseBody
    public Map<String, Object> handleParameters(
            @RequestParam String name,
            @RequestParam(defaultValue = "0") int age,
            HttpServletRequest request) {
        
        Map<String, Object> result = new HashMap<>();
        result.put("name", name);
        result.put("age", age);
        result.put("remoteAddr", request.getRemoteAddr());
        
        return result;
    }
}

参考资源

• Oracle Java EE API文档
• Apache Tomcat官方文档
• Spring Framework官方文档