404错误页面

构建一个404错误页面的指南

在开发Web应用程序时，经常会遇到用户请求的页面不存在的情况，为了提供更好的用户体验，我们需要为这些不存在的页面创建一个友好的404错误页面，本文将介绍如何使用PHP、Java和C++等编程语言来构建一个404错误页面。

1. PHP 404错误页面

对于PHP应用程序，我们可以在index.php文件中添加以下代码来自定义404错误页面：

<?php
// 设置正确的MIME类型
header("Content-Type: text/html; charset=UTF-8");
// 获取请求的URL
$request_uri = $_SERVER["REQUEST_URI"];
// 自定义404错误页面的路径
$error_page = "404.php";
// 如果请求的URL是"/",则重定向到首页
if ($request_uri == "/") {
    header("Location: index.php");
} else {
    // 否则，检查是否存在对应的文件
    if (file_exists($error_page)) {
        // 如果存在，读取并输出文件内容
        include $error_page;
    } else {
        // 否则，显示默认的404错误页面
        echo "<h1>404 Not Found</h1>";
        echo "<p>The requested URL was not found on this server.</p>";
    }
?&gt;</pre><p>2. Java 404错误页面</p><p>对于Java Web应用程序，我们可以在<code>web.xml</code>文件中配置一个Servlet来处理404错误：</p><pre class="brush:xml;toolbar:false">
&lt;servlet&gt;
    &lt;servlet-name&gt;ErrorPageServlet&lt;/servlet-name&gt;
    &lt;servlet-class&gt;com.example.ErrorPageServlet&lt;/servlet-class&gt;
&lt;/servlet&gt;
&lt;servlet-mapping&gt;
    &lt;servlet-name&gt;ErrorPageServlet&lt;/servlet-name&gt;
    &lt;url-pattern&gt;/error/404&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;</pre><p>在<code>ErrorPageServlet</code>类中处理404错误：</p><pre class="brush:java;toolbar:false">
package com.example;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ErrorPageServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String errorCode = request.getParameter("errorCode");
        if (errorCode != null && errorCode.equals("404")) {
            response.setContentType("text/html; charset=UTF-8");
            response.getWriter().println("<h1>404 Not Found</h1>");
            response.getWriter().println("<p>The requested URL was not found on this server.</p>");
        } else {
            // 其他错误处理逻辑
        }
    }
}</pre><p>3. C++ 404错误页面</p><p>对于C++ Web应用程序，我们可以使用C++标准库中的<code>&lt;cstdlib&gt;</code>头文件中的<code>system()</code>函数来调用Shell命令生成自定义的404错误页面。</p><pre class="brush:cpp;toolbar:false">
#include &lt;iostream&gt;
#include &lt;cstdlib&gt; // for system() function and other C standard library functions
#include &lt;string&gt; // for string manipulation functions like find_last_of() and substr()
#include &lt;fstream&gt; // for file input/output operations using ifstream and ofstream classes
#include &lt;sstream&gt; // for string stream operations like istringstream and ostringstream classes
#include &lt;algorithm&gt; // for find_last_of() function used to extract the file extension from the URL path and replace it with ".html" to generate the HTML content of the error page dynamically at runtime. Also used to convert the generated HTML content to a string using a string stream object and store it in a char array variable called "htmlContent" for further processing by the web server or browser. The "contentType" variable is used to set the HTTP Content-Type header field of the HTTP response message sent by the web server or browser to indicate that the response contains an HTML document. The "statusCode" variable is used to set the HTTP status code of the HTTP response message sent by the web server or browser to indicate that an error occurred (e.g., a "404 Not Found" error). The "reasonPhrase" variable is used to set the reason phrase that will be displayed in the HTTP response message sent by the web server or browser to provide additional information about the error that occurred (e.g., "The requested URL was not found on this server"). The "body" variable is used to store the generated HTML content of the error page as a string for further processing by the web server or browser.</pre>