Dynamic Web Project GET表单创建对象及404错误排查方案

表单提交时触发HTTP 404错误，需要实现表单参数接收、TextLog日志实例创建功能，后续还要扩展日志列表展示、数据库持久化能力。

前端表单 #

<html lang="en">
    <head>
        <title>Example</title>
    </head>
    <body>
        <h1>Welcome to Loggy!</h1>
        
        <form id="logForm" action="LogsServlet" method="GET">
        <h3>What have you been up to today?</h3>
        <br>
        <label id="logTitleLabel" for="logTitle">Title :</label>
        <br>
        <input type="text" id="logTitle" name="logTitle">
        <br>
        <label id="logDescriptionLabel" for="LogDescription">Description</label>
        <br>
        <input type="text" id="logDescription" name="logDescription">
        <label id="logContentLabel" for="logContent">Content :</label>
        <br>
        <input type="text" id="logContent" name="logContent">
        <button type="submit" id="submitLog">Submit Log</button>
        
        </form>
    </body>
</html>

实体类代码 #

import java.sql.Timestamp;
import java.util.Date;
import java.util.UUID;

public abstract class Log {
    private UUID id;
    private String title;
    private String description;
    private String content;
    private Timestamp createTimestamp;
    
    
    //Constructor 
    Log(String title,String description, String content){
        this.setTitle(title);
        this.description=description;
        this.content=content;
    };
    

    public void create() {
        //call UUID method
        id();
        //create new timeStamp
        Date date= new Date();
        Timestamp createTimestamp = new Timestamp(date.getTime());
        this.createTimestamp=createTimestamp;
    }
    
    public UUID id() {
        UUID uuid = UUID.randomUUID();
        id = uuid;  
        return id;
    }

    
    //GETTERS AND SETTERS
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
       public UUID getId() {
            return id;
        }

        public void setId(UUID id) {
            this.id = id;
        }

        public String getDescription() {
            return description;
        }

        public void setDescription(String description) {
            this.description = description;
        }

        public String getContent() {
            return content;
        }

        public void setContent(String content) {
            this.content = content;
        }

        public Timestamp getCreateTimestamp() {
            return createTimestamp;
        }

        public void setCreateTimestamp(Timestamp createTimestamp) {
            this.createTimestamp = createTimestamp;
        }

  
}

public class TextLog extends Log {

    public TextLog(String title,String description, String content) {
        super(title,description, content);
        
    }

}

Servlet代码 #

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;



/**
 * Servlet implementation class LogsServlet
 */
//@WebServlet(description = "Loggy Logs", urlPatterns = { "/LogsServlet" })
public class LogsServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public LogsServlet() {
        super();
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //set content type
       response.setContentType("text/html");
       //get print writer
       PrintWriter writer = response.getWriter();
       //generate content
       
       request.getParameter("logTitle");
       request.getParameter("logDescription");
       request.getParameter("logContent");
       
      
    }
}

1. 解决404错误 #

404的直接原因是Servlet没有完成请求映射：代码里的@WebServlet注解被注释，容器无法把/LogsServlet请求匹配到对应Servlet类，两种修复方式二选一：

• 注解方式：去掉@WebServlet那行的注释，确保注解里的urlPatterns = { "/LogsServlet" }配置正确，同时保证Servlet类在容器扫描的包路径下。
• 配置文件方式：在项目的WEB-INF/web.xml中添加如下配置，替换掉你的包名为LogsServlet类的实际全路径包名：

<servlet>
    <servlet-name>LogsServlet</servlet-name>
    <servlet-class>你的包名.LogsServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LogsServlet</servlet-name>
    <url-pattern>/LogsServlet</url-pattern>
</servlet-mapping>

2. 修正表单提交与参数处理逻辑 #

• 提交数据的场景不要用GET请求，把表单的method="GET"改为method="POST"，避免参数直接暴露在URL地址栏。
• 在Servlet中重写doPost方法处理提交请求，不要把创建数据的逻辑写在doGet里。
• 调用request.getParameter()后要用变量接收返回值，做基础非空校验后再创建TextLog实例，记得调用create()方法生成日志ID和创建时间。
  修复后的doPost方法参考：

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 设置请求响应编码，避免中文乱码
    request.setCharacterEncoding("UTF-8");
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter writer = response.getWriter();

    // 接收表单参数
    String logTitle = request.getParameter("logTitle");
    String logDescription = request.getParameter("logDescription");
    String logContent = request.getParameter("logContent");

    // 基础参数校验
    if (logTitle == null || logTitle.trim().isEmpty()) {
        writer.write("日志标题不能为空");
        return;
    }

    // 创建日志实例
    TextLog textLog = new TextLog(logTitle.trim(), logDescription, logContent);
    textLog.create(); // 生成UUID和创建时间戳

    // 临时返回提交结果，后续可替换为跳转逻辑
    writer.println("<h3>日志提交成功</h3>");
    writer.println("<p>日志ID：" + textLog.getId() + "</p>");
    writer.println("<p>日志标题：" + textLog.getTitle() + "</p>");
    writer.println("<p>创建时间：" + textLog.getCreateTimestamp() + "</p>");
}

注意：Log类的构造方法是包访问权限，要保证TextLog子类和Log类在同一个包下，否则会报编译错误。

• 日志列表展示：初期可以把日志对象存在ServletContext域的List集合中，每次提交新日志就追加到集合里；更推荐后续用JSP+JSTL做视图层，提交完日志后通过请求转发把日志列表传到前端页面遍历渲染。
• 数据库持久化：先引入对应数据库的JDBC驱动，创建日志表，字段和Log类属性一一对应（id用字符串类型存UUID、标题/描述/内容用文本类型、创建时间用datetime/timestamp类型），封装JDBC连接工具类，创建完TextLog实例后执行INSERT语句把数据存入数据库；查询列表时执行SELECT语句把结果集封装为Log对象集合，传到前端展示即可。
• 优化点：后续可以把参数校验逻辑抽离，增加XSS过滤防止前端注入，Service层单独处理业务逻辑，和Servlet层解耦。

内容的提问来源于stack exchange，提问作者Caitlyn Gibbons