feat(interactive): enhance struts learning pages with task cards and quick experiments

src/main/java/com/example/struts2/CalculatorAction.java

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+package com.example.struts2;
+
+import com.opensymphony.xwork2.ActionSupport;
+
+/**
+ * 计算器 Action - 表单处理示例
+ * 
+ * 学习点：
+ * - Action 接收表单参数（通过 setter）
+ * - 数据验证（validate 方法）
+ * - 结果类型
+ */
+public class CalculatorAction extends ActionSupport {
+    
+    private Double num1;
+    private Double num2;
+    private String operator;
+    private Double result;
+    
+    // 默认执行方法
+    public String execute() {
+        return SUCCESS;
+    }
+    
+    // 计算方法
+    public String calculate() {
+        if (num1 == null || num2 == null || operator == null) {
+            return INPUT;
+        }
+        
+        switch (operator) {
+            case "+":
+                result = num1 + num2;
+                break;
+            case "-":
+                result = num1 - num2;
+                break;
+            case "*":
+                result = num1 * num2;
+                break;
+            case "/":
+                if (num2 == 0) {
+                    addFieldError("num2", "除数不能为0");
+                    return INPUT;
+                }
+                result = num1 / num2;
+                break;
+            default:
+                return INPUT;
+        }
+        return SUCCESS;
+    }
+    
+    // 验证方法
+    @Override
+    public void validate() {
+        if (num1 == null) {
+            addFieldError("num1", "请输入第一个数字");
+        }
+        if (num2 == null) {
+            addFieldError("num2", "请输入第二个数字");
+        }
+    }
+    
+    // Getter and Setter（Struts2 通过这些接收参数）
+    public Double getNum1() { return num1; }
+    public void setNum1(Double num1) { this.num1 = num1; }
+    
+    public Double getNum2() { return num2; }
+    public void setNum2(Double num2) { this.num2 = num2; }
+    
+    public String getOperator() { return operator; }
+    public void setOperator(String operator) { this.operator = operator; }
+    
+    public Double getResult() { return result; }
+    public void setResult(Double result) { this.result = result; }
+}

src/main/java/com/example/struts2/HelloAction.java

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+package com.example.struts2;
+
+import com.opensymphony.xwork2.ActionSupport;
+
+public class HelloAction extends ActionSupport {
+    private String message = "Hello from Struts2 Scaffold!";
+    
+    public String execute() {
+        return SUCCESS;
+    }
+    
+    public String getMessage() {
+        return message;
+    }
+}

src/main/java/com/example/struts2/InterceptorDemoAction.java

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+package com.example.struts2;
+
+import com.opensymphony.xwork2.ActionSupport;
+import com.example.struts2.interceptor.MonitorInterceptor;
+import org.apache.struts2.interceptor.RequestAware;
+import java.util.Map;
+
+/**
+ * 拦截器演示 Action
+ * 
+ * 学习点：
+ * - 拦截器与 Action 的协作
+ * - RequestAware 接口获取 request
+ */
+public class InterceptorDemoAction extends ActionSupport implements RequestAware {
+    
+    private Map<String, Object> request;
+    private Map<String, Long> interceptorStats;
+    private Long executionTime;
+    
+    public String execute() {
+        interceptorStats = MonitorInterceptor.getStats();
+        if (request != null) {
+            executionTime = (Long) request.get("executionTimeNs");
+        }
+        return SUCCESS;
+    }
+    
+    @Override
+    public void setRequest(Map<String, Object> request) {
+        this.request = request;
+    }
+    
+    public Map<String, Long> getInterceptorStats() { return interceptorStats; }
+    public Long getExecutionTime() { return executionTime; }
+}

src/main/java/com/example/struts2/LearnAction.java

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+package com.example.struts2;
+
+import com.opensymphony.xwork2.ActionSupport;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.struts2.interceptor.ServletRequestAware;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * 学习示例 Action
+ * 
+ * 学习点：
+ * - 获取原始 HttpServletRequest
+ * - 多种结果类型
+ * - Action 配置
+ */
+public class LearnAction extends ActionSupport implements ServletRequestAware {
+    
+    private HttpServletRequest request;
+    private Map<String, Object> data;
+    
+    // 默认方法 - 显示学习菜单
+    public String execute() {
+        data = new HashMap<>();
+        data.put("message", "欢迎学习 Struts2！");
+        data.put("features", new String[]{
+            "MVC 架构模式",
+            "拦截器机制",
+            "OGNL 表达式语言",
+            "标签库",
+            "类型转换",
+            "输入验证"
+        });
+        data.put("actions", new String[]{
+            "hello - 基础示例",
+            "calculator - 表单处理",
+            "user - CRUD 操作",
+            "learn/info - 本页面"
+        });
+        return SUCCESS;
+    }
+    
+    // 显示请求信息
+    public String info() {
+        data = new HashMap<>();
+        data.put("method", request.getMethod());
+        data.put("contextPath", request.getContextPath());
+        data.put("remoteAddr", request.getRemoteAddr());
+        data.put("header_UserAgent", request.getHeader("User-Agent"));
+        return SUCCESS;
+    }
+    
+    @Override
+    public void setServletRequest(HttpServletRequest request) {
+        this.request = request;
+    }
+    
+    public Map<String, Object> getData() { return data; }
+    public void setData(Map<String, Object> data) { this.data = data; }
+}

src/main/java/com/example/struts2/UserFormAction.java

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+package com.example.struts2;
+
+import com.opensymphony.xwork2.ActionSupport;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 用户管理 Action - CRUD 示例
+ * 
+ * 学习点：
+ * - Session 范围数据
+ * - 多个处理方法
+ * - 动态方法调用
+ */
+public class UserFormAction extends ActionSupport {
+    
+    private static List<User> users = new ArrayList<>();
+    private static Long idCounter = 1L;
+    
+    private User user = new User();
+    private Long id;
+    private List<User> userList;
+    
+    static {
+        users.add(new User(idCounter++, "张三", "zhangsan@example.com", 25));
+        users.add(new User(idCounter++, "李四", "lisi@example.com", 30));
+        users.add(new User(idCounter++, "王五", "wangwu@example.com", 28));
+    }
+    
+    // 列表
+    public String list() {
+        userList = new ArrayList<>(users);
+        return SUCCESS;
+    }
+    
+    // 添加
+    public String add() {
+        user.setId(idCounter++);
+        users.add(user);
+        return SUCCESS;
+    }
+    
+    // 编辑页面
+    public String edit() {
+        for (User u : users) {
+            if (u.getId().equals(id)) {
+                user = u;
+                break;
+            }
+        }
+        return SUCCESS;
+    }
+    
+    // 更新
+    public String update() {
+        for (int i = 0; i < users.size(); i++) {
+            if (users.get(i).getId().equals(user.getId())) {
+                users.set(i, user);
+                break;
+            }
+        }
+        return SUCCESS;
+    }
+    
+    // 删除
+    public String delete() {
+        users.removeIf(u -> u.getId().equals(id));
+        return SUCCESS;
+    }
+    
+    // Getters and Setters
+    public User getUser() { return user; }
+    public void setUser(User user) { this.user = user; }
+    
+    public Long getId() { return id; }
+    public void setId(Long id) { this.id = id; }
+    
+    public List<User> getUserList() { return userList; }
+    public void setUserList(List<User> userList) { this.userList = userList; }
+    
+    // 内部类 - 用户实体
+    public static class User {
+        private Long id;
+        private String name;
+        private String email;
+        private Integer age;
+        
+        public User() {}
+        
+        public User(Long id, String name, String email, Integer age) {
+            this.id = id;
+            this.name = name;
+            this.email = email;
+            this.age = age;
+        }
+        
+        public Long getId() { return id; }
+        public void setId(Long id) { this.id = id; }
+        public String getName() { return name; }
+        public void setName(String name) { this.name = name; }
+        public String getEmail() { return email; }
+        public void setEmail(String email) { this.email = email; }
+        public Integer getAge() { return age; }
+        public void setAge(Integer age) { this.age = age; }
+    }
+}

src/main/java/com/example/struts2/interceptor/LoggingInterceptor.java

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+package com.example.struts2.interceptor;
+
+import com.opensymphony.xwork2.ActionInvocation;
+import com.opensymphony.xwork2.interceptor.AbstractInterceptor;
+import java.util.Map;
+
+/**
+ * 日志拦截器 - 演示自定义拦截器
+ * 
+ * 学习点：
+ * - AbstractInterceptor 基类
+ * - intercept() 方法
+ * - ActionInvocation 对象
+ * - 拦截器链执行顺序
+ */
+public class LoggingInterceptor extends AbstractInterceptor {
+    
+    @Override
+    public String intercept(ActionInvocation invocation) throws Exception {
+        String actionName = invocation.getProxy().getActionName();
+        String method = invocation.getProxy().getMethod();
+        
+        System.out.println("[LoggingInterceptor] 进入 Action: " + actionName + 
+            ", Method: " + method);
+        
+        long startTime = System.currentTimeMillis();
+        
+        // 执行下一个拦截器或 Action
+        String result = invocation.invoke();
+        
+        long duration = System.currentTimeMillis() - startTime;
+        
+        System.out.println("[LoggingInterceptor] 退出 Action: " + actionName + 
+            ", Result: " + result + ", 耗时: " + duration + "ms");
+        
+        return result;
+    }
+}

src/main/java/com/example/struts2/interceptor/MonitorInterceptor.java

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+package com.example.struts2.interceptor;
+
+import com.opensymphony.xwork2.ActionInvocation;
+import com.opensymphony.xwork2.interceptor.Interceptor;
+import com.opensymphony.xwork2.ActionContext;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * 拦截器状态监控 - 演示拦截器生命周期
+ */
+public class MonitorInterceptor implements Interceptor {
+    
+    private static final Map<String, Long> actionCallCounts = new ConcurrentHashMap<>();
+    private static long interceptorInitTime;
+    
+    @Override
+    public void init() {
+        interceptorInitTime = System.currentTimeMillis();
+        System.out.println("[MonitorInterceptor] 初始化 - " + new java.util.Date());
+    }
+    
+    @Override
+    public void destroy() {
+        System.out.println("[MonitorInterceptor] 销毁 - " + new java.util.Date());
+        System.out.println("[MonitorInterceptor] 最终统计: " + actionCallCounts);
+    }
+    
+    @Override
+    public String intercept(ActionInvocation invocation) throws Exception {
+        String actionName = invocation.getProxy().getActionName();
+        actionCallCounts.merge(actionName, 1L, Long::sum);
+        
+        // 通过 invocation 获取 context
+        ActionContext context = invocation.getInvocationContext();
+        Map<String, Object> request = (Map<String, Object>) context.get("request");
+        if (request != null) {
+            request.put("interceptorInitTime", interceptorInitTime);
+            request.put("actionCallCounts", new ConcurrentHashMap<>(actionCallCounts));
+        }
+        
+        return invocation.invoke();
+    }
+    
+    public static Map<String, Long> getStats() {
+        return new ConcurrentHashMap<>(actionCallCounts);
+    }
+}

src/main/java/com/example/struts2/interceptor/RateLimitInterceptor.java

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+package com.example.struts2.interceptor;
+
+import com.opensymphony.xwork2.ActionInvocation;
+import com.opensymphony.xwork2.interceptor.AbstractInterceptor;
+import com.opensymphony.xwork2.ActionContext;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.struts2.StrutsStatics;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * 限流拦截器 - 演示拦截器实现横切关注点
+ * 
+ * 学习点：
+ * - 拦截器实现非功能性需求
+ * - IP 限流算法
+ * - 返回自定义结果
+ */
+public class RateLimitInterceptor extends AbstractInterceptor {
+    
+    // IP 请求计数器
+    private final Map<String, AtomicLong> ipRequestCounts = new ConcurrentHashMap<>();
+    private final Map<String, Long> ipLastAccess = new ConcurrentHashMap<>();
+    
+    // 每分钟最大请求数
+    private long maxRequestsPerMinute = 60;
+    
+    @Override
+    public String intercept(ActionInvocation invocation) throws Exception {
+        // 获取客户端 IP
+        String clientIp = getClientIp(invocation);
+        
+        long currentTime = System.currentTimeMillis();
+        Long lastAccess = ipLastAccess.get(clientIp);
+        
+        // 每分钟重置计数器
+        if (lastAccess == null || currentTime - lastAccess > 60000) {
+            ipRequestCounts.put(clientIp, new AtomicLong(0));
+            ipLastAccess.put(clientIp, currentTime);
+        }
+        
+        AtomicLong count = ipRequestCounts.get(clientIp);
+        long currentCount = count.incrementAndGet();
+        
+        if (currentCount > maxRequestsPerMinute) {
+            System.out.println("[RateLimitInterceptor] IP: " + clientIp + 
+                " 超过限流阈值: " + currentCount);
+            return "rateLimitExceeded";
+        }
+        
+        System.out.println("[RateLimitInterceptor] IP: " + clientIp + 
+            " 请求计数: " + currentCount + "/" + maxRequestsPerMinute);
+        
+        return invocation.invoke();
+    }
+    
+    /**
+     * 获取客户端真实 IP
+     */
+    private String getClientIp(ActionInvocation invocation) {
+        ActionContext context = invocation.getInvocationContext();
+        HttpServletRequest request = (HttpServletRequest) 
+            context.get(StrutsStatics.HTTP_REQUEST);
+        
+        String ip = request.getHeader("X-Forwarded-For");
+        if (ip == null || ip.isEmpty() || "unknown".equalsIgnoreCase(ip)) {
+            ip = request.getHeader("X-Real-IP");
+        }
+        if (ip == null || ip.isEmpty() || "unknown".equalsIgnoreCase(ip)) {
+            ip = request.getRemoteAddr();
+        }
+        
+        // 多个代理时取第一个
+        if (ip != null && ip.contains(",")) {
+            ip = ip.split(",")[0].trim();
+        }
+        
+        return ip;
+    }
+    
+    // Getter/Setter for configuration
+    public void setMaxRequestsPerMinute(long max) {
+        this.maxRequestsPerMinute = max;
+    }
+}

src/main/java/com/example/struts2/interceptor/TimingInterceptor.java

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+package com.example.struts2.interceptor;
+
+import com.opensymphony.xwork2.ActionInvocation;
+import com.opensymphony.xwork2.interceptor.AbstractInterceptor;
+import com.opensymphony.xwork2.ActionContext;
+import java.util.Map;
+
+/**
+ * 计时拦截器 - 演示拦截器统计功能
+ * 
+ * 学习点：
+ * - 拦截器状态保持
+ * - ActionContext 获取上下文
+ * - 多个拦截器协作
+ */
+public class TimingInterceptor extends AbstractInterceptor {
+    
+    // 统计数据
+    private long totalRequests = 0;
+    private long totalTime = 0;
+    
+    @Override
+    public String intercept(ActionInvocation invocation) throws Exception {
+        totalRequests++;
+        
+        String actionName = invocation.getProxy().getActionName();
+        long startTime = System.nanoTime();
+        
+        // 执行 Action
+        String result = invocation.invoke();
+        
+        long duration = System.nanoTime() - startTime;
+        totalTime += duration;
+        
+        // 存储到 request 作用域
+        Map<String, Object> request = (Map<String, Object>) 
+            ActionContext.getContext().get("request");
+        if (request != null) {
+            request.put("executionTimeNs", duration);
+            request.put("totalRequests", totalRequests);
+        }
+        
+        System.out.println("[TimingInterceptor] " + actionName + 
+            " 执行时间: " + (duration / 1_000_000.0) + " ms");
+        
+        return result;
+    }
+    
+    public long getTotalRequests() { return totalRequests; }
+    public long getTotalTime() { return totalTime; }
+}

src/main/java/com/example/struts2/interceptor/ValidationInterceptor.java

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+package com.example.struts2.interceptor;
+
+import com.opensymphony.xwork2.ActionInvocation;
+import com.opensymphony.xwork2.interceptor.AbstractInterceptor;
+import com.opensymphony.xwork2.ActionContext;
+import org.apache.struts2.dispatcher.HttpParameters;
+import java.util.Map;
+
+/**
+ * 参数验证拦截器 - 演示拦截器预处理
+ */
+public class ValidationInterceptor extends AbstractInterceptor {
+    
+    @Override
+    public String intercept(ActionInvocation invocation) throws Exception {
+        System.out.println("[ValidationInterceptor] 开始参数验证");
+        
+        // 获取参数 (Struts2 6.x 使用 HttpParameters)
+        HttpParameters params = invocation.getInvocationContext().getParameters();
+        
+        for (String paramName : params.keySet()) {
+            String[] values = params.get(paramName).getMultipleValues();
+            if (values != null) {
+                for (String value : values) {
+                    if (containsXss(value)) {
+                        System.out.println("[ValidationInterceptor] 检测到可疑参数: " + paramName);
+                        return "invalidInput";
+                    }
+                }
+            }
+        }
+        
+        System.out.println("[ValidationInterceptor] 参数验证通过");
+        return invocation.invoke();
+    }
+    
+    private boolean containsXss(String value) {
+        if (value == null) return false;
+        String lower = value.toLowerCase();
+        return lower.contains("<script") || 
+               lower.contains("javascript:") ||
+               lower.contains("onerror=");
+    }
+}

src/main/resources/struts.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE struts PUBLIC
+    "-//Apache Software Foundation//DTD Struts Configuration 6.0//EN"
+    "http://struts.apache.org/dtds/struts-6.0.dtd">
+<struts>
+    <!-- 开发模式 -->
+    <constant name="struts.devMode" value="true" />
+    <constant name="struts.enable.DynamicMethodInvocation" value="true" />
+    <constant name="struts.action.extension" value="action,," />
+    
+    <package name="default" namespace="/" extends="struts-default">
+        
+        <!-- ========== 自定义拦截器配置 ========== -->
+        <interceptors>
+            <interceptor name="logging" class="com.example.struts2.interceptor.LoggingInterceptor"/>
+            <interceptor name="timing" class="com.example.struts2.interceptor.TimingInterceptor"/>
+            <interceptor name="rateLimit" class="com.example.struts2.interceptor.RateLimitInterceptor"/>
+            <interceptor name="validation" class="com.example.struts2.interceptor.ValidationInterceptor"/>
+            <interceptor name="monitor" class="com.example.struts2.interceptor.MonitorInterceptor"/>
+            
+            <interceptor-stack name="customStack">
+                <interceptor-ref name="logging"/>
+                <interceptor-ref name="timing"/>
+                <interceptor-ref name="monitor"/>
+                <interceptor-ref name="defaultStack"/>
+            </interceptor-stack>
+            
+            <interceptor-stack name="apiStack">
+                <interceptor-ref name="logging"/>
+                <interceptor-ref name="rateLimit">
+                    <param name="maxRequestsPerMinute">100</param>
+                </interceptor-ref>
+                <interceptor-ref name="validation"/>
+                <interceptor-ref name="timing"/>
+                <interceptor-ref name="defaultStack"/>
+            </interceptor-stack>
+        </interceptors>
+        
+        <!-- 默认拦截器栈 -->
+        <default-interceptor-ref name="customStack"/>
+        
+        <!-- 默认 Action -->
+        <default-action-ref name="index" />
+        
+        <!-- 全局结果 -->
+        <global-results>
+            <result name="rateLimitExceeded">/error-rate-limit.jsp</result>
+            <result name="invalidInput">/error-invalid-input.jsp</result>
+        </global-results>
+        
+        <!-- ========== Actions ========== -->
+        <action name="index">
+            <result>/index.jsp</result>
+        </action>
+        
+        <action name="hello" class="com.example.struts2.HelloAction">
+            <result>/hello.jsp</result>
+        </action>
+        
+        <action name="learn" class="com.example.struts2.LearnAction">
+            <result>/learn.jsp</result>
+        </action>
+        
+        <action name="interceptor" class="com.example.struts2.InterceptorDemoAction">
+            <result>/interceptor-demo.jsp</result>
+        </action>
+        
+        <action name="interceptor_api" class="com.example.struts2.InterceptorDemoAction">
+            <interceptor-ref name="apiStack"/>
+            <result>/interceptor-demo.jsp</result>
+        </action>
+        
+        <action name="calc" class="com.example.struts2.CalculatorAction">
+            <result>/calculator.jsp</result>
+        </action>
+        
+        <action name="calc_execute" class="com.example.struts2.CalculatorAction" method="calculate">
+            <result>/calculator.jsp</result>
+            <result name="input">/calculator.jsp</result>
+        </action>
+        
+        <action name="user" class="com.example.struts2.UserFormAction" method="list">
+            <result>/user-list.jsp</result>
+        </action>
+        
+        <action name="user_add" class="com.example.struts2.UserFormAction" method="add">
+            <result type="redirectAction">user</result>
+        </action>
+        
+        <action name="user_edit" class="com.example.struts2.UserFormAction" method="edit">
+            <result>/user-form.jsp</result>
+        </action>
+        
+        <action name="user_update" class="com.example.struts2.UserFormAction" method="update">
+            <result type="redirectAction">user</result>
+        </action>
+        
+        <action name="user_delete" class="com.example.struts2.UserFormAction" method="delete">
+            <result type="redirectAction">user</result>
+        </action>
+        
+    </package>
+</struts>

src/main/webapp/calculator.jsp

@@ -0,0 +1,85 @@
+<%@ page contentType="text/html;charset=UTF-8" language="java" %>
+<%@ taglib prefix="s" uri="/struts-tags" %>
+<!DOCTYPE html>
+<html>
+<head>
+    <title>计算器 - Struts2 表单示例</title>
+    <style>
+        body { font-family: Arial, sans-serif; max-width: 600px; margin: 50px auto; padding: 20px; }
+        h1 { color: #e74c3c; }
+        .form-group { margin: 15px 0; }
+        label { display: inline-block; width: 100px; }
+        input, select { padding: 8px; font-size: 14px; }
+        button { background: #3498db; color: white; padding: 10px 20px; border: none; cursor: pointer; }
+        button:hover { background: #2980b9; }
+        .result { background: #2ecc71; color: white; padding: 15px; margin: 20px 0; border-radius: 5px; }
+        .error { color: #e74c3c; font-size: 12px; }
+        .tip { background: #f9f9f9; padding: 15px; border-left: 4px solid #3498db; margin: 20px 0; }
+        .quickbar { background:#fff7e6; padding:12px; border-left:4px solid #fa8c16; margin:20px 0; border-radius:6px; }
+        .quickbar button { margin-right:8px; }
+    </style>
+</head>
+<body>
+    <h1>🔢 计算器 - Struts2 表单示例</h1>
+    
+    <s:if test="result != null">
+        <div class="result">
+            计算结果: <s:property value="num1"/> 
+            <s:property value="operator"/> 
+            <s:property value="num2"/> 
+            = <s:property value="result"/>
+        </div>
+    </s:if>
+    
+    <div class="quickbar">
+        <strong>快速实验：</strong>
+        <button type="button" onclick="fillExample(12, '+', 8)">填入正确示例</button>
+        <button type="button" onclick="fillExample(12, '/', 0)">填入除零错误</button>
+        <button type="button" onclick="fillExample('', '*', '')">填入校验错误</button>
+    </div>
+
+    <s:form action="calc_execute" method="post">
+        <div class="form-group">
+            <label>数字 1:</label>
+            <s:textfield name="num1" placeholder="输入第一个数字"/>
+            <s:fielderror fieldName="num1" cssClass="error"/>
+        </div>
+        
+        <div class="form-group">
+            <label>运算符:</label>
+            <s:select name="operator" list="{'+', '-', '*', '/'}" headerKey="" headerValue="选择运算符"/>
+        </div>
+        
+        <div class="form-group">
+            <label>数字 2:</label>
+            <s:textfield name="num2" placeholder="输入第二个数字"/>
+            <s:fielderror fieldName="num2" cssClass="error"/>
+        </div>
+        
+        <div class="form-group">
+            <button type="submit">计算</button>
+        </div>
+    </s:form>
+    
+    <div class="tip">
+        <strong>学习点:</strong>
+        <ul>
+            <li><code>name</code> 属性对应 Action 的 setter 方法</li>
+            <li><code>&lt;s:fielderror&gt;</code> 显示验证错误</li>
+            <li><code>validate()</code> 方法进行数据验证</li>
+        </ul>
+    </div>
+    
+    <p><a href="learn">← 返回学习中心</a></p>
+
+    <script>
+        function fillExample(n1, op, n2) {
+            const fields = document.querySelectorAll('input[type="text"]');
+            const select = document.querySelector('select');
+            if (fields[0]) fields[0].value = n1;
+            if (select) select.value = op;
+            if (fields[1]) fields[1].value = n2;
+        }
+    </script>
+</body>
+</html>

src/main/webapp/interceptor-demo.jsp

@@ -0,0 +1,80 @@
+<%@ page contentType="text/html;charset=UTF-8" language="java" %>
+<%@ taglib prefix="s" uri="/struts-tags" %>
+<!DOCTYPE html>
+<html>
+<head>
+    <title>拦截器演示 - Struts2</title>
+    <style>
+        body { font-family: Arial, sans-serif; max-width: 900px; margin: 50px auto; padding: 20px; }
+        h1 { color: #e74c3c; }
+        h2 { color: #3498db; border-bottom: 2px solid #3498db; padding-bottom: 10px; }
+        .card { background: #f9f9f9; padding: 20px; margin: 15px 0; border-radius: 8px; }
+        .card h3 { margin-top: 0; color: #2c3e50; }
+        code { background: #eee; padding: 2px 6px; border-radius: 3px; }
+        pre { background: #2c3e50; color: #ecf0f1; padding: 15px; border-radius: 5px; overflow-x: auto; }
+        table { width: 100%; border-collapse: collapse; margin: 10px 0; }
+        th, td { border: 1px solid #ddd; padding: 8px; text-align: left; }
+        th { background: #3498db; color: white; }
+        .time { color: #27ae60; font-weight: bold; }
+        .api-link { display: inline-block; background: #9b59b6; color: white; padding: 10px 20px; 
+                    text-decoration: none; border-radius: 5px; margin: 5px; }
+        .lab { background:#fff7e6; border-left:4px solid #fa8c16; padding:15px; border-radius:8px; margin:20px 0; }
+    </style>
+</head>
+<body>
+    <h1>🛡️ Struts2 拦截器演示</h1>
+
+    <div class="lab">
+        <strong>实验观察点：</strong>
+        <ul>
+            <li>连续刷新页面，观察 Action 调用次数如何累积</li>
+            <li>切换到“API 限流栈”，理解为什么拦截器顺序会影响结果</li>
+            <li>注意执行时间显示，这就是拦截器注入到 request 的数据</li>
+        </ul>
+    </div>
+    
+    <div class="card">
+        <h3>📊 执行统计</h3>
+        <p>本次请求执行时间: <span class="time"><s:property value="executionTime / 1000000.0"/> ms</span></p>
+        
+        <h4>Action 调用统计:</h4>
+        <table>
+            <tr><th>Action</th><th>调用次数</th></tr>
+            <s:iterator value="interceptorStats" var="entry">
+                <tr>
+                    <td><s:property value="#entry.key"/></td>
+                    <td><s:property value="#entry.value"/></td>
+                </tr>
+            </s:iterator>
+        </table>
+    </div>
+    
+    <div class="card">
+        <h3>🔗 拦截器链演示</h3>
+        <p>当前使用: <code>customStack</code> (日志 + 计时 + 监控 + 默认栈)</p>
+        <a class="api-link" href="interceptor_api">使用 API 限流栈</a>
+        <p>API 栈包含: 日志 + 限流 + 验证 + 计时 + 默认栈</p>
+    </div>
+    
+    <div class="card">
+        <h3>📚 拦截器执行顺序</h3>
+        <pre>
+请求 → LoggingInterceptor → TimingInterceptor → MonitorInterceptor → Action
+响应 ← LoggingInterceptor ← TimingInterceptor ← MonitorInterceptor ← Result
+        </pre>
+        <p><strong>注意:</strong> 拦截器像洋葱一样，先进入的后退出</p>
+    </div>
+    
+    <div class="card">
+        <h3>💡 拦截器核心概念</h3>
+        <ul>
+            <li><strong>Interceptor 接口:</strong> init() → intercept() → destroy()</li>
+            <li><strong>intercept() 方法:</strong> 调用 invocation.invoke() 继续链</li>
+            <li><strong>拦截器栈:</strong> 多个拦截器按顺序组成链</li>
+            <li><strong>责任链模式:</strong> 每个拦截器决定是否继续</li>
+        </ul>
+    </div>
+    
+    <p><a href="learn">← 返回学习中心</a></p>
+</body>
+</html>

src/main/webapp/learn.jsp

@@ -0,0 +1,112 @@
+<%@ page contentType="text/html;charset=UTF-8" language="java" %>
+<%@ taglib prefix="s" uri="/struts-tags" %>
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Struts2 学习中心</title>
+    <style>
+        body { font-family: Arial, sans-serif; max-width: 900px; margin: 50px auto; padding: 20px; }
+        h1 { color: #e74c3c; }
+        h2 { color: #3498db; border-bottom: 2px solid #3498db; padding-bottom: 10px; }
+        .card { background: #f5f5f5; padding: 20px; border-radius: 8px; margin: 20px 0; }
+        .card h3 { margin-top: 0; }
+        ul { line-height: 2; }
+        a { color: #3498db; text-decoration: none; }
+        a:hover { text-decoration: underline; }
+        .btn { display: inline-block; background: #3498db; color: white; padding: 10px 20px; 
+                border-radius: 5px; margin: 5px; }
+        .btn:hover { text-decoration: none; background: #2980b9; }
+        .btn-green { background: #27ae60; }
+        .btn-purple { background: #9b59b6; }
+        code { background: #eee; padding: 2px 6px; border-radius: 3px; }
+        .lab { background:#fff7e6; border-left:4px solid #fa8c16; padding:15px; border-radius:8px; margin:20px 0; }
+        .quick-tools { display:flex; gap:10px; flex-wrap:wrap; margin-top:10px; }
+    </style>
+</head>
+<body>
+    <h1>🎓 Struts2 学习中心</h1>
+
+    <div class="lab">
+        <strong>🧪 学习任务卡</strong>
+        <ul>
+            <li>先点“拦截器演示”，观察执行统计和链路顺序</li>
+            <li>再点“计算器”，故意输入非法值体验 Struts2 验证</li>
+            <li>最后点“用户管理”，理解 Action + JSP + 表单提交流程</li>
+        </ul>
+        <div class="quick-tools">
+            <a class="btn btn-purple" href="interceptor">直接去拦截器实验</a>
+            <a class="btn" href="calc">直接去计算器实验</a>
+            <a class="btn btn-green" href="user">直接去用户管理实验</a>
+        </div>
+    </div>
+    
+    <div class="card">
+        <h3>🛡️ 拦截器 (核心特性)</h3>
+        <p>拦截器是 Struts2 最强大的特性之一，基于责任链模式实现 AOP。</p>
+        <div>
+            <a class="btn btn-purple" href="interceptor">拦截器演示</a>
+        </div>
+        <ul>
+            <li><a href="interceptor">LoggingInterceptor</a> - 日志记录</li>
+            <li><a href="interceptor">TimingInterceptor</a> - 性能计时</li>
+            <li><a href="interceptor">RateLimitInterceptor</a> - IP 限流</li>
+            <li><a href="interceptor">ValidationInterceptor</a> - 参数验证</li>
+            <li><a href="interceptor">MonitorInterceptor</a> - 状态监控</li>
+        </ul>
+    </div>
+    
+    <div class="card">
+        <h3>📝 基础示例</h3>
+        <div>
+            <a class="btn" href="hello">Hello World</a>
+            <a class="btn" href="calc">计算器</a>
+            <a class="btn btn-green" href="user">用户管理</a>
+        </div>
+    </div>
+    
+    <h2>📚 学习路径</h2>
+    
+    <div class="card">
+        <h3>1. MVC 架构</h3>
+        <ul>
+            <li><strong>Model:</strong> Action 类 + JavaBean</li>
+            <li><strong>View:</strong> JSP + Struts 标签库</li>
+            <li><strong>Controller:</strong> StrutsPrepareAndExecuteFilter</li>
+        </ul>
+    </div>
+    
+    <div class="card">
+        <h3>2. 拦截器机制</h3>
+        <ul>
+            <li><code>Interceptor</code> 接口: init() → intercept() → destroy()</li>
+            <li><code>interceptor-stack</code>: 组合多个拦截器</li>
+            <li>执行顺序: 责任链模式（先入后出）</li>
+        </ul>
+    </div>
+    
+    <div class="card">
+        <h3>3. OGNL 表达式</h3>
+        <ul>
+            <li><code>&lt;s:property value="name"/&gt;</code> - 输出属性</li>
+            <li><code>&lt;s:iterator value="list"&gt;</code> - 遍历集合</li>
+            <li><code>#request.key</code> - 访问 request</li>
+        </ul>
+    </div>
+    
+    <div class="card">
+        <h3>4. 项目结构</h3>
+        <pre>
+├── src/main/java/com/example/struts2/
+│   ├── action/          # Action 类
+│   └── interceptor/     # 自定义拦截器
+├── src/main/resources/
+│   └── struts.xml       # 核心配置
+└── src/main/webapp/
+    ├── WEB-INF/web.xml  # Servlet 配置
+    └── *.jsp            # 视图页面
+        </pre>
+    </div>
+    
+    <p><a href="/">← 返回首页</a></p>
+</body>
+</html>