08 Web综合

应用程序启动
    ↓
ServletContext初始化
    ↓
触发contextInitialized()  ← 在这里进行资源初始化
    ↓
应用运行中...
    ↓
应用程序关闭
    ↓
ServletContext销毁
    ↓
触发contextDestroyed()   ← 在这里进行资源释放

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener  // 无需指定value，自动监听
public class CustomServletContextListener implements ServletContextListener {
    
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        // 应用启动时执行
        System.out.println("✅ 应用程序启动，ServletContext初始化完成");
    }
    
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        // 应用关闭时执行
        System.out.println("❌ 应用程序关闭，ServletContext销毁");
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
                             http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    
    <!-- 监听器配置 -->
    <listener>
        <listener-class>com.example.listener.CustomServletContextListener</listener-class>
    </listener>
    
</web-app>

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import java.io.IOException;
import java.io.InputStream;

@WebListener
public class MyBatisInitListener implements ServletContextListener {
    
    private static final String CONFIG_FILE = "mybatis-config.xml";
    private static final String CONTEXT_KEY = "SqlSessionFactory";
    
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        ServletContext context = sce.getServletContext();
        
        try (InputStream is = Resources.getResourceAsStream(CONFIG_FILE)) {
            SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
            
            // 存入ServletContext，全局共享
            context.setAttribute(CONTEXT_KEY, factory);
            
            System.out.println("✅ MyBatis初始化成功，SqlSessionFactory已存入ServletContext");
        } catch (IOException e) {
            System.err.println("❌ MyBatis初始化失败: " + e.getMessage());
            throw new RuntimeException("MyBatis初始化失败", e);
        }
    }
    
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        // 清理资源
        ServletContext context = sce.getServletContext();
        context.removeAttribute(CONTEXT_KEY);
        System.out.println("✅ MyBatis资源已清理");
    }
}

import org.apache.ibatis.session.SqlSessionFactory;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/user/list")
public class UserListServlet extends HttpServlet {
    
    private SqlSessionFactory sqlSessionFactory;
    
    @Override
    public void init() throws ServletException {
        // 从ServletContext获取已初始化的工厂
        sqlSessionFactory = (SqlSessionFactory) getServletContext()
                .getAttribute("SqlSessionFactory");
        
        if (sqlSessionFactory == null) {
            throw new ServletException("SqlSessionFactory未初始化");
        }
    }
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {
        // 使用sqlSessionFactory执行业务操作
        // ...
    }
}

客户端请求
    ↓
Filter预处理（请求过滤）
    ↓
Servlet业务处理
    ↓
Filter后处理（响应过滤）
    ↓
返回客户端

请求 → Filter.doFilter()前半部分 
          ↓
      chain.doFilter()  ← 放行
          ↓
      Servlet处理
          ↓
      Filter.doFilter()后半部分 → 响应

请求 → FilterA → FilterB → FilterC → Servlet
                                      ↓
响应 ← FilterA ← FilterB ← FilterC ← 处理完成

FilterA开始
  FilterB开始
    FilterC开始
      Servlet处理
    FilterC结束
  FilterB结束
FilterA结束

// 放行方法：必须调用才能继续后续流程
filterChain.doFilter(request, response);

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

@WebFilter("/*")  // 过滤所有请求
public class LoggingFilter implements Filter {
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化操作
        String encoding = filterConfig.getInitParameter("encoding");
        System.out.println("Filter初始化，编码参数: " + encoding);
    }
    
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
                         FilterChain chain) throws IOException, ServletException {
        // 前置处理
        System.out.println("请求到达Filter");
        
        // 放行
        chain.doFilter(request, response);
        
        // 后置处理
        System.out.println("响应离开Filter");
    }
    
    @Override
    public void destroy() {
        // 销毁操作
        System.out.println("Filter销毁");
    }
}

<web-app>
    <!-- Filter定义 -->
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.example.filter.CharacterEncodingFilter</filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
    </filter>
    
    <!-- Filter映射 -->
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * 字符编码过滤器
 * 统一设置请求和响应的字符编码为UTF-8
 */
@WebFilter("/*")
public class CharacterEncodingFilter implements Filter {
    
    private String encoding = "UTF-8";
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 读取初始化参数
        String configEncoding = filterConfig.getInitParameter("encoding");
        if (configEncoding != null && !configEncoding.isEmpty()) {
            this.encoding = configEncoding;
        }
    }
    
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
                         FilterChain chain) throws IOException, ServletException {
        
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        
        // 设置请求编码（解决POST中文乱码）
        httpRequest.setCharacterEncoding(encoding);
        
        // 设置响应编码（解决响应中文乱码）
        httpResponse.setContentType("application/json;charset=" + encoding);
        // 或者 HTML: text/html;charset=UTF-8
        
        // 放行
        chain.doFilter(request, response);
    }
    
    @Override
    public void destroy() {
        // 清理资源
    }
}

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;

/**
 * 登录验证过滤器
 * 拦截需要登录才能访问的资源
 */
@WebFilter({"/user/*", "/order/*", "/cart/*"})
public class LoginCheckFilter implements Filter {
    
    // 白名单：不需要登录就能访问的路径
    private static final List<String> WHITE_LIST = Arrays.asList(
        "/user/login",
        "/user/register",
        "/user/logout"
    );
    
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
                         FilterChain chain) throws IOException, ServletException {
        
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        
        String requestURI = httpRequest.getRequestURI();
        String contextPath = httpRequest.getContextPath();
        String path = requestURI.substring(contextPath.length());
        
        // 1. 检查是否在白名单中
        if (isWhiteListed(path)) {
            chain.doFilter(request, response);
            return;
        }
        
        // 2. 检查是否已登录
        HttpSession session = httpRequest.getSession(false);
        Object user = (session != null) ? session.getAttribute("user") : null;
        
        if (user == null) {
            // 未登录，返回401或重定向到登录页
            // AJAX请求
            if (isAjaxRequest(httpRequest)) {
                httpResponse.setStatus(401);
                httpResponse.setContentType("application/json;charset=UTF-8");
                httpResponse.getWriter().write("{\"code\":401,\"msg\":\"请先登录\"}");
            } else {
                // 普通请求，重定向到登录页
                httpResponse.sendRedirect(contextPath + "/login.html");
            }
            return;  // 不放行，中断请求
        }
        
        // 已登录，放行
        chain.doFilter(request, response);
    }
    
    /**
     * 检查路径是否在白名单中
     */
    private boolean isWhiteListed(String path) {
        return WHITE_LIST.stream().anyMatch(path::startsWith);
    }
    
    /**
     * 判断是否为AJAX请求
     */
    private boolean isAjaxRequest(HttpServletRequest request) {
        return "XMLHttpRequest".equals(request.getHeader("X-Requested-With"));
    }
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}
    
    @Override
    public void destroy() {}
}

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * 跨域请求处理过滤器
 * 解决前后端分离项目的跨域问题
 */
@WebFilter("/*")
public class CORSFilter implements Filter {
    
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
                         FilterChain chain) throws IOException, ServletException {
        
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        
        // 允许的源（生产环境应配置具体域名）
        httpResponse.setHeader("Access-Control-Allow-Origin", "*");
        // 允许的请求方法
        httpResponse.setHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
        // 允许的请求头
        httpResponse.setHeader("Access-Control-Allow-Headers", "Content-Type, Authorization, X-Requested-With");
        // 预检请求缓存时间
        httpResponse.setHeader("Access-Control-Max-Age", "3600");
        // 允许携带Cookie
        httpResponse.setHeader("Access-Control-Allow-Credentials", "true");
        
        // 预检请求直接返回
        if ("OPTIONS".equalsIgnoreCase(httpRequest.getMethod())) {
            httpResponse.setStatus(HttpServletResponse.SC_OK);
            return;
        }
        
        chain.doFilter(request, response);
    }
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}
    
    @Override
    public void destroy() {}
}

<!-- 先执行字符编码 -->
<filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<!-- 再执行登录验证 -->
<filter-mapping>
    <filter-name>LoginCheckFilter</filter-name>
    <url-pattern>/user/*</url-pattern>
</filter-mapping>

// 通过WebApplicationContext获取
WebApplicationContext context = WebApplicationContextUtils
    .getRequiredWebApplicationContext(request.getServletContext());
UserService userService = context.getBean(UserService.class);

@Override
public void contextInitialized(ServletContextEvent sce) {
    ServletContext context = sce.getServletContext();
    // 检查是否已初始化
    if (context.getAttribute("SqlSessionFactory") != null) {
        return;  // 已存在，跳过
    }
    // 初始化代码...
}

@WebFilter(
    value = "/*",
    initParams = {
        @WebInitParam(name = "encoding", value = "UTF-8"),
        @WebInitParam(name = "forceEncoding", value = "true")
    }
)
public class CharacterEncodingFilter implements Filter {
    private String encoding;
    
    @Override
    public void init(FilterConfig config) throws ServletException {
        this.encoding = config.getInitParameter("encoding");
    }
}

@Override
public void doFilter(ServletRequest request, ServletResponse response, 
                     FilterChain chain) throws IOException, ServletException {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    String path = httpRequest.getRequestURI();
    
    // 排除静态资源
    if (path.startsWith("/static/") || path.endsWith(".js") || path.endsWith(".css")) {
        chain.doFilter(request, response);
        return;
    }
    
    // 继续过滤逻辑...
}