过滤器 与 拦截器

过滤器 与 拦截器

一、过滤器（Filter）

1、特点

过滤器是基于Java Servlet规范的一部分，用于在请求 到达Servlet之前 或 响应离开Servlet之后 对请求和响应进行处理。

• 过滤器可以对所有请求进行处理，不仅限于特定的Servlet或Spring MVC控制器。
• 过滤器在Servlet容器层面工作，而不是Spring层面。
• 适合用于日志记录、身份验证、权限检查等通用功能。

2、生命周期

public interface Filter {// 初始化方法default void init(FilterConfig filterConfig) throws ServletException {}// 执行拦截方法void doFilter(ServletRequest var1, ServletResponse var2, FilterChain var3) throws IOException, ServletException;// 销毁方法default void destroy() {}
}

# 创建【init方法】
1. 特点：服务器启动，项目加载，创建filter对象，执行【init方法】（只执行一次）
2. 对比Servlet：先于Servlet的init方法执行# 拦截【doFilter方法】
1. 特点：用户访问被拦截的目标资源时，执行【doFilter方法】（浏览器每访问一次，就会执行一次）
2. 对比Servlet：先于Servlet的service方法执行# 销毁【destroy方法】
1. 特点：服务器关闭，项目关闭，销毁filter对象，执行【destroy方法】（只执行一次）
2. 对比Servlet：后于Servlet的destroy方法执行

3、实现

定义拦截器只要实现Filter接口，重写doFilter方法即可

public class MyFilter implements Filter {@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {// 前置处理...System.out.println("Filter doFilter before");// 处理请求chain.doFilter(request, response);// 后置处理...System.out.println("Filter doFilter after");}
}

注册拦截器（SpringBoot示例）

@Configuration
public class FilterConfig {@Beanpublic FilterRegistrationBean<MyFilter> myFilter() {FilterRegistrationBean<MyFilter> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new MyFilter());// 过滤路径（/*表示所有）registrationBean.addUrlPatterns("/*");// 过滤顺序（多个Filter按Order从小到大顺序执行）registrationBean.setOrder(1);return registrationBean;}
}

4、过滤器链

1）配置 order

多个 Filter 按 Order的大小 从小到大 执行（如果没有配置Order，按 Bean声明的顺序 从上到下 执行）

@Configuration
public class FilterConfig {@Beanpublic FilterRegistrationBean<MyFilter> myFilter1() {FilterRegistrationBean<MyFilter> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new MyFilter1());registrationBean.addUrlPatterns("/*");registrationBean.setOrder(1);return registrationBean;}@Beanpublic FilterRegistrationBean<MyFilter> myFilter2() {FilterRegistrationBean<MyFilter> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new MyFilter2());registrationBean.addUrlPatterns("/*");registrationBean.setOrder(2);return registrationBean;}@Beanpublic FilterRegistrationBean<MyFilter> myFilter3() {FilterRegistrationBean<MyFilter> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new MyFilter3());registrationBean.addUrlPatterns("/*");registrationBean.setOrder(3);return registrationBean;}
}

2）执行顺序

Filter1 doFilter before
Filter2 doFilter before
Filter3 doFilter beforeServlet service// 如果发生异常，就不会执行 doFilter after 了
Filter3 doFilter after
Filter2 doFilter after
Filter1 doFilter after

二、拦截器 Inteceptor

1、特点

拦截器是Spring MVC提供的功能，用于在请求到达控制器之前和响应离开控制器之后进行处理。

• 拦截器主要用于Spring MVC层面，处理的是控制器层的请求和响应。
• 适合用于权限检查、日志记录、请求计时等与业务逻辑密切相关的操作。

2、生命周期

public interface HandlerInterceptor {// Controller执行之前调用default boolean preHandle(HttpServletRequest request,  HttpServletResponse response, Object handler) throws Exception {return true;}// Controller执行之后调用（发生异常 或 preHandle=false 不会调用）default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {}// Controller执行之后调用（发生异常也会调用，preHandle=false不会调用）default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {}
}

3、实现

自定义拦截器只要实现HandlerInterceptor接口，按需重写指定即可。

public class MyInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("Pre Handle method is Called");return true; // 继续处理请求}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("Post Handle method is Called");}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("Request and Response is completed");}
}

注册拦截器

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configuration
public class WebConfig implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {// 添加自定义拦截器registry.addInterceptor(new MyInterceptor())// 配置拦截路径.addPathPatterns("/**")// 配置放过路径.excludePathPatterns();}
}

4、拦截器链

1）配置 order

多个 Interceptor 按 Order的大小 从小到大 执行（如果没有配置Order，按 添加的顺序 从上到下 执行）

@Configuration
public class MyAdapter implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new MyInterceptor1()).addPathPatterns("/**").order(1);registry.addInterceptor(new MyInterceptor2()).addPathPatterns("/**").order(2);registry.addInterceptor(new MyInterceptor3()).addPathPatterns("/**").order(3);}
}

2）执行顺序（没有异常）

Interceptor1 preHandle	// true
Interceptor2 preHandle	// true
Interceptor3 preHandle	// trueServlet serviceInterceptor3 postHandle
Interceptor2 postHandle
Interceptor1 postHandle  Interceptor3 afterCompletion
Interceptor2 afterCompletion
Interceptor1 afterCompletion

3）某拦截器 preHandle 返回false

这里我们假设中间的 Interceptor2 的 preHandle 返回 false

Interceptor1 preHandle	// true
Interceptor2 preHandle	// falseInterceptor1 afterCompletion

之前的拦截器（即 Interceptor1）: 执行了 preHandle 和 afterCompletion
阻隔的拦截器（即 Interceptor2）: 执行了 preHandle
之后的拦截器（即 Interceptor3）: 全部不执行

4）执行顺序（有异常）

Interceptor1 preHandle	// true
Interceptor2 preHandle	// true
Interceptor3 preHandle	// true// 发生异常之前
Servlet service// 这个竟然是在 异常的堆栈信息 之前执行的
Interceptor3 afterCompletion
Interceptor2 afterCompletion
Interceptor1 afterCompletion异常的堆栈信息// 发生异常之后，又整体执行了一遍....
Interceptor1 preHandle
Interceptor2 preHandle
Interceptor3 preHandleInterceptor3 postHandle
Interceptor2 postHandle
Interceptor1 postHandleInterceptor3 afterCompletion
Interceptor2 afterCompletion
Interceptor1 afterCompletion

5）小结

整体顺序：所有 preHandle -> Controller -> 所有 postHandle -> 所有 afterCompletion

# preHandle
1. 调用前提无
2. 调用时机Controller方法处理之前
3. 调用链顺序顺序执行：preHandle1 ==> preHandle2 ==> preHandle3# postHandle
1. 调用前提preHandle返回true 且 Controller没有发生异常
2. 调用时机Controller方法处理完之后，afterCompletion调用之前
3. 调用链顺序倒序执行：postHandle3 ==> postHandle2 ==> postHandle1# afterCompletion
1. 调用前提preHandle返回true（Controller发生异常也会调用）
2. 调用时机Controller方法处理完之后
3. 调用链顺序倒序执行：afterCompletion3 ==> afterCompletion2 ==> afterCompletion1

三、执行顺序

1、自定义 Servlet

public class MyServlet extends HttpServlet {@Overridepublic void destroy() {System.out.println("Servlet destroy");super.destroy();}@Overridepublic void init(ServletConfig config) throws ServletException {System.out.println("Servlet init");super.init(config);}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("Servlet service");resp.getWriter().write("Hello from MyServlet");}
}

@Configuration
public class ServletConfig {@Beanpublic ServletRegistrationBean<MyServlet> myServlet() {return new ServletRegistrationBean<>(new MyServlet(), "/myServlet");}
}

2、自定义 Filter

public class MyFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {System.out.println("Filter init");Filter.super.init(filterConfig);}@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {// 前置处理...System.out.println("Filter doFilter before");// 处理请求chain.doFilter(request, response);// 后置处理...System.out.println("Filter doFilter after");}@Overridepublic void destroy() {System.out.println("Filter destroy");Filter.super.destroy();}
}

@Configuration
public class FilterConfig {@Beanpublic FilterRegistrationBean<MyFilter> myFilter() {FilterRegistrationBean<MyFilter> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new MyFilter());registrationBean.addUrlPatterns("/*");registrationBean.setOrder(1);return registrationBean;}
}

3、自定义 Inteceptor

public class MyInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("Interceptor preHandle");return true; // 继续处理请求}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("Interceptor postHandle");}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("Interceptor afterCompletion");}
}

@Configuration
public class WebConfig implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new MyInterceptor()).addPathPatterns("/**").excludePathPatterns();}
}

4、对比：Servlet 与 Filter

// 项目启动
Filter init// 访问 http://localhost:8080/myServlet
Servlet init
Filter doFilter before
Servlet service
Filter doFilter after// 项目关闭
Servlet destroy
Filter destroy

5、对比：Filter 与 Inteceptor

@RestController
public class TestController {@GetMapping("/interceptor")public ResponseEntity<String> interceptor() {System.out.println("Servlet service");return ResponseEntity.ok("SUCCESS");}
}

// 项目启动
Filter init// 访问 http://localhost:8080/interceptor
Filter doFilter before
Interceptor preHandle
Servlet service
Interceptor postHandle
Interceptor afterCompletion
Filter doFilter after// 项目关闭
Filter destroy

6、小结

// 项目启动
Filter init// 访问接口
Servlet init
Filter doFilter before
Interceptor preHandle
Servlet service
Interceptor postHandle
Interceptor afterCompletion
Filter doFilter after// 项目关闭
Servlet destroy
Filter destroy