过滤器与拦截器 - ToB企服应用市场:ToB评测及商务社交产业平台

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() {
}
}

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# 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

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public class MyFilter implements Filter {
@Override
public 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");
}
}

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@Configuration
public class FilterConfig {
@Bean
public 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;
}
}

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

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

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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 {
}
}

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public class MyInterceptor implements HandlerInterceptor {
@Override
public 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
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
System.out.println("Post Handle method is Called");
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
System.out.println("Request and Response is completed");
}
}

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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 {
@Override
public 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();
}
}

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@Configuration
public class MyAdapter implements WebMvcConfigurer {
@Override
public 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);
}
}

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Interceptor1 preHandle // true
Interceptor2 preHandle // true
Interceptor3 preHandle // true
Servlet service
Interceptor3 postHandle
Interceptor2 postHandle
Interceptor1 postHandle
Interceptor3 afterCompletion
Interceptor2 afterCompletion
Interceptor1 afterCompletion

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Interceptor1 preHandle // true
Interceptor2 preHandle // false
Interceptor1 afterCompletion

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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

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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 preHandle
Interceptor3 postHandle
Interceptor2 postHandle
Interceptor1 postHandle
Interceptor3 afterCompletion
Interceptor2 afterCompletion
Interceptor1 afterCompletion

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# 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

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

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

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public class MyFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("Filter init");
Filter.super.init(filterConfig);
}
@Override
public 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");
}
@Override
public void destroy() {
System.out.println("Filter destroy");
Filter.super.destroy();
}
}

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

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

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

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// 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

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

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// 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

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// 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

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