
首先说明一下二者的区别:
1. 拦截器基于java的反射机制,而过滤器是基于函数回调
2. 拦截器不依赖于servlet容器,过滤器依赖servlet容器
3. 拦截器只能对action请求起作用,而过滤器则可以对几乎所有的请求起作用
4. 在action的生命周期中,拦截器可以多次被调用,而过滤器只能在容器初始化时被调用一次
5. 拦截器可以获取IOC容器中的各个bean,而过滤器就不行,这点很重要,在拦截器注入一个service,可以调用业务逻辑
过滤器和拦截器之间的关系如下图,Filter包裹Servlet,Servlet包裹Interceptor
过滤器的触发时机是容器后,servlet之前,所以过滤器的 doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) 的入参是ServletRequest,而不是HttpServletRequest,因为过滤器在HttpServlet之前
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { System.out.println("before..."); chain.doFilter(request, response); System.out.println("after...");
}
这个chain.doFilter(request, response) 作用是将请求转发给过滤器链上下一个对象,下一个对象是指filter,如果没有filter那就是你请求的资源
拦截器是被包裹在过滤器之中
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
System.out.println("preHandle");
return true;
} @Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
System.out.println("postHandle");
} @Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
System.out.println("afterCompletion");
}
preHandle 这个方法是在过滤器的 chain.doFilter( request, response ) 方法的前一步执行,且在调用Controller之前调用,当返回false后,会跳过之后的拦截器,并且不会执行所有的拦截器 postHandle ,并且调用返回true的拦截器的 afterCompletion 方法
postHandle 是调用 Controller 之后被调用,但是在渲染 View 页面之前
afterCompletion 是调用完 Controller 接口,渲染 View 页面最后调用,返回true的拦截器都会调用该拦截器的 afterCompletion 方法,顺序相反。这个方法也是在过滤器返回给前端前一步执行
多个过滤器和拦截器是如何配置的呢,下面结合Spring Boot写个demo,地址是 https://gitee.com/colin220/intercept
首先写一个Controller,内容如下:
@Controller
public class InterceptController { @RequestMapping("/index")
public ResponseEntity<?> index() {
System.out.println("Controller Handler");
return ResponseEntity.ok("index");
}
}
这个Controller比较简单,浏览器访问 http://localhost:8080/index 会返回一个字符串 "index"。
写三个过滤器,需要实现javax.servlet.Filter接口,实现其中的三个方法。这三个过滤器分别命名为 FirstFilter SecondFilter ThirdFilter,以FirstFilter为例,其他的两个类内容和其基本一致,其代码内容如下:
import javax.servlet.*;
import java.io.IOException;
@component
public class FirstFilter implements Filter { @Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("FirstFilter init");
} @Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
throws IOException, ServletException {
System.out.println("FirstFilter doFilter pre");
filterChain.doFilter(servletRequest, servletResponse);
System.out.println("FirstFilter doFilter aft");
} @Override
public void destroy() {
System.out.println("FirstFilter destroy");
}
}
然后写一个配置类,来配置这三个过滤器,其代码内容如下:
@Configuration
public class FilterConfig {
@Autowired
private FirstFilter firstFilter;
@Autowired
private SecondFilter secondFilter;
@Autowired
private ThirdFilter thirdFilter; @Bean
public FilterRegistrationBean filterRegistrationBeanFirst() {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
// 可以采用 spring 的依赖注入 20191117update
filterRegistrationBean.setFilter(firstFilter);
filterRegistrationBean.addUrlPatterns("/index/*");
filterRegistrationBean.setName("FirstFilter");
filterRegistrationBean.setOrder(1);
return filterRegistrationBean;
} @Bean
public FilterRegistrationBean filterRegistrationBeanSecond() {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
filterRegistrationBean.setFilter(new SecondFilter());
filterRegistrationBean.addUrlPatterns("/index/*");
filterRegistrationBean.setName("SecondFilter");
filterRegistrationBean.setOrder(2);
return filterRegistrationBean;
} @Bean
public FilterRegistrationBean filterRegistrationBeanThird() {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
filterRegistrationBean.setFilter(new ThirdFilter());
filterRegistrationBean.addUrlPatterns("/index/*");
filterRegistrationBean.setName("ThirdFilter");
filterRegistrationBean.setOrder(3);
return filterRegistrationBean;
} }
因为有三个Filter,因此需要三个org.springframework.boot.web.servlet.FilterRegistrationBean,每个FilterRegisterationBean中需要设置属性 filterRegistrationBean.setFilter(new FirstFilter( )) ,并设置这个Filter拦截的url,顺序order等属性。
接下来写三个拦截器,需要实现 org.springframework.web.servlet.HandlerInterceptor 接口,重写其中的三个方法,这三个拦截器分别命名为FirstInterceptor SecondInterceptor ThirdInterceptor,以FirstInterceptor为例,其他两个类内容基本一致,其代码内容如下:
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView; import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@component
public class FirstInterceptor implements HandlerInterceptor {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
// 在请求处理之前进行调用(Controller方法调用之前)
System.out.println("FirstInterceptor preHandle");
return true;
} @Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
// 请求处理之后进行调用,但是在视图被渲染之前(Controller方法调用之后 )
System.out.println("FirstInterceptor postHandle");
} @Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
// 在整个请求结束之后被调用,也就是在DispatcherServlet 渲染了对应的视图之后执行(主要是用于进行资源清理工作)
System.out.println("FirstInterceptor afterCompletion");
}
}
然后写一个配置类,来配置这三个拦截器。这个配置类要实现org.springframework.web.servlet.config.annotation.WebMvcConfigurer。因为WebMvcConfigurerAdapter 在Spring5.0已被废弃,所以采用WebMvcConfigurer,其代码内容如下:
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 InterceptorConfig implements WebMvcConfigurer {
@Autowired
private FirstInterceptor firstInterceptor;
@Autowired
private SecondInterceptor secondInterceptor;
@Autowired
private ThirdInterceptor thirdInterceptor;
@Override
public void addInterceptors(InterceptorRegistry registry) {
// 可以将 FirstInterceptor 之类的由 spring 进行管理 不建议采用 new 的方法创建对象 20191117update
registry.addInterceptor(firstInterceptor).addPathPatterns("/index/**");
registry.addInterceptor(secondInterceptor).addPathPatterns("/index/**");
registry.addInterceptor(thirdInterceptor).addPathPatterns("/index/**");
} }
其中InterceptorRegistry内部有个List,这个addInterceptor( )方法是用来存放添加进去的interceptor,按照添加的先后顺序,依次拦截。
这样就完成了多个过滤器和多个拦截器的配置,浏览器访问 http://localhost:8080/index 可以看到控制台打印内容如下: