一.本文通过实现服务请求时间统计,来说明拦截器,过滤器,以及切片在spring boot中的使用以及配置

一.过滤器(Filter)

1,配置方法一(实现Filter,并添加@Component注解 )

import org.springframework.stereotype.Component;

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

/**
 * @author Mr_li
 */
@Component
public class TimeFilter implements Filter {

    @Override
    public void destroy() {
        System.out.println("time filter destroy");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        System.out.println("time filter start");
        long start = System.currentTimeMillis();
        chain.doFilter(request, response);
        System.out.println("time filter 耗时:" + (System.currentTimeMillis() - start));
        System.out.println("time filter finish");
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        System.out.println("time filter init");
    }

}

2,配置方法二(实现Filter,使用Bean配置 )

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

/**
 * @author Mr_li
 */
public class TimeFilter implements Filter {

    @Override
    public void destroy() {
        System.out.println("time filter destroy");
    }
    
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
        System.out.println("time filter start");
        long start = System.currentTimeMillis();
        chain.doFilter(request, response);
        System.out.println("time filter 耗时:" + (System.currentTimeMillis() - start));
        System.out.println("time filter finish");
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        System.out.println("time filter init");
    }

}

-----------------------------------------------------------------------------------------

import java.util.ArrayList;
import java.util.List;

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.imooc.web.filter.TimeFilter;

/**
 * @author Mr_li
 */
@Configuration
public class WebConfig {

    @Bean
    public FilterRegistrationBean timeFilter() {

        FilterRegistrationBean registrationBean = new FilterRegistrationBean();

        TimeFilter timeFilter = new TimeFilter();
        registrationBean.setFilter(timeFilter);

        List<String> urls = new ArrayList<>();
        urls.add("/*");
        registrationBean.setUrlPatterns(urls);

        return registrationBean;

    }

}

二.拦截器(Filter)

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Component;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

/**
 * @author Mr_li
 */
@Component
public class TimeInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        System.out.println("preHandle");

        System.out.println(((HandlerMethod) handler).getBean().getClass().getName());
        System.out.println(((HandlerMethod) handler).getMethod().getName());

        request.setAttribute("startTime", System.currentTimeMillis());
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle");
        Long start = (Long) request.getAttribute("startTime");
        System.out.println("time interceptor 耗时:" + (System.currentTimeMillis() - start));

    }
    
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion");
        Long start = (Long) request.getAttribute("startTime");
        System.out.println("time interceptor 耗时:" + (System.currentTimeMillis() - start));
        System.out.println("ex is " + ex);
    }
}

-----------------------------------------------------------------------------------------

@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {

    @Autowired
    private TimeInterceptor timeInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(timeInterceptor);
    }
}

二.springmvc中中央控制器、处理器、过滤器和拦截器的执行时机

过滤器和拦截器的区别：

①拦截器是基于java的反射机制的，而过滤器是基于函数回调。

②拦截器不依赖与servlet容器，过滤器依赖与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拦截器可以访问action上下文、值栈里的对象，而过滤器不能访问。

⑤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

1.过滤器是JavaEE标准，采用函数回调的方式进行。是在请求进入容器之后，还未进入Servlet之前进行预处理，并且在请求结束返回给前端这之间进行后期处理。

@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...");
}

chain.doFilter(request, response);这个方法的调用作为分水岭。事实上调用Servlet的doService()方法是在chain.doFilter(request, response);这个方法中进行的。

2.拦截器是被包裹在过滤器之中的。

  @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，也就是在 [System.out.println("before...")][chain.doFilter(request, response)]之间执行。

preHandle()方法之后，在return ModelAndView之前进行，可以操控Controller的ModelAndView内容。

afterCompletion()方法是在过滤器返回给前端前一步执行，也就是在[chain.doFilter(request, response)][System.out.println("after...")]之间执行。

过滤器,拦截器,aop