use

AOP-- Oriented Programming. In the process of object-oriented programming, we can easily through inheritance, polymorphism to solve scale up. But for lateral features, such as uniform or unified logging encryption rule checking functions, object-oriented can not be solved. So we need to use AOP-- way Oriented Programming supplement. Filter and interceptors are all embodied aspect-oriented programming.

Difference between the two

1, Filter Servlet container is dependent on, part of the Servlet specification, and the interceptor is independent existence, may be used in any case.

2, is completed by the execution Filter callback Servlet container, the interceptor is typically performed by a dynamic proxy.

3, Filter Servlet container life cycle managed by the interceptor can be managed by IoC container, it is possible to obtain by other examples Bean injection, etc., and therefore will be more convenient to use.

 

filter

Configuration

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class LogRecordFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
 
    }
 
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        long start = System.currentTimeMillis();
        HttpServletRequest httpServletRequest = (HttpServletRequest)servletRequest;
        filterChain.doFilter(servletRequest,servletResponse);
        // TODO Logging section
                 System.out.println (httpServletRequest.getRequestURL () + "; Request Processed cost =" + (System.currentTimeMillis () - start));
    }
 
    @Override
    public void destroy() {
 
    }
}

This class must inherit Filter class, this is the Servlet specification, this is no difference with the previous Web project. However, later with the filter class, the previous web project can be configured in web.xml, but the project did not spring boot the web.xml file, how to configure?

In Spring boot, there are two ways

1, FilterRegistrationBean need to complete the configuration. Which process is as follows:

@Configuration
public class FilterConfig {
 
    @Bean
    public FilterRegistrationBean registFilter() {
        FilterRegistrationBean registration = new FilterRegistrationBean();
        registration.setFilter(new LogRecordFilter());
        registration.addUrlPatterns("/*");
        registration.setName("LogRecordFilter");
        registration.setOrder(1);
        return registration;
    }
 
}

Configuration is complete, you need to configure the options include instantiating Filter class, and then specify the url of the match mode, set the filter name and the execution order, and this process configuration in web.xml in fact no difference, just different forms

2, WebFilter comment

@WebFilter(urlPatterns = "/*", filterName = "logRecordFilter ")
public class LogRecordFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
 
    }
 
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        long start = System.currentTimeMillis();
        HttpServletRequest httpServletRequest = (HttpServletRequest)servletRequest;
        filterChain.doFilter(servletRequest, servletResponse);
        System.out.println(httpServletRequest.getRequestURL() + ";Execute cost=" + (System.currentTimeMillis() - start));
    }
 
    @Override
    public void destroy() {
 
    }
}

Can be configured with @WebFilter, likewise, you may be provided url matching mode, the filter names. It should be noted that it is important @WebFilter this annotation is Servlet3.0 the norm, not the Spring boot provided. In addition to this comment, we still need to add another comment in the configuration class: @ServletComponetScan, specify the scan package.

@SpringBootApplication
@ServletComponentScan("com.xxxx.xxx.filters")
public class Application {
    public static void main(String[] args) throws Exception {
        SpringApplication.run(Application.class, args);
    }
}

The second Filter does not specify the order of execution, but before the first implementation of a Filter. This annotation @WebFilter attribute does not specify the execution order, the execution order which depends on the name Filter is (note that the name is not arranged filter) Filter according to the class name in alphabetical order reverse order, and the specified filter @WebFilter priority FilterRegistrationBean higher than the filter configuration.

Interceptor

Configuration

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

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

public class LogReocrdInterceptor implements HandlerInterceptor {
    long start = System.currentTimeMillis();
    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        start = System.currentTimeMillis();
        return true;
    }
 
    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println("Interceptor cost="+(System.currentTimeMillis()-start));
    }
 
    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
    }
}

HandlerInterceptor need to implement this interface, which consists of three methods:

1. preHandle is a request before execution;
2. postHandler end of the request is carried out, but only when the method returns true preHandle will be performed;
3. afterCompletion view is rendered after the completion of the implementation, we also need preHandle returns true, the method commonly used to clean up resources and so on.

In addition to implementing the above interface, we need to configure

@Configuration
public class InterceptorConfig extends WebMvcConfigurerAdapter {
 
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LogRecordInterceptor()).addPathPatterns("/**");
        super.addInterceptors(registry);
    }
}

Inheritance WebMVCConfigurerAdapter, rewritten addInterceptors this method to configure the interceptor, the configuration item on the main two, one is designated interceptor, the second is designated to intercept URL

to sum up

By intercepting and filters can achieve the same functionality. However, the filter preHandle and postHandle are two methods, so had to start to set up a shared variable to store the start values, but this will be the presence of thread-safety issues. Of course, we can be resolved by other means, for example, can be a good solution to this problem through ThreadLocal.

By this point you can see, although the interceptor filter is better than in many scenes, but in this scenario, the filter to implement than the interceptor easier.