What is the difference between JAVA filter and interceptor?

Preface

In Java Web development, filters and interceptors are two commonly used components that are used to intercept and process requests at different stages of request processing. They have different uses and implementation mechanisms, and the difference is detailed below.

Filter

A filter is a component defined in the Java Servlet specification that pre-processes and post-processes requests and responses before a request reaches the target resource or before a response returns to the client. Filters are mainly used in the following scenarios:

• Logging: Log information about requests and responses.
• Certification and authorization: Check whether the user has permission to access a resource.
• Enter verification: Verify the legality of the request parameters.
• Compress and decompress: Compress and decompress requests and responses.
• Character encoding: Set the character encoding of request and response.

Implementation mechanism

Filters are implemented byThe interface is defined, usually inConfigure in the file, or use annotation configuration. The workflow of the filter is as follows:

• initialization: The filter is initialized when the web application starts.
• Intercept requests: When the request arrives, the filter intercepts the request and callsdoFilterMethods to process.
• Pass the request: Filters can choose to pass the request to the next filter or target resource.
• Processing response: The filter can process the response before it returns to the client.
• destroy: The filter is destroyed when the web application is closed.

Sample code

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public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // Initialize the filter    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // Code executed before request processing        ("Before request processing");

        // Pass the request to the next filter or target resource        (request, response);

        // Code executed before the response returns        ("After response processing");
    }

    @Override
    public void destroy() {
        // Destroy the filter    }
}

Interceptor

Interceptor is a component defined in the Spring framework for intercepting requests during Spring MVC processing requests. Interceptors are mainly used in the following scenarios:

• Logging: Log information about requests and responses.
• Certification and authorization: Check whether the user has permission to access a resource.
• Enter verification: Verify the legality of the request parameters.
• Performance monitoring: Monitor the time of request processing.

Implementation mechanism

Interceptor is implemented byInterface definition, usually configured in Spring configuration files, or using annotation configuration. The interceptor workflow is as follows:

• Preprocessing: The interceptor will call before the request reaches the controllerpreHandleMethods are pre-processed.
• Post-processing: After the controller handles the request, but before the view renders, the interceptor callspostHandleMethods are post-processed.
• Complete processing: After the view is rendered, the interceptor will callafterCompletionThe method completes the processing.

Sample code

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public class MyInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        // Code executed before request processing        ("Before request processing");
        return true; // Return true means continue processing of the request, return false means interrupt request processing    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           ModelAndView modelAndView) throws Exception {
        // Code executed after the controller handles the request, but before the view renders        ("After request processing, before view rendering");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
                                Exception ex) throws Exception {
        // Code executed after view rendering        ("After view rendering");
    }
}

Summary of the difference

• Specifications and frameworks：

  • Filter: belongs to the Java Servlet specification and is suitable for all Servlet-based web applications.
  • Interceptor: Belongs to the Spring Framework and is only suitable for Spring MVC applications.

• Range of action：

  • Filter: Acts on all requests and responses, including static resources.
  • Interceptor: Only for requests processed by Spring MVC, and do not include static resources.

• Execution timing：

  • Filter: Execute before the request reaches the target resource and before the response returns to the client.
  • Interceptor: Execute before, after, and after view rendering.

• Configuration method：

  • Filter: Usually inConfigure in the file, or use annotation configuration.
  • Interceptor: Usually configured in Spring configuration files, or using annotation configuration.

Summarize

Filters and interceptors are components used to intercept and process requests, but they have different uses and implementation mechanisms. Filters belong to the Java Servlet specification and are suitable for all Servlet-based web applications; interceptors belong to the Spring framework and are only suitable for Spring MVC applications. Selecting the appropriate components according to specific needs can better implement pre-processing and post-processing of requests.

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