What is Spring Filter example code

What is Spring Filter API

In the context of the Spring Framework, a filter is a Java object that can be used to intercept requests and responses made by a web application. Filters can be used to perform various tasks, such as modifying request or response headers, adding security checks, or logging requests and responses.

Spring filters are typically implemented as classes that implement the javax.servlet.Filter interface. This interface defines three methods that a filter must implement: init, doFilter, and destroy. The init method is called when the filter is initialized, the doFilter method is called for each request and response that passes through the filter, and the destroy method is called when the filter is taken out of service.

Filters can be configured in the web application’s deployment descriptor (web.xml) or using Java configuration classes. In a Spring application, filters can be configured using the FilterRegistrationBean class.

Filters are useful for tasks that need to be performed on a large number of requests and responses, as they can be easily applied to an entire web application or a specific group of URLs. They can also be used to add functionality to a web application without modifying the application’s existing code.

SpringBoot Filter API example code

Here is an example of how you can create a filter in Spring Boot:

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

public class MyFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest req = (HttpServletRequest) request;
        String requestURI = req.getRequestURI();
        System.out.println("Request URI: " + requestURI);

        // You can add your own logic here to do something with the request before it is processed by the controller

        // Call the next filter in the chain
        chain.doFilter(request, response);
    }
}

To use this filter, you can either register it in your Spring Boot application by creating a @Bean of type FilterRegistrationBean, or by using the @WebFilter annotation on the filter class.

For example, you can register the filter using FilterRegistrationBean like this:

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

@Configuration
public class MyFilterConfig {

    @Bean
    public FilterRegistrationBean myFilter() {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean<>();
        registrationBean.setFilter(new MyFilter());
        registrationBean.addUrlPatterns("/api/*");
        return registrationBean;
    }
}

Alternatively, you can use the @WebFilter annotation on the filter class like this:

import javax.servlet.annotation.WebFilter;

@WebFilter(urlPatterns = "/api/*")
public class MyFilter implements Filter {
    // implementation as shown above
}

How many built-in Filter in SpringBoot

Spring Boot does not provide any built-in filters. However, it does provide several convenient features for working with filters, such as support for registering filters using FilterRegistrationBean or the @WebFilter annotation, and automatic ordering of filters based on their @Order annotation or the order property of FilterRegistrationBean.

You can create your own filters and register them in your Spring Boot application as needed. For example, you might create a filter to add security checks, modify the request or response, or perform logging.

There are also many third-party libraries that provide useful filters that you can use in your Spring Boot application, such as the Spring Security filter chain for adding security checks to your application.

Use-case to work with Filter in Spring

There are many use cases for using filters in a Spring application. Here are a few examples:

1. Security: You can use filters to add security checks to your application, such as authenticating users or checking for the presence of valid security tokens.

2. Request and response modification: You can use filters to modify the request or response before it is processed by the rest of the application. For example, you might use a filter to add headers to the response, or to transform the request body.

3. Logging: You can use filters to perform logging, such as recording the details of each request and response.

4. Performance monitoring: You can use filters to monitor the performance of your application, such as measuring the time it takes to process each request.

5. Caching: You can use filters to cache the results of certain requests, so that subsequent requests for the same data can be served more quickly.

6. Compression: You can use filters to compress the response body, to reduce the amount of data that needs to be transmitted over the network.

7. Internationalization: You can use filters to handle internationalization, such as selecting the appropriate language or locale based on the user’s preferences.

8. Error handling: You can use filters to handle errors that occur during the processing of a request, such as by returning a custom error page or logging the error details.

9. Redirection: You can use filters to redirect requests to different URLs based on certain conditions, such as the user’s role or the type of request.