Updated April 17, 2023
Introduction to Spring boot filter
In Spring boot, we have filters to filter the HTTP request; filter, in general, is used to intercept the request, i.e. HTTP request and the response from the client-side. By the use of a filter, we can perform two operations which can be done on response and request. This is very useful when we want to restrict any URL to be accessed from the user, and also, we can do many things on the request and response instance in Spring boot. In the coming section, we will see how it works internally and what configurations are required to use this in spring boot, usage, and implementation to understand it better.
Syntax
As we have seen it is a class which is used to filter the request and response that we receive on the spring boot application, but to use this we have to follow some standard and need to do some configuration in order to use this properly, see below for better understanding;
@Component
public class filter_name implements Filter {
// need to implement the required methods here ..
}As you can see in the above syntax, we are creating a simple filter by using the Filter interface here. After this, we need to implement the methods also inside it. Let’s take a closer look at the practice piece of syntax for better clarity for beginners to see below;
Example:
@Component
public class MyFilter implements Filter {
// need to implement the required methods here ..
}In the coming section of the tutorial, we will take a closer look at all the configurations and annotations we have used to define this filter in detail in order to use this without any error in the application for beginners.
How to apply the filter in Spring boot?
As of now, we already know that filter in spring boot or, in general, is used to perform the action on the request and response instance. By the use of this, we can restrict the URL; first, it will come to the filter, then only it will navigate to the respective controller if applicable else, we can send the request back to the client mentioning some reason as well. In this section, first, we will see the basic two things about filter then we will start creating a filter class in spring boot with all required configurations; let’s get started to see below;
1. It is used to intercept or filter the HTTP response and request instance.
2. It can perform operations on the request instance before sending the request instance to the controller.
3. It can perform operations on the response instance before sending the response instance to the requested client.
4. In the spring boot application, we have to use the @Component annotation in the filter class.
5. We will use the javax.servlet.Filter fr this, we do not require adding the external dependency as well; it can be used directly.
6. WE can also create multiple filters by mentioning the Order for them in Spring boot.
Let’s take a sample piece of code to understand the filter working in more details see below;
@Component
@Order(1)
public class MyFilter implements Filter {
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest r1 = (HttpServletRequest) request;
Logger.info("convert the object to this URL is ::" +r1.getRequestURI());
chain.doFilter(request, response);
Logger.info("done with request sending response URL is ::" +r1.getRequestURI());
}
}As you can see in the above Filter that we have created, it is very simple and easy to understand where we are just processing the request and response to the client. Let’s understand it better;
1. First, we have used to @Component annotation to treat this class as Filter and tell spring to initialize this class while startup.
2. Secondly, we have used the @Order annotation, which will execute this filter first in the application; we have also mentioned the precedence for this filter as (1).
3. From here, we have created one class that implements the Filter interface from Servlet. This interface has this doFilter() method, which needs to be implemented while using the filter infract.
4. So, we have overridden the filter methods inside the class; this method will trigger if we receive any request or any HTTP request from the client in the spring boot application. So inside this method, we have ServletRequest and ServletResponse objects.
5. We have now tried to cast the ServletRequest object to the HttpServletRequest object and try to get the URI from it. After that, we have called the doFilter again and passed the request and response object inside it. This method will now hand over the object to the controller, and all the required operations will get performed there. Once all the things are done, at last again, the control is back to this methods only, then if we want we can do.
6. We are here just trying to log this flow by using loggers inside the class.
7. In this way, a basic filter works in general in spring boot or any other framework, let say, spring framework.
8. Other configurations and structures of the spring boot application will be the same; there will be no changes. Also, we need to have all the required dependency, mainspring class in place in order to use this and run the application without errors.
9. We can create the basic structure of the spring boot application by the spring initializer online; it will create the application with all necessary dependency. One more thing in order to run this and test, we have to have a controller in place.
Conclusion
Using a filter, we can do many things before and after they receive and respond, it just depends on the requirement. Also, we can restrict some URL, make changes to the committed transaction before sending it to the client, and so many more. As you have seen, it is also easy to handle, readable, and understandable by the developers.
Recommended Articles
This is a guide to the Spring boot filter. Here we discuss how it works internally and also what configurations are required to use this in spring boot, usage, and implementation in detail. You may also have a look at the following articles to learn more –
