For register Single custom filter
Creating a custom filter in microservices using Java with
advanced mathematical formulas can help fine-tune traffic control, load
balancing, and other service-specific requirements. Here's a practical
implementation that includes a custom filter class in Java, using a scoring
formula to prioritize or throttle incoming requests. This example can be
integrated into a Spring Cloud Gateway or Spring Boot application.
Scenario
We'll design a filter that calculates a "priority
score" based on user subscription level, request rate, and service load to
control access dynamically. The filter will:
- Throttle
requests if the priority score is low.
- Delay
processing if the score is moderate.
- Allow
immediate access for high scores.
Mathematical Formula for Priority Score
Here's a sample formula to calculate the priority score:
$$priorityScore=\frac{subscriptionLevel×baseWeight}{requestRate+serviceLoad}$$
Where:
Ø subscriptionLevel:
Integer value based on user level (e.g., 1 for Basic, 3 for Premium).
Ø baseWeight:
A constant multiplier, say 10.
Ø requestRate:
Number of requests by the user in a short interval (e.g., 10 seconds).
Ø serviceLoad:
Dynamic load metric representing current service usage (e.g., requests per
second).
Implementing the Filter in Java (Spring Boot)
Below is a custom filter in Java using Spring Boot, which
calculates the priority score and determines access based on that score.
Custom Filter Class
- Create
a filter in Spring Boot using OncePerRequestFilter.
- Calculate
the priority score using the formula above.
- Decide
the course of action based on the calculated score.
Code Example
java
import
org.springframework.stereotype.Component; import
javax.servlet.FilterChain; import
javax.servlet.Filter; import
javax.servlet.FilterConfig; import
javax.servlet.ServletException; import
javax.servlet.ServletRequest; import
javax.servlet.ServletResponse; import
javax.servlet.http.HttpServletRequest; import
javax.servlet.http.HttpServletResponse; import
java.io.IOException; @Component public class
CustomMathFilter implements Filter { private static final int BASE_WEIGHT =
10; @Override public void doFilter(ServletRequest
request, ServletResponse response, FilterChain chain) throws IOException,
ServletException { HttpServletRequest httpRequest =
(HttpServletRequest) request; HttpServletResponse httpResponse =
(HttpServletResponse) response; // Simulating request rate and
service load int requestRate =
getRequestRateForUser(httpRequest); // Example function int serviceLoad =
getCurrentServiceLoad(); // Example function int subscriptionLevel =
getUserSubscriptionLevel(httpRequest); // Example function // Calculate priority score based on
our formula double priorityScore =
calculatePriorityScore(subscriptionLevel, requestRate, serviceLoad); // Apply actions based on priority
score if (priorityScore < 1) { // Block request
httpResponse.setStatus(HttpServletResponse.SC_TOO_MANY_REQUESTS);
httpResponse.getWriter().write("Request rate too high. Please try
again later."); } else if (priorityScore < 2) { // Delay request try { Thread.sleep(1000); // Delay
processing by 1 second } catch (InterruptedException e)
{
Thread.currentThread().interrupt(); } chain.doFilter(request,
response); } else { // Allow request immediately chain.doFilter(request,
response); } } // Priority score calculation method private double calculatePriorityScore(int
subscriptionLevel, int requestRate, int serviceLoad) { return (double) (subscriptionLevel *
BASE_WEIGHT) / (requestRate + serviceLoad); } // Dummy method to simulate retrieving
user subscription level private int
getUserSubscriptionLevel(HttpServletRequest request) { String userId =
request.getHeader("user-id"); return
getUserSubscriptionLevelFromDb(userId); // Replace with actual retrieval
logic } // Dummy method to simulate request rate
per user private int
getRequestRateForUser(HttpServletRequest request) { String userId =
request.getHeader("user-id"); return
getRequestCountInLast10Seconds(userId); // Replace with actual tracking logic } // Dummy method to simulate current
service load private int getCurrentServiceLoad() { return getCurrentRequestsPerSecond();
// Replace with actual load calculation } @Override public void init(FilterConfig
filterConfig) throws ServletException {} @Override public void destroy() {} } |
Explanation of Code
Ø
calculatePriorityScore: Computes the
priority score based on subscription level, request rate, and current service
load.
Ø
Decision Logic:
ü
Low score (< 1): Rejects the request
with a 429 Too Many Requests error.
ü
Moderate score (1 ≤ score < 2): Delays
processing by 1 second.
ü
High score (≥ 2): Allows immediate
processing.
Ø
Helper Methods (getUserSubscriptionLevel,
getRequestRateForUser, getCurrentServiceLoad): Simulates retrieval of dynamic
values like user subscription, request rate, and load. Replace these with
actual implementations or database queries as needed.
Adding the Filter to Spring Boot Configuration
To make the filter active, you may add it to the filter
chain configuration in your Spring Boot application.
java
import
org.springframework.boot.SpringApplication; import
org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class
Application { public static void main(String[] args) {
SpringApplication.run(Application.class, args); } } |
Testing and Tuning
- Load
Testing: Test the filter under different simulated loads to ensure it
performs as expected and handles request rates gracefully.
- Monitoring:
Use logging or monitoring tools to observe filter decisions and identify
any need for formula adjustments.
UML Sequence Diagram for Filter Process
The following UML sequence describes the flow through the
custom filter logic based on the calculated score:
Building Custom Microservice Filters with Java and Math |
Summary
This custom filter:
- Calculates
a priority score using mathematical operations.
- Controls
request access dynamically based on calculated metrics.
- Improves
responsiveness and manages load by selectively throttling or delaying
requests.
This setup is particularly useful for microservices handling
high traffic where dynamic access control is essential for maintaining stable
performance.
For register multiple custom filters
To register multiple custom filters as beans in a Spring
Boot application, you can configure each filter individually and define the
order in which they are executed. Here’s how you can set up and register
multiple filters:
1. Define Each Custom Filter as a Spring Bean
Each filter should be implemented as a separate class,
implementing either the javax.servlet.Filter interface or extending OncePerRequestFilter
(a Spring-specific filter base class that guarantees a single execution per
request).
Example of Custom Filter 1: CustomMathFilter
java
import
org.springframework.stereotype.Component; import
javax.servlet.FilterChain; import
javax.servlet.Filter; import
javax.servlet.FilterConfig; import
javax.servlet.ServletException; import
javax.servlet.ServletRequest; import
javax.servlet.ServletResponse; import
javax.servlet.http.HttpServletRequest; import
javax.servlet.http.HttpServletResponse; import
java.io.IOException; @Component public class
CustomMathFilter implements Filter { @Override public void doFilter(ServletRequest
request, ServletResponse response, FilterChain chain) throws IOException,
ServletException { // Custom filtering logic for
mathematical calculations chain.doFilter(request, response); } @Override public void init(FilterConfig
filterConfig) throws ServletException {} @Override public void destroy() {} } |
Example of Custom Filter 2: CustomAuthFilter
java
import
org.springframework.stereotype.Component; import
javax.servlet.FilterChain; import
javax.servlet.Filter; import
javax.servlet.FilterConfig; import
javax.servlet.ServletException; import
javax.servlet.ServletRequest; import
javax.servlet.ServletResponse; import
javax.servlet.http.HttpServletRequest; import
javax.servlet.http.HttpServletResponse; import
java.io.IOException; @Component public class
CustomAuthFilter implements Filter { @Override public void doFilter(ServletRequest
request, ServletResponse response, FilterChain chain) throws IOException,
ServletException { // Custom authentication logic chain.doFilter(request, response); } @Override public void init(FilterConfig
filterConfig) throws ServletException {} @Override public void destroy() {} } |
2. Register the Filters as Beans and Define Order
In Spring Boot, you can specify the order of filters using @Order.
Filters with lower order values will execute first.
java
import
org.springframework.boot.web.servlet.FilterRegistrationBean; import
org.springframework.context.annotation.Bean; import
org.springframework.context.annotation.Configuration; import
org.springframework.core.Ordered; @Configuration public class
FilterConfig { @Bean public
FilterRegistrationBean<CustomMathFilter> mathFilterRegistration() {
FilterRegistrationBean<CustomMathFilter> registrationBean = new
FilterRegistrationBean<>(); registrationBean.setFilter(new
CustomMathFilter()); registrationBean.setOrder(Ordered.HIGHEST_PRECEDENCE);
// Execute first return registrationBean; } @Bean public
FilterRegistrationBean<CustomAuthFilter> authFilterRegistration() {
FilterRegistrationBean<CustomAuthFilter> registrationBean = new
FilterRegistrationBean<>(); registrationBean.setFilter(new
CustomAuthFilter()); registrationBean.setOrder(Ordered.HIGHEST_PRECEDENCE +
1); // Execute second return registrationBean; } } |
Explanation
Ø mathFilterRegistration
registers CustomMathFilter as a bean with the highest precedence.
Ø authFilterRegistration
registers CustomAuthFilter to execute right after CustomMathFilter.
Ø Order
Management: Ordered.HIGHEST_PRECEDENCE ensures that the filters execute in
the desired sequence.
3. Testing the Filters
When you start the Spring Boot application, the filters will
automatically apply to all incoming requests in the specified order. You can
verify their execution by adding logging statements inside each filter’s doFilter
method.
Real Example: Setting Up Math-Related Filters in
Spring Boot
Let's create two custom filters:
- AdditionFilter:
Adds two numbers passed as query parameters and forwards the result.
- MultiplicationFilter:
Multiplies the result from AdditionFilter by another factor passed in the
request.
Each filter will be registered as a Spring bean and ordered
in sequence to process the request flow.
Step 1: Create the Filters
AdditionFilter: Performs Addition Based on Query
Parameters
This filter will add two numbers (a and b) that are passed
in the query parameters of the request and store the result in an attribute for
further processing.
Java
import
org.springframework.stereotype.Component; import
javax.servlet.Filter; import
javax.servlet.FilterChain; import
javax.servlet.FilterConfig; import
javax.servlet.ServletException; import
javax.servlet.ServletRequest; import
javax.servlet.ServletResponse; import
java.io.IOException; @Component public class
AdditionFilter implements Filter { @Override public void doFilter(ServletRequest
request, ServletResponse response, FilterChain chain) throws IOException,
ServletException { // Retrieve numbers a and b from
query parameters String aParam =
request.getParameter("a"); String bParam =
request.getParameter("b"); try { int a = Integer.parseInt(aParam); int b = Integer.parseInt(bParam); int sum = a + b; // Store the sum as a request
attribute for the next filter
request.setAttribute("sum", sum); } catch (NumberFormatException e) { throw new
ServletException("Invalid input for addition. Please provide integer
values for 'a' and 'b'."); } chain.doFilter(request, response); //
Pass control to the next filter } @Override public void init(FilterConfig
filterConfig) throws ServletException {} @Override public void destroy() {} } |
MultiplicationFilter: Multiplies the Sum by a Factor
This filter retrieves the sum attribute set by AdditionFilter
and multiplies it by a factor query parameter.
java
import
org.springframework.stereotype.Component; import
javax.servlet.Filter; import
javax.servlet.FilterChain; import
javax.servlet.FilterConfig; import
javax.servlet.ServletException; import
javax.servlet.ServletRequest; import
javax.servlet.ServletResponse; import
java.io.IOException; @Component public class
MultiplicationFilter implements Filter { @Override public void doFilter(ServletRequest
request, ServletResponse response, FilterChain chain) throws IOException,
ServletException { Integer sum = (Integer)
request.getAttribute("sum"); String factorParam =
request.getParameter("factor"); if (sum == null) { throw new
ServletException("Addition result not found. Ensure AdditionFilter is
applied."); } try { int factor =
Integer.parseInt(factorParam); int result = sum * factor; // Set the final result as a
request attribute
request.setAttribute("result", result); } catch (NumberFormatException e) { throw new
ServletException("Invalid input for multiplication. Please provide an
integer value for 'factor'."); } chain.doFilter(request, response); //
Pass control to the next component } @Override public void init(FilterConfig
filterConfig) throws ServletException {} @Override public void destroy() {} } |
Step 2: Register the Filters as Beans in Spring Boot
Now, register the filters and set their order so that AdditionFilter
runs before MultiplicationFilter.
java
import
org.springframework.boot.web.servlet.FilterRegistrationBean; import
org.springframework.context.annotation.Bean; import
org.springframework.context.annotation.Configuration; import
org.springframework.core.Ordered; @Configuration public class
FilterConfig { @Bean public
FilterRegistrationBean<AdditionFilter> additionFilterRegistration() {
FilterRegistrationBean<AdditionFilter> registrationBean = new
FilterRegistrationBean<>(); registrationBean.setFilter(new
AdditionFilter());
registrationBean.setOrder(Ordered.HIGHEST_PRECEDENCE); // First filter
to run return registrationBean; } @Bean public
FilterRegistrationBean<MultiplicationFilter>
multiplicationFilterRegistration() {
FilterRegistrationBean<MultiplicationFilter> registrationBean =
new FilterRegistrationBean<>(); registrationBean.setFilter(new
MultiplicationFilter());
registrationBean.setOrder(Ordered.HIGHEST_PRECEDENCE + 1); // Runs
after AdditionFilter return registrationBean; } } |
Step 3: Access the Final Result in the Controller
Create a simple Spring REST controller to access the final
result after both filters have processed the request.
java
import
org.springframework.web.bind.annotation.GetMapping; import
org.springframework.web.bind.annotation.RequestAttribute; import
org.springframework.web.bind.annotation.RestController; @RestController public class
MathController { @GetMapping("/calculate") public String
calculate(@RequestAttribute("result") Integer result) { return "Final result after
addition and multiplication is: " + result; } } |
How It Works
- The
request first passes through AdditionFilter, which calculates the sum of
parameters a and b and stores it as a request attribute.
- MultiplicationFilter
then retrieves this sum and multiplies it by the factor parameter.
- The
controller accesses the final result attribute and returns it as a
response.
Example Request
Assume you run the application and send a request as
follows:
bash
GET
http://localhost:8080/calculate?a=2&b=3&factor=4 |
Ø Addition
Filter: Adds a (2) and b (3) → sum = 5
Ø Multiplication
Filter: Multiplies sum (5) by factor (4) → result = 20
Response:
Plain text
Final result
after addition and multiplication is: 20 |
This setup demonstrates a chain of custom filters, where
each filter performs a mathematical operation, passing results to the next
filter in sequence. This modular approach is powerful for processing complex
mathematical or logical operations in microservices.
For more information, visit
Ø
Microservices:
Custom Filters for Debouncing, Throttling, Rate Limits & Backoff
Ø
Mastering Debouncing, Throttling, Rate Limiting, and Exponential
Backoff.
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