Question

Write a Java Program for API rate Limiter. Design an API rate limiter which can allows R requests in T seconds. Solve it using a map of seconds and counts. For every hit the rate Limit function would check the last T seconds count. Implement a rate limiter based on user ID.

Answer 1

To implement an API rate limiter in Java, use a map to store timestamps and counts of requests made in the last T seconds, and remove expired entries from the map. The RateLimiter class has a constructor that takes the time limit and a time unit, and the allowRequest checks if a user has exceeded the limit of R requests in T seconds.

Step-by-step explanation:

To implement an API rate limiter in Java, you can use a map to store the timestamps and counts of requests made in the last T seconds. Here's an example code:

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

class RateLimiter {
private final Map requestCounts;
private final long timeLimit;

public RateLimiter(long timeLimit, TimeUnit timeUnit) {
this.timeLimit = timeUnit.toMillis(timeLimit);
this.requestCounts = new HashMap<>();
}

public boolean allowRequest(String userId) {
long currentTime = System.currentTimeMillis();
long count = requestCounts.getOrDefault(userId, 0L);

if (count >= R) {
return false;
}

requestCounts.put(userId, count + 1);
requestCounts.entrySet().removeIf(entry -> currentTime - entry.getValue() >= timeLimit);

return true;
}
}

In this example, the RateLimiter class has a constructor that takes the time limit in seconds and a time unit. The allowRequest method checks if the user has exceeded the limit of R requests in T seconds. If not, it increments the count and removes any expired entries from the map. If the limit is reached, it returns false.