add rate limit: 3 request per minute

Author: Matheus Vieira

src/main/java/MyServlet.java

@@ -6,13 +6,28 @@
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
+import utils.RateLimit;
+
 @WebServlet("/MyServlet")
 public class MyServlet extends HttpServlet {
 
+RateLimit rateLimit;
+
+public MyServlet() {
+if (rateLimit == null) {
+rateLimit = new RateLimit();
+}
+}
+
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
-response.setContentType("application/json");
- String json = "{\"status\": \"server running\"}";
- response.getWriter().write(json);
+
+if (rateLimit.doFilter(request)) {
+response.setContentType("application/json");
+String json = "{\"status\": \"server running\"}";
+response.getWriter().write(json);
+} else {
+response.setStatus(429);
+}
 }
 
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

src/main/java/utils/RateLimit.java

@@ -0,0 +1,76 @@
+ package utils;
+
+ import java.util.ArrayList;
+ import java.util.Calendar;
+ import java.util.concurrent.ConcurrentHashMap;
+ import java.util.Map;
+
+ import javax.servlet.http.HttpServletRequest;
+
+ public class RateLimit {
+
+ private static final int MAX_REQUESTS = 3;
+ private static final int INTERVAL = 1 * 60 * 1000; // 6000 ms || 1 min
+
+ private Map<String, ArrayList<Calendar>> requestsList;
+
+ public RateLimit() {
+ requestsList = new ConcurrentHashMap<String, ArrayList<Calendar>>();
+ }
+
+ public boolean doFilter(HttpServletRequest request) {
+
+ String sessionId = request.getSession().getId();
+ Calendar currentTime = this.getCurrentTime();
+
+ if (requestsList.containsKey(sessionId)) {
+ if (isAnExceedingRequest(sessionId)) {
+ return false;
+ }
+
+ requestsList.get(sessionId).add(currentTime);
+ } else {
+ ArrayList<Calendar> test = new ArrayList<Calendar>();
+ test.add(currentTime);
+
+ requestsList.put(sessionId, test);
+ }
+
+ return true;
+ }
+
+ public Boolean isAnExceedingRequest(String sessionId) {
+
+ ArrayList<Calendar> requestsListArray = requestsList.get(sessionId);
+ int requestsListArraySize = requestsListArray.size();
+ Calendar currentTime = getCurrentTime();
+
+ if (requestsListArraySize < MAX_REQUESTS) {
+ return false;
+ }
+
+ int countRequestLessThanOneMinute = 0;
+
+ // getting the last items from list
+ for (int i = 0; i < MAX_REQUESTS; i++) {
+
+ if ((currentTime.getTimeInMillis()
+ - requestsListArray.get(requestsListArraySize - (i + 1)).getTimeInMillis()) < INTERVAL) {
+ countRequestLessThanOneMinute++;
+ }
+
+ }
+
+ if (countRequestLessThanOneMinute == MAX_REQUESTS) {
+ return true;
+ }
+
+ return false;
+ }
+
+ public Calendar getCurrentTime() {
+ Calendar now = Calendar.getInstance();
+ return now;
+ }
+
+ }