diff --git a/tomcat/src/main/java/nextstep/jwp/db/InMemoryUserRepository.java b/tomcat/src/main/java/nextstep/jwp/db/InMemoryUserRepository.java
index 1ca30e8383..d043a8f1f2 100644
--- a/tomcat/src/main/java/nextstep/jwp/db/InMemoryUserRepository.java
+++ b/tomcat/src/main/java/nextstep/jwp/db/InMemoryUserRepository.java
@@ -1,27 +1,35 @@
 package nextstep.jwp.db;
 
-import nextstep.jwp.model.User;
-
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicLong;
+import nextstep.jwp.model.User;
 
 public class InMemoryUserRepository {
 
     private static final Map<String, User> database = new ConcurrentHashMap<>();
+    private static final AtomicLong auto_increment = new AtomicLong(1);
 
     static {
-        final User user = new User(1L, "gugu", "password", "hkkang@woowahan.com");
+        final User user = new User(auto_increment.getAndIncrement(), "gugu", "password", "hkkang@woowahan.com");
         database.put(user.getAccount(), user);
     }
 
     public static void save(User user) {
-        database.put(user.getAccount(), user);
+        final User saveUser = new User(
+                auto_increment.getAndIncrement(),
+                user.getAccount(),
+                user.getPassword(),
+                user.getEmail()
+        );
+        database.put(saveUser.getAccount(), saveUser);
     }
 
     public static Optional<User> findByAccount(String account) {
         return Optional.ofNullable(database.get(account));
     }
 
-    private InMemoryUserRepository() {}
+    private InMemoryUserRepository() {
+    }
 }
diff --git a/tomcat/src/main/java/nextstep/jwp/model/User.java b/tomcat/src/main/java/nextstep/jwp/model/User.java
index 4c2a2cd184..158ae5cce5 100644
--- a/tomcat/src/main/java/nextstep/jwp/model/User.java
+++ b/tomcat/src/main/java/nextstep/jwp/model/User.java
@@ -26,6 +26,14 @@ public String getAccount() {
         return account;
     }
 
+    public String getPassword() {
+        return password;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
     @Override
     public String toString() {
         return "User{" +
diff --git a/tomcat/src/main/java/org/apache/catalina/connector/Connector.java b/tomcat/src/main/java/org/apache/catalina/connector/Connector.java
index 3b2c4dda7c..fd71342758 100644
--- a/tomcat/src/main/java/org/apache/catalina/connector/Connector.java
+++ b/tomcat/src/main/java/org/apache/catalina/connector/Connector.java
@@ -1,13 +1,16 @@
 package org.apache.catalina.connector;
 
-import org.apache.coyote.http11.Http11Processor;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.net.ServerSocket;
 import java.net.Socket;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.LinkedBlockingDeque;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import org.apache.coyote.http11.Http11Processor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public class Connector implements Runnable {
 
@@ -15,15 +18,25 @@ public class Connector implements Runnable {
 
     private static final int DEFAULT_PORT = 8080;
     private static final int DEFAULT_ACCEPT_COUNT = 100;
+    private static final int MAX_THREAD = 250;
+    private static final int MAX_WAITING_COUNT = 100;
 
+    private final ExecutorService executorService;
     private final ServerSocket serverSocket;
     private boolean stopped;
 
     public Connector() {
-        this(DEFAULT_PORT, DEFAULT_ACCEPT_COUNT);
+        this(DEFAULT_PORT, DEFAULT_ACCEPT_COUNT, MAX_THREAD);
     }
 
-    public Connector(final int port, final int acceptCount) {
+    public Connector(final int port, final int acceptCount, final int maxThreads) {
+        this.executorService = new ThreadPoolExecutor(
+                maxThreads,
+                maxThreads,
+                0,
+                TimeUnit.MILLISECONDS,
+                new LinkedBlockingDeque<>(MAX_WAITING_COUNT)
+        );
         this.serverSocket = createServerSocket(port, acceptCount);
         this.stopped = false;
     }
@@ -67,12 +80,13 @@ private void process(final Socket connection) {
             return;
         }
         var processor = new Http11Processor(connection);
-        new Thread(processor).start();
+        executorService.submit(processor);
     }
 
     public void stop() {
         stopped = true;
         try {
+            executorService.shutdown();
             serverSocket.close();
         } catch (IOException e) {
             log.error(e.getMessage(), e);
diff --git a/tomcat/src/main/java/org/apache/coyote/common/SessionManager.java b/tomcat/src/main/java/org/apache/coyote/common/SessionManager.java
index 3044cbe1b5..59b81b058e 100644
--- a/tomcat/src/main/java/org/apache/coyote/common/SessionManager.java
+++ b/tomcat/src/main/java/org/apache/coyote/common/SessionManager.java
@@ -1,11 +1,11 @@
 package org.apache.coyote.common;
 
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 public class SessionManager {
 
-    private static final Map<String, Session> SESSIONS = new HashMap<>();
+    private static final Map<String, Session> SESSIONS = new ConcurrentHashMap<>();
 
     private SessionManager() {
     }
@@ -15,6 +15,9 @@ public static void add(final Session session) {
     }
 
     public static Session findSession(final String id) {
+        if (id == null) {
+            return null;
+        }
         return SESSIONS.get(id);
     }