Adding Validator class for arguments

src/command/CommandValidator.java

+package command;
+
+import model.Command;
+
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+public class CommandValidator {
+
+    private CommandValidator() {
+
+    }
+
+    private static final class InstanceHolder {
+        private static final CommandValidator instance = new CommandValidator();
+    }
+
+    public static CommandValidator getInstance() {
+        return InstanceHolder.instance;
+    }
+
+    public boolean validateSetCommand(List<String> args) {
+        if (args == null || args.isEmpty()) {
+            return false;
+        }
+
+        if (args.size() < 2) {
+            return false;
+        }
+
+        if (args.size() > 2) {
+            Map<String, String> commandsMap = IntStream.iterate(2, i -> i < args.size(), i -> i + 2)
+                    .boxed()
+                    .collect(Collectors.toMap(i -> args.get(i).toLowerCase(), i -> args.get(i + 1), (a, b) -> b));
+
+            String expiration = commandsMap.get(Command.PX.getValue().toLowerCase());
+            if (expiration != null) {
+                try {
+                    Long.parseLong(expiration);
+                } catch (NumberFormatException e) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+
+    public boolean validateGetCommand(List<String> args) {
+
+        return args != null && args.size() == 1;
+    }
+
+}

src/command/GetCommand.java

@@ -9,6 +9,7 @@ import java.util.List;
 public class GetCommand implements CommandExecutable<byte[]> {
     private final Storage storage = Storage.getInstance();
     private final List<String> args;
+    private final CommandValidator validator = CommandValidator.getInstance();
 
     public GetCommand(List<String> args) {
         this.args = args;
@@ -16,7 +17,9 @@ public class GetCommand implements CommandExecutable<byte[]> {
 
     @Override
     public byte[] execute() {
-
+        if (!validator.validateGetCommand(args)) {
+            return "wrong args".getBytes();
+        }
         String response = storage.get(args.getFirst().toLowerCase());
         if (response == null || response.isEmpty() || response.isBlank()) {
             return ("$-1\r\n".getBytes());

src/command/SetCommand.java

@@ -11,6 +11,7 @@ import java.util.stream.IntStream;
 public class SetCommand implements CommandExecutable<byte[]> {
     private final Storage storage = Storage.getInstance();
     private final List<String> args;
+    private final CommandValidator validator = CommandValidator.getInstance();
 
     public SetCommand(List<String> args) {
         this.args = args;
@@ -18,7 +19,10 @@ public class SetCommand implements CommandExecutable<byte[]> {
 
     @Override
     public byte[] execute() {
-        if (!args.isEmpty()) {
+        if (!validator.validateSetCommand(args)) {
+            return "wrong args".getBytes();
+        }
+
         Map<String, String> commandsMap = IntStream.iterate(2, i -> i < args.size(), i -> i + 2)
                 .boxed()
                 .collect(Collectors.toMap(i -> args.get(i).toLowerCase(), i -> args.get(i + 1), (a, b) -> b));
@@ -36,8 +40,5 @@ public class SetCommand implements CommandExecutable<byte[]> {
             storage.save(args.getFirst().toLowerCase(), value);
         }
         return ("+OK\r\n".getBytes());
-        } else {
-            return "wrong args".getBytes();
-        }
     }
 }