Add a commmand validator.

src/main/java/space/kklochko/jdbc_hospital_example/cli/validators/CommandValidator.java

@@ -0,0 +1,22 @@
+package space.kklochko.jdbc_hospital_example.cli.validators;
+
+import java.util.regex.Pattern;
+
+public class CommandValidator extends Validator {
+    String command;
+
+    String formatRegEx = "(readAll|insert|update|remove)\\s(indicator|patient|department)\\(.*\\)";
+
+    public CommandValidator(String command) {
+        this.command = command;
+    }
+
+    public boolean isValid() {
+        Pattern pattern = Pattern.compile(formatRegEx);
+        return pattern.matcher(command).matches();
+    }
+
+    public String getMessage() {
+        return "Please, check the format: `command item(arg1=value1, ...)`. Or check the `help`";
+    }
+}