use pattern to handle a commands

src/main/java/juja/sqlcmd/DatabaseManager.java

@@ -16,4 +16,6 @@ public interface DatabaseManager {
     boolean update(String tableName, int id);
 
     void close() throws SQLException;
+
+    boolean hasConnection();
 }

src/main/java/juja/sqlcmd/InMemoryDatabaseManager.java

@@ -65,6 +65,11 @@ public void close() throws SQLException {
         //NOP
     }
 
+    @Override
+    public boolean hasConnection() {
+        return true;
+    }
+
     private Table tableByName(String tableName) {
         for (Table currentTable : tables) {
             if (currentTable.getTableName().equals(tableName)) {

src/main/java/juja/sqlcmd/JdbcDatabaseManager.java

@@ -112,6 +112,11 @@ private DataSet[] tableRows(ResultSet resultSet, int rowSize, int tableSize) thr
         return tableData;
     }
 
+    @Override
+    public boolean hasConnection() {
+        return connection != null;
+    }
+
     private int numberOfEntries(String tableName) throws SQLException {
         String sqlQuery = String.format("SELECT COUNT(*) as RECORDS FROM %s", tableName);
         try (Statement statement = connection.createStatement();

src/main/java/juja/sqlcmd/Main.java

@@ -11,4 +11,4 @@ public static void main(String[] args) {
         MainController controller = new MainController(view, databaseManager);
         controller.run();
     }
-}
+}

src/main/java/juja/sqlcmd/controller/CommandHandler.java

@@ -0,0 +1,50 @@
+package juja.sqlcmd.controller;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import juja.sqlcmd.DatabaseManager;
+import juja.sqlcmd.controller.command.Command;
+import juja.sqlcmd.controller.command.CommandType;
+import juja.sqlcmd.controller.command.Connect;
+import juja.sqlcmd.controller.command.Exit;
+import juja.sqlcmd.controller.command.UnsupportedCommand;
+import juja.sqlcmd.view.View;
+
+public class CommandHandler {
+    private View view;
+    private Map<CommandType, Command> registeredCommands = new HashMap<>();
+    private CommandType[] allCommandTypes;
+
+    public CommandHandler(DatabaseManager databaseManager, View view) {
+        this.view = view;
+        register(CommandType.CONNECT, new Connect(databaseManager, view));
+        register(CommandType.EXIT, new Exit(databaseManager, view));
+        allCommandTypes = CommandType.values();
+    }
+
+    public void handleCommand(String strCommand) {
+        if (strCommand.toLowerCase().equals("help")) {
+            view.write("List of available commands to execute:");
+            for (CommandType commandType : allCommandTypes) {
+                view.write(commandType.getDescription());
+            }
+        } else {
+            Command command = getCommandByName(strCommand);
+            command.execute();
+        }
+    }
+
+    private Command getCommandByName(String commandName) {
+        for (CommandType commandType : allCommandTypes) {
+            if (commandName.toLowerCase().equals(commandType.getName())) {
+                return registeredCommands.get(commandType);
+            }
+        }
+        return new UnsupportedCommand(view);
+    }
+
+    private void register(CommandType commandType, Command command) {
+        registeredCommands.put(commandType, command);
+    }
+}

src/main/java/juja/sqlcmd/controller/MainController.java

@@ -12,7 +12,20 @@ public MainController(View view, DatabaseManager databaseManager) {
         this.databaseManager = databaseManager;
     }
 
-    public void run(){
-
+    public void run() {
+        CommandHandler handler = new CommandHandler(databaseManager, view);
+        view.write("Welcome to SqlCmd application!\n" +
+                "Please enter help to see a list of commands");
+        view.write("-----");
+        while (true) {
+            String command = view.read();
+            handler.handleCommand(command);
+            if (command.toLowerCase().equals("exit")) {
+                view.write("Bye!");
+                break;
+            }
+            view.write("-----");
+            view.write("Please enter next command");
+        }
     }
 }

src/main/java/juja/sqlcmd/controller/command/Command.java

@@ -0,0 +1,5 @@
+package juja.sqlcmd.controller.command;
+
+public interface Command {
+    void execute();
+}

src/main/java/juja/sqlcmd/controller/command/CommandType.java

@@ -0,0 +1,28 @@
+package juja.sqlcmd.controller.command;
+
+public enum CommandType {
+
+    CONNECT("connect", "\tconnect"
+            + System.lineSeparator()
+            + "\t\tconnection with database. Require to enter credentials"),
+
+    EXIT("exit", "\texit"
+            + System.lineSeparator()
+            + "\t\tto exit from this session");
+
+    private String name;
+    private String description;
+
+    CommandType(String name, String description) {
+        this.name = name;
+        this.description = description;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getDescription() {
+        return description;
+    }
+}

src/main/java/juja/sqlcmd/controller/command/Connect.java

@@ -0,0 +1,41 @@
+package juja.sqlcmd.controller.command;
+
+import juja.sqlcmd.DatabaseManager;
+import juja.sqlcmd.view.View;
+
+public class Connect implements Command {
+    private DatabaseManager databaseManager;
+    private View view;
+
+    public Connect(DatabaseManager databaseManager, View view) {
+        this.databaseManager = databaseManager;
+        this.view = view;
+    }
+
+    @Override
+    public void execute() {
+        if (databaseManager.hasConnection()) {
+            view.write("Connection already exists. To close current connection use Disconnect or Exit command");
+        } else {
+            view.write("Please enter required data in format:\n" +
+                    "databaseName|login|password|");
+            String command = view.read();
+            if (isCommandValid(command)) {
+                String[] splittedCommand = command.split("\\|");
+                String dbName = splittedCommand[0];
+                String login = splittedCommand[1];
+                String password = splittedCommand[2];
+                if (databaseManager.connect(dbName, login, password)) {
+                    view.write("Successful connection to database " + dbName);
+                    return;
+                }
+            }
+            view.write("Unsuccessful connection to database. Check if entered data is correct");
+        }
+    }
+
+    private boolean isCommandValid(String command) {
+        String[] splittedCommand = command.split("\\|");
+        return splittedCommand.length == 3;
+    }
+}

src/main/java/juja/sqlcmd/controller/command/Exit.java

@@ -0,0 +1,30 @@
+package juja.sqlcmd.controller.command;
+
+import java.sql.SQLException;
+
+import juja.sqlcmd.DatabaseManager;
+import juja.sqlcmd.view.View;
+
+public final class Exit implements Command {
+    private DatabaseManager databaseManager;
+    private View view;
+
+    public Exit(DatabaseManager databaseManager, View view) {
+        this.databaseManager = databaseManager;
+        this.view = view;
+    }
+
+    @Override
+    public void execute() {
+        if (databaseManager.hasConnection()) {
+            try {
+                databaseManager.close();
+                view.write("Connection is closed.");
+            } catch (SQLException e) {
+                view.write("Cannot close current connection! Reason: " + e.getMessage());
+            }
+        } else {
+            view.write("There's no connection to close.");
+        }
+    }
+}

src/main/java/juja/sqlcmd/controller/command/UnsupportedCommand.java

@@ -0,0 +1,16 @@
+package juja.sqlcmd.controller.command;
+
+import juja.sqlcmd.view.View;
+
+public class UnsupportedCommand implements Command {
+    private View view;
+
+    public UnsupportedCommand(View view) {
+        this.view = view;
+    }
+
+    @Override
+    public void execute() {
+        view.write("Entered command is not supported. Enter 'help' to see a list of available commands");
+    }
+}

src/main/java/juja/sqlcmd/view/Console.java

@@ -22,6 +22,7 @@ public Console(InputStream inputStream, OutputStream outputStream) {
     @Override
     public void write(String message) {
         try {
+            message += "\n";
             outputStream.write(message.getBytes());
         } catch (IOException e) {
             throw new RuntimeException("Something goes wrong with write method... Reason:" + e.getMessage());