Smart Home Controller

A Java console application that simulates a smart home controller managing multiple device types (lights, thermostats, and locks). The application intentionally contains bugs and missing features that you must implement across four tasks.

Prerequisites

• Java 21+
• Maven 3.8+

Running the Application

mvn compile exec:java -Dexec.mainClass="com.bootcamp.smarthome.Main"

Project Structure

src/main/java/com/bootcamp/smarthome/
├── Main.java                    # Entry point and demo scenarios
├── controller/
│   ├── CommandParser.java       # Parses command strings
│   └── HomeController.java      # Manages registered devices
└── device/
    ├── Device.java              # Abstract base class
    ├── SmartLight.java          # Dimmable light bulb
    ├── SmartThermostat.java     # Programmable thermostat
    └── SmartLock.java           # PIN-protected door lock

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Task 1 — Custom Exception Hierarchy

Create the following exception classes in a new package com.bootcamp.smarthome.exception:

Class	Type	Extends
HomeAutomationException	checked	Exception
DeviceOfflineException	checked	HomeAutomationException
InvalidCommandException	checked	HomeAutomationException
DeviceNotFoundException	unchecked	RuntimeException
InvalidValueException	checked	HomeAutomationException

InvalidValueException must provide a constructor with the following signature:

public InvalidValueException(String field, Object value, String constraint)

No changes to Main are required for this task.

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Task 2 — Exception Handling

Add validation and proper exception throwing to the following methods:

• SmartLight.setBrightness(int level) — throw InvalidValueException when level is outside [0, 100]
• SmartThermostat.setTemperature(double temp) — throw InvalidValueException when temp is outside [10.0, 35.0]
• SmartLock.validatePin(String pin) — throw InvalidCommandException when the PIN is null or does not match
• HomeController.sendCommand(String fullCommand) — wrap the method body in try-catch-finally:
  • Catch HomeAutomationException, then throw a new HomeAutomationException whose message includes the deviceId and the original fullCommand string (e.g. "Command '" + fullCommand + "' failed for device '" + deviceId + "'") and pass the caught exception as the cause argument — do not re-throw the original exception unchanged
  • The finally block must always print: Command processing ended for device [id]

Update Main to handle or declare all checked exceptions where needed.

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Task 3 — SLF4J + Logback Logging

• Add a private static final Logger field to HomeController and SmartLock — use SLF4J (org.slf4j.Logger / org.slf4j.LoggerFactory): private static final Logger logger = LoggerFactory.getLogger(ClassName.class);
• Log the following events in HomeController:
  • DEBUG — a command is received (include device ID and raw command)
  • INFO — a command executed successfully
  • WARN — the target device is offline and the command is skipped
  • ERROR — an exception is caught during command processing
• Replace the corresponding System.out.println statements in HomeController.sendCommand with these logger calls; remove the old print statements rather than keeping both
• SmartLock must log at ERROR every failed unlock attempt (security audit trail) — replace the existing System.out.println("SECURITY ALERT: ...") line with the logger call
• In logback.xml, uncomment the FILE appender and register it in the root logger
• Demonstration: change the root logger level to WARN, run the app, and observe which log lines no longer appear in the output

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Task 4 — Debug & Fix Planted Bugs

The codebase contains four deliberate bugs. Use the debugger and stack traces to find and fix each one.

Stack trace bugs

Run Main and read the exception output to locate the exact line:

1. NullPointerException in SmartLock.validatePin() — triggered by scenario 6 (null PIN passed in)
2. ArrayIndexOutOfBoundsException in HomeController.findDevice() — triggered by scenario 7 (array is full, device not found)

Fix bug 1 first; bug 2 only becomes reachable after bug 1 is resolved.

Logic bugs

The application does not crash, but produces incorrect output. Use breakpoints and the Variables / Watch panel to find the mistake:

3. SmartThermostat.setTemperature() silently accepts values outside the valid range — triggered by scenario 3 (temperature 99.0 should be rejected)
4. CommandParser.extractCommand() drops the value part of commands that have one — triggered by scenario 2 (brightness should be set to 80, not 50)