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  IT6003 - Advanced Java Programming
  Lab Session 6: Networking & Design Patterns
  State University of Zanzibar (SUZA)
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OBJECTIVES:
- Understand TCP client-server communication
- Build multi-threaded server applications
- Use URL and HttpURLConnection for HTTP requests
- Implement common design patterns in Java

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PART A: TCP Networking [30 minutes]
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Exercise 1: Simple Echo Server/Client
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Server (EchoServer.java):
a) Create ServerSocket on port 5000.
b) Accept a client connection.
c) Read message from client using BufferedReader(InputStreamReader(socket.getInputStream())).
d) Echo it back using PrintWriter(socket.getOutputStream(), true).
e) Repeat until client sends "bye".

Client (EchoClient.java):
a) Create Socket("localhost", 5000).
b) Read user input from Scanner.
c) Send to server using PrintWriter.
d) Read response from server using BufferedReader.
e) Print response. Exit on "bye".

Exercise 2: Multi-Client Server
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a) Modify EchoServer to handle multiple clients using threads.
b) Accept connections in a loop.
c) For each connection, create a new ClientHandler thread.
d) ClientHandler implements Runnable, handles one client's communication.
e) Test with 3 terminal windows connecting simultaneously.

Exercise 3: Chat Application
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Server (ChatServer.java):
a) Maintain Set<PrintWriter> of all connected client output streams.
b) When a message arrives from any client, broadcast to ALL clients.
c) Handle client disconnection (remove from set, close streams).

Client (ChatClient.java):
a) Two threads: one for reading server messages, one for user input.
b) Display received messages with sender name.
c) Support /quit command to disconnect.

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PART B: HTTP and URLs [30 minutes]
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Exercise 4: URL Parsing
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a) Create URL object from "https://api.github.com/users/octocat".
b) Print: protocol, host, port, path, query.
c) Open HttpURLConnection.
d) Print: response code, content type, content length.
e) Read response body line by line using BufferedReader.
f) Print first 500 characters.

Exercise 5: HTTP GET Request
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a) Write a method: String httpGet(String urlString) throws IOException
b) Open HttpURLConnection, set method to "GET".
c) Set timeouts: setConnectTimeout(5000), setReadTimeout(5000).
d) Check response code (200 = OK).
e) Read full response into a String using StringBuilder.
f) Test with a public JSON API.

Exercise 6: Simple HTTP Server
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Using com.sun.net.httpserver.HttpServer:
a) Create server on port 8080.
b) Add context "/hello" returning "Hello, World!".
c) Add context "/time" returning current date/time as JSON.
d) Add context "/echo" that reads query parameter "msg" and returns it.
e) Start server and test with browser or curl.

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PART C: Design Patterns [30 minutes]
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Exercise 7: Singleton Pattern
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a) Create DatabaseConnection class with private constructor.
b) Private static instance.
c) Public static getInstance() method (lazy initialization).
d) Make it thread-safe using synchronized or double-checked locking.
e) Add methods: getConnection(), closeConnection().
f) Verify: DatabaseConnection.getInstance() == DatabaseConnection.getInstance().

Exercise 8: Factory Pattern
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a) Create interface Shape with double area() and String describe().
b) Create implementations: Circle, Rectangle, Triangle.
c) Create ShapeFactory with static method: Shape createShape(String type, double... params).
d) Factory creates appropriate shape based on type string.
e) Test: Shape s = ShapeFactory.createShape("circle", 5.0);

Exercise 9: Observer Pattern
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a) Create interface Observer with void update(String event, Object data).
b) Create class EventManager (Subject/Observable):
   - Map<String, List<Observer>> listeners
   - subscribe(String eventType, Observer o)
   - unsubscribe(String eventType, Observer o)
   - notify(String eventType, Object data)
c) Create concrete observers: EmailNotifier, LogObserver, DisplayObserver.
d) Create ProductStore that uses EventManager.
e) When price changes or new product added, notify all observers.

Exercise 10: Strategy Pattern
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a) Create interface SortStrategy with void sort(int[] array).
b) Implement: BubbleSortStrategy, QuickSortStrategy, MergeSortStrategy.
c) Create Sorter class with setSortStrategy(SortStrategy) and performSort(int[]).
d) Switch strategies at runtime:
   sorter.setSortStrategy(new QuickSortStrategy());
   sorter.performSort(data);
e) Add timing to each strategy. Print performance comparison.

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PART D: Integration Challenge [30 minutes]
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Exercise 11: Networked Student Lookup
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Combine networking and design patterns:
a) Server: Singleton database connection, loads students from file.
b) Server: Factory pattern for handling different request types (SEARCH, ADD, DELETE, LIST).
c) Client sends request type and parameters.
d) Server processes and returns result.
e) Observer: Log all requests to a file.

Exercise 12: Builder Pattern for HTTP Request
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a) Create HttpRequest class with url, method, headers (Map), body, timeout.
b) Create HttpRequestBuilder:
   HttpRequest request = new HttpRequestBuilder("https://api.example.com")
       .method("POST")
       .header("Content-Type", "application/json")
       .body("{\"name\": \"Ali\"}")
       .timeout(5000)
       .build();
c) Create HttpClient that executes HttpRequest objects.
d) Validate: url is required, method defaults to "GET", timeout defaults to 10000.

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SUBMISSION:
Submit all .java files in a folder named Lab06_RegNo/
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