Client-Server Model & Java Streams

Client-Server Architecture

• Servers provide services to clients that connect to them.
• A server operates on a hosting machine and responds when a client initiates communication.
• Common server services include web page hosting.
• Web browsers like Firefox and Chrome function as clients accessing web servers.

Java I/O Streams

• Java Input/Output is structured around streams, which are sequences of data.
• Input streams read data, while output streams write data; both types share fundamental read and write methods.
• Filter streams can modify data during the reading or writing process.
• Readers and writers are specialized for text handling, converting it instead of just working with bytes.

Output Streams

• Java's output class is java.io.OutputStream, which includes key methods:
  • write(int b): Writes a single byte.
  • write(byte[] data): Writes an array of bytes.
  • write(byte[] data, int off, int len): Writes a portion of an array.
  • flush(): Ensures all buffered data is written out.
  • close(): Releases resources associated with the stream.

Importance of Closing Streams

• The close() method frees resources like file handles and network ports.
• Closing the stream ends any associated network connection.
• Attempting to write to a closed stream will throw an IOException.
• Not closing streams in long-running applications can lead to resource leaks.

Flushing Streams

• Flushing a stream before closing prevents data loss.
• It helps mitigate hard-to-diagnose errors that might arise from incomplete data writing.

Input Streams

• The core input class for Java is java.io.InputStream, with essential methods:
  • int read(): Reads a single byte.
  • int read(byte[] data): Reads bytes into an array.
  • int read(byte[] data, int off, int len): Reads bytes with an offset.
  • long skip(long n): Skips over a defined number of bytes.
  • int available(): Returns the number of bytes that can be read.
  • close(): Closes the stream and frees resources.
• The end of a stream is signaled by returning -1.

Filter Streams

• Filter streams enhance byte streams by converting raw data formats, such as compression.
• Two types of filters exist: filter streams (for bytes) and readers/writers (for text).
• Both filter input and output streams support similar methods as their respective streams.

Buffered Streams

• BufferedOutputStream temporarily collects data in a buffer until it's full or flushed for efficiency.
• Constructors for BufferedOutputStream include:
  • BufferedOutputStream(OutputStream out)
  • BufferedOutputStream(OutputStream out, int bufferSize)
• BufferedInputStream uses a buffer to read data first and only fetches from the source if needed.

Print Streams

• PrintStream is widely used, with System.out being a common instance.
• Additional constructors for PrintStream allow attachment to other output streams, including auto-flushing functionality.
• Features print() and println() methods for outputting various data types.

Predefined Streams

• Three predefined stream variables in the System class:
  • System.out: Standard output to the console.
  • System.in: Standard input from the keyboard.
  • System.err: Outputs error messages to the console.
• System.in is an InputStream, while System.out and System.err are PrintStream objects.

Readers and Writers

• java.io.Reader and java.io.Writer classes are designed for character read/write operations using Unicode.
• FileReader and FileWriter are specific for file reading and writing.
• Methods in the Writer class support various forms of writing characters and include flush() and close().

Input/Output Stream Classes

• InputStreamReader: Converts bytes from an input stream to characters using encoding.
• BufferedReader: Improves reading efficiency by utilizing a buffer.
• File creation for reading and writing involves FileReader and FileWriter, typically wrapped around buffered or print streams for better performance.

File Handling

• Use FileInputStream and FileOutputStream for file operations.
• Constructors throw FileNotFoundException if issues arise with file accessibility or existence.
• File class methods (e.g., canRead(), delete(), exists(), length()) enable various file-related operations.

Command-Line Parameters

• Java allows passing parameters during execution, accessible in the main method via an array of Strings.

Serialization

• Serialization saves an object's state in a byte stream for persistent storage, retrievable through deserialization.
• Classes implementing the Serializable interface can be serialized and deserialized using ObjectOutputStream and ObjectInputStream.

Ports and Sockets

• A port is a numbered connection point for services, ranging from 1 to 65,535, with ports 1-1023 being "well-known" for standard services.
• Sockets facilitate communication between client and server, with each end of the connection represented by a socket.
• Servers generate a dedicated socket for communication after receiving connection requests from clients.