CompressedFileExample.java - Example for writing and reading compressed text files in Java

CompressedFileExample.java

import java.io.*;
import java.util.zip.DeflaterOutputStream;
import java.util.zip.InflaterInputStream;

public class CompressedFileExample {

    public static void main(String[] args) {
        
        // === COMPRESSED WRITING ===
        try {
            // Step 1: Create a BufferedWriter
            // This is the stream the program interacts with directly
            BufferedWriter writer = new BufferedWriter(
                // Step 2: Convert characters to bytes
                new OutputStreamWriter(
                    // Step 3: Compress the byte stream
                    new DeflaterOutputStream(
                        // Step 4: Write bytes to the file
                        new FileOutputStream(
                            new File("compressed.txt")))));

            // Write 10 lines of "Hello World!" to the compressed file
            for (int i = 0; i < 10; ++i) {
                writer.write("Hello World!\n");
            }

            writer.close(); // Always close streams to flush and release resources

        } catch (FileNotFoundException ex) {
            ex.printStackTrace();
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        // === DECOMPRESSED READING ===
        try {
            // Step 1: Create a BufferedReader
            BufferedReader reader = new BufferedReader(
                // Step 2: Convert bytes to characters
                new InputStreamReader(
                    // Step 3: Decompress the incoming byte stream
                    new InflaterInputStream(
                        // Step 4: Read raw bytes from the file
                        new FileInputStream(
                            new File("compressed.txt")))));

            // Read and print all lines until null is returned (end of file)
            String line = reader.readLine();
            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }

            reader.close();

        } catch (FileNotFoundException ex) {
            ex.printStackTrace();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

💡 About This Code

This Java program demonstrates how to store and read compressed text files using a chain of DataStreams (also called a pipeline).

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🛠 What It Does

1. Compressed Writing:
   The program creates a file called compressed.txt, writes "Hello World!" 10 times into it, and compresses the output using the DEFLATE algorithm.

2. Decompressed Reading:
   It then reads that same file, decompresses the data, and prints the original lines back to the console.

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🧱 Stream Pipeline Breakdown

For Writing:

BufferedWriter → OutputStreamWriter → DeflaterOutputStream → FileOutputStream → File
BufferedWriter: Used directly by the program to write text

OutputStreamWriter: Converts characters to bytes

DeflaterOutputStream: Compresses the byte stream

FileOutputStream: Writes raw bytes to the file

For Reading:

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BufferedReader → InputStreamReader → InflaterInputStream → FileInputStream → File
BufferedReader: Used by the program to read lines of text

InputStreamReader: Converts bytes back to characters

InflaterInputStream: Decompresses the byte stream

FileInputStream: Reads raw bytes from the file

📚 Key Concepts
The program always interacts with the outermost stream (BufferedReader or BufferedWriter).

The file is always the end target (FileInputStream or FileOutputStream).

You write the stream chain from outermost to innermost in code, but data flows in the opposite direction.

This code is beginner-friendly and aligns with the examples from the DLBCSDSJCL01 course book on Java I/O streams and compression.

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You can copy and paste this directly into the **GitHub Gist comment** area (as shown in your screenshot), or into your Notion snippet vault for future reference.

Want to add a visual pipeline diagram as well?