Java I/O Streams overview

Importing Data in Java

Anthony Markham

VP Quant Developer

Stream fundamentals

Streams are unidirectional pipes of data with FIFO (First In, First Out) order
Byte streams work with raw binary data (InputStream/OutputStream)
Character streams handle text with automatic encoding (Reader/Writer)

Streams representation

Byte Streams

Used for binary data (images, audio, etc.)
Base abstract classes: InputStream (reading), OutputStream (writing)
Key implementations: FileInputStream, FileOutputStream
Key methods: read() returns bytes, write() outputs bytes

Binary files: images and audios

Byte Streams

try (FileInputStream fis = new FileInputStream("data.bin")) {

    byte[] buffer = new byte[1024];
    int bytesRead;

    while ((bytesRead = fis.read(buffer)) != -1) {
        // Process bytes in buffer

        System.out.println("Read " + bytesRead + " bytes");
    }

} catch (Exception e) {
    System.err.println("Error: " + e.getMessage());
}

Character Streams

Designed specifically for text data
Base abstract classes: Reader (reading text), Writer (writing text)
Key implementations: FileReader, FileWriter, BufferedReader, BufferedWriter
Convenient methods: readLine() reads a full line of text

CSV files

Character Streams

try (BufferedReader reader = new BufferedReader(new FileReader("data.csv"))) {
    String line;

    while ((line = reader.readLine()) != null) {
        // Process each line
        System.out.println(line);
    }

} catch (Exception e) {
    System.err.println("Error: " + e.getMessage());
}

Buffered Streams - performance

Improves performance by reducing disk operations
Read/write byte streams with BufferedInputStream and BufferedOutputStream
Read/write character streams with BufferedReader, BufferedWriter
- Read an entire line with readLine()

Buffered Streams - performance

try (BufferedReader reader = new BufferedReader(new FileReader("data.csv"))) {
    // Header processing
    String header = reader.readLine();
    System.out.println("Header: " + header);


    // Efficient data reading
    String line;
    int count = 0;
    while ((line = reader.readLine()) != null) {
        count++;
    }
    System.out.println("Read " + count + " data rows");
} catch (Exception e) {
    System.out.println("Error: " + e.getMessage());
}

Stream chaining

Each stream in the chain adds specific functionality
Common pattern: FileInputStream -> InputStreamReader -> BufferedReader
Always close the outermost stream (others close automatically)

Stream chaining

import java.nio.charset.StandardCharsets;

try (

    BufferedReader reader = new BufferedReader(

        new InputStreamReader(

            new FileInputStream("data.csv"),

            StandardCharsets.UTF_8
        )

   )

) {
    String line;
    while ((line = reader.readLine()) != null) {
        System.out.println(line);}
} catch (Exception e) {
    System.err.println("Error: " + e.getMessage());
}

Exception handling

Crucial for I/O operations
Common exceptions: IOException, FileNotFoundException
Always use try-with-resources to catch exceptions

Exception handling

import java.util.ArrayList;
import java.util.List;

public static List<String> readLines(String filePath) throws IOException {

    List<String> lines = new ArrayList<>();

    try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
        String line;
        while ((line = reader.readLine()) != null) {
            lines.add(line);
        }
    } // Stream automatically closed here
    return lines;

}

Let's practice!

Importing Data in Java