io2ByteStreams

1package pkg9io;2 3import java.io.BufferedInputStream;4import java.io.BufferedOutputStream;5import java.io.ByteArrayInputStream;6import java.io.ByteArrayOutputStream;7import java.io.FileInputStream;8import java.io.FileOutputStream;9import java.io.IOException;10import java.io.InputStream;11import java.io.OutputStream;12import java.nio.file.Files;13import java.nio.file.Path;14 15/*16 * io2ByteStreams.java17 * -------------------18 * Byte streams: reading/writing raw bytes with InputStream / OutputStream.19 *20 * DEFINITION:21 *   Byte streams move 8-bit bytes and are the foundation of all I/O. Use them22 *   for binary data (images, audio, files of any kind). For text prefer the23 *   character streams in io3.24 *25 * KEY POINTS:26 *   - FileInputStream / FileOutputStream talk to files; ByteArray*Stream to memory.27 *   - Wrap in Buffered*Stream to batch syscalls and dramatically speed up I/O.28 *   - Always use try-with-resources so streams are closed (and flushed).29 *   - transferTo() (Java 9+) copies a whole stream in one call.30 */31public class io2ByteStreams {32 33    public static void main(String[] args) throws IOException {34        Path file = Files.createTempFile("io2", ".bin");35        byte[] payload = "Bytes: \u2600\u2764 0123".getBytes();36 37        // WRITE bytes (buffered for speed)38        try (OutputStream out = new BufferedOutputStream(new FileOutputStream(file.toFile()))) {39            out.write(payload);40        } // try-with-resources auto-closes (and flushes) here41 42        // READ bytes back43        try (InputStream in = new BufferedInputStream(new FileInputStream(file.toFile()))) {44            byte[] read = in.readAllBytes();      // Java 9+ convenience45            System.out.println("Read " + read.length + " bytes: " + new String(read));46        }47 48        // Copy one stream into another with transferTo (no manual loop)49        ByteArrayOutputStream sink = new ByteArrayOutputStream();50        try (InputStream src = new ByteArrayInputStream(payload)) {51            long copied = src.transferTo(sink);52            System.out.println("transferTo copied " + copied + " bytes into memory");53        }54 55        // Manual read loop (how buffering works under the hood)56        int total = 0;57        try (InputStream in = new FileInputStream(file.toFile())) {58            byte[] buf = new byte[4];59            int n;60            while ((n = in.read(buf)) != -1) total += n;   // -1 signals EOF61        }62        System.out.println("Manual loop counted " + total + " bytes");63 64        Files.deleteIfExists(file);65    }66}