Copy cat > /tmp/AdvLab07.java << 'JAVAEOF'
import java.nio.*;
import java.nio.channels.*;
import java.nio.file.*;
import java.io.*;
import java.util.*;
import java.util.stream.*;
public class AdvLab07 {
public static void main(String[] args) throws Exception {
Path tmp = Files.createTempDirectory("innozverse_nio");
// Step 1: ByteBuffer operations
System.out.println("=== ByteBuffer ===");
ByteBuffer buf = ByteBuffer.allocate(64);
buf.putInt(1); // id
buf.putDouble(864.0); // price
buf.putInt(15); // stock
for (byte b : "Surface Pro".getBytes()) buf.put(b);
System.out.println("Position after writes: " + buf.position());
buf.flip(); // switch to read mode: limit=position, position=0
int id = buf.getInt();
double price = buf.getDouble();
int stock = buf.getInt();
byte[] nameBytes = new byte[buf.remaining()];
buf.get(nameBytes);
System.out.printf("Read: id=%d price=$%.2f stock=%d name=%s%n", id, price, stock, new String(nameBytes));
// Direct buffer (off-heap)
ByteBuffer direct = ByteBuffer.allocateDirect(128);
System.out.println("Direct buffer: " + direct.isDirect() + " capacity=" + direct.capacity());
// Step 2: FileChannel with scatter/gather I/O
System.out.println("\n=== FileChannel: Scatter/Gather ===");
Path file = tmp.resolve("products.bin");
try (var fc = FileChannel.open(file, StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
ByteBuffer header = ByteBuffer.allocate(8);
header.putInt(5); // product count
header.putInt(3); // format version
header.flip();
ByteBuffer data = ByteBuffer.allocate(256);
for (var p : List.of("Surface Pro,864.0,15", "Surface Pen,49.99,80", "Office 365,99.99,999")) {
byte[] bytes = (p + "\n").getBytes();
data.put(bytes);
}
data.flip();
long written = fc.write(new ByteBuffer[]{header, data}); // gather: single syscall
System.out.println("Gathered write: " + written + " bytes");
}
try (var fc = FileChannel.open(file, StandardOpenOption.READ)) {
ByteBuffer header = ByteBuffer.allocate(8);
ByteBuffer data = ByteBuffer.allocate(256);
fc.read(new ByteBuffer[]{header, data}); // scatter: single syscall
header.flip(); data.flip();
System.out.println("Header: count=" + header.getInt() + " version=" + header.getInt());
byte[] bytes = new byte[data.limit()];
data.get(bytes);
System.out.println("Data:");
Arrays.stream(new String(bytes).trim().split("\n")).forEach(l -> System.out.println(" " + l));
}
// Step 3: MappedByteBuffer (memory-mapped file — zero-copy)
System.out.println("\n=== MappedByteBuffer (Memory-Mapped) ===");
Path mapped = tmp.resolve("catalog.bin");
int[] ids = {1,2,3,4,5};
double[] prices = {864.0,49.99,99.99,29.99,1299.0};
int[] stocks = {15,80,999,0,5};
try (var fc = FileChannel.open(mapped, StandardOpenOption.CREATE,
StandardOpenOption.READ, StandardOpenOption.WRITE)) {
MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_WRITE, 0, ids.length * 16L);
for (int i = 0; i < ids.length; i++) {
mbb.putInt(ids[i]); mbb.putDouble(prices[i]); mbb.putInt(stocks[i]);
}
mbb.force(); // flush to disk
System.out.println("Mapped and wrote " + (ids.length * 16) + " bytes");
mbb.rewind();
System.out.println("Read back:");
for (int i = 0; i < ids.length; i++) {
int pid = mbb.getInt(); double p = mbb.getDouble(); int s = mbb.getInt();
System.out.printf(" id=%d $%.2f stock=%d%n", pid, p, s);
}
}
// Step 4: Path glob patterns
System.out.println("\n=== Path & Glob ===");
var reportsDir = tmp.resolve("reports");
Files.createDirectory(reportsDir);
for (String name : List.of("jan.csv","feb.csv","mar.csv","q1.xlsx","annual.pdf")) {
Files.writeString(reportsDir.resolve(name), "data");
}
try (var stream = Files.newDirectoryStream(reportsDir, "*.csv")) {
var csvFiles = new ArrayList<String>();
stream.forEach(p -> csvFiles.add(p.getFileName().toString()));
Collections.sort(csvFiles);
System.out.println("*.csv: " + csvFiles);
}
// Step 5: Walk with filter
System.out.println("\nAll files in tmp:");
try (var walk = Files.walk(tmp)) {
walk.filter(Files::isRegularFile)
.forEach(p -> System.out.printf(" %-30s %d bytes%n",
tmp.relativize(p).toString(), p.toFile().length()));
}
// Cleanup
try (var walk = Files.walk(tmp)) {
walk.sorted(Comparator.reverseOrder()).forEach(p -> { try { Files.delete(p); } catch (IOException e) {} });
}
System.out.println("\nCleanup done");
}
}
JAVAEOF
docker run --rm -v /tmp/AdvLab07.java:/tmp/AdvLab07.java zchencow/innozverse-java:latest sh -c "javac /tmp/AdvLab07.java -d /tmp && java -cp /tmp AdvLab07" 