Topic: I/O

I/O

Deserialization filters

Old // Dangerous: accepts any class ObjectInputStream ois = new ObjectInputStream(input); Object obj = ois.readObject(); // deserialization attacks possible!

Modern ObjectInputFilter filter = ObjectInputFilter.Config .createFilter( "com.myapp.*;!*" ); ois.setObjectInputFilter(filter); Object obj = ois.readObject();

hover to see modern →

JDK 9+ learn more →

I/O

File memory mapping

Old try (FileChannel channel = FileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE)) { MappedByteBuffer buffer = channel.map( FileChannel.MapMode.READ_WRITE, 0, (int) channel.size()); // Limited to 2GB // Freed by GC, no control }

Modern FileChannel channel = FileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE); try (Arena arena = Arena.ofShared()) { MemorySegment segment = channel.map( FileChannel.MapMode.READ_WRITE, 0, channel.size(), arena); // No size limit // ... } // Deterministic cleanup

hover to see modern →

JDK 22+ learn more →

I/O

Files.mismatch()

Old // Compare two files byte by byte byte[] f1 = Files.readAllBytes(path1); byte[] f2 = Files.readAllBytes(path2); boolean equal = Arrays.equals(f1, f2); // loads both files entirely into memory

Modern long pos = Files.mismatch(path1, path2); // -1 if identical // otherwise: position of first difference

hover to see modern →

JDK 12+ learn more →

I/O

Modern HTTP client

Old URL url = new URL("https://api.com/data"); HttpURLConnection con = (HttpURLConnection) url.openConnection(); con.setRequestMethod("GET"); BufferedReader in = new BufferedReader( new InputStreamReader(con.getInputStream())); // read lines, close streams...

Modern var client = HttpClient.newHttpClient(); var request = HttpRequest.newBuilder() .uri(URI.create("https://api.com/data")) .build(); var response = client.send( request, BodyHandlers.ofString()); String body = response.body();

hover to see modern →

JDK 11+ learn more →

I/O

InputStream.transferTo()

Old byte[] buf = new byte[8192]; int n; while ((n = input.read(buf)) != -1) { output.write(buf, 0, n); }

Modern input.transferTo(output);

hover to see modern →

JDK 9+ learn more →

I/O

IO class for console I/O

Old import java.util.Scanner; Scanner sc = new Scanner(System.in); System.out.print("Name: "); String name = sc.nextLine(); System.out.println("Hello, " + name); sc.close();

Modern String name = IO.readln("Name: "); IO.println("Hello, " + name);

hover to see modern →

JDK 25+ learn more →

I/O

Path.of() factory

Old Path path = Paths.get("src", "main", "java", "App.java");

Modern var path = Path.of("src", "main", "java", "App.java");

hover to see modern →

JDK 11+ learn more →

I/O

Reading files

Old StringBuilder sb = new StringBuilder(); try (BufferedReader br = new BufferedReader( new FileReader("data.txt"))) { String line; while ((line = br.readLine()) != null) sb.append(line).append("\n"); } String content = sb.toString();

Modern String content = Files.readString(Path.of("data.txt"));

hover to see modern →

JDK 11+ learn more →

I/O

Try-with-resources improvement

Old Connection conn = getConnection(); // Must re-declare in try try (Connection c = conn) { use(c); }

Modern Connection conn = getConnection(); // Use existing variable directly try (conn) { use(conn); }

hover to see modern →

JDK 9+ learn more →

I/O

Writing files

Old try (FileWriter fw = new FileWriter("out.txt"); BufferedWriter bw = new BufferedWriter(fw)) { bw.write(content); }

Modern Files.writeString( Path.of("out.txt"), content );

hover to see modern →

JDK 11+ learn more →