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I/O Beginner

InputStream.transferTo()

Copy an InputStream to an OutputStream in one call.

I/O

Code Comparison

✕ Java 8

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

✓ Java 9+

input.transferTo(output);

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Why the modern way wins

📏

One line

Replace the entire read/write loop with one method call.

⚡

Optimized

Internal buffer size is tuned for performance.

🛡️

No bugs

No off-by-one errors in buffer management.

Old Approach

Manual Copy Loop

Modern Approach

transferTo()

Since JDK

Difficulty

Beginner

JDK Support

InputStream.transferTo()

Available

Widely available since JDK 9 (Sept 2017)

How it works

transferTo() reads all bytes from the input stream and writes them to the output stream. No buffer management, no loop. It uses an optimized internal buffer.

Writing files

Java 8

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

Java 11+

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

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JDK 11+ →

I/O Advanced

Deserialization filters

Java 8

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

Java 9+

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

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JDK 9+ →

I/O Beginner

Try-with-resources improvement

Java 8

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

Java 9+

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

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JDK 9+ →