---

id: 97

slug: "file-memory-mapping"

title: "File memory mapping"

category: "io"

difficulty: "advanced"

jdkVersion: "22"

oldLabel: "Java 8"

modernLabel: "Java 22+"

oldApproach: "MappedByteBuffer"

modernApproach: "MemorySegment with Arena"

oldCode: |-

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

}

modernCode: |-

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

summary: "Map files larger than 2GB with deterministic cleanup using MemorySegment."

explanation: "The Foreign Function & Memory API (JEP 454) introduces MemorySegment\

\ for safe and efficient memory access. Unlike MappedByteBuffer, MemorySegment supports\

\ files larger than 2GB (Integer.MAX_VALUE), provides deterministic cleanup via\

\ Arena, and offers better performance with modern hardware."

whyModernWins:

- icon: "📏"

title: "No size limit"

desc: "Map files larger than 2GB without workarounds."

- icon: "🔒"

title: "Deterministic cleanup"

desc: "Arena ensures memory is freed at scope exit, not GC time."

- icon: "⚡"

title: "Better performance"

desc: "Aligned with modern memory models and hardware."

support:

state: "available"

description: "Available since JDK 22 (March 2024)"

prev: "io/try-with-resources-effectively-final"

next: "io/files-mismatch"

related:

- "io/http-client"

- "io/reading-files"

- "io/writing-files"

docs:

- title: "MemorySegment (Java 22)"

href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/foreign/MemorySegment.html"

- title: "Arena (Java 22)"

href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/foreign/Arena.html"

- title: "JEP 454: Foreign Function & Memory API"

href: "https://openjdk.org/jeps/454"