🏷 Performance
5 patterns
Topic: Performance
All Java patterns related to Performance — java.evolved
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 →
Tooling
JFR for profiling
Old
// Install VisualVM / YourKit / JProfiler
// Attach to running process
// Configure sampling
// Export and analyze
// External tool required
Modern
// Start with profiling enabled
$ java -XX:StartFlightRecording=
filename=rec.jfr MyApp
// Or attach to running app:
$ jcmd <pid> JFR.start
hover to see modern →
JDK 9+
learn more →
Tooling
Lazy stack inspection with StackWalker
Old
StackTraceElement caller = Thread.currentThread()
.getStackTrace()[2];
String callerClass = caller.getClassName();
Modern
String callerClass = StackWalker.getInstance()
.walk(frames -> frames.skip(1)
.findFirst()
.orElseThrow()
.getClassName());
hover to see modern →
JDK 9+
learn more →
Tooling
Compact object headers
Old
// Default: 128-bit object header
// = 16 bytes overhead per object
// A boolean field object = 32 bytes!
// Mark word (64) + Klass pointer (64)
Modern
// -XX:+UseCompactObjectHeaders
// 64-bit object header
// = 8 bytes overhead per object
// 50% less header memory
// More objects fit in cache
hover to see modern →
JDK 25+
learn more →
Tooling
AOT class preloading
Old
// Every startup:
// - Load 10,000+ classes
// - Verify bytecode
// - JIT compile hot paths
// Startup: 2-5 seconds
Modern
// Training run:
$ java -XX:AOTCacheOutput=app.aot \
-cp app.jar com.App
// Production:
$ java -XX:AOTCache=app.aot \
-cp app.jar com.App
hover to see modern →
JDK 25+
learn more →