Les nouveautés de Java 21 : partie 2

  try (var client = HttpClient.newHttpClient()) {
    // utilisation du client
  }

-XX:+UseZGC -XX:+ZGenerational

-XX:FlightRecorderOptions=preserve-repository=[true|false]

C:\java>java -XX:StartFlightRecording=filename=app.jfr,filename=app.jfr MonApp
[0.068s][error][jfr,startup] Duplicates in diagnostic command arguments
Error occurred during initialization of VM
Failure when starting JFR on_create_vm_3

C:\java>java -XX:StartFlightRecording=filename=app.jfr,filename=app.jfr MonApp
[0.057s][error][jfr,startup] Option filename can only be specified once.
Error occurred during initialization of VM
Failure when starting JFR on_create_vm_3

C:\java>jfr view
jfr view: missing file

Usage:

 jfr view [--verbose]
          [--width <integer>]
          [--truncate <mode>]
          [--cell-height <integer>]
          <view>
          <file>

  --verbose               Displays the query that makes up the view

  --width <integer>       The width of the view in characters. Default value depends on the view

  --truncate <mode>       How to truncate content that exceeds space in a table cell.
                          Mode can be 'beginning' or 'end'. Default value is 'end'

  --cell-height <integer> Maximum number of rows in a table cell. Default value
depends on the view

  <view>                  Name of the view or event type to display. See list below for
                          available views

  <file>                  Location of the recording file (.jfr)

Java virtual machine views:
 class-modifications       gc-concurrent-phases longest-compilations
 compiler-configuration    gc-configuration     native-memory-committed
 compiler-phases           gc-cpu-time          native-memory-reserved
 compiler-statistics       gc-pause-phases      safepoints
 deoptimizations-by-reason gc-pauses            tlabs
 deoptimizations-by-site   gc-references        vm-operations
 gc                        heap-configuration

Environment views:
 active-recordings        cpu-information       jvm-flags
 active-settings          cpu-load              native-libraries
 container-configuration  cpu-load-samples      network-utilization
 container-cpu-throttling cpu-tsc               recording
 container-cpu-usage      environment-variables system-information
 container-io-usage       events-by-count       system-processes
 container-memory-usage   events-by-name        system-properties

Application views:
 allocation-by-class   exception-count       native-methods
 allocation-by-site    file-reads-by-path    object-statistics
 allocation-by-thread  file-writes-by-path   pinned-threads
 class-loaders         finalizers            socket-reads-by-host
 contention-by-address hot-methods           socket-writes-by-host
 contention-by-class   latencies-by-type     thread-allocation
 contention-by-site    longest-class-loading thread-count
 contention-by-thread  memory-leaks-by-class thread-cpu-load
 exception-by-message  memory-leaks-by-site  thread-start
 exception-by-site     modules

 The <view> parameter can be an event type name. Use the 'jfr view types <file>'
 to see a list. To display all views, use 'jfr view all-views <file>'. To display
 all events, use 'jfr view all-events <file>'.

Example usage:

 jfr view gc recording.jfr

 jfr view --width 160 hot-methods recording.jfr

 jfr view --verbose allocation-by-class recording.jfr

 jfr view contention-by-site recording.jfr

 jfr view jdk.GarbageCollection recording.jfr

 jfr view --cell-height 10 ThreadStart recording.jfr

 jfr view --truncate beginning SystemProcess recording.jfr

C:\java>jfr view gc monapp.jfr

                                Garbage Collections

Start    GC ID Type                     Heap Before GC Heap After GC Longest Pause
-------- ----- ------------------------ -------------- ------------- -------------
14:46:51   298 Young Garbage Collection       602,1 MB        4,7 MB       1,25 ms
14:46:51   299 Young Garbage Collection       600,7 MB        5,7 MB       1,38 ms
14:46:51   300 Young Garbage Collection       601,7 MB        5,2 MB       1,22 ms
14:46:52   301 Young Garbage Collection       601,2 MB        5,1 MB       1,30 ms
14:46:52   302 Young Garbage Collection       599,1 MB        4,7 MB       1,04 ms
14:46:52   303 Young Garbage Collection       600,7 MB        4,1 MB      0,862 ms
…

C:\java>jfr view gc-pauses hotmethods_fixed.jfr

GC Pauses
---------

Total Pause Time: 830 ms

Number of Pauses: 812

Minimum Pause Time: 0,493 ms

Median Pause Time: 1,02 ms

Average Pause Time: 1,02 ms

P90 Pause Time: 1,24 ms

P95 Pause Time: 1,30 ms

P99 Pause Time: 1,37 ms

P99.9% Pause Time: 1,42 ms

Maximum Pause Time: 1,42 ms

import java.util.List;;

import java.util.Set;

class MaClasse { }

C:\>javac MaClasse.java

C:\>

C:\>javac MaClasse.java
MaClasse.java:1: error: extraneous semicolon
import java.util.List;;
                      ^
1 error

C:\java>jshell
|  Welcome to JShell -- Version 21
|  For an introduction type: /help intro

jshell> /open TOOLING

jshell> interface MonInterface {}
|  created interface MonInterface

jshell> javap(MonInterface.class)
Classfile /C:/Users/JEAN-M~1/AppData/Local/Temp/TOOLING-16027415010418519056.class
  Last modified 19 sept. 2023; size 205 bytes
  SHA-256 checksum 303d5b68f16eae0e11484ba508593099ab2ad6ea2a6c20e3b049fbbf18513a43
  Compiled from "$JShell$43.java"
public interface REPL.$JShell$43$MonInterface
  minor version: 0
  major version: 65
  flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: #1                          // REPL/$JShell$43$MonInterface
  super_class: #3                         // java/lang/Object
  interfaces: 0, fields: 0, methods: 0, attributes: 3
Constant pool:
   #1 = Class              #2             // REPL/$JShell$43$MonInterface
   #2 = Utf8               REPL/$JShell$43$MonInterface
   #3 = Class              #4             // java/lang/Object
   #4 = Utf8               java/lang/Object
   #5 = Utf8               SourceFile
   #6 = Utf8               $JShell$43.java
   #7 = Utf8               NestHost
   #8 = Class              #9             // REPL/$JShell$43
   #9 = Utf8               REPL/$JShell$43
  #10 = Utf8               InnerClasses
  #11 = Utf8               MonInterface
{
}
SourceFile: "$JShell$43.java"
NestHost: class REPL/$JShell$43
InnerClasses:
  public static #11= #1 of #8;            // MonInterface=class REPL/$JShell$43$MonInterface of class REPL/$JShell$43

C:\java>java -XX:MetaspaceReclaimPolicy=balanced HelloWorld
OpenJDK 64-Bit Server VM warning: Ignoring option MetaspaceReclaimPolicy; support was removed in 21.0
Hello world

WARNING: the GTK 2 library is deprecated and its support will be removed in a future release.

C:\java>java -Djava.locale.providers=COMPAT HelloWorld
Hello world
sept. 20, 2023 5:48:43 PM sun.util.locale.provider.LocaleProviderAdapter <clinit>
WARNING: COMPAT locale provider will be removed in a future release