Java9

Java 9
That's one small step for a man, one giant leap for mankind.
Neil Amstrong
The New Module System
and
Other Features

Agenda

History

Main Features

JPMS Demo

Jshell Demo

Oracle Java History

JDK 1.0 (January 23, 1996)

JDK 1.1 (February 19, 1997)

J2SE 1.2 (December 8, 1998)

J2SE 1.3 (May 8, 2000)

J2SE 1.4 (February 6, 2002)

J2SE 5.0 (September 30, 2004)

Java SE 6 (December 11, 2006)

Java SE 7 (July 28, 2011)

Java SE 8 (March 18, 2014)

Java 9 (September 21, 2017) (planned)

IBM Java 9

IBM Java 9 beta is open for business

SDK are rewritten to use the new Java module system

Join IBM Open Beta Program
https://developer.ibm.com/javasdk/2017/02/08/our-java-9-beta-is-open-for-business/

Main Features of Java 9

JDK

Module System (JPMS)

Versioning Schema

Tools

+Multi-Release JAR Files

+Compile for Older Versions

+jshell +jlink +jmod

-hprof -jhat

~javac ~java ~jcmd

Security

-SHA-1

+SHA-3


Deployment

Deprecate Java Plugin (Applet)

jlink

Language

@SafeVargs

Try-with-resources

Diamond w/ anonymous classes

Identifier name Underscore (_) removal

Private interface methods.

Javadoc

HTML5 output

Javadoc search

Module System support


Core Libraries

Process API Updates

Variable Handles

Compact Strings

Platform Logging API and Service

More Concurrency Updates

Factory Methods for Collections

Enhanced Method Handles

Enhanced Deprecation

Spin-Wait Hints

Filter Incoming Serialization Data

Stack-Walking API


JVM

Compiler control

Segmented Code Cache (for native code)

JVM Tuning

Unified JVM/GC Logging

Remove GC Combinations Deprecated in JDK 8

Make G1 the Default Garbage Collector

Deprecate the CMS GC

Internationalization

Unicode 8.0

UTF-8 properties

Installer


Client

TIFF Image I/O

Multi-Resolution Images

JavaFX module system support

BeanInfo annotations

HiDPI Graphics on Windows and Linux

Platform-Specific Desktop Features

Nashorn (JS Engine)

Parser API for Nashorn

Implement Selected ECMAScript 6 Features in Nashorn
− Template strings
− let, const, and block scope
− Iterators and for..of loops
− Map, Set, WeakMap, and WeakSet
− Symbols
− Binary and octal literals

JPMS – Module System
GOALS

Make the Java SE Platform/JDK, more easily
scalable down to small computing devices

Improve the security and maintainability of
Java SE Platform Implementations in general,
and the JDK in particular;

Enable improved application performance

Make it easier for developers to construct and
maintain libraries and large applications,
for both the Java SE and EE Platforms.

JPMS – Module System
THUS

Strong encapsulation (among modules)

Better architectural design

Improve security

Reliable configuration

Introduce dependency management (sort of)

Space efficiency & performance

Run on small devices (IoT)

Compile-Run time errors reduce.

JPMS – Module Definition
A module is a named, self-describing collection of code and data.
And contains packages (classes&interfaces),
resources, other static information (e.g. META-INF)
module modul.demo.a {} // depends on java.base
module modul.demo.bank {
exports modul.demo.bank;
}
module modul.demo.bank.client {
requires modul.demo.bank;
}

JPMS – Module Definition
Directory Structure
ModulDemo2BankClient/ → Eclipse project base
src/ → Source folder
modul.demo.bank.client/ → module source folder
module-info.java → module descriptor
modul/demo/bank/client/ → package
BankClient.java → java Class
Jar Structure
META-INF/
META-INF/MANIFEST.MF
module-info.class
modul/demo/bank/client/BankClient.class

JPMS – Platform Modules
Java Platform is divided into modules.
https://blog.codecentric.de/files/2015/11/jdk-tr1.png

JPMS – Platform Modules
Base Module (“java.base”)

Always present

Only module known by module system

Exports all of the platform's core packages

Every other module depends implicitly upon base module

Base module depends upon no other module
module java.base {
exports java.io;
exports java.lang;
exports java.lang.invoke;
exports java.lang.module;
exports java.lang.ref;
exports java.lang.reflect;
exports java.net;
...
}

JPMS – Using Modules
Module Path

Means to locate whole modules (similar to classpath)

Resolves module dependences

System path contains module artifacts (jars) or
module directories
e.g. %JAVA_HOME%/jmods;libs

If the module system cannot find a dependent module
or if it encounters two modules w/ same name
then the compiler or virtual machine report an error and exits

JPMS – Module Resolution
module com.foo.bar {
requires
org.baz.qux;
}
module com.foo.app {
requires
com.foo.bar;
requires java.sql;
}
module org.baz.qux {
}
Resolution Start Here:
Initial Application Module
module java.sql {
requires java.logging;
requires java.xml;
exports java.sql;
exports javax.sql;
exports
javax.transaction.xa;
}
MODULE
GRAPH
Explicit dependence
vs
Implicit dependence

JPMS – Implied Readibility
// Application Code
Driver d = DriverManager.getDriver(url); java.sql→
Connection c = d.connect(url, props); java.sql→
d.getParentLogger().info("Connection acquired"); java.logging→
How can the application access “java.logging” module?
Revise “java.sql” module descriptor
module java.sql {
requires public java.logging;
requires public java.xml;
exports java.sql;
exports javax.sql;
exports javax.transaction.xa;
}
If one module exports a package containing a type whose signature refers to a package
in a second module then the declaration of the first module should include a requires
public dependence upon the second.

JPMS – Unnamed Module

All jars loaded from the classpath are considered
as a member of Unnamed Module.

Ensures that every type is associated with a module.

The unnamed module reads every other module
(i.e. all named & built-in platform modules)
Thus existing Java 8 application compile and run on Java 9.
(unless api's are deprecated or removed)

The unnamed module exports all of its packages.
But named module can not access types in the unnamed module.

If a package is defined in both a named module and the unnamed
module then the package in the unnamed module is ignored.

JPMS – Unnamed Module
If our application is written before Java 8, module dependences
in Java 9 is as below:
Grey covered jars are in classpath, therefore they are defined
as “unnamed module”.

JPMS – Bottom-Up Migration
What to migrate to Java 9?
 Find the intermodule dependencies (using jdep)
 Use buttom-up approach to select&migrate to modules.
com-foo-app.jar
com-foo-bar.jar
org-baz-qux.jar
It is easy to migrate “org.baz.qux” to module system.
Because it has no dependences.

JPMS – Bottom-Up Migration
Continue to bottom-up migration
What if “org.baz.qux.jar” is maintained by another organization and
cannot be converted to a named module?
Is it possible to migrate other jars into modules?

JPMS – Automatic Module

A jar w/o module descriptor in modulepath is defined as
automatic module

Accesses all other modules

Implicitly exports all of its packages Unnamed Module
thus can be depend upon by Named Modules

Mudule name is automatically determined using jar name
(subject to change)

Removes the file extension

Removes trailing version number

replaces all the non-alphanumeric characters with dots
mysql-connector-java-6.1.6.jar → mysql.connector.java

JPMS – Top-Down Migration
− Application jars are not module.
− JRE is Java9. Therefore, platform (java.*) modules exists
in environment.
− Want to convert application jars into modules.

Only com-foo-app.jar and com-foo-bar.jar can be converted

org-baz-qux.jar is maintained by another organization.
com-foo-app.jar
com-foo-bar.jar
org-baz-qux.jar
Current Situation

module com.foo.bar {
requires
org.baz.qux;
}
module com.foo.app {
requires
com.foo.bar;
requires java.sql;
}

Move org-baz-qux.jar to module-path. It will have
automodule name: org-baz-qux.jar → org.baz.qux

Now com-foo-app.jar and com-foo-bar.jar can
depend upon org.baz.qux module.

Notes

Automatic Modules allow an existing application to be migrated
to modules from the top down (first app.jar then other jars)

To migrate the jars in classpath

Find and analyze interdependency (jdeps)

Convert the source code of your organization into modules

Move 3rd
party jars into module-path to make them automodule
thus, your module code may depend/read the automodules.
(until module versions of 3rd
party jars are prepared)

JPMS – Module Types Summary
MODULE TYPE MODULE DESCRIPTOR LOCATION
Application Module Exists Module-path
Automatic Module Doesn't exist Module-path
Unnamed Module Exists or Doesn't exist Class-path
Platform Module Exists Platform's Module-path
MODULE TYPE EXPORTS
PACKAGES
CAN READ
MODULES
CAN BE READ BY
MODULES
Application Module Explicitly Application
Platform
Automatic
Application
Automatic
Unnamed
Platform Module Explicitly Platform All types of modules
Unnamed Module All All types of modules Application
Automatic
Unnamed
Automatic Module All All types of modules Application
Automatic
Unnamed

JPMS – ServiceLoader

Provides loose-coupling among modules.

Based on the java.util.ServiceLoader mechanism.

Service Loader locates the service providers at run-time
by searching jars in classpath.

Automatic modules (old jars) may also provide services by
placing the service class into META-INF/services.
Service File: META-INF/services/com.example.CodecSet
File Content: com.example.impl.StandardCodecs # Standard codecs
Iterator<CodecSet> codecs =
ServiceLoader.load(CodecSet.class).iterator();
foreach(codec) {
//select codec instance.
}

JPMS – Services
module java.sql {
requires public java.logging;
requires public java.xml;
exports java.sql;
exports javax.sql;
exports javax.transaction.xa;
uses java.sql.Driver;
}
module com.mysql.jdbc {
requires java.sql;
requires org.slf4j;
exports com.mysql.jdbc;
provides java.sql.Driver
with com.mysql.jdbc.Driver;
}

JPMS – Services
Highligts
Declaring service relation is module declaration

Improves efficiency and clarity (locating/loading time)

Provides compile&run time accessibility check

Provides compile-time type compatibility check

Provides capability to run Ahead-of-Time Compilation

Provides safe linking prior to run-time

JPMS – Reflection
package java.lang.reflect;
public final class Module {
public String getName();
public ModuleDescriptor getDescriptor();
public ClassLoader getClassLoader();
public boolean canRead(Module target);
public boolean isExported(String packageName);
}

Every Class object has an associated Module object

Module object returns by the Class::getModule method

ModuleDescriptor class represents module descriptor

canRead() tells whether the module can read the target module

isExported() tells whether the module exports given package

Class.forName() continues to work as soon as the reflected class
is exported in target module and readable by caller module.

JPMS – Class Loader

Modules names/packages don't have to interfere with each other

A module has to be loaded/associated by only one class loader

Exception: Unnamed Module is associated by all class loaders.

Existing Hierarchy is
preserved.

Bootstrap and extension
class loaders load platform
modules

Application class loader
loads classes of modules in
the module path.

Can load classes from one or
more modules


Besides application modules, new layer may contain upgradable
platform modules as soon as they are loaded from a different location.

During resolution process, modules in new layer can read modules in
lower layers.
CONTAINER
JPMS – Layers
Upgradeable modules
v1.0v1.1

Container launches the
application w/ initial layer (L1)

An upgrade necessitates and
v1.1 modules are loaded in a
new layer (L2) on the top of
initial layer (L1) from a
different jar location.

Container performs this loading
operation by using module
reflection API's and dynamic
class loading.

JPMS – Qualified Exports

Allows a package to be exported to specifically-named modules.
module java.base {
...
exports sun.reflect to
java.corba,
java.logging,
java.sql,
java.sql.rowset,
jdk.scripting.nashorn;
}

Can be used to hide the internal implementation from the
unintended users.

Provides a kind of module security. (e.g. in container environment)

JJJJJJJJJJJPPPPPPPPPPPPPPPPP MMMMMMMM MMMMMMMM SSSSSSSSSSSSSSS
J:::::::::JP::::::::::::::::P M:::::::M M:::::::M SS:::::::::::::::S
J:::::::::JP::::::PPPPPP:::::P M::::::::M M::::::::MS:::::SSSSSS::::::S
JJ:::::::JJPP:::::P P:::::PM:::::::::M M:::::::::MS:::::S SSSSSSS
J:::::J P::::P P:::::PM::::::::::M M::::::::::MS:::::S
J:::::J P::::P P:::::PM:::::::::::M M:::::::::::MS:::::S
J:::::J P::::PPPPPP:::::P M:::::::M::::M M::::M:::::::M S::::SSSS
J:::::j P:::::::::::::PP M::::::M M::::M M::::M M::::::M SS::::::SSSSS
J:::::J P::::PPPPPPPPP M::::::M M::::M::::M M::::::M SSS::::::::SS
JJJJJJJ J:::::J P::::P M::::::M M:::::::M M::::::M SSSSSS::::S
J:::::J J:::::J P::::P M::::::M M:::::M M::::::M S:::::S
J::::::J J::::::J P::::P M::::::M MMMMM M::::::M S:::::S
J:::::::JJJ:::::::J PP::::::PP M::::::M M::::::MSSSSSSS S:::::S
JJ:::::::::::::JJ P::::::::P M::::::M M::::::MS::::::SSSSSS:::::S
JJ:::::::::JJ P::::::::P M::::::M M::::::MS:::::::::::::::SS
JJJJJJJJJ PPPPPPPPPP MMMMMMMM MMMMMMMM SSSSSSSSSSSSSSS
DDDDDDDDDDDDD EEEEEEEEEEEEEEEEEEEEEEMMMMMMMM MMMMMMMM OOOOOOOOO
D::::::::::::DDD E::::::::::::::::::::EM:::::::M M:::::::M OO:::::::::OO
D:::::::::::::::DD E::::::::::::::::::::EM::::::::M M::::::::M OO:::::::::::::OO
DDD:::::DDDDD:::::DEE::::::EEEEEEEEE::::EM:::::::::M M:::::::::MO:::::::OOO:::::::O
D:::::D D:::::D E:::::E EEEEEEM::::::::::M M::::::::::MO::::::O O::::::O
D:::::D D:::::DE:::::E M:::::::::::M M:::::::::::MO:::::O O:::::O
D:::::D D:::::DE::::::EEEEEEEEEE M:::::::M::::M M::::M:::::::MO:::::O O:::::O
D:::::D D:::::DE:::::::::::::::E M::::::M M::::M M::::M M::::::MO:::::O O:::::O
D:::::D D:::::DE:::::::::::::::E M::::::M M::::M::::M M::::::MO:::::O O:::::O
D:::::D D:::::DE::::::EEEEEEEEEE M::::::M M:::::::M M::::::MO:::::O O:::::O
D:::::D D:::::DE:::::E M::::::M M:::::M M::::::MO:::::O O:::::O
D:::::D D:::::D E:::::E EEEEEEM::::::M MMMMM M::::::MO::::::O O::::::O
DDD:::::DDDDD:::::DEE::::::EEEEEEEE:::::EM::::::M M::::::MO:::::::OOO:::::::O
D:::::::::::::::DD E::::::::::::::::::::EM::::::M M::::::M OO:::::::::::::OO
D::::::::::::DDD E::::::::::::::::::::EM::::::M M::::::M OO:::::::::OO
DDDDDDDDDDDDD EEEEEEEEEEEEEEEEEEEEEEMMMMMMMM MMMMMMMM OOOOOOOOO

Build Tools – Javac
https://docs.oracle.com/javase/9/tools/javac.htm
IN WINDOWS
> javac --module-path ..mods -d ..modsmodul.demo.bank.client
srcmodul.demo.bank.clientmodule-info.java
srcmodul.demo.bank.clientmoduldemobankclientBankClient.java
javac [ options ] [ sourcefiles ]
Option Description
--module-path Where the dependent modules are located.
-d Destination folder to generate class files.
IN UNIX
$ javac --module-path ..mods -d ..modsmodul.demo.bank.client
$(find src -name "*.java")

Build Tools – Jar
https://docs.oracle.com/javase/9/tools/jar.htm
> jar -c -f libsmodul.demo.bank.client-2.0.jar --main-
class=modul.demo.bank.client.BankClient --module-version=2.0 -C
modul.demo.bank.client .
jar [OPTION...] [ [--release VERSION] [-C dir] files] ...
Option Description
-c Create jar.
-f Location and name of the generated jar file.
--main-class Main class of the jar which is placed in manifest.
--module-version Version of the modul (informative).
-C <dir> <files> Changes the directory to <dir> and includes the <files> in there.
Main Operation Modes
--create --update --extract --list --print-module-
descriptor

Build Tools – Jar (multi release)
jar9 --create –file out-sample/sample.jar -C out-sample/out8 .
--release 9 -C out-sample/out9 .

Single jar may differentiate wrt java versions it's running.

That is, a jar may contain different versions of classes for
different java versions.
JAR FILE CONTENT
└ com
└ sample
├ Main.class
└ Sample.class
└ META-INF
└ versions
└ 9
└ com
└ sample
└ Sample.class

Build Tools – JLink
jlink [options] --module-path modulepath --add-modules mods --output path
> jlink --module-path "%JAVA_HOME%/jmods;libs" --add-modules
modul.demo.bank,modul.demo.bank.client,modul.demo.bank.impl --compress=2
--output bankapp2 --launcher
startBankClient=modul.demo.bank.client/modul.demo.bank.client.BankClient

Used to assemble (and optimize) modules and their
dependencies into a custom runtime image(?).

Custom Runtime Image: An distribution of our application that
contains only necessary application and java runtime modules,
other application files, optionally start script, etc.

Simplifies and reduces the size of deployment.
https://docs.oracle.com/javase/9/tools/jlink.htm

Build Tools – JLink
├───bin
│ │ java.dll
│ │ java.exe
│ │ javaw.exe
│ │ jimage.dll
│ │ keytool.exe
│ │ net.dll
│ │ nio.dll
│ │ startBankClient
│ │ startBankClient.bat
│ │ zip.dll
├───conf
│ │ net.properties
│ └───security
│ └───policy
...
├───include
│ │ jni.h
│ └───win32
│ jni_md.h
├───legal
│ └───java.base
│ aes.md
├───lib
│ │ jvm.cfg
│ │ jvm.lib
│ │ modules
│ ├───security
│ └───server
└─── release

Build Tools – Java
https://docs.oracle.com/javase/9/tools/java.htm
> cd bankappbin
> java --list-modules
> java -m modul.demo.bank.client
> java -m modul.demo.bank.client/modul.demo.bank.client.BankClient
java [options] -p modulepath -m modulename[/mainclass] [args...]
CONTENT OF START SCRIPT
@echo off
set JLINK_VM_OPTIONS=
set DIR=%~dp0
"%DIR%java" %JLINK_VM_OPTIONS% -m
modul.demo.bank.client/modul.demo.bank.client.BankClient %*

Build Tools – Jdeps
https://docs.oracle.com/javase/9/tools/jdeps.htm
jdeps [options] classes ...
> jdeps -dotoutput dot --module-path . modul.demo.bank.client-2.0.jar
modul.demo.bank.impl-2.0.jar modul.demo.bank@2.0.jar
Generated files: modul.demo.bank.client.dot modul.demo.bank.dot
modul.demo.bank.impl.dot summary.dot
Content of summary.dot:
digraph "summary" {
"modul.demo.bank.client" -> "java.base (java.base)";
"modul.demo.bank.client" -> "modul.demo.bank";
"modul.demo.bank" -> "java.base (java.base)";
"modul.demo.bank.impl" -> "java.base (java.base)";
"modul.demo.bank.impl" -> "modul.demo.bank";
}
Shows the package-level or class-level dependencies of Java
class files.

Build Tools – Jdep
http://www.webgraphviz.com/

Build Tools – Jmod
jmod (create|extract|list|describe|hash) [options] jmod-file
> jmod create --module-path "%JAVA_HOME%jmods";. --class-path
modul.demo.bank.client --module-version 1.2
jmodfilesmodul.demo.bank.client.jmod

File format that aggregates not only .class files but also
metadata, and other resource files.

Intented to kill jar format.

Allows to transport files, not to execute. That is, it can be used
during compile and link-time, but not at run-time.

Jmod is actually zip format. Zip tool can be used to manage.

Platform modules are distributed in jmod format.

Build Tools – Jmod
c:Workworkspace_oxygenmods>jmod list modul.demo.bank
Error: mode must be one of create, extract, list, describe, or hash: list
Usage: jmod (create|extract|list|describe|hash) <OPTIONS> <jmod-file>
use --help for a list of possible options

There are still bugs in tools. Use with cautions.

Build Tools – Jimage

Is a container format for storing (and indexing) modules,
classes and resources in the JDK.

Aims to replaces rt.jar, resources.jar, tools.jar and other jars in
JDK and JRE.

Used to create binary runtime images.

Intended to be internal to JDK.

Can be created by jlink tool. (<generated-app>libmodules)

Jimage tool can be used to print information about and extract
necessary files from jimage file.

Build Tools – Jimage
>jimage info bankapplibmodules
Major Version: 1
Minor Version: 0
Flags: 0
Resource Count: 6155
Table Length: 6155
Offsets Size: 24620
Redirects Size: 24620
Locations Size: 131167
Strings Size: 135107
Index Size: 315542
jimage <extract | info | list | verify> <options> jimage...
>jimage list bankapplibmodules
Module: java.base
...
Module: modul.demo.bank.client
...
Module: modul.demo.bank.impl
...
Module: modul.demo.bank
META-INF/MANIFEST.MF
modul/demo/bank/IAccount.class
modul/demo/bank/IAccountProvider.class
module-info.class

Build Tools – Jdeprscan
https://docs.oracle.com/javase/9/tools/jdeprscan.htm
>jdeprscan --class-path libs*.jar libsmodul.demo.bank.client@2.0.jar
Jar file libsmodul.demo.bank.impl@2.0.jar:
error: cannot find class modul/demo/bank/IAccount
error: cannot find class modul/demo/bank/IAccountProvider
Jar file libsmodul.demo.bank@2.0.jar:
Jar file libsmodul.demo.bank.client@2.0.jar:

Scans files for usage of deprecated API elements.
jdeprscan [ options ]{dir|jar|class}
>jdeprscan Resource.class
class deneme/Resource uses deprecated method java/lang/Thread::stop()V

Diag Tools – Jcmd

Send diagnostic command requests to the JVM.

Used to control Java Flight Recordings, troubleshoot, and
diagnose JVM and Java Applications.
jcmd <process id/main class> VM.version
jcmd <process id/main class> VM.system_properties
jcmd <process id/main class> VM.uptime
jcmd <process id/main class> GC.class_histogram
jcmd <process id/main class> GC.heap_dump filename=Myheapdump
// jmap -dump:file=<file> <pid>→
jcmd <process id/main class> Thread.print
// kill -3
jcmd <process id/main class> PerfCounter.print
// prints all performance counters in the process

Diag Tools –
Native Memory Tracking

Tracks internal memory usage for a Java HotSpot VM.

5-10% JVM performance drop and memory usage.

2 commands are available

-XX:NativeMemoryTracking=summary

-XX:NativeMemoryTracking=detail

Create a baseline: jcmd <pid> VM.native_memory baseline

Monitor memory change: jcmd <pid> VM.native_memory detail.diff

Diag Tools –
Native Memory Tracking
Total: reserved=664192KB, committed=253120KB
- Java Heap (reserved=516096KB, committed=204800KB)
(mmap: reserved=516096KB, committed=204800KB)
- Class (reserved=6568KB, committed=4140KB)
(classes #665)
(malloc=424KB, #1000)
- Thread (reserved=6868KB, committed=6868KB)
(thread #15)
(stack: reserved=6780KB, committed=6780KB)
(malloc=27KB, #66)
(arena=61KB, #30)
- Code (reserved=102414KB, committed=6314KB)
(malloc=2574KB, #74316)
...

Diag Tools –
Java Mission Control

JDK profiling and diagnostics tools platform for HotSpot JVM.

Provides basic monitoring, managing, and production time
profiling and diagnostics with high performance.

JMC uses Java Flight Recording (JFR) outcome and JFR is a
commercial feature in production, not in dev/test/preprod.

JFR records the java application and runtime w/ little overhead.

Overhead is depend on the selected triggers before recording.

JMC displays the detailed profiling data about Memory, Cpu,
Code, Threads, I/O, System, Events.
>jcmd 7060 JFR.start name=MyRecording settings=profile delay=20s
duration=2m filename=C:TEMPmyrecording.jfr
>jcmd 7060 JFR.check
>jcmd 7060 JFR.stop
>jcmd 7060 JFR.dump name=MyRecording filename=C:TEMPmyrecording.jfr

Diag Tools –
Java Mission Control

Diag Tools – JConsole

JMX compliant monitoring tool.

Monitor Memory, Threads, Classes, VM summary, other Mbeans.

Diag Tools – Jdb

The command-line debugger which uses Java Debug Interface
(JDI).

JDK ships with several Serviceability Agent (SA) connectors to
attach to a crash dump or hung process in a local or remote
host.

SACoreAttachingConnector

SADebugServerAttachingConnector

SAPIDAttachingConnector

These connectors are used by IDEs. (e.g. Eclipse)
// Attach to running process
jdb -connect sun.jvm.hotspot.jdi.SAPIDAttachingConnector:pid=9302
> threads
...
> thread 0x7
...

Diag Tools – Jinfo

Use jcmd instead of old jinfo utility.

Gets configuration, system properties, command-line flags
information from a running Java process or core file.
>jinfo 16172
Java System Properties:
#Mon Jul 31 11:00:27 EET 2017
awt.toolkit=sun.awt.windows.WToolkit
file.encoding.pkg=sun.io
java.specification.version=9
...
VM Flags:
-XX:CICompilerCount=1 -XX:CodeCacheExpansionSize=32768
...
VM Arguments:
jvm_args:
-agentlib:jdwp=transport=dt_socket,suspend=y,address=localhost:64982
-Dfile.encoding=Cp1254
java_command: deneme.Resource
...

Diag Tools – Jmap

Use jcmd or JMC/JFR instead of old jmap utility.

Displays memory-related statistics for a running VM or core file.
Jmap Samples
>jmap -heap 29620
>jmap -histo 29620
>jmap -histo /solaris-sparcv9/bin/java core
// the exact java executable is needed to parse core file.
>jmap -permstat 29620

Diag Tools – Jps

Displays the running Java processes for current user on the host
machine.
Jps Samples
>jps
10196 Jps
6292
16172 Resource
>jps -ml
6292
9300 jdk.jcmd/sun.tools.jps.Jps -ml
16172 deneme.Resource

Diag Tools – Jstack

Use jcmd instead of old jstack utility.

Displays the stack traces of all threads of the virtual machine.

Can attach to the specified process or core file.

Can perform deadlock detection.

Can be obtained programmatically: Thread.getAllStackTraces

Mixed Stack: Native Stack + Java Stack
Jstack Samples
>jstack 16172
2017-07-31 11:32:01
Full thread dump Java HotSpot(TM) Server VM (9+178 mixed mode, emulated-
client):
...
"Service Thread" #12 daemon prio=9 os_prio=0 tid=0x05125400 nid=0x3fa8
runnable [0x00000000]
java.lang.Thread.State: RUNNABLE
...

1111111 000000000 MMMMMMMM MMMMMMMM
1::::::1 00:::::::::00 M:::::::M M:::::::M
1:::::::1 00:::::::::::::00 M::::::::M M::::::::M
111:::::1 0:::::::000:::::::0 M:::::::::M M:::::::::M
1::::1 0::::::0 0::::::0 M::::::::::M M::::::::::M
1::::1 0:::::0 0:::::0 M:::::::::::M M:::::::::::M
1::::1 0:::::0 0:::::0 M:::::::M::::M M::::M:::::::M
1::::l 0:::::0 000 0:::::0 M::::::M M::::M M::::M M::::::M
1::::l 0:::::0 000 0:::::0 M::::::M M::::M::::M M::::::M
1::::l 0:::::0 0:::::0 M::::::M M:::::::M M::::::M
1::::l 0:::::0 0:::::0 M::::::M M:::::M M::::::M
1::::l 0::::::0 0::::::0 M::::::M MMMMM M::::::M
111::::::1110:::::::000:::::::0 M::::::M M::::::M
1::::::::::1 00:::::::::::::00 M::::::M M::::::M
1::::::::::1 00:::::::::00 M::::::M M::::::M
111111111111 000000000 MMMMMMMM MMMMMMMM
BBBBBBBBBBBBBBBBB RRRRRRRRRRRRRRRRR EEEEEEEEEEEEEEEEEEEEEE AAA KKKKKKKKK KKKKKKK
B::::::::::::::::B R::::::::::::::::R E::::::::::::::::::::E A:::A K:::::::K K:::::K
B::::::BBBBBB:::::B R::::::RRRRRR:::::R E::::::::::::::::::::E A:::::A K:::::::K K:::::K
BB:::::B B:::::BRR:::::R R:::::REE::::::EEEEEEEEE::::E A:::::::A K:::::::K K::::::K
B::::B B:::::B R::::R R:::::R E:::::E EEEEEE A:::::::::A KK::::::K K:::::KKK
B::::B B:::::B R::::R R:::::R E:::::E A:::::A:::::A K:::::K K:::::K
B::::BBBBBB:::::B R::::RRRRRR:::::R E::::::EEEEEEEEEE A:::::A A:::::A K::::::K:::::K
B:::::::::::::BB R:::::::::::::RR E:::::::::::::::E A:::::A A:::::A K:::::::::::K
B::::BBBBBB:::::B R::::RRRRRR:::::R E:::::::::::::::E A:::::A A:::::A K:::::::::::K
B::::B B:::::B R::::R R:::::R E::::::EEEEEEEEEE A:::::AAAAAAAAA:::::A K::::::K:::::K
B::::B B:::::B R::::R R:::::R E:::::E A:::::::::::::::::::::A K:::::K K:::::K
B::::B B:::::B R::::R R:::::R E:::::E EEEEEE A:::::AAAAAAAAAAAAA:::::A KK::::::K K:::::KKK
BB:::::BBBBBB::::::BRR:::::R R:::::REE::::::EEEEEEEE:::::E A:::::A A:::::A K:::::::K K::::::K
B:::::::::::::::::B R::::::R R:::::RE::::::::::::::::::::E A:::::A A:::::A K:::::::K K:::::K
B::::::::::::::::B R::::::R R:::::RE::::::::::::::::::::E A:::::A A:::::A K:::::::K K:::::K
BBBBBBBBBBBBBBBBB RRRRRRRR RRRRRRREEEEEEEEEEEEEEEEEEEEEEAAAAAAA AAAAAAAKKKKKKKKK KKKKKKK

Java Language Changes

Underscore (_) is not allowed as an identifier

try-with-resources
// A final resource
final Resource resource1 = new Resource("resource1");
// An effectively final resource
Resource resource2 = new Resource("resource2");
// IN JAVA 7/8
try (Resource r1 = resource1; Resource r2 = resource2) {
// Use of resource1 and resource 2 through r1 and r2.
}
// JAVA 9
try (resource1; resource2) {
// Use of resource1 and resource 2.
}

@SafeVarargs
public static void faultyMethod(List<String>... l) {
Object[] objectArray = l; // Valid
objectArray[0] = Arrays.asList(42);
String s = l[0].get(0); // ClassCastException
}
faultyMethod(Arrays.asList("Hello!"),
Arrays.asList("World!"));

Type Erasure translates List<String>... List[] Object[]→ →

If your method handles varargs properly, use @SafeVarargs

Can be used in static and non-constructor method (non-private)

Private methods are added in Java 9.

Diamond w/ anonymous classes
MyHandler<Integer> intHandler = new MyHandler<>(1) {
public void handle() {
// handling code...
}
};

Java 9 allows diamond(<>) in annonymous classes.

Private interface methods

Before Java 9
public interface MyInterface {
default void init(Params params) { //logic }
default void m2(Params params) { init(params); }
default void m3() { init(null); }
}

After Java 9
public interface MyInterface {
private void init(Params params) { //logic }
default void m2(Params params) { init(params); }
default void m3() { init(null); }
}
Supported:
* public static * public abstract * public default
* private static * private
Compile error:
* private abstract * private default
See: https://docs.oracle.com/javase/tutorial/java/IandI/defaultmethods.html

Core Library Changes -
Process API
ProcessHandle and Info classes are added to API to interact
conveniently w/ processes (and trees).
ProcessHandle handle = ProcessHandle.current();
Optional<ProcessHandle> handle = ProcessHandle.of(pid);
Stream<ProcessHandle> stream = ProcessHandle.allProcesses();
interface ProcessHandle {
long pid();
Optional<ProcessHandle> parent();
Stream<ProcessHandle> children();
Stream<ProcessHandle> descendants();
CompletableFuture<ProcessHandle>
onExit();
boolean supportsNormalTermination();
boolean destroy();
boolean destroyForcibly();
boolean isAlive();
Info info();
}
interface Info {
public Optional<Duration>
totalCpuDuration();
public Optional<String> command();
public Optional<String> commandLine();
public Optional<String[]> arguments();
public Optional<Instant> startInstant();
public Optional<String> user();
}

Variable Handles
Completely copied and pasted :-)
Excerpt from JEP 193
“As concurrent and parallel programming in Java continue to expand,
programmers are increasingly frustrated by not being able to use Java
constructs to arrange atomic or ordered operations on the fields of
individual classes; for example, atomically incrementing a count field.”
The existing possibilities to do this are all lacking in some sense or the
other:
Atomic... classes add “both space overhead and additional concurrency
issues to manage indirection”
FieldUpdaters often lead to “more overhead than the operation itself”
Unsafe is, well, unsafe – it’s neither standardized nor supported and slated
to become inaccessible in Java 10.
“A variable handle is a typed reference to a variable, which supports read
and write access to the variable under a variety of access modes.
Supported variable kinds include instance fields, static fields and array

Variable Handles
Define a standard means to invoke the equivalents of various
java.util.concurrent.atomic and sun.misc.Unsafe operations upon object
fields and array elements, a standard set of fence operations for fine-
grained control of memory ordering, and a standard reachability-fence
operation to ensure that a referenced object remains strongly reachable.
public class AtomicBoolean implements java.io.Serializable {
private static final VarHandle VALUE;
static {
try {
MethodHandles.Lookup l = MethodHandles.lookup();
VALUE = l.findVarHandle(AtomicBoolean.class, "value", int.class);
} catch (ReflectiveOperationException e) {
throw new Error(e);
}}
private volatile int value;
public final boolean compareAndSet(boolean expectedValue, boolean newValue) {
return VALUE.compareAndSet(this,
(expectedValue ? 1 : 0),
(newValue ? 1 : 0));
}

Compact Strings

20%-30% of an average application's live data is char[] inside String
objects.

char = 2 bytes for UTF-16 representation.

But, for most of the strings ISO-8859-1, which is 1 byte, is sufficient.

Compress the data as byte[], if all characters are ISO-8859-1 encoded.

In average java application, memory consumption reduces by 10%-15%
and causes less time for GC.

Disabled if necessary: XX:-CompactStrings

Platform Logging API &
Service
Defines a minimal logging API (java.util.logging) and service interface
(System.Logger) which platform classes can use to log messages.

Application can provide its own logging API (e.g. LogBack) to the
platform via ServiceLoader, thus, platform and the application can use
the same logging API.

If no logging API is provided, default platform logger (java.util.logging) is
used.

Concurrency Updates

Publish-subscriber feature of Reactive Stream is supported by
Concurrency API using Flow class.

CompletableFuture API enhencements.

Other small concurrency enhencements & documentation/javadoc
updates.

Reactive Streams

Flow.Publisher: Publishes item to the subscribers. Subscriber
should Publisher.subscribe() in order to receive requests.

Flow.Subscriber: Subscribes to Publisher and consume request
from it via onNext(T), onError(Exception), onComplete()

Flow.Subscription: Link between Publisher and Subscriber.
request(n) method is called to start messaging.
Subscriber.onNext(T) method is called at most n times or fewer if
cancel() is called or application is terminated.

Completable Future

Future class is introduced to Java in 1.5 to ease async processing.

But it doesn't have a mechanism to combine computation or handle
errors.

In Java 8, CompletableFuture is added to handle composing,
combining, executing steps, and handling error in async computation.
CompletableFuture<String> completableFuture = new CompletableFuture<>();
Executors.newCachedThreadPool().submit(() -> {
Thread.sleep(1000);
completableFuture.complete("completed");
return null;
});
Executors.newCachedThreadPool().submit(() -> {
Thread.sleep(500);
completableFuture.cancel(false);
return null;
});

Completable Future

Java 9 additions are below:
Executor defaultExecutor()
CompletableFuture newIncompleteFuture()
CompletableFuture<T> copy()
CompletionStage<T> minimalCompletionStage()
CompletableFuture<T> completeAsync(Supplier<? extends T> supplier,
Executor executor)
CompletableFuture<T> completeAsync(Supplier<? extends T> supplier)
CompletableFuture<T> orTimeout(long timeout, TimeUnit unit)
CompletableFuture<T> completeOnTimeout(T value, long timeout, TimeUnit
unit)
Executor delayedExecutor(long delay, TimeUnit unit, Executor executor)
Executor delayedExecutor(long delay, TimeUnit unit)
 CompletionStage completedStage(U value)
 CompletionStage failedStage(Throwable ex)
 CompletableFuture failedFuture(Throwable ex)

Factory Methods for Collections

New factory methods are added to List, Set, and Map interfaces.

Only immutable instances are created.
List<String> list = List.of("a", "b", "c");
Set<String> set = Set.of("a", "b", "c");
Map<String, Integer> mapImmediate = Map.of(
"one", 1,
"two", 2,
"three", 3);
Map<String, Integer> mapEntries = Map.ofEntries(
entry("one", 1),
entry("two", 2),
entry("three", 3));

Enhanced Deprecation

2 new elements are added to @Deprecated annotation

@Deprecated(forRemoval=true): API will be release in the next
release.

@Deprecated(since="version"): Deprecated since the depicted
version.

Jdeprscan can be used to find deprecated API elements.
@Deprecated(forRemoval=true, since="9")
private void method() {
// old algorithm
}

Spin-Wait Hints

Used to (busy) wait the caller on a condition.

Busy-wait implemented by Thread.onSpinWait() method.

Some OS/processor architectures may optimize the spin-wait
operations.

This method is just a hint. It doesn't guaranties to optimize spin-wait.
class EventHandler {
volatile boolean eventNotificationNotReceived;
void waitForEventAndHandleIt() {
while ( eventNotificationNotReceived ) {
java.lang.Thread.onSpinWait();
}
readAndProcessEvent();
}
void readAndProcessEvent() {
// Read event from some source and process it
}
}

Stack-Walking API

Provides easy filtering and lazy access to stack trace information.

Functionality is provided by java.lang.StackWalker class.

Short walk and long walk on stack trace can be stopped by the given
criteria. Thus, the cost of examining all stack trace is avoided.
List<StackFrame> frames =
StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE)
.walk((s) -> s.collect(Collectors.toList()));
System.out.println("All frames : n" + frames.toString());
List<StackFrame> frames = StackWalker.getInstance().walk(s ->
s.dropWhile(f -> f.getClassName().startsWith("com.foo."))
.limit(10)
.collect(Collectors.toList()));
System.out.println("Ten frames : n" + frames.toString());

JVM Tuning - GC Changes

GC combinations - deprecated in Java8 / removed in Java9:

DefNew + CMS

ParNew + SerialOld

Incremental CMS

G1 has better overall performance than throughput collector. Thus G1
became default collector.

CMS GC is deprecated. When -XX:+UseConcMarkSweepGC option is
used, a warning message is displayed.

The "foreground" mode for CMS has also been removed.

The following command line flags have been removed:
-Xincgc -XX:+UseCMSCompactAtFullCollection
-XX:+CMSIncrementalMode -XX:+CMSFullGCsBeforeCompaction
-XX:+UseCMSCollectionPassing

-XX:+UseParNewGC flag has been deprecated and will likely be
removed in a future release.

Highlights

91 JEP is implemented in Java 9.

JPMS (Jigsaw) is main feature of Java 9.

Planned to release more frequently (2 year period).

http://openjdk.java.net/projects/jdk10/

http://openjdk.java.net/projects/valhalla/

Homework

How to migrate to Java 9?

TTTTTTTTTTTTTTTTTTTTTTTHHHHHHHHH HHHHHHHHH AAA NNNNNNNN NNNNNNNNKKKKKKKKK KKKKKKK
T:::::::::::::::::::::TH:::::::H H:::::::H A:::A N:::::::N N::::::NK:::::::K K:::::K
T:::::::::::::::::::::TH:::::::H H:::::::H A:::::A N::::::::N N::::::NK:::::::K K:::::K
T:::::TT:::::::TT:::::THH::::::H H::::::HH A:::::::A N:::::::::N N::::::NK:::::::K K::::::K
TTTTTT T:::::T TTTTTT H:::::H H:::::H A:::::::::A N::::::::::N N::::::NKK::::::K K:::::KKK
T:::::T H:::::H H:::::H A:::::A:::::A N:::::::::::N N::::::N K:::::K K:::::K
T:::::T H::::::HHHHH::::::H A:::::A A:::::A N:::::::N::::N N::::::N K::::::K:::::K
T:::::T H:::::::::::::::::H A:::::A A:::::A N::::::N N::::N N::::::N K:::::::::::K
T:::::T H:::::::::::::::::H A:::::A A:::::A N::::::N N::::N:::::::N K:::::::::::K
T:::::T H::::::HHHHH::::::H A:::::AAAAAAAAA:::::A N::::::N N:::::::::::N K::::::K:::::K
T:::::T H:::::H H:::::H A:::::::::::::::::::::A N::::::N N::::::::::N K:::::K K:::::K
T:::::T H:::::H H:::::H A:::::AAAAAAAAAAAAA:::::A N::::::N N:::::::::NKK::::::K K:::::KKK
TT:::::::TT HH::::::H H::::::HH A:::::A A:::::A N::::::N N::::::::NK:::::::K K::::::K
T:::::::::T H:::::::H H:::::::H A:::::A A:::::A N::::::N N:::::::NK:::::::K K:::::K
T:::::::::T H:::::::H H:::::::H A:::::A A:::::A N::::::N N::::::NK:::::::K K:::::K
TTTTTTTTTTT HHHHHHHHH HHHHHHHHHAAAAAAA AAAAAAANNNNNNNN NNNNNNNKKKKKKKKK KKKKKKK
YYYYYYY YYYYYYY OOOOOOOOO UUUUUUUU UUUUUUUU
Y:::::Y Y:::::Y OO:::::::::OO U::::::U U::::::U
Y:::::Y Y:::::Y OO:::::::::::::OO U::::::U U::::::U
Y::::::Y Y::::::YO:::::::OOO:::::::OUU:::::U U:::::UU
YYY:::::Y Y:::::YYYO::::::O O::::::O U:::::U U:::::U
Y:::::Y Y:::::Y O:::::O O:::::O U:::::D D:::::U
Y:::::Y:::::Y O:::::O O:::::O U:::::D D:::::U
Y:::::::::Y O:::::O O:::::O U:::::D D:::::U
Y:::::::Y O:::::O O:::::O U:::::D D:::::U
Y:::::Y O:::::O O:::::O U:::::D D:::::U
Y:::::Y O:::::O O:::::O U:::::D D:::::U
Y:::::Y O::::::O O::::::O U::::::U U::::::U
Y:::::Y O:::::::OOO:::::::O U:::::::UUU:::::::U
YYYY:::::YYYY OO:::::::::::::OO UU:::::::::::::UU
Y:::::::::::Y OO:::::::::OO UU:::::::::UU
YYYYYYYYYYYYY OOOOOOOOO UUUUUUUUU

Java9

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