Java 9-10 What's New

Simone Bordet
● @simonebordet
● sbordet@webtide.com
● Java Champion
● Works @ Webtide
● The company behind Jetty and CometD
● JVM Tuning Expert

Java 9
● Java 9 & 10 are NOTLong Term Support (LTS) Releases
● Java 8 current LTS Release supported March 2014 - January 2019
● Java 9 supported September 2017 - March 2018
● Java 10 supported March 2018 - September 2018
● Java 11 new LTS Release September 2018
● But “LTS” has a special meaning

Java 9
● “Long Term Support” is only for Oracle customers
● For Oracle customers Java 11 will be supported for 3 years
● For all the others Java 11 will last the usual 6 months only
● You will be “Long Term Supported” by moving to Java 12
● Other JDK vendors may give you support where Oracle does not
○ Azul, RedHat, London Java Community (LJC), etc.

https://www.azul.com/products/zulu-and-zulu-enterprise/zulu-enterprise-java-support-options/

Java 9
● Java 9 comes with a MASSIVE number of changes
○ 91 JEPs (!)
● Biggest change: Jigsaw modules
● Upgrade to Java 9 not as smooth as past JDKs
○ Needs very thorough testing

● Removed tools.jar
○ Attach APIs
○ Programmatically call javac (JSP compilation), javadoc, etc.
● tools.jar content split into packages
○ jdk.attach
○ jdk.compiler (but use module java.compiler)
○ jdk.javadoc
● Removed JavaDB
○ Rebranding of Apache Derby
Java 9 Removals

Java 9 Removals
● Removed endorsed directory mechanism
$JAVA_HOME/lib/endorsed
● Could only contain updates for:
○ CORBA
○ XML DOM
○ XML SAX
● Rarely used to update the implementations shipped with the JDK

Java 9 Removals
● Removed Extension Directory Mechanism
○ Moved to modules
$JAVA_HOME/jre/lib/ext
nashorn.jar
jfxrt.jar
sunec.jar
sunjce_provider.jar
zipfs.jar
...

Java 9 Changes
● ClassLoader Hierarchy
● Java 8
Boot CL <- Extension CL <- System CL
ClassLoader.getSystemClassLoader()
● Java 9
Boot CL <- Platform CL <- System CL
ClassLoader.getPlatformClassLoader()
ClassLoader.getSystemClassLoader()

Java 9 Changes
● ClassLoading Implementation Changes
// Throws ClassCastException now!
URLClassLoader system = (URLClassLoader)ClassLoader.getSystemClassLoader();
● ClassLoader Resources
URL resource = system.getResource("java/lang/String.class");
resource = jrt:/java.base/java/lang/String.class
● Class scanning for annotations
○ Previous techniques not working in JDK 9
○ Cannot retrieve the list of jars to open

Java 9 Changes
● JEP 223 - New Version String Scheme
○ System.getProperty("java.version")
○ 1.8.0_152 -> 9.0.1
○ Broke many Maven Plugins, Jetty, etc.
● JDK 9’s java.lang.Runtime.Version class
○ Cannot parse JDK 8 version string
○ Must implement custom parsing to support both

Java 9 New Features
● JEP 260 - Encapsulate Internal APIs
● Non-critical internal APIs have been removed
○ sun.misc.Base64Decoder
● Critical internal APIs without replacement -> retained
○ In module jdk.unsupported
○ For example, sun.misc.Unsafe
○ Don’t use them
● Critical internal APIs with replacement -> encapsulated
○ Use the replacements

Java 9 New Features
● Most internal APIs now have a public replacement
● Finalization
○ sun.misc.Cleaner replaced by java.lang.ref.Cleaner
○ Object.finalize() is now deprecated
● Unsafe access
○ Some sun.misc.Unsafe usage replaced by VarHandle

Java 9 New Features
● jdeps tool produces a report of class/jar/module dependencies
$ jdeps -s jetty-util-9.4.8-SNAPSHOT.jar
jetty-util-9.4.8-SNAPSHOT.jar -> java.base
jetty-util-9.4.8-SNAPSHOT.jar -> java.desktop
jetty-util-9.4.8-SNAPSHOT.jar -> java.logging
jetty-util-9.4.8-SNAPSHOT.jar -> java.naming
jetty-util-9.4.8-SNAPSHOT.jar -> java.sql
jetty-util-9.4.8-SNAPSHOT.jar -> java.xml
jetty-util-9.4.8-SNAPSHOT.jar -> not found

Java 9 New Features
● JEP 247 - Compile for older platforms
● New switch --release to javac
○ Supports up to 3 previous releases
● $JAVA_HOME/lib/ct.sym
○ Zipped file containing the symbols for each platform

Java 9 New Features
<profile>
<id>jdk9</id>
<activation>
<jdk>[1.9,)</jdk>
</activation>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.0+</version>
<configuration>
<release>8</release>
</configuration>
</plugin>
</plugins>
</build>
</profile>

Java 9 New Features
● JEP 238 - Multi Release jars
com/
acme/
A.class
B.class
C.class
META-INF/
versions/
9/
com/
acme/
A.class
D.class

Java 9 Changes
● URLStreamHandler
● Java 8: Magic Reflection
○ sun.net.www.protocol.<scheme>.Handler
● Java 9: ServiceLoader
○ Implement java.net.spi.URLStreamHandlerProvider
● Difficult to make a jar with both solutions
○ Service files cannot be versioned

Java 9 New Features
● JEP 213 - Small Language Changes
● Cannot use "_" as identifier
○ Object _ = new Object();
● Improved type inference
○ Use diamond notation in anonymous inner classes
● Private methods in interfaces
○ Useful to AOP frameworks
○ Avoids code duplications in default methods

Java 9 New Features
● JEP 213 - Small Language Changes
● Enhanced try-with-resources
InputStream input = ...;
...
try (input) {
...
}

Java 9 New Features
● JEP 264 - Platform Logging APIs
○ Implementation defaults to java.util.logging
System.getLogger("name")
.log(Level.INFO, () -> "a" + " - " + "b");
System.getLogger("name")
.log(Level.INFO, "%s - %s", a, b);

Java 9 New Features
● JEP 254 - Compact Strings
○ java.lang.String now stores a byte[], not a char[]
● JEP 280 - String concatenation using invokedynamic
○ Faster and allocates less
● JEP 269 - Collections factory methods
○ Space efficient
List.of("a", "b", "c");
Set.of("a", "b", "c");
Map.of("a", 1, "b", 2, "c", 3);

Java 9 New Features
● JEP 193 - Variable Handles
class ConcurrentLinkedQueue_BAD {
AtomicReference<Node> head; // BAD, adds indirection
}
class ConcurrentLinkedQueue {
Node head;
private static final VarHandle HEAD;
static {
HEAD = MethodHandles.lookup()
.findVarHandle(ConcurrentLinkedQueue.class, "head", Node.class);
}
public void m() {
if (HEAD.compareAndSet(...))
...
}
}

Java 9 New Features
● JEP 102 - Process API
Process p = new ProcessBuilder()
.command("java")
.directory(new File("/tmp"))
.redirectOutput(Redirect.DISCARD)
.start();
ProcessHandle.of(p.pid())
.orElseThrow(IllegalStateException::new)
.onExit()
.thenAccept(h ->
System.err.printf("%d exited%n", h.pid())
);

Java 9 New Features
● JEP 266 - Concurrent APIs Enhancements
● java.util.concurrent.Flow
○ Identical API and semantic of ReactiveStreams
● CompletableFuture Enhancements
○ Common scheduler for timeout functionalities
CompletableFuture.supplyAsync(() -> longJob())
.completeOnTimeout("N/A", 1, TimeUnit.SECONDS)
CompletableFuture.supplyAsync(() -> longJob())
.orTimeout(1, TimeUnit.SECONDS)

● JEP 143 - Improve Contended Locking
○ synchronized now as scalable as java.util.concurrent.Lock
http://vmlens.com/articles/performance-improvements-of-java-monitor/
Java 9 Changes

Java 9 New Features
● JEP 295: Ahead-of-Time Compilation
○ Experimental
○ Based on the Java-based Graal JIT compiler
https://mjg123.github.io/2017/10/02/JVM-startup.html

Java 9 New Features
● JEP 222 - jshell Read-Eval-Print-Loop (REPL)
○ Can be accessed programmatically via module jdk.jshell
● Pretty powerful !
○ Completion
○ Imports
○ Variable creation
○ Documentation
○ Functions and Forward References
○ History
○ Search
○ External Editor

Java 9 Changes
● JEP 248 - Make G1 the Default Collector
● 250+ Improvements
○ Adaptive start of concurrent mark -XX:+G1UseAdaptiveIHOP
○ Made internal data structures more concurrent
○ More phases parallelized
○ Reduced contention
○ Reduced memory consumption
○ …
● 180+ Bug Fixes

Java 9 Changes
● JEP 158 - Unified JVM Logging
● Logs have a message, tags (finally) and a level; can be decorated
● Tags
○ gc, ref, ergo, …
● Levels
○ error, warning, info, debug, trace
● Output
○ stdout, stderr, file
● Decorators
○ time (various formats), pid, tid, level, tags
● Default
○ -Xlog:all=warning:stderr:uptime,level,tags

Java 9 Changes
● JEP 271 - Unified GC Logging
○ Done using JEP 158 - Unified JVM Logging
● Example for GC logging
○ -Xlog:gc*,ergo*=trace,ref*=debug:file=logs/gc.log:time,level,tags
● Not compatible with previous logging formats
○ Need to parse the logs differently

Java 9 Changes
● JVM Options Changes
○ 50 Removed - JVM refuses to start
○ 18 Ignored, 12 Deprecated
● Important JVM Options Removed
○ GCLogFileSize
○ NumberOfGCLogFiles
○ PrintAdaptiveSizePolicy
○ PrintGCApplicationStoppedTime
○ PrintGCCause
○ PrintGCDateStamps
○ PrintGCTimeStamps
○ PrintReferenceGC
○ PrintTenuringDistribution
○ ...

Java 9 Changes
● JEP 277 - Enhanced Deprecation
@Deprecated(since="1.8", forRemoval=true)
● jdeprscan
○ Produces a report of deprecations

Java 9 Changes
● JEP 229 - Keystore Defaults to PKCS12
● PKCS12
○ Standard format, more secure, more extensible
○ Already supported in JDK 8
● JDK 9
○ keytool by default creates PKCS12 keystores
○ Autodetects JKS and PKCS12 keystores

Java 9 New Features
● JEP 219 - Datagram Transport Layer Security (DTLS)
● JEP 244 - TLS Application-Layer Protocol Negotiation Extension (ALPN)
● JEP 246 - Leverage CPU Instructions for GHASH and RSA
● JEP 249 - OCSP Stapling for TLS
● JEP 273 - DRBG-Based SecureRandom Implementations
● JEP 287 - SHA-3 Hash Algorithms
● JEP 288 - Disable SHA-1 Certificates

Java 10
● Parallel full GC for G1
● In Java 9, if G1 must perform a full GC it’s single threaded
○ Very slow
● In Java 10, it has been parallelized
[5.423s] GC(59) Pause Full 4028M->3286M(4096M) 513.026ms
[5.423s] GC(59) User=2.80s Sys=0.04s Real=0.52s

Java 10
● Experimental Graal JIT
○ https://www.graalvm.org/
● -XX:+UnlockExperimentalVMOptions -XX:+UseJVMCICompiler
● Not yet recommended in production

Java 10
● Application class-data sharing
○ https://blog.codefx.org/java/application-class-data-sharing/
● -Xshare:dump
○ Dumps JDK classes
○ Faster startup times
$ java
-XX:+UseAppCDS
-Xshare:dump
-XX:SharedClassListFile=classes.lst
-XX:SharedArchiveFile=app-cds.jsa
--class-path app.jar

Java 10
● Thread-Local Handshakes
● Improves JVM performance
○ Reduces Time-To-SafePoint (TTSP)
● No need to have a global SafePoint to get stack traces
○ Great benefit to profilers for stack sampling

Java 10
● Docker awareness (Linux only)
○ https://blog.docker.com/2018/04/improved-docker-container-integration-with-java-10/
○ It is on by default
● -XX:-UseContainerSupport
● -XX:ActiveProcessorCount=n
● -XX:MinRAMPercentage=p
● -XX:InitialRAMPercentage=p
● -XX:MaxRAMPercentage=p

Java 10
● Planned removals for JDK 11
● java.corba (CORBA)
● java.xml.bind (JAXB)
● java.xml.ws (SOAP)
● java.xml.ws.annotation (@PostConstruct, @PreDestroy, ...)

Java 10
● Local variable type inference (a.k.a. var)
○ http://openjdk.java.net/projects/amber/LVTIstyle.html
var list = new ArrayList<String>(); // infers ArrayList<String>
var stream = list.stream(); // infers Stream<String>
● var is not a keyword, it is a reserved type name
○ It’s a valid identifier, unless used in places where the compiler expects a type name
int var = 13;

Java 10
● var comes with some controversy
var message = "warning, too many features"; // Good
● Consider:
List<String> list = new ArrayList<>();
list.trimToSize(); // Does not compile
var list = new ArrayList<String>();
list.trimToSize(); // Compiles

Java 10
● More controversy:
var result = processor.run(); // What type ?
var list = new <ctrl+space> // IDE cannot help you

Java 9/10 Migration
● Migrating to Java 9/10 is an iterative process
○ Typically cannot be done in one step only
● Update dependencies
○ Build tools
○ Libraries
● Run jdeps -jdkinternals
● Fix usages of encapsulated APIs
● Using EE modules ?
● Add --add-modules to command line

Java 9/10 Migration
● Update command line options
● Fix GC logging
● Fix your System.getProperty("java.version") usages
● Do not do deep reflection on JDK classes
○ Do not use setAccessible(true);
● Verify your ClassLoader usages
● Verify your sun.* usages

Java 9/10 Migration
● Java 9 upgrade may introduce different behaviors at runtime
● Java code may throw exceptions when running in Java 9
○ Parsing of "java.version"
○ Playing with ClassLoaders and resources
○ URLStreamHandlers
○ Use of internal APIs
○ Etc.
● You can only discover these incompatibilities by extensive testing
○ Requires time to do, so start immediately !

Java 9-10 What's New

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