JDK 9: Migrating Applications

© Copyright Azul Systems 2017
@speakjava
Migrating Applications
To JDK 9
Simon Ritter
Deputy CTO, Azul Systems
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JDK 9: Big And Small Changes
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Migration Guidance From Oracle
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"Clean applications that just depend on java.se
should just work"

Quick Poll
 What are your plans for moving to JDK 9
1. Mission accomplished, already using it
2. Actively working on moving applications
3. Thinking about it
4. We're waiting for the next LTS release, JDK 18.9
5. We're still using JDK 6!

Module System

Java Platform Module System
 The core Java libraries are now a set of modules
– 97 modules for JDK, 28 of which are Java SE
– No more rt.jar or tools.jar files
 Most internal APIs are now encapsulated
– sun.misc.Unsafe, etc.
– Numerous libraries and frameworks use internal APIs
 Module path used to locate modules
– Separate and distinct from classpath
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JPMS And Applications
 Initially, leave everything on the classpath
 Anything on the classpath is in the unnamed module
– All packages are exported
– The unnamed module depends on all modules
 Migrate to modules as required
– Try automatic modules
– Move existing jar files from classpath to modulepath
7

Breaking Encapsulation
 "The Big Kill Switch" to turn off encapsulation
– --illegal-access
 permit: Warning for first use of an encapsulated API
 warn: Warning for every use of an encapsulated API
 debug: Warning and stack trace for every use
 deny: No access to encapsulated APIs
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 Allowing direct access to encapsulated APIs
– --add-exports
 Allowing reflective access to encapsulated APIs
– --add-opens
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--add-exports java.management/com.sun.jmx.remote.internal=mytest
--add-exports java.management/sun.management=ALL-UNNAMED
--add-opens java.base/java.util=ALL-UNNAMED

 Using the JAR file manifest
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Add-Exports: java.base/sun.security.provider

Finding Encapsulated API Use
 jdeps
– Analyses dependencies on APIs
 Example: Minecraft
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jdeps --list-deps 1.8.jar
java.base
java.datatransfer
java.desktop
java.management
java.naming
not found
unnamed module: 1.8.jar

"Missing" Modules
 Remember, "Clean applications that only use java.se..."
 The java.se.ee module not included by default
– Compilation and runtime
 Affected modules
– java.corba
– java.transaction
– java.activation
– java.xml.bind
– java.xml.ws
– java.xml.ws.annotation
12

Using "Missing" Modules
 Use the command line option
– --add-modules java.corba
 All modules (except CORBA) have standalone versions
– Maven central
– Relevant JSR RI
 Deploy standalone version on the upgrade module path
– --upgrade-module-path <path>
 Deploy standalone version on the classpath
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Small Incompatibilities

Milling Project Coin (JEP 213)
 A single underscore is now a keyword in Java
 Fear not, two or more underscores can still be used
15
error: as of release 9, '_' is a keyword, and may not be used as
an identifier

Unexpected Exception
 Thread.stop(Throwable) now throws an exception
– UnsupportedOperationException
 The no-arg method, Thread.stop(), does not
16

Deleted Deprecated Methods
 Classes
– java.util.jar.Pack200
– java.util.jar.Unpack200
– java.util.logging.LogManager
 Methods
– addPropertyChangeListener()
– removePropertyChangeListener()
 Removal required for clean modularisation
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Deleted Deprecated Class
 com.sun.security.auth.callback.DialogCallbackHandle
r
 Part of the Java Authentication and Authorisation Service
– JAAS
– Deprecated in JDK 7
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Finding Deprecated API Use
 jdeprscan
– New tool in JDK 9
– Statically analyses class files and jar files against Java
SE APIs
– Looks for and reports usage of deprecated Java SE APIs
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JDK/JRE File Structure (JEP 220)
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bin
Pre-JDK 9 JDK 9
lib
tools.jar
jre
bin
rt.jar
lib
libconfbin
jre directory
tools.jar
rt.jar
jmods

New Version String Format (JEP 223)
 Old
– Limited update release/Critical patch update (CPU)
– Download: Java SE 8u131, java -version: jdk1.8.0_131
– Which has more patches, JDK 7u55 or JDK 7u60?
 New
– JDK $MAJOR.$MINOR.$SECURITY
– Easy to understand by humans and apps
– Semantic versioning
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Non-Programmatic Issues
 Java Network Launch Protocol (JNLP) [JSR 52]
– Now uses strict parsing of configuration files
– Some files that did parse may now fail
 Extension mechanism/Endorsed Standards Override
mechanisms removed
– Directories removed
 $JAVA_HOME/lib/ext
 $JAVA_HOME/lib/endorsed
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<JAVA_HOME>/lib/ext exists, extensions mechanism no longer
supported; Use -classpath instead.
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

Removed GC Options (JEP 214)
 Deprecated in JDK 8 (JEP 173)
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DefNew + CMS : -XX:-UseParNewGC -XX:+UseConcMarkSweepGC
ParNew + SerialOld : -XX:+UseParNewGC
ParNew + iCMS : -Xincgc
ParNew + iCMS : -XX:+CMSIncrementalMode -XX:+UseConcMarkSweepGC
DefNew + iCMS : -XX:+CMSIncrementalMode -XX:+UseConcMarkSweepGC
-XX:-UseParNewGC
CMS foreground : -XX:+UseCMSCompactAtFullCollection
CMS foreground : -XX:+CMSFullGCsBeforeCompaction
CMS foreground : -XX:+UseCMSCollectionPassing

JVM Logging
 Unified JVM logging (JEP 158)
– Common logging system for all components of JVM
 Unified GC logging (JEP 271)
– Re-implement GC logging using unified JVM logging
– Many command line options changed
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Removed JVM Flags: Ignored
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 AdaptiveSizePausePolicy
 CodeCacheMinimumFreeSpace
 DefaultThreadPriority
 JNIDetachReleasesMonitors
 LazyBootClassLoader
 NmethodSweepCheckInterval
 NmethodSweepFraction
 PrintOopAddress
 ReflectionWrapResolutionErrors
 StarvationMonitorInterval
 ThreadSafetyMargin
 UseAltSigs
 UseBoundThreads
 UseCompilerSafepoints
 UseFastAccessorMethods
 UseFastEmptyMethods
 BackEdgeThreshold
 PreInflateSpin
Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option
<Option>; support was removed in 9.0

Deprecated JVM Flags
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Deprecated JVM Flags
 Two forms of warning message
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warning[gc] -XX:+PrintGC is deprecated. Will use -Xlog:gc instead.
Java HotSpot(TM) 64-Bit Server VM warning: Option
CreateMinidumpOnCrash was deprecated in version 9.0 and will likely
be removed in a future release. Use option CreateCoredumpOnCrash
instead.

JVM Flags: Non-Starters (1)
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 AdjustConcurrency
 CMSCompactWhenClearAllSoftRefs
 CMSDumpAtPromotionFailure
 CMSFullGCsBeforeCompaction
 CMSIncrementalDutyCycle
 CMSIncrementalDutyCycleMin
 CMSIncrementalMode
 CMSIncrementalOffset
 CMSIncrementalPacing
 CMSParPromoteBlocksToClaim
 CMSPrintEdenSurvivorChunks
 CollectGen0First
 GCLogFileSize
 NumberOfGCLogFiles
 ParallelGCVerbose
 PrintAdaptiveSizePolicy
 PrintCMSInitiationStatistics
 PrintCMSStatistics
 PrintClassHistogramAfterFullGC
 PrintClassHistogramBeforeFullGC
 PrintFLSCensus
 PrintFLSStatistics
 PrintGCApplicationConcurrentTime
 PrintGCApplicationStoppedTime
 PrintGCCause
 PrintGCDateStamps

JVM Flags: Non-Starters (2)
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 PrintGCTaskTimeStamps
 PrintGCTimeStamps
 PrintHeapAtGC
 PrintHeapAtGCExtended
 PrintJNIGCStalls
 PrintOldPLAB
 PrintPLAB
 PrintParallelOldGCPhaseTimes
 PrintPromotionFailure
 PrintReferenceGC
 PrintTLAB
 PrintTenuringDistribution
 TraceDynamicGCThreads
 TraceGen0Time
 TraceGen1Time
 TraceMetadataHumongousAllocation
 TraceParallelOldGCTasks
 UseCMSCollectionPassing
 UseCMSCompactAtFullCollection
 UseGCLogFileRotation
 UseMemSetInBOT
 UsePPCLWSYNC
 UseVMInterruptibleIO
 WorkAroundNPTLTimedWaitHang

JVM Flags: Non-Starters
 50 command line flags from JDK 8
 Use will cause the JVM to abort at start
– It won't run your application
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Unrecognized VM option '<Option>'
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

Real World Example

HdrHistogram Library
 Open source library (created by Gil Tene, Azul CTO)
 Ideally this should work with JDK 6, 7, 8 and 9 code
– Unchanged and with no special command line flags
 Problem:
– Needs to encode and decode using Base64
 Solutions:
– sun.misc.BASE64Encoder/Decoder (JDK 6, 7, 8)
– javax.xml.bind.DatatypeConverter (JDK 6, 7, 8)
– java.util.Base64.{Encoder,Decoder} (JDK 8, 9)
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Solution
 Helper class with same named methods as from xml.bind
– printBase64Binary(byte[] array)
– parseBase64Binary(String input)
 Static code to determine which class is available
– Initialise Method object reference
 Helper methods invoke through method reference to
available implementation
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Solution (1)
 Code in static block
try {
Class<?> javaUtilClass = Class.forName("java.util.Base64");
Method getDecoderMethod = javaUtilClass.getMethod("getDecoder");
decoderObj = getDecoderMethod.invoke(null);
decodeMethod = decoderObj.getClass().getMethod("decode", String.class);
Method getEncoderMethod = javaUtilClass.getMethod("getEncoder");
encoderObj = getEncoderMethod.invoke(null);
encodeMethod = encoderObj.getClass()
.getMethod("encodeToString", byte[].class);
} catch (Throwable e) { // ClassNotFoundException, NoSuchMethodException
decodeMethod = null;
encodeMethod = null;
}

Solution (2)
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if (encodeMethod == null) {
decoderObj = null;
encoderObj = null;
try {
Class<?> xmlBindClass = Class.forName("javax.xml.bind.DatatypeConverter");
decodeMethod = xmlBindClass.getMethod("parseBase64Binary", String.class);
encodeMethod = xmlBindClass.getMethod("printBase64Binary", byte[].class);
} catch (Throwable e) {
decodeMethod = null;
encodeMethod = null;
}
}

Conclusions

Migrating To JDK 9
 Simple applications will run [almost] unchanged
– Leave everything on the classpath
– May need to change JVM flags
 Encapsulation
– Additional JVM flags
– Identify and rectify issues
 Smaller changes may cause issues
– Removed APIs
– JVM flag changes
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Useful Links
 docs.oracle.com/javase/9/migrate
 www.azul.com/jdk-9-pitfalls-for-the-unwary
 www.azul.com/jdk-9-xxtra-command-line-options
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Zulu Java
 Azul’s binary distribution of OpenJDK
– Passes all TCK tests
– Multi-platform (Windows, Linux, Mac)
– FREE!
 Happy to sell you support, including older versions
 JDK 6, 7, 8 and 9
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www.zulu.org/download

@speakjava
Thank You!
Simon Ritter
Deputy CTO, Azul Systems
40

JDK 9: Migrating Applications

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