to work with Java 9 Jigsaw Uwe Schindler Apache Lucene PMC & - - PowerPoint PPT Presentation

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to work with Java 9 Jigsaw Uwe Schindler Apache Lucene PMC & - - PowerPoint PPT Presentation

Mar 16, 2023 101 likes •639 views

Challenges updating your code to work with Java 9 Jigsaw Uwe Schindler Apache Lucene PMC & Apache Software Foundation Member uschindler@apache.org https://www.thetaphi.de, http://blog.thetaphi.de @ThetaPh1 SD DataSolutions GmbH ,

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Challenges updating your code to work with Java 9 Jigsaw

Uwe Schindler

Apache Lucene PMC & Apache Software Foundation Member uschindler@apache.org https://www.thetaphi.de, http://blog.thetaphi.de @ThetaPh1

SD DataSolutions GmbH, Wätjenstr. 49, 28213 Bremen, Germany Tel: +49 421 40889785-0, https://www.sd-datasolutions.de

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What is this talk about?

  • Migrating your current project so it works

with Java 9 (Jigsaw)

  • Common pitfalls with Java 7 / Java 8

code, that just used to work

  • Not an introduction to the module system!
  • It does not show you how to “convert your

project” to be a module

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What changed in Jigsaw?

(module system)

  • Strong encapsulation:

– Code only sees classes from packages exported to your code – Private APIs are private – especially those in the JDK!

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What changed in Jigsaw?

(module system)

  • Strong encapsulation:

– Code only sees classes from packages exported to your code – Private APIs are private – especially those in the JDK!

  • Your code behaves as if it will be executed

with a security manager! 

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COMPILE TIME PROBLEMS

Examples

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Direct use of invisible/removed APIs

  • sun.misc.BASE64Encoder / -Decoder
  • sun.misc.Unsafe
  • com.sun.javafx.*

(http://openjdk.java.net/jeps/253)

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Direct use of invisible/removed APIs

  • sun.misc.BASE64Encoder / -Decoder
  • sun.misc.Unsafe
  • com.sun.javafx.*

(http://openjdk.java.net/jeps/253) If compiled with older Java version it will result in IllegalAccessError on Java 9

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Solution

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Solution

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Solution

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Solution

  • Scan your code with jdeps tool

– Maven plugin available – Works only with Java 8+

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Solution

  • Scan your code with jdeps tool

– Maven plugin available – Works only with Java 8+

  • Alternative: ForbiddenAPIs

– https://github.com/policeman-tools/forbidden-apis – jdk-non-portable or jdk-internal-* signatures – Maven/Gradle/Ant plugin for Java 6+

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Solution

  • Scan your code with jdeps tool

– Maven plugin available – Works only with Java 8+

  • Alternative: ForbiddenAPIs

– https://github.com/policeman-tools/forbidden-apis – jdk-non-portable or jdk-internal-* signatures – Maven/Gradle/Ant plugin for Java 6+

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Solution

  • Scan your code with jdeps tool

– Maven plugin available – Works only with Java 8+

  • Alternative: ForbiddenAPIs

– https://github.com/policeman-tools/forbidden-apis – jdk-non-portable or jdk-internal-* signatures – Maven/Gradle/Ant plugin for Java 6+

  • Won’t help if reflection was used!
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REFLECTION

Examples

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Reflection “hacks”

  • Clever people use reflection to access

private / internal Java APIs:

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Reflection “hacks”

  • Clever people use reflection to access

private / internal Java APIs:

– No compile-time dependency on Oracle JDK – Sometimes needed to access private members, e.g. “sun.misc.Unsafe” instance

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Reflection “hacks”

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Reflection “hacks”

  • Downside: Static

analysis can’t help

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Reflection “hacks”

  • Downside: Static

analysis can’t help

  • Much worse: No

correct error handling (if APIs are missing/incompatible)!

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Brokeness around the world

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  • People use setAccessible()

everywhere to break into internal APIs

Brokeness around the world

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  • People use setAccessible()

everywhere to break into internal APIs

– Almost no library does this correct

Brokeness around the world

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  • People use setAccessible()

everywhere to break into internal APIs

– Almost no library does this correct

  • People don’t wrap with

AccessController.doPrivileged()

Brokeness around the world

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Brokeness around the world

  • People forget to add correct try/catch:
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Brokeness around the world

  • People forget to add correct try/catch:

– e.printStackTrace() – throw new RuntimeException(e)

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Brokeness around the world

  • People forget to add correct try/catch:

– e.printStackTrace() – throw new RuntimeException(e) – …inside static initializers!

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Brokeness around the world

  • People forget to add correct try/catch:

– e.printStackTrace() – throw new RuntimeException(e) – …inside static initializers!

  • No alternative solution:
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Brokeness around the world

  • People forget to add correct try/catch:

– e.printStackTrace() – throw new RuntimeException(e) – …inside static initializers!

  • No alternative solution:

– static initializer breaks – NoClassDefFoundError forever!

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What’s wrong with Jigsaw?

#ReflectiveAccessToNonExportedTypes #AwkwardStrongEncapsulation

  • New since build 148 of Java 9
  • Prevents reflective access to any class

from Java runtime

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What’s wrong with Jigsaw?

#ReflectiveAccessToNonExportedTypes #AwkwardStrongEncapsulation

  • New since build 148 of Java 9
  • Prevents reflective access to any class

from Java runtime

#AwkwardStrongEncapsulation: A non-public element of an exported package can still be accessed via the AccessibleObject::setAccessible method

  • f the core reflection API. The only way to strongly

encapsulate such an element is to move it to a non-exported package. This makes it awkward, at best, to encapsulate the internals of a package that defines a public API.

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What’s wrong with Jigsaw?

#ReflectiveAccessToNonExportedTypes #AwkwardStrongEncapsulation

  • New since build 148 of Java 9
  • Prevents reflective access to any class

from Java runtime

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What does no longer work?

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What does no longer work?

  • Class.forName()

–on non-exported packages

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What does no longer work?

  • Class.forName()

–on non-exported packages

  • AccessibleObject

.setAccessible(true)

–on any public runtime class

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What does no longer work?

  • Class.forName()

–on non-exported packages

  • AccessibleObject

.setAccessible(true)

–on any public runtime class

  • Some exceptions:

–sun.misc.Unsafe

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Problems

  • No tool to detect reflective access to

private APIs with earlier Java versions during testing/compilation

  • Forbidden-APIs can disallow

AccessibleObject::setAccessible

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SOLUTIONS

What can I do?

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Run tests with SecurityManager!

(Apache Lucene, Apache Solr, Elasticsearch)

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Howto: Important patterns!

  • Add fallbacks for private APIs (try…catch

in static initializers)

  • Catch SecurityException AND

RuntimeException

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Howto: Important patterns!

  • Add fallbacks for private APIs (try…catch

in static initializers)

  • Catch SecurityException AND

RuntimeException

– InaccessibleObjectException extends RuntimeException 

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Howto: Important patterns!

  • Don’t fail in static initializers if you have

no workaround!

– Save error details while trying to initialize your private API hacks (Unsafe & Co.) – Use AccessController#doPrivileged – If consumer of your library calls a method using the hack, throw useful exception

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Early binding using MethodHandles

  • MethodHandles are bound early

– like javac is compiling and type-checking a method call

  • MethodHandles can be used to add

“programming logic” with if/then/else

– MethodHandles.guardWithTest() & Co.

  • No linkage errors possible at call time
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APACHE LUCENE’S MAPPEDBYTEBUFFER UNMAPPING

EXAMPLE

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https://issues.apache.org/jira/browse/LUCENE-6989 https://bugs.openjdk.java.net/browse/JDK-4724038

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Thank You!