Migrating to Java 9 Modules

1. By Sander Mak Migrating to Java 9 Modules @Sander_Mak

2. Migrating to Java 9 java -cp .. -jar myapp.jarJava 8

3. Migrating to Java 9 java -cp .. -jar myapp.jar java -cp .. -jar myapp.jar Java 8 Java 9

4. Today's journey Running on Java 9 Java 9 modules Migrating to modules Modularising code

5. Migrating to Java 9 Let's try it! java -cp .. -jar myapp.jar java -cp .. -jar myapp.jar Java 8 Java 9

6. Classpath migration problems ‣ Unresolved platform modules ‣ (Ab)use of platform internals

7. Missing platform modules error: package javax.xml.bind does not exist import javax.xml.bind.DatatypeConverter; public class Main { public static void main(String... args) { DatatypeConverter.parseBase64Binary("SGVsbG8gd29ybGQh"); } }

8. Modular JDK

9. Modular JDK

10. Modular JDK

11. Modular JDK

12. Modular JDK

13. ‣ Classpath compile-time “java.se” module is used ‣ This does not resolve: java.activation java.corba java.transaction java.xml.bind java.xml.ws java.xml.ws.annotation Missing platform modules

14. Add unresolved platform modules jdeps demo/Main.class Main.class -> java.base Main.class -> not found <unnamed> -> java.lang java.base <unnamed> -> javax.xml.bind not found Find

15. javac --add-modules java.xml.bind demo/Main.java Add unresolved platform modules jdeps demo/Main.class Main.class -> java.base Main.class -> not found <unnamed> -> java.lang java.base <unnamed> -> javax.xml.bind not found Find Fix

16. javac --add-modules java.xml.bind demo/Main.java Add unresolved platform modules java --add-modules java.xml.bind demo/Main.java jdeps demo/Main.class Main.class -> java.base Main.class -> not found <unnamed> -> java.lang java.base <unnamed> -> javax.xml.bind not found Find Fix

17. javac --add-modules java.xml.bind demo/Main.java Add unresolved platform modules java --add-modules java.xml.bind demo/Main.java Let's try it!

18. public class Main { public static void main(String... args) throws Exception { sun.security.x509.X500Name name = new sun.security.x509.X500Name("CN=user"); } } Using encapsulated APIs

19. public class Main { public static void main(String... args) throws Exception { sun.security.x509.X500Name name = new sun.security.x509.X500Name("CN=user"); } } Using encapsulated APIs Main.java:4: error: package sun.security.x509 does not exist sun.security.x509.X500Name name = ^

20. jdeps -jdkinternals Main.class Main.class -> java.base Main -> sun.security.x509.X500Name JDK internal API (java.base) JDK Internal API Suggested Replacement ---------------- --------------------- sun.security.x509.X500Name Use javax.security.auth.x500.X500Principal @since 1.4 Use jdeps to find problems

21. Using encapsulated APIs Compile with 1.8, run with 9:

22. Using encapsulated APIs Exception in thread "main" java.lang.IllegalAccessError: class Main (in unnamed module @0x4cdbe50f) cannot access class sun.security.x509.X500Name (in module java.base) because module java.base does not export sun.security.x509 to unnamed module @0x4cdbe50f at Main.main(Main.java:4) Compile with 1.8, run with 9:

23. Using encapsulated APIs java --add-exports java.base/sun.security.x509=ALL-UNNAMED Main Exception in thread "main" java.lang.IllegalAccessError: class Main (in unnamed module @0x4cdbe50f) cannot access class sun.security.x509.X500Name (in module java.base) because module java.base does not export sun.security.x509 to unnamed module @0x4cdbe50f at Main.main(Main.java:4) Compile with 1.8, run with 9:

24. Using encapsulated APIs Exception in thread "main" java.lang.IllegalAccessError: class Main (in unnamed module @0x4cdbe50f) cannot access class sun.security.x509.X500Name (in module java.base) because module java.base does not export sun.security.x509 to unnamed module @0x4cdbe50f at Main.main(Main.java:4) Compile with 1.8, run with 9: java --permit-illegal-access Main New 'kill-switch':

25. Back to Modules...

26. main books.api books.impl bookstore Mental picture of your app

27. Actual view of your app

28. main books.api books.impl bookstore Java 9 modules make this possible!

29. Migrating to modules

30. Top down migration commons.lang3.3.4.jar demonstrator.jar classpath java.base module path

31. package com.javamodularity.demonstrator; import org.apache.commons.lang3.StringUtils; public class Demo { public static void main(String args[]) { String output = StringUtils.leftPad("Leftpad FTW!", 20); System.out.println(output); } } Classic classpath

32. package com.javamodularity.demonstrator; import org.apache.commons.lang3.StringUtils; public class Demo { public static void main(String args[]) { String output = StringUtils.leftPad("Leftpad FTW!", 20); System.out.println(output); } } Classic classpath javac -cp lib/commons-lang3-3.4.jar -d out $(find src -name '*.java') java -cp out:lib/commons-lang3-3.4.jar com.javamodularity.demonstrator.Demo Compile Run

33. Top down migration commons.lang3.3.4.jar demonstrator.jar classpath java.base module path

34. Top down migration commons.lang3.3.4.jar demonstrator.jar classpath java.base module path Can’t reference the classpath from named modules!

35. Top down migration demonstrator.jar classpath java.base module path commons.lang But this isn’t our code!

36. Automatic Modules ‣ A plain JAR on the module path becomes an Automatic Module ‣ Module name derived from JAR name ‣ Exports everything ‣ Reads all other modules

37. module demonstrator { requires commons.lang; } Using Automatic Modules

38. module demonstrator { requires commons.lang; } Using Automatic Modules javac --module-path lib --module-source-path src -d mods $(find src -name '*.java') java --module-path mods:lib -m demonstrator/com.javamodularity.demonstrator.Demo Compile Run

39. Migrating the books app 1. Create a “monolith module” 2. Declare exports 3. Figure out “requires” 4. Move some libs to Automatic Modules Step 2

40. commons.pool spring.context classpath Application code module path spring.tx hibernate.core hibernate.jpa javax.inject Automatic modules Named modules commons.logging spring.beans spring.aop spring.core hsqldb spring.orm …

42. DEMO

43. Open Modules ‣ Reliable configuration like normal modules ‣ Requires for every dependency ‣ Opens all packages for deep reflection ‣ Easy compatibility with existing code and frameworks ‣ Allows reflection

44. Type Compile time Reﬂection on public Deep reﬂection Exports ✓ ✓ ✘ Open ✘ ✓ ✓ Exports + Open ✓ ✓ ✓

45. Open Packages Opens the package for deep reﬂection, but not compile time access A package can be both open and exported

46. Tip 1 Move libraries to module path one by one Start with direct dependencies

47. Tip 2 open when no compile time dependency should exist (possibly qualiﬁed)

48. Tip 3 requires only for direct dependencies --add-modules for run-time dependencies

49. Tip 4 Use open modules for framework compatibility Fine tune open later

50. Migrating the books app 1. Split monolith module 2. Move requires/exports 3. (optional) Move conﬁg ﬁles Step 3

52. commons.pool spring.context classpath module path spring.tx hibernate.core hibernate.jpa javax.inject Automatic modules Named modules commons.logging spring.beans spring.aop spring.core hsqldb spring.orm … main books.api books.impl bookstore

53. Migration steps - recap

54. Migration steps - recap ‣ Migrate to Java 9 using classpath only

55. Migration steps - recap ‣ Migrate to Java 9 using classpath only ‣ Create a module around your whole app

56. Migration steps - recap ‣ Migrate to Java 9 using classpath only ‣ Create a module around your whole app ‣ Modularize your application!

57. Thank you. bit.ly/java9book @javamodularity code @ bit.ly/java9mig

58. Thank you. bit.ly/java9book @javamodularity http://bit.ly/java9course Java 9 Modularity: First Look code @ bit.ly/java9mig

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