With Java 9 modules coming to us soon, you want your existing code to be fully ready for the module system. Making code modular can be a daunting task, but Java 9 comes with a number features to ease migration. This includes automatic modules, the unnamed module and a number of command line arguments. In this talk we will look at examples of migrating real code. It discusses common problems you’ll run into during migration, leading to practical tips and the ability to set realistic goals. It’s also a good way to understand the module system itself and the various migration paths it supports. This talk is an excellent preparation to start migrating your own code. * Understanding modules and the module path * Automatic modules * Mixing classpath and modulepath * Dealing with reflection * Escape switches * Jdeps All topics will be based on examples of often used libraries and frameworks.

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

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

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

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

9. 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");
}
}

10. Modular JDK

11. Modular JDK

12. Modular JDK

13. Modular JDK

14. Modular JDK

15. ‣ 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

16. 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

17. 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

18. 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

19. 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!

20. 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

21. 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 =
^

22. 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

23. Using encapsulated APIs
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:

25. 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:

26. 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':

27. Back to Modules...

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

29. Actual view of your app

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

31. Migrating to modules

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

33. 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

34. 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

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

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

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

38. 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

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

40. 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

41. 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

42. 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
…

43. 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
…

44. DEMO

45. 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

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

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

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

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

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

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

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

53. 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
…

54. 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

55. Migration steps - recap

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

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

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

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

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