The document discusses Java interoperability in Ballerina during a community call, covering topics like calling Java code, generating bindings with the bindgen tool, and packaging Java libraries. It provides updates on the Ballerina Swan Lake releases, detailing new features and improvements in language, standard libraries, and the platform. Additionally, it explains various annotations for external function handling and type mappings between Java and Ballerina.

1. Java Interoperability in Ballerina
Irushi Liyanage
@IrushiL

2. About Ballerina Community Call
● Monthly meeting
● Community call structure
○ Feature explanation + demonstration
○ Open discussion
● Useful links
○ Agenda
○ Notify me form
○ Topic suggestion form

3. Agenda
● Update on Ballerina Swan Lake releases
● Java Interoperability in Ballerina
○ Calling Java code from Ballerina
○ Generating bindings using the Bindgen Tool
○ Packaging Java Libraries with Ballerina Programs
● Open discussion

4. Update on Ballerina Swan Lake

5. Ballerina Releases
2020
Dec
jBallerina
1.0
2019
Sep
2019
Dec
jBallerina
1.1
2020
Mar
jBallerina
1.2
jBallerina
1.2.11
2020 June
Swan Lake
Preview 1
Swan Lake
Preview 7

6. Ballerina Swan Lake Previews
● Swan Lake - Preview 8 (Mid December, 2020)
○ Introducing new service design
○ Improved HTTP, Websocket, gRPC and more services
○ New GraphQL Listener
● Swan Lake - Alpha (Mid January, 2021)
○ All major features will be ready

7. New Features in Swan Lake Alpha
● Language Features
○ New service support
○ Immunitibility support
○ Type system improvements
○ Improved error handling
○ New transaction support
○ Enhanced query expression support
○ Raw template support
○ Configurability support and more

8. New Features in Swan Lake Alpha
● Standard Libraries
○ New services such as HTTP, Websocket, and gRPC etc.
○ Support for GraphQL services
○ New IO, Log API, SQL modules and more

9. New Features in Swan Lake Alpha
● Ballerina Platform
○ Introduce Ballerina packages
○ New Code2Cloud extension
○ Ballerina Parser
○ Compiler APIs
○ Ballerina Shell (experimental) and more

10. Calling Java Code from Ballerina

11. Using Java Code in Ballerina

12. FFI in jBallerina
● External function annotations:
○ @java:Method
○ @java:Constructor
○ @java:FieldGet
○ @java:FieldSet
● Handle type - a reference to an externally-managed storage

13. Java Types to Ballerina Types
Java Type Ballerina Type
Any reference type including “null type” handle
boolean boolean
byte byte, int, float
short int, float
char int, float
int int, float
long int, float
float float
double float

14. Ballerina Types to Java Types
Ballerina type Java type
handle Any reference type
boolean boolean
byte byte, short, char, int, long, float, double
int byte, char, short, int, long
float byte, char, short, int, long, float, double

15. FFI in jBallerina
● Static method invocation
● Instance method invocation
● Constructor invocation
function xyz(handle a) returns handle = @java:Constructor {
class: "a.b.c.Foo",
paramTypes: ["java.lang.String"]
} external;
function abc(handle a, int b) returns handle = @java:Method {
name: "bar",
class: "a.b.c.Foo",
paramTypes: ["java.util.UUID", "int"]
} external;
function cdf(handle receiver, int a) returns handle = @java:Method
{
name: "poll",
class: "a.b.c.Foo",
paramTypes: ["int"]
} external;

16. FFI in jBallerina
● Instance field getter
● Instance field setter
● Static field getter
function getENTER() returns int = @java:FieldGet {
name: "ENTER",
class: "a.b.c.Foo"
} external;
function getId(handle receiver) returns int = @java:FieldGet
{
name: "id",
class: "a.b.c.Foo"
} external;
function setId(handle receiver, int arg) = @java:FieldSet {
name: "id",
class: "a.b.c.Foo"
} external;

17. Using the Bindgen Tool

18. Bindgen CLI Command
A CLI tool for generating Ballerina bridge code for Java APIs
ballerina bindgen [(-cp|--classpath) <classpath>...]
[(-mvn|--maven) <groupId>:<artifactId>:<version>]
[(-o|--output) <output>]
[--public]
(<class-name>...)

19. Java to Ballerina Mappings
● Java class -> Ballerina object
● Java instance method -> Ballerina object method
● Java instance field -> Ballerina object methods for a getter and a setter
● Java constructor -> Ballerina function
● Java static method -> Ballerina function
● Java static field -> Ballerina functions for a getter and a setter

20. Java to Ballerina Type Mappings
● java.lang.String object -> Ballerina string type
● java.lang.Throwable object -> Ballerina error type
Java Subtyping
Java Casting

21. Packaging Java Libraries with Ballerina Programs

22. Ballerina.toml
[platform]
target = "java8"
[[platform.libraries]]
path = "./javalibs/mysql-connector-java-<version>.jar"
modules = ["ordermgt"]
[[platform.libraries]]
modules = ["load_yaml"]
groupId = "org.yaml"
artifactId = "snakeyaml"
version = "1.25"
target/platform-libs

23. References
● https://ballerina.io/learn/calling-java-code-from-ballerina/
● https://ballerina.io/learn/by-example/invoke-java-methods.html
● https://ballerina.io/learn/api-docs/ballerina/java/
● https://docs.oracle.com/javase/8/docs/api/
● https://bitbucket.org/asomov/snakeyaml/wiki/Documentation

24. Open Discussion