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Using Go
to call Java libraries
Jumpei Takiyasu
M3, Inc.
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Me
Jumpei Takiyasu
M3, Inc.
Github/Twitter: @juntaki
https://juntaki.com
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This talk
What is Go?
How to use Java library from Go
The Go gopher was designed by Renee French.
(http://reneefrench.blogspot.com/)
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What is Go?
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Go
● Simple language spec.
● Official development tools
● Statically typed
● Compile to native code
● Concurrency
etc..
Go is an open source programming language that makes
it easy to build simple, reliable, and efficient software.
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Simple
Low learning cost to start.
package main
import "fmt"
func main() {
fmt.Println("hello world")
}
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Tools / go-fmt
End of coding style war
● Tab vs Space
● Curly brackets { do something
$ gofmt ./… # or use editor plugin
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Tools / go get
Easy to publish and use library/tools
No central repository
$ go get github.com/juntaki/gogtags
$ gogtags -v
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go-doc
Generates documentation from comments and tests
godoc.org/github.com/username/repository
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Go is fun!
Let’s use Go
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How to use Java libraries from Go
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Motivation
My team is using Kotlin - Why?
Statically typed
ʕ ◔ϖ◔ʔ < OK
“Kotlin” sounds cute (for Japanese)
ʕ ◔ϖ◔ʔ < cute
Kotlin can be used with our Java libraries
ʕ - ϖ - ʔ < mmm...
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Go can call Java libraries now
github.com/juntaki/javago
github.com/juntaki/jnigo
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jnigo
Java binding to Go, using JNI
Go C Java
cgo JNI
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javago
Generate go wrapper code for Java library with jnigo
$ javago --classfile java.lang.Math
$ ls java
java.lang.Math.go
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Demo
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Garbage collection, Memory management
Java and C things are wrapped by Go object.
GoObject C (JNI) Java
GetObject / malloc GetObject
Object reference
Pointer to Object ref.
NewGlobalRef
Go GC
runtime.Finalizer
DeleteGlobalRef
free
Java GC
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Method overloading
func Mathmax(args ...interface{}) (jnigo.JObject, error) {
convertedArgs, err := jvm.ConvertAll(args)
if err != nil {
return nil, err
}
sigArgs := ""
for _, arg := range convertedArgs {
sigArgs += arg.Signature()
}
sigMap := map[string]string{"JJ":"(JJ)J", "FF":"(FF)F", "DD":"(DD)D", "II":"(II)I"}
return jvm.CallStaticFunction("java/lang/Math", "max", sigMap[sigArgs], convertedArgs)
}
Simulated by reflection.
Switch function signature by
argument signatures
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Conclusion
Go is fun!