JavaCall.jl

Call Java programs from Julia.

Documentation

Documentation is available at http://juliainterop.github.io/JavaCall.jl

Quick Start Example Usage

$ JULIA_NUM_THREADS=1 JULIA_COPY_STACKS=1 julia

julia> using Pkg; Pkg.activate(; temp = true)
  Activating new project at `/tmp/jl_e6uPja`

julia> using JavaCall
 │ Package JavaCall not found, but a package named JavaCall is available from a
 │ registry. 
 │ Install package?
 │   (jl_e6uPja) pkg> add JavaCall 
 └ (y/n) [y]: y

...

julia> JavaCall.addClassPath(pwd()) # Set appropriate classpath

julia> JavaCall.addOpts("-Xmx1024M") # Use 1 GB of memory
OrderedCollections.OrderedSet{String} with 1 element:
  "-Xmx1024M"

julia> JavaCall.addOpts("-Xrs") # Disable signal handling in the JVM, reducing performance but enhancing compatability
OrderedCollections.OrderedSet{String} with 2 elements:
  "-Xmx1024M"
  "-Xrs"

julia> JavaCall.init() # Call before using `jcall` or `jfield`. Do not use this in package `__init__()` to allow other packages to add classpaths or options.

julia> jls = @jimport java.lang.System
JavaObject{Symbol("java.lang.System")}

julia> out = jfield(jls, "out", @jimport java.io.PrintStream) # Third arg is optional, but helps type stability.
JavaObject{Symbol("java.io.PrintStream")}(JavaCall.JavaLocalRef(Ptr{Nothing} @0x0000000003ecda38))

julia> jcall(out, "println", Nothing, (JString,), "Hello World")
Hello World

Julia version compatibility

The CI tests for Julia 1.6 as min, Julia LTS, and the latest stable release.

macOS and Linux

For Julia 1.3 onwards, please set the environment variable JULIA_COPY_STACKS = 1. For Julia 1.11 onwards, please also set JULIA_NUM_THREADS = 1

Multithreaded access to the JVM is supported as JavaCall version 0.8.0, but doesn't work in recent Julia versions.

Windows

Do not set the environmental variable JULIA_COPY_STACKS or set the variable to 0.

To use jcall with @async, start Julia in the following way:

$ julia -i -e "using JavaCall; JavaCall.init()"

Windows currently lacks support for multithreaded access to the JVM.

Other Operating Systems

JavaCall has not been tested on operating systems other than macOS, Windows, or Linux. You should probably set the environment variable JULIA_COPY_STACKS = 1 and JULIA_NUM_THREADS = 1. If you have success using JavaCall on another operating system than listed above, please create an issue or pull request to let us know about compatability.