1. JRuby hacking guide
David Calavera
@calavera

2. +70
contributors

3. 9
core
members

4. ~ 30
single
commits

5. we want
you

6. core

7. rule of
thumb

8. jruby-1.6.2 :003 > raise ArgumentError.new
ArgumentError: ArgumentError
from (irb):3:in `evaluate'
from org/jruby/RubyKernel.java:1088:in `e
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:158:in `eval_input'
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:271:in `signal_status'
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:155:in `eval_input'
from org/jruby/RubyKernel.java:1419:in `l
from org/jruby/RubyKernel.java:1191:in `c
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:154:in `eval_input'
from /Users/david/.rvm/rubies/jruby-1.6.2

9. do not
freak out

10. ruby-1.8.7 :001 > raise ArgumentError.new
ArgumentError: ArgumentError
from (irb):1

11. jruby-1.6.2 :001 > raise ArgumentError.new
ArgumentError: ArgumentError
from (irb):1:in `evaluate'
from org/jruby/RubyKernel.java:1088:in `e
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:158:in `eval_input'
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:271:in `signal_status'
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:155:in `eval_input'
from org/jruby/RubyKernel.java:1419:in `l
from org/jruby/RubyKernel.java:1191:in `c
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:154:in `eval_input'
from /Users/david/.rvm/rubies/jruby-1.6.2

12. jruby-1.6.2 :001 > raise ArgumentError.new
ArgumentError: ArgumentError
from (irb):1:in `evaluate'
from org/jruby/RubyKernel.java:1088:in `e
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:158:in `eval_input'
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:271:in `signal_status'
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:155:in `eval_input'
from org/jruby/RubyKernel.java:1419:in `l
from org/jruby/RubyKernel.java:1191:in `c
from /Users/david/.rvm/rubies/jruby-1.6.2
irb.rb:154:in `eval_input'
from /Users/david/.rvm/rubies/jruby-1.6.2

13. your ruby
code is our
test case

14. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

15. Rspec
describe "glob file path" do
it "lists contents of a file" do
dir = Dir.new(@local_file_path)
dir.entries.should include("junit.jar")
end
end

16. follow
the
specification

17. RubySpec
describe "Dir.entries" do
...
it "returns an Array of filenames in an
existing directory including dotfiles" do
...

18. RubySpec
describe "Dir.entries" do
...
ruby_version_is "1.9" do
it "calls #to_path on ..." do
...

19. RubySpec
$ bin/jruby -S mspec
spec/ruby/core/dir/entries_spec.rb
$ bin/jruby --1.9 -S mspec
spec/ruby/core/dir/entries_spec.rb

20. go to the
source

21. ruby code
static VALUE
dir_entries(int argc, VALUE *argv, VALUE io)
{
VALUE dir;
dir = dir_open_dir(argc, argv);
return rb_ensure(rb_Array, dir, dir_close, dir);
}

22. taming
the beast

23. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

24. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

25. Ruby class
$ vi src/org/jruby/RubyDir.java
@JRubyClass(name = "Dir",
include = "Enumerable")
public class RubyDir extends RubyObject {

26. Ruby class
$ vi src/org/jruby/RubyDir.java
@JRubyClass(name = "Dir",
include = "Enumerable")
public class RubyDir extends RubyObject {

27. Ruby class
$ vi src/org/jruby/RubyDir.java
@JRubyClass(name = "Dir",
include = "Enumerable")
public class RubyDir extends RubyObject {

28. Ruby class
$ vi src/org/jruby/RubyDir.java
@JRubyClass(name = "Dir",
include = "Enumerable")
public class RubyDir extends RubyObject {

29. Ruby class
$ vi src/org/jruby/RubyDir.java
@JRubyClass(name = "Dir",
include = "Enumerable")
public class RubyDir extends RubyObject {

30. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

31. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

32. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

33. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

34. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

35. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

36. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

37. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

38. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

39. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

40. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

41. Ruby method
@JRubyMethod(name = "mkdir", required = 1,
optional = 1, meta = true, compat = RUBY1_8)
public static
IRubyObject mkdir(IRubyObject recv,
IRubyObject[] args) {

42. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

43. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

44. initialize
private static final ObjectAllocator
DIR_ALLOCATOR = new ObjectAllocator()
@JRubyMethod(compat = RUBY1_8)
public IRubyObject initialize(IRubyObject arg)

45. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

46. Test::Unit
def test_dir_enumerable
Dir.mkdir("./testDir_1")
d = Dir.new("./testDir_1")
assert(d.kind_of?(Enumerable))
end

47. Ruby module
$ vi src/org/jruby/RubyKernel.java
@JRubyModule(name="Kernel")
public class RubyKernel {

48. Ruby module
$ vi src/org/jruby/RubyKernel.java
@JRubyModule(name="Kernel")
public class RubyKernel {

49. Ruby module
$ vi src/org/jruby/RubyObject.java
@JRubyClass(name="Object", include="Kernel")
public class RubyObject extends ... {

50. Ruby module
@JRubyMethod(name = {"kind_of?", "is_a?"},
required = 1)
public static RubyBoolean kind_of_p
(ThreadContext context,
IRubyObject recv,
IRubyObject type) {

51. Ruby module
@JRubyMethod(name = {"kind_of?", "is_a?"},
required = 1)
public static RubyBoolean kind_of_p
(ThreadContext context,
IRubyObject recv,
IRubyObject type) {

52. Ruby module
@JRubyMethod(name = {"kind_of?", "is_a?"},
required = 1)
public static RubyBoolean kind_of_p
(ThreadContext context,
IRubyObject recv,
IRubyObject type) {

53. learn more

54. http://tinyurl.com/
jruby-hacking-guide
by Hiroshi Nakamura

55. http://tinyurl.com/
distilling-jruby
by R.J. Lorimer

56. http://jruby.org

57. thank you!

58. Credits
Charles Nutter’s Photo Booth
http://www.flickr.com/photos/zpeckler/2648345658/
http://www.flickr.com/photos/dcmetroblogger/3298543398/
http://www.flickr.com/photos/jenny-pics/4520503357/