JRuby json conversion

jruby-json.rb

# test conversion of Java objects to json in JRuby
# jrjackson is the only gem doing it right, the others quote the result
# the trick for the other ones is to convert maps and lists to ruby hashes and arrays before

array = java.util.ArrayList.new().to_array
list = java.util.ArrayList.new()
map = java.util.HashMap.new()
nested = { :list => list }

require 'jrjackson'
puts "*** jrjackson"
puts "Array:               " + JrJackson::Json.dump([])
puts "Java Array:          " + JrJackson::Json.dump(array)
puts "Java List to_a:      " + JrJackson::Json.dump(list.to_a)
puts "Java List:           " + JrJackson::Json.dump(list)
puts "Hash                 " + JrJackson::Json.dump({})
puts "Java Map:            " + JrJackson::Json.dump(map)
puts "Java Map to_hash:    " + JrJackson::Json.dump(map.to_hash)
puts "Nested list:         " + JrJackson::Json.dump(nested)
puts "Nested list to_hash: " + JrJackson::Json.dump(nested.to_hash)

require 'gson'
puts "\n*** Gson"
puts "Array:               " + Gson::Encoder.new.encode([])
puts "Java Array:          " + Gson::Encoder.new.encode(array)
puts "Java List to_a:      " + Gson::Encoder.new.encode(list.to_a)
puts "Java List:           " + Gson::Encoder.new.encode(list)
puts "Hash                 " + Gson::Encoder.new.encode({})
puts "Java Map:            " + Gson::Encoder.new.encode(map)
puts "Java Map to_hash:    " + Gson::Encoder.new.encode(map.to_hash)
puts "Nested list:         " + Gson::Encoder.new.encode(nested)
puts "Nested list to_hash: " + Gson::Encoder.new.encode(nested.to_hash)

require 'json'
puts "\n*** json"
puts "Array:               " + JSON.dump([])
puts "Java Array:          " + JSON.dump(array)
puts "Java List to_a:      " + JSON.dump(list.to_a)
puts "Java List:           " + JSON.dump(list)
puts "Hash                 " + JSON.dump({})
puts "Java Map:            " + JSON.dump(map)
puts "Java Map to_hash:    " + JSON.dump(map.to_hash)
puts "Nested list:         " + JSON.dump(nested)
puts "Nested list to_hash: " + JSON.dump(nested.to_hash)

output.log

$ rvm jruby-1.7.14 do ruby json.rb
*** jrjackson
Array:               []
Java Array:          [Ljava.lang.Object;@21bcffb5
Java List to_a:      []
Java List:           []
Hash                 {}
Java Map:            {}
Java Map to_hash:    {}
Nested list:         {"list":[]}
Nested list to_hash: {"list":[]}

*** Gson
Array:               []
Java Array:          "[Ljava.lang.Object;@21bcffb5"
Java List to_a:      []
Java List:           "[]"
Hash                 {}
Java Map:            "{}"
Java Map to_hash:    {}
Nested list:         {"list":"[]"}
Nested list to_hash: {"list":"[]"}

*** json
Array:               []
Java Array:          "[Ljava.lang.Object;@21bcffb5"
Java List to_a:      []
Java List:           "[]"
Hash                 {}
Java Map:            "{}"
Java Map to_hash:    {}
Nested list:         {"list":"[]"}
Nested list to_hash: {"list":"[]"}

Is this problem only for dumping the string or there is another problem?