2 files changed, 56 insertions, 1 deletions
diff --git a/activesupport/lib/active_support/json/backends/yajl.rb b/activesupport/lib/active_support/json/backends/yajl.rb
new file mode 100644
index 0000000000..d76f8b03e4
--- /dev/null
+++ b/activesupport/lib/active_support/json/backends/yajl.rb
@@ -0,0 +1,40 @@
+require 'yajl-ruby' unless defined?(Yajl)
+
+module ActiveSupport
+  module JSON
+    module Backends
+      module Yajl
+        ParseError = ::Yajl::ParseError
+        extend self
+
+        # Parses a JSON string or IO and convert it into an object
+        def decode(json)
+          data = ::Yajl::Parser.new.parse(json)
+          if ActiveSupport.parse_json_times
+            convert_dates_from(data)
+          else
+            data
+          end
+        end
+
+      private
+        def convert_dates_from(data)
+          case data
+          when nil
+            nil
+          when DATE_REGEX
+            DateTime.parse(data)
+          when Array
+            data.map! { |d| convert_dates_from(d) }
+          when Hash
+            data.each do |key, value|
+              data[key] = convert_dates_from(value)
+            end
+          else
+            data
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activesupport/lib/active_support/json/decoding.rb b/activesupport/lib/active_support/json/decoding.rb
index a5908365af..e357b6837a 100644
--- a/activesupport/lib/active_support/json/decoding.rb
+++ b/activesupport/lib/active_support/json/decoding.rb
@@ -6,12 +6,15 @@ module ActiveSupport
   mattr_accessor :parse_json_times
 
   module JSON
+    # Listed in order of preference.
+    DECODERS = %w(Yajl JSONGem Yaml)
+
     class << self
       attr_reader :parse_error
       delegate :decode, :to => :backend
 
       def backend
-        self.backend = "Yaml" unless defined?(@backend)
+        set_default_backend unless defined?(@backend)
         @backend
       end
 
@@ -31,6 +34,18 @@ module ActiveSupport
       ensure
         self.backend = old_backend
       end
+
+      def set_default_backend
+        DECODERS.find do |name|
+          begin
+            self.backend = name
+            true
+          rescue LoadError
+            # Try next decoder.
+            false
+          end
+        end
+      end
     end
   end
 end