diff --git a/lib/jbuilder.rb b/lib/jbuilder.rb
index b12624b..db2f25c 100644
--- a/lib/jbuilder.rb
+++ b/lib/jbuilder.rb
@@ -12,14 +12,18 @@ class Jbuilder
   @@ignore_nil    = false
   @@deep_format_keys = false
 
-  def initialize(options = {})
+  def initialize(
+    key_formatter: @@key_formatter,
+    ignore_nil: @@ignore_nil,
+    deep_format_keys: @@deep_format_keys,
+    &block
+  )
     @attributes = {}
+    @key_formatter = key_formatter
+    @ignore_nil = ignore_nil
+    @deep_format_keys = deep_format_keys
 
-    @key_formatter = options.fetch(:key_formatter){ @@key_formatter ? @@key_formatter.clone : nil}
-    @ignore_nil = options.fetch(:ignore_nil, @@ignore_nil)
-    @deep_format_keys = options.fetch(:deep_format_keys, @@deep_format_keys)
-
-    yield self if ::Kernel.block_given?
+    yield self if block
   end
 
   # Yields a builder and automatically turns the result into a JSON string
@@ -100,13 +104,13 @@ def method_missing(*args, &block)
   #
   #   { "_first_name": "David" }
   #
-  def key_format!(*args)
-    @key_formatter = KeyFormatter.new(*args)
+  def key_format!(...)
+    @key_formatter = KeyFormatter.new(...)
   end
 
   # Same as the instance method key_format! except sets the default.
-  def self.key_format(*args)
-    @@key_formatter = KeyFormatter.new(*args)
+  def self.key_format(...)
+    @@key_formatter = KeyFormatter.new(...)
   end
 
   # If you want to skip adding nil values to your JSON hash. This is useful
diff --git a/lib/jbuilder/jbuilder_template.rb b/lib/jbuilder/jbuilder_template.rb
index 55f2d5f..2984aaf 100644
--- a/lib/jbuilder/jbuilder_template.rb
+++ b/lib/jbuilder/jbuilder_template.rb
@@ -10,10 +10,11 @@ class << self
 
   self.template_lookup_options = { handlers: [:jbuilder] }
 
-  def initialize(context, *args)
+  def initialize(context, options = nil)
     @context = context
     @cached_root = nil
-    super(*args)
+
+    options.nil? ? super() : super(**options)
   end
 
   # Generates JSON using the template specified with the `:partial` option. For example, the code below will render
diff --git a/lib/jbuilder/key_formatter.rb b/lib/jbuilder/key_formatter.rb
index c9e7eca..2c0f1f9 100644
--- a/lib/jbuilder/key_formatter.rb
+++ b/lib/jbuilder/key_formatter.rb
@@ -1,32 +1,28 @@
 require 'jbuilder/jbuilder'
-require 'active_support/core_ext/array'
 
 class Jbuilder
   class KeyFormatter
-    def initialize(*args)
-      @format = {}
-      @cache = {}
-
-      options = args.extract_options!
-      args.each do |name|
-        @format[name] = []
-      end
-      options.each do |name, parameters|
-        @format[name] = parameters
-      end
-    end
-
-    def initialize_copy(original)
+    def initialize(*formats, **formats_with_options)
+      @mutex = Mutex.new
+      @formats = formats
+      @formats_with_options = formats_with_options
       @cache = {}
     end
 
     def format(key)
-      @cache[key] ||= @format.inject(key.to_s) do |result, args|
-        func, args = args
-        if ::Proc === func
-          func.call result, *args
-        else
-          result.send func, *args
+      @mutex.synchronize do
+        @cache[key] ||= begin
+          value = key.is_a?(Symbol) ? key.name : key.to_s
+
+          @formats.each do |func|
+            value = func.is_a?(Proc) ? func.call(value) : value.send(func)
+          end
+
+          @formats_with_options.each do |func, params|
+            value = func.is_a?(Proc) ? func.call(value, *params) : value.send(func, *params)
+          end
+
+          value
         end
       end
     end
diff --git a/test/jbuilder_test.rb b/test/jbuilder_test.rb
index 76569bb..4f2cbe2 100644
--- a/test/jbuilder_test.rb
+++ b/test/jbuilder_test.rb
@@ -784,12 +784,12 @@ class JbuilderTest < ActiveSupport::TestCase
     assert_equal ['camelStyle'], result.keys
   end
 
-  test 'do not use default key formatter directly' do
+  test 'use default key formatter when configured' do
     Jbuilder.key_format
     jbuild{ |json| json.key 'value' }
     formatter = Jbuilder.send(:class_variable_get, '@@key_formatter')
     cache = formatter.instance_variable_get('@cache')
-    assert_empty cache
+    assert_includes cache, :key
   end
 
   test 'ignore_nil! without a parameter' do