application_responder.rb

class ApplicationResponder < ActionController::Responder

  def to_json
    if has_errors?
      display_errors
    elsif save? || destroy?
      render action: :show
    else
      super
    end
  end

  private

  def save?
    post? || put?
  end

  def destroy?
    delete?
  end

end

products_controller_after.rb

class ProductsController < ApplicationController

  respond_to :json

  self.responder = ApplicationResponder

  # def index
  # def show

  def create
    @product = Product.new(product_params)
    @product.save
    respond_with(@product)
  end

  def update
    @product = find_product
    @product.attributes = product_params
    @product.save
    respond_with(@product)
  end

  def destroy
    @product = find_product
    @product.destroy
    respond_with(@product)
  end

  private

  # def find_product
  # def product_params

end

products_controller_before.rb

class ProductsController < ApplicationController

  respond_to :json
  
  # def index
  # def show

  def create
    @product = Product.new(product_params)
    
    if @product.save
      render action: :show
    else
      render_errors
    end
  end

  def update
    @product = find_product
    @product.attributes = product_params

    if @product.save
      render action: :show
    else
      render_errors
    end
  end

  def destroy
    @product = find_product
    
    if @product.destroy
      render action: :show
    else
      render_errors
    end
  end

  private
  
  # def find_product
  # def product_params
  # def render_errors

end