利用配置文件解耦工厂类型

public interface IFactory
{
IProduct Create();              //  返回默认的 concrete product
IProduct Create(string name);   //  按照配置的逻辑名称返回指定的concrete product
}

public class ProductRegistry
{
const string SectionName = "concreteProducts";
static NameValueCollection collection =
(NameValueCollection)ConfigurationManager.GetSection(SectionName);

public Type this[string name]
{
get { return Type.GetType(collection[name]); }
}
}

public class Factory : IFactory
{

public const string DefaultName = "DEFAULT";
public readonly ProductRegistry productRegistry = new ProductRegistry();

#region IFactory Members

public IProduct Create()
{
return (IProduct)Activator.CreateInstance(productRegistry[DefaultName]);
}

public IProduct Create(string name)
{
if (string.IsNullOrEmpty(name)) throw new ArgumentNullException("name");
return (IProduct)Activator.CreateInstance(productRegistry[name]);
}

#endregion
}

public interface IBatchFactory : IFactory
{
IEnumerable<IProduct> Create(string name, int quantity);
IEnumerable<IProduct> Create(int quantity);
}

public class BatchFactory : Factory, IBatchFactory
{
#region IBatchFactory Members

/// <summary>
/// batch create
/// </summary>
/// <param name="quantity"></param>
/// <returns></returns>
public IEnumerable<IProduct> Create(int quantity)
{
if (quantity <= 0) throw new IndexOutOfRangeException("quantity");
return InternalCreate<IProduct>(productRegistry[DefaultName], quantity);
}

/// <summary>
/// batch create
/// </summary>
/// <param name="name"></param>
/// <param name="quantity"></param>
/// <returns></returns>
public IEnumerable<IProduct> Create(string name, int quantity)
{
if (string.IsNullOrEmpty(name)) throw new ArgumentNullException("name");
return InternalCreate<IProduct>(productRegistry[name], quantity);
}

/// <summary>
/// Helper method
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="type"></param>
/// <param name="quantity"></param>
/// <returns></returns>
IEnumerable<T> InternalCreate<T>(Type type, int quantity)
{
if (quantity <= 0) throw new IndexOutOfRangeException("quantity");
if (type == null) throw new ArgumentNullException("type");
IList<T> result = new List<T>();
for (int i = 0; i < quantity; i++)
result.Add((T)Activator.CreateInstance(type));
return result;
}

#endregion
}