我希望能够编写优美的代码。
优美的代码就像一篇散文，易懂易读，而且看起来很漂亮。在《代码之美》一书中，收录了Ruby之父松本行宏的一篇文章，名为《把代码当作文章》，大约表达了同样的含义。Thoughtworks的一位工程师在《软件开发沉思录》一书中提出，每个类的方法最好不要超过5行。最初让我感觉很惊诧，继而觉得不可能。虽然这位工程师言之凿凿，提到在自己参与的项目中，所有代码都完全遵循了这一规范，我仍然表示怀疑。最近，阅读了Robert C. Martin的著作《代码整洁之道》（英文版名为Clean Code），看到Uncle Bob演示的代码，真是漂亮极了。仔细一看，这些好的代码在每个方法中大多数都没有超过5行。诀窍在哪里？那就是重构手法中最常用的Extract Method。进一步讲，如果我们能够为每个类与方法以及变量定义出好的名字，代码确实可以变成一篇散文。当然，是英文散文。
今天，我在重温.NET的序列化时，在MSDN上找到一篇演示Xml序列化的示范代码。或许是因为示范代码的缘故，这一段代码写得极其地不优雅，甚至显得有些丑陋：
public
class
Test {
???? public static void Main() {
???????? // Read and write purchase orders.
???????? Test t = new Test();
????????t.CreatePO( "po.xml");
????????t.ReadPO( "po.xml");
????}
???? private void CreatePO( string filename) {
???????? // Create an instance of the XmlSerializer class;
???????? // specify the type of object to serialize.
????????XmlSerializer serializer =
???????? new XmlSerializer( typeof( PurchaseOrder));
????????TextWriter writer = new StreamWriter(filename);
???????? PurchaseOrder po = new PurchaseOrder();
???????? // Create an address to ship and bill to.
???????? Address billAddress = new Address();
????????billAddress.Name = "Teresa Atkinson";
????????billAddress.Line1 = "1 Main St.";
????????billAddress.City = "AnyTown";
????????billAddress.State = "WA";
????????billAddress.Zip = "00000";
???????? // Set ShipTo and BillTo to the same addressee.
????????po.ShipTo = billAddress;
????????po.OrderDate = System. DateTime.Now.ToLongDateString();
???????? // Create an OrderedItem object.
???????? OrderedItem i1 = new OrderedItem();
????????i1.ItemName = "Widget S";
????????i1.Description = "Small widget";
????????i1.UnitPrice = ( decimal)5.23;
????????i1.Quantity = 3;
????????i1.Calculate();
???????? // Insert the item into the array.
???????? OrderedItem[] items = { i1 };
????????po.OrderedItems = items;
???????? // Calculate the total cost.
???????? decimal subTotal = new decimal();
???????? foreach ( OrderedItem oi in items) {
????????????subTotal += oi.LineTotal;
????????}
????????po.SubTotal = subTotal;
????????po.ShipCost = ( decimal)12.51;
????????po.TotalCost = po.SubTotal + po.ShipCost;
???????? // Serialize the purchase order, and close the TextWriter.
????????serializer.Serialize(writer, po);
????????writer.Close();
????}
???? protected void ReadPO( string filename) {
???????? // Create an instance of the XmlSerializer class;
???????? // specify the type of object to be deserialized.
????????XmlSerializer serializer = new XmlSerializer( typeof( PurchaseOrder));
???????? /* If the XML document has been altered with unknown
???????? nodes or attributes, handle them with the
???????? UnknownNode and UnknownAttribute events.*/
????????serializer.UnknownNode += new
????????XmlNodeEventHandler(serializer_UnknownNode);
????????serializer.UnknownAttribute += new
????????XmlAttributeEventHandler(serializer_UnknownAttribute);
???????? // A FileStream is needed to read the XML document.
????????FileStream fs = new FileStream(filename, FileMode.Open);
???????? // Declare an object variable of the type to be deserialized.
???????? PurchaseOrder po;
???????? /* Use the Deserialize method to restore the object's state with
???????? data from the XML document. */
????????po = ( PurchaseOrder)serializer.Deserialize(fs);
???????? // Read the order date.
???????? Console.WriteLine( "OrderDate: " + po.OrderDate);
???????? // Read the shipping address.
???????? Address shipTo = po.ShipTo;
????????ReadAddress(shipTo, "Ship To:");
???????? // Read the list of ordered items.
???????? OrderedItem[] items = po.OrderedItems;
???????? Console.WriteLine( "Items to be shipped:");
???????? foreach ( OrderedItem oi in items) {
???????????? Console.WriteLine( "\t" +
????????????oi.ItemName + "\t" +
????????????oi.Description + "\t" +
????????????oi.UnitPrice + "\t" +
????????????oi.Quantity + "\t" +
????????????oi.LineTotal);
????????}
???????? // Read the subtotal, shipping cost, and total cost.
???????? Console.WriteLine( "\t\t\t\t\t Subtotal\t" + po.SubTotal);
???????? Console.WriteLine( "\t\t\t\t\t Shipping\t" + po.ShipCost);
???????? Console.WriteLine( "\t\t\t\t\t Total\t\t" + po.TotalCost);
????}
???? protected void ReadAddress( Address a, string label) {
???????? // Read the fields of the Address object.
???????? Console.WriteLine(label);
???????? Console.WriteLine( "\t" + a.Name);
???????? Console.WriteLine( "\t" + a.Line1);
???????? Console.WriteLine( "\t" + a.City);
???????? Console.WriteLine( "\t" + a.State);
???????? Console.WriteLine( "\t" + a.Zip);
???????? Console.WriteLine();
????}
???? private void serializer_UnknownNode
????( object sender, XmlNodeEventArgs e) {
???????? Console.WriteLine( "Unknown Node:" + e.Name + "\t" + e.Text);
????}
???? private void serializer_UnknownAttribute
????( object sender, XmlAttributeEventArgs e) {
????????System.Xml. XmlAttribute attr = e.Attr;
???????? Console.WriteLine( "Unknown attribute " +
????????attr.Name + "='" + attr.Value + "'");
????}
}
???? public static void Main() {
???????? // Read and write purchase orders.
???????? Test t = new Test();
????????t.CreatePO( "po.xml");
????????t.ReadPO( "po.xml");
????}
???? private void CreatePO( string filename) {
???????? // Create an instance of the XmlSerializer class;
???????? // specify the type of object to serialize.
????????XmlSerializer serializer =
???????? new XmlSerializer( typeof( PurchaseOrder));
????????TextWriter writer = new StreamWriter(filename);
???????? PurchaseOrder po = new PurchaseOrder();
???????? // Create an address to ship and bill to.
???????? Address billAddress = new Address();
????????billAddress.Name = "Teresa Atkinson";
????????billAddress.Line1 = "1 Main St.";
????????billAddress.City = "AnyTown";
????????billAddress.State = "WA";
????????billAddress.Zip = "00000";
???????? // Set ShipTo and BillTo to the same addressee.
????????po.ShipTo = billAddress;
????????po.OrderDate = System. DateTime.Now.ToLongDateString();
???????? // Create an OrderedItem object.
???????? OrderedItem i1 = new OrderedItem();
????????i1.ItemName = "Widget S";
????????i1.Description = "Small widget";
????????i1.UnitPrice = ( decimal)5.23;
????????i1.Quantity = 3;
????????i1.Calculate();
???????? // Insert the item into the array.
???????? OrderedItem[] items = { i1 };
????????po.OrderedItems = items;
???????? // Calculate the total cost.
???????? decimal subTotal = new decimal();
???????? foreach ( OrderedItem oi in items) {
????????????subTotal += oi.LineTotal;
????????}
????????po.SubTotal = subTotal;
????????po.ShipCost = ( decimal)12.51;
????????po.TotalCost = po.SubTotal + po.ShipCost;
???????? // Serialize the purchase order, and close the TextWriter.
????????serializer.Serialize(writer, po);
????????writer.Close();
????}
???? protected void ReadPO( string filename) {
???????? // Create an instance of the XmlSerializer class;
???????? // specify the type of object to be deserialized.
????????XmlSerializer serializer = new XmlSerializer( typeof( PurchaseOrder));
???????? /* If the XML document has been altered with unknown
???????? nodes or attributes, handle them with the
???????? UnknownNode and UnknownAttribute events.*/
????????serializer.UnknownNode += new
????????XmlNodeEventHandler(serializer_UnknownNode);
????????serializer.UnknownAttribute += new
????????XmlAttributeEventHandler(serializer_UnknownAttribute);
???????? // A FileStream is needed to read the XML document.
????????FileStream fs = new FileStream(filename, FileMode.Open);
???????? // Declare an object variable of the type to be deserialized.
???????? PurchaseOrder po;
???????? /* Use the Deserialize method to restore the object's state with
???????? data from the XML document. */
????????po = ( PurchaseOrder)serializer.Deserialize(fs);
???????? // Read the order date.
???????? Console.WriteLine( "OrderDate: " + po.OrderDate);
???????? // Read the shipping address.
???????? Address shipTo = po.ShipTo;
????????ReadAddress(shipTo, "Ship To:");
???????? // Read the list of ordered items.
???????? OrderedItem[] items = po.OrderedItems;
???????? Console.WriteLine( "Items to be shipped:");
???????? foreach ( OrderedItem oi in items) {
???????????? Console.WriteLine( "\t" +
????????????oi.ItemName + "\t" +
????????????oi.Description + "\t" +
????????????oi.UnitPrice + "\t" +
????????????oi.Quantity + "\t" +
????????????oi.LineTotal);
????????}
???????? // Read the subtotal, shipping cost, and total cost.
???????? Console.WriteLine( "\t\t\t\t\t Subtotal\t" + po.SubTotal);
???????? Console.WriteLine( "\t\t\t\t\t Shipping\t" + po.ShipCost);
???????? Console.WriteLine( "\t\t\t\t\t Total\t\t" + po.TotalCost);
????}
???? protected void ReadAddress( Address a, string label) {
???????? // Read the fields of the Address object.
???????? Console.WriteLine(label);
???????? Console.WriteLine( "\t" + a.Name);
???????? Console.WriteLine( "\t" + a.Line1);
???????? Console.WriteLine( "\t" + a.City);
???????? Console.WriteLine( "\t" + a.State);
???????? Console.WriteLine( "\t" + a.Zip);
???????? Console.WriteLine();
????}
???? private void serializer_UnknownNode
????( object sender, XmlNodeEventArgs e) {
???????? Console.WriteLine( "Unknown Node:" + e.Name + "\t" + e.Text);
????}
???? private void serializer_UnknownAttribute
????( object sender, XmlAttributeEventArgs e) {
????????System.Xml. XmlAttribute attr = e.Attr;
???????? Console.WriteLine( "Unknown attribute " +
????????attr.Name + "='" + attr.Value + "'");
????}
}
看看CreatePO()和ReadPO()，多么地冗长。虽然这个实现极为简单，但对于代码的阅读者而言，想要一下子抓住该方法的中心思想，仍然比较困难。此外，方法中的注释也显得多余，因为，代码本身就可以给予很好的说明。
下面，是我对这段代码的重构，大家可以对比对比，是否更加容易阅读呢？
????
public
static
class
PurchaseOrderHandler {
???????? public static void CreatePurchaseOrder( string filename) {
???????????? PurchaseOrder po = BuildPurchaseOrder();
???????????? XmlSerializer serializer = new XmlSerializer( typeof( PurchaseOrder));
???????????? using ( var writer = new StreamWriter(filename)) {
????????????????serializer.Serialize(writer, po);
????????????}
????????}
???????? private static PurchaseOrder BuildPurchaseOrder() {
???????????? Address address = CreateAddress();
???????????? OrderedItem i1 = CreateOrderedItem();
???????????? OrderedItem[] items = { i1 };
???????????? PurchaseOrder po = new PurchaseOrder();
????????????po.ShipTo = address;
????????????po.OrderDate = System. DateTime.Now.ToLongDateString();
????????????po.OrderedItems = items;
????????????po.SubTotal = CalculateSubTotal(items);
????????????po.ShipCost = ( decimal)12.51;
????????????po.TotalCost = po.SubTotal + po.ShipCost;
???????????? return po;
????????}
???????? private static decimal CalculateSubTotal( OrderedItem[] items) {
???????????? decimal subTotal = new decimal();
???????????? foreach ( OrderedItem oi in items) {
????????????????subTotal += oi.LineTotal;
????????????}
???????????? return subTotal;
????????}
???????? private static OrderedItem CreateOrderedItem() {
???????????? OrderedItem i1 = new OrderedItem();
????????????i1.ItemName = "Widget S";
????????????i1.Description = "Small widget";
????????????i1.UnitPrice = ( decimal)5.23;
????????????i1.Quantity = 3;
????????????i1.Calculate();
???????????? return i1;
????????}
???????? private static Address CreateAddress() {
???????????? Address billAddress = new Address();
????????????billAddress.Name = "Bruce Zhang";
????????????billAddress.Line1 = "1 Main St.";
????????????billAddress.City = "Chong Qing";
????????????billAddress.State = "Chong Qing";
????????????billAddress.Zip = "400000";
???????????? return billAddress;
????????}
???????? public static void ReadPurchaseOrder( string filename) {
???????????? XmlSerializer serializer = new XmlSerializer( typeof( PurchaseOrder));
????????????serializer.UnknownNode += new XmlNodeEventHandler(serializer_UnknownNode);
????????????serializer.UnknownAttribute += new XmlAttributeEventHandler(serializer_UnknownAttribute);
???????????? FileStream fs = new FileStream(filename, FileMode.Open);
???????????? PurchaseOrder po;
????????????po = ( PurchaseOrder)serializer.Deserialize(fs);
???????????? PurchaseOrderPrinter.PrintPurchaseOrder(po);
????????}
???????? private static void serializer_UnknownNode
????????( object sender, XmlNodeEventArgs e) {
???????????? Console.WriteLine( "Unknown Node:" + e.Name + "\t" + e.Text);
????????}
???????? private static void serializer_UnknownAttribute
????????( object sender, XmlAttributeEventArgs e) {
????????????System.Xml. XmlAttribute attr = e.Attr;
???????????? Console.WriteLine( "Unknown attribute " +
????????????attr.Name + "='" + attr.Value + "'");
????????}
???????? private static class PurchaseOrderPrinter {
???????????? public static void PrintPurchaseOrder( PurchaseOrder po) {
????????????????PrintOrderDate(po);
????????????????PrintAddress(po.ShipTo);
????????????????PrintOrderedItem(po.OrderedItems);
????????????????PrintOrderCost(po);
????????????}
???????????? private static void PrintOrderCost( PurchaseOrder po) {
???????????????? Console.WriteLine( "\t\t\t\t\t Subtotal\t" + po.SubTotal);
???????????????? Console.WriteLine( "\t\t\t\t\t Shipping\t" + po.ShipCost);
???????????????? Console.WriteLine( "\t\t\t\t\t Total\t\t" + po.TotalCost);
????????????}
???????????? private static void PrintOrderDate( PurchaseOrder po) {
???????????????? Console.WriteLine( "OrderDate: " + po.OrderDate);
????????????}
???????????? private static void PrintOrderedItem( OrderedItem[] items) {
???????????????? Console.WriteLine( "Items to be shipped:");
???????????????? foreach ( OrderedItem oi in items) {
???????????????????? Console.WriteLine( "\t" +
????????????????????oi.ItemName + "\t" +
????????????????????oi.Description + "\t" +
????????????????????oi.UnitPrice + "\t" +
????????????????????oi.Quantity + "\t" +
????????????????????oi.LineTotal);
????????????????}
????????????}
???????????? private static void PrintAddress( Address a) {
???????????????? // Read the fields of the Address object.
???????????????? Console.WriteLine( "Ship To:");
???????????????? Console.WriteLine( "\t" + a.Name);
???????????????? Console.WriteLine( "\t" + a.Line1);
???????????????? Console.WriteLine( "\t" + a.City);
???????????????? Console.WriteLine( "\t" + a.State);
???????????????? Console.WriteLine( "\t" + a.Zip);
???????????????? Console.WriteLine();
????????????}
????????}
????}
???????? public static void CreatePurchaseOrder( string filename) {
???????????? PurchaseOrder po = BuildPurchaseOrder();
???????????? XmlSerializer serializer = new XmlSerializer( typeof( PurchaseOrder));
???????????? using ( var writer = new StreamWriter(filename)) {
????????????????serializer.Serialize(writer, po);
????????????}
????????}
???????? private static PurchaseOrder BuildPurchaseOrder() {
???????????? Address address = CreateAddress();
???????????? OrderedItem i1 = CreateOrderedItem();
???????????? OrderedItem[] items = { i1 };
???????????? PurchaseOrder po = new PurchaseOrder();
????????????po.ShipTo = address;
????????????po.OrderDate = System. DateTime.Now.ToLongDateString();
????????????po.OrderedItems = items;
????????????po.SubTotal = CalculateSubTotal(items);
????????????po.ShipCost = ( decimal)12.51;
????????????po.TotalCost = po.SubTotal + po.ShipCost;
???????????? return po;
????????}
???????? private static decimal CalculateSubTotal( OrderedItem[] items) {
???????????? decimal subTotal = new decimal();
???????????? foreach ( OrderedItem oi in items) {
????????????????subTotal += oi.LineTotal;
????????????}
???????????? return subTotal;
????????}
???????? private static OrderedItem CreateOrderedItem() {
???????????? OrderedItem i1 = new OrderedItem();
????????????i1.ItemName = "Widget S";
????????????i1.Description = "Small widget";
????????????i1.UnitPrice = ( decimal)5.23;
????????????i1.Quantity = 3;
????????????i1.Calculate();
???????????? return i1;
????????}
???????? private static Address CreateAddress() {
???????????? Address billAddress = new Address();
????????????billAddress.Name = "Bruce Zhang";
????????????billAddress.Line1 = "1 Main St.";
????????????billAddress.City = "Chong Qing";
????????????billAddress.State = "Chong Qing";
????????????billAddress.Zip = "400000";
???????????? return billAddress;
????????}
???????? public static void ReadPurchaseOrder( string filename) {
???????????? XmlSerializer serializer = new XmlSerializer( typeof( PurchaseOrder));
????????????serializer.UnknownNode += new XmlNodeEventHandler(serializer_UnknownNode);
????????????serializer.UnknownAttribute += new XmlAttributeEventHandler(serializer_UnknownAttribute);
???????????? FileStream fs = new FileStream(filename, FileMode.Open);
???????????? PurchaseOrder po;
????????????po = ( PurchaseOrder)serializer.Deserialize(fs);
???????????? PurchaseOrderPrinter.PrintPurchaseOrder(po);
????????}
???????? private static void serializer_UnknownNode
????????( object sender, XmlNodeEventArgs e) {
???????????? Console.WriteLine( "Unknown Node:" + e.Name + "\t" + e.Text);
????????}
???????? private static void serializer_UnknownAttribute
????????( object sender, XmlAttributeEventArgs e) {
????????????System.Xml. XmlAttribute attr = e.Attr;
???????????? Console.WriteLine( "Unknown attribute " +
????????????attr.Name + "='" + attr.Value + "'");
????????}
???????? private static class PurchaseOrderPrinter {
???????????? public static void PrintPurchaseOrder( PurchaseOrder po) {
????????????????PrintOrderDate(po);
????????????????PrintAddress(po.ShipTo);
????????????????PrintOrderedItem(po.OrderedItems);
????????????????PrintOrderCost(po);
????????????}
???????????? private static void PrintOrderCost( PurchaseOrder po) {
???????????????? Console.WriteLine( "\t\t\t\t\t Subtotal\t" + po.SubTotal);
???????????????? Console.WriteLine( "\t\t\t\t\t Shipping\t" + po.ShipCost);
???????????????? Console.WriteLine( "\t\t\t\t\t Total\t\t" + po.TotalCost);
????????????}
???????????? private static void PrintOrderDate( PurchaseOrder po) {
???????????????? Console.WriteLine( "OrderDate: " + po.OrderDate);
????????????}
???????????? private static void PrintOrderedItem( OrderedItem[] items) {
???????????????? Console.WriteLine( "Items to be shipped:");
???????????????? foreach ( OrderedItem oi in items) {
???????????????????? Console.WriteLine( "\t" +
????????????????????oi.ItemName + "\t" +
????????????????????oi.Description + "\t" +
????????????????????oi.UnitPrice + "\t" +
????????????????????oi.Quantity + "\t" +
????????????????????oi.LineTotal);
????????????????}
????????????}
???????????? private static void PrintAddress( Address a) {
???????????????? // Read the fields of the Address object.
???????????????? Console.WriteLine( "Ship To:");
???????????????? Console.WriteLine( "\t" + a.Name);
???????????????? Console.WriteLine( "\t" + a.Line1);
???????????????? Console.WriteLine( "\t" + a.City);
???????????????? Console.WriteLine( "\t" + a.State);
???????????????? Console.WriteLine( "\t" + a.Zip);
???????????????? Console.WriteLine();
????????????}
????????}
????}
阅读代码时，我们可以先关注最主要的方法，即CreatePurchaseOrder()和ReadPurchaseOrder()方法。如果并不希望了解过多构造PO对象的细节，通过阅读这样简短的方法，可以很容易地抓住这两个方法的实现，那就是通过构建一个PO对象，进行序列化，而在反序列化时，将获得的PO对象信息打印出来。
其实，糟糕的代码不一定就是初学者的“专利”，让我们看看NHibernate中的一段代码：
public SessionFactoryImpl(
Configuration cfg,
IMapping mapping,
Settings settings,
EventListeners listeners)
{
????Init();
????log.Info( "building session factory");
????properties = new Dictionary< string, string>(cfg.Properties);
????interceptor = cfg.Interceptor;
???? this.settings = settings;
????sqlFunctionRegistry = new SQLFunctionRegistry(settings.Dialect, cfg.SqlFunctions);
????eventListeners = listeners;
????filters = new Dictionary< string, FilterDefinition>(cfg.FilterDefinitions);
???? if (log.IsDebugEnabled)
????{
????????log.Debug( "Session factory constructed with filter configurations : " + CollectionPrinter.ToString(filters));
????}
???? if (log.IsDebugEnabled)
????{
????????log.Debug( "instantiating session factory with properties: " + CollectionPrinter.ToString(properties));
????}
???? try
????{
???????? if (settings.IsKeywordsImportEnabled)
????????{
???????????? SchemaMetadataUpdater.Update( this);
????????}
???????? if (settings.IsAutoQuoteEnabled)
????????{
???????????? SchemaMetadataUpdater.QuoteTableAndColumns(cfg);
????????}
????}
???? catch ( NotSupportedException)
????{
???????? // Ignore if the Dialect does not provide DataBaseSchema
????}
???? #region Caches
????settings.CacheProvider.Start(properties);
???? #endregion
???? #region Generators
????identifierGenerators = new Dictionary< string, IIdentifierGenerator>();
???? foreach ( PersistentClass model in cfg.ClassMappings)
????{
???????? if (!model.IsInherited)
????????{
???????????? IIdentifierGenerator generator =
????????????????model.Identifier.CreateIdentifierGenerator(settings.Dialect, settings.DefaultCatalogName,
???????????????????????????????????????????????????????????settings.DefaultSchemaName, ( RootClass) model);
????????????identifierGenerators[model.EntityName] = generator;
????????}
????}
???? #endregion
???? #region Persisters
???? Dictionary< string, ICacheConcurrencyStrategy> caches = new Dictionary< string, ICacheConcurrencyStrategy>();
????entityPersisters = new Dictionary< string, IEntityPersister>();
????implementorToEntityName = new Dictionary<System. Type, string>();
???? Dictionary< string, IClassMetadata> classMeta = new Dictionary< string, IClassMetadata>();
???? foreach ( PersistentClass model in cfg.ClassMappings)
????{
????????model.PrepareTemporaryTables(mapping, settings.Dialect);
???????? string cacheRegion = model.RootClazz.CacheRegionName;
???????? ICacheConcurrencyStrategy cache;
???????? if (!caches.TryGetValue(cacheRegion, out cache))
????????{
????????????cache =
???????????????? CacheFactory.CreateCache(model.CacheConcurrencyStrategy, cacheRegion, model.IsMutable, settings, properties);
???????????? if (cache != null)
????????????{
????????????????caches.Add(cacheRegion, cache);
????????????????allCacheRegions.Add(cache.RegionName, cache.Cache);
????????????}
????????}
???????? IEntityPersister cp = PersisterFactory.CreateClassPersister(model, cache, this, mapping);
????????entityPersisters[model.EntityName] = cp;
????????classMeta[model.EntityName] = cp.ClassMetadata;
???????? if (model.HasPocoRepresentation)
????????{
????????????implementorToEntityName[model.MappedClass] = model.EntityName;
????????}
????}
????classMetadata = new UnmodifiableDictionary< string, IClassMetadata>(classMeta);
???? Dictionary< string, ISet< string>> tmpEntityToCollectionRoleMap = new Dictionary< string, ISet< string>>();
????collectionPersisters = new Dictionary< string, ICollectionPersister>();
???? foreach (Mapping. Collection model in cfg.CollectionMappings)
????{
???????? ICacheConcurrencyStrategy cache =
???????????? CacheFactory.CreateCache(model.CacheConcurrencyStrategy, model.CacheRegionName, model.Owner.IsMutable, settings,
?????????????????????????????????????properties);
???????? if (cache != null)
????????{
????????????allCacheRegions[cache.RegionName] = cache.Cache;
????????}
???????? ICollectionPersister persister = PersisterFactory.CreateCollectionPersister(cfg, model, cache, this);
????????collectionPersisters[model.Role] = persister;
???????? IType indexType = persister.IndexType;
???????? if (indexType != null && indexType.IsAssociationType && !indexType.IsAnyType)
????????{
???????????? string entityName = (( IAssociationType) indexType).GetAssociatedEntityName( this);
???????????? ISet< string> roles;
???????????? if (!tmpEntityToCollectionRoleMap.TryGetValue(entityName, out roles))
????????????{
????????????????roles = new HashedSet< string>();
????????????????tmpEntityToCollectionRoleMap[entityName] = roles;
????????????}
????????????roles.Add(persister.Role);
????????}
???????? IType elementType = persister.ElementType;
???????? if (elementType.IsAssociationType && !elementType.IsAnyType)
????????{
???????????? string entityName = (( IAssociationType) elementType).GetAssociatedEntityName( this);
???????????? ISet< string> roles;
???????????? if (!tmpEntityToCollectionRoleMap.TryGetValue(entityName, out roles))
????????????{
????????????????roles = new HashedSet< string>();
????????????????tmpEntityToCollectionRoleMap[entityName] = roles;
????????????}
????????????roles.Add(persister.Role);
????????}
????}
???? Dictionary< string, ICollectionMetadata> tmpcollectionMetadata = new Dictionary< string, ICollectionMetadata>(collectionPersisters.Count);
???? foreach ( KeyValuePair< string, ICollectionPersister> collectionPersister in collectionPersisters)
????{
????????tmpcollectionMetadata.Add(collectionPersister.Key, collectionPersister.Value.CollectionMetadata);
????}
????collectionMetadata = new UnmodifiableDictionary< string, ICollectionMetadata>(tmpcollectionMetadata);
????collectionRolesByEntityParticipant = new UnmodifiableDictionary< string, ISet< string>>(tmpEntityToCollectionRoleMap);
???? #endregion
???? #region Named Queries
????namedQueries = new Dictionary< string, NamedQueryDefinition>(cfg.NamedQueries);
????namedSqlQueries = new Dictionary< string, NamedSQLQueryDefinition>(cfg.NamedSQLQueries);
????sqlResultSetMappings = new Dictionary< string, ResultSetMappingDefinition>(cfg.SqlResultSetMappings);
???? #endregion
????imports = new Dictionary< string, string>(cfg.Imports);
???? #region after *all* persisters and named queries are registered
???? foreach ( IEntityPersister persister in entityPersisters.Values)
????{
????????persister.PostInstantiate();
????}
???? foreach ( ICollectionPersister persister in collectionPersisters.Values)
????{
????????persister.PostInstantiate();
????}
???? #endregion
???? #region Serialization info
????name = settings.SessionFactoryName;
???? try
????{
????????uuid = ( string) UuidGenerator.Generate( null, null);
????}
???? catch ( Exception)
????{
???????? throw new AssertionFailure( "Could not generate UUID");
????}
???? SessionFactoryObjectFactory.AddInstance(uuid, name, this, properties);
???? #endregion
????log.Debug( "Instantiated session factory");
???? #region Schema management
???? if (settings.IsAutoCreateSchema)
????{
???????? new SchemaExport(cfg).Create( false, true);
????}
???? if ( settings.IsAutoUpdateSchema )
????{
???????? new SchemaUpdate(cfg).Execute( false, true);
????}
???? if (settings.IsAutoValidateSchema)
????{
????????? new SchemaValidator(cfg, settings).Validate();
????}
???? if (settings.IsAutoDropSchema)
????{
????????schemaExport = new SchemaExport(cfg);
????}
???? #endregion
???? #region Obtaining TransactionManager
???? // not ported yet
???? #endregion
????currentSessionContext = BuildCurrentSessionContext();
???? if (settings.IsQueryCacheEnabled)
????{
????????updateTimestampsCache = new UpdateTimestampsCache(settings, properties);
????????queryCache = settings.QueryCacheFactory.GetQueryCache( null, updateTimestampsCache, settings, properties);
????????queryCaches = new ThreadSafeDictionary< string, IQueryCache>( new Dictionary< string, IQueryCache>());
????}
???? else
????{
????????updateTimestampsCache = null;
????????queryCache = null;
????????queryCaches = null;
????}
???? #region Checking for named queries
???? if (settings.IsNamedQueryStartupCheckingEnabled)
????{
???????? IDictionary< string, HibernateException> errors = CheckNamedQueries();
???????? if (errors.Count > 0)
????????{
???????????? StringBuilder failingQueries = new StringBuilder( "Errors in named queries: ");
???????????? foreach ( KeyValuePair< string, HibernateException> pair in errors)
????????????{
????????????????failingQueries.Append( '{').Append(pair.Key).Append( '}');
????????????????log.Error( "Error in named query: " + pair.Key, pair.Value);
????????????}
???????????? throw new HibernateException(failingQueries.ToString());
????????}
????}
???? #endregion
????Statistics.IsStatisticsEnabled = settings.IsStatisticsEnabled;
???? // EntityNotFoundDelegate
???? IEntityNotFoundDelegate enfd = cfg.EntityNotFoundDelegate;
???? if (enfd == null)
????{
????????enfd = new DefaultEntityNotFoundDelegate();
????}
????entityNotFoundDelegate = enfd;
}
{
????Init();
????log.Info( "building session factory");
????properties = new Dictionary< string, string>(cfg.Properties);
????interceptor = cfg.Interceptor;
???? this.settings = settings;
????sqlFunctionRegistry = new SQLFunctionRegistry(settings.Dialect, cfg.SqlFunctions);
????eventListeners = listeners;
????filters = new Dictionary< string, FilterDefinition>(cfg.FilterDefinitions);
???? if (log.IsDebugEnabled)
????{
????????log.Debug( "Session factory constructed with filter configurations : " + CollectionPrinter.ToString(filters));
????}
???? if (log.IsDebugEnabled)
????{
????????log.Debug( "instantiating session factory with properties: " + CollectionPrinter.ToString(properties));
????}
???? try
????{
???????? if (settings.IsKeywordsImportEnabled)
????????{
???????????? SchemaMetadataUpdater.Update( this);
????????}
???????? if (settings.IsAutoQuoteEnabled)
????????{
???????????? SchemaMetadataUpdater.QuoteTableAndColumns(cfg);
????????}
????}
???? catch ( NotSupportedException)
????{
???????? // Ignore if the Dialect does not provide DataBaseSchema
????}
???? #region Caches
????settings.CacheProvider.Start(properties);
???? #endregion
???? #region Generators
????identifierGenerators = new Dictionary< string, IIdentifierGenerator>();
???? foreach ( PersistentClass model in cfg.ClassMappings)
????{
???????? if (!model.IsInherited)
????????{
???????????? IIdentifierGenerator generator =
????????????????model.Identifier.CreateIdentifierGenerator(settings.Dialect, settings.DefaultCatalogName,
???????????????????????????????????????????????????????????settings.DefaultSchemaName, ( RootClass) model);
????????????identifierGenerators[model.EntityName] = generator;
????????}
????}
???? #endregion
???? #region Persisters
???? Dictionary< string, ICacheConcurrencyStrategy> caches = new Dictionary< string, ICacheConcurrencyStrategy>();
????entityPersisters = new Dictionary< string, IEntityPersister>();
????implementorToEntityName = new Dictionary<System. Type, string>();
???? Dictionary< string, IClassMetadata> classMeta = new Dictionary< string, IClassMetadata>();
???? foreach ( PersistentClass model in cfg.ClassMappings)
????{
????????model.PrepareTemporaryTables(mapping, settings.Dialect);
???????? string cacheRegion = model.RootClazz.CacheRegionName;
???????? ICacheConcurrencyStrategy cache;
???????? if (!caches.TryGetValue(cacheRegion, out cache))
????????{
????????????cache =
???????????????? CacheFactory.CreateCache(model.CacheConcurrencyStrategy, cacheRegion, model.IsMutable, settings, properties);
???????????? if (cache != null)
????????????{
????????????????caches.Add(cacheRegion, cache);
????????????????allCacheRegions.Add(cache.RegionName, cache.Cache);
????????????}
????????}
???????? IEntityPersister cp = PersisterFactory.CreateClassPersister(model, cache, this, mapping);
????????entityPersisters[model.EntityName] = cp;
????????classMeta[model.EntityName] = cp.ClassMetadata;
???????? if (model.HasPocoRepresentation)
????????{
????????????implementorToEntityName[model.MappedClass] = model.EntityName;
????????}
????}
????classMetadata = new UnmodifiableDictionary< string, IClassMetadata>(classMeta);
???? Dictionary< string, ISet< string>> tmpEntityToCollectionRoleMap = new Dictionary< string, ISet< string>>();
????collectionPersisters = new Dictionary< string, ICollectionPersister>();
???? foreach (Mapping. Collection model in cfg.CollectionMappings)
????{
???????? ICacheConcurrencyStrategy cache =
???????????? CacheFactory.CreateCache(model.CacheConcurrencyStrategy, model.CacheRegionName, model.Owner.IsMutable, settings,
?????????????????????????????????????properties);
???????? if (cache != null)
????????{
????????????allCacheRegions[cache.RegionName] = cache.Cache;
????????}
???????? ICollectionPersister persister = PersisterFactory.CreateCollectionPersister(cfg, model, cache, this);
????????collectionPersisters[model.Role] = persister;
???????? IType indexType = persister.IndexType;
???????? if (indexType != null && indexType.IsAssociationType && !indexType.IsAnyType)
????????{
???????????? string entityName = (( IAssociationType) indexType).GetAssociatedEntityName( this);
???????????? ISet< string> roles;
???????????? if (!tmpEntityToCollectionRoleMap.TryGetValue(entityName, out roles))
????????????{
????????????????roles = new HashedSet< string>();
????????????????tmpEntityToCollectionRoleMap[entityName] = roles;
????????????}
????????????roles.Add(persister.Role);
????????}
???????? IType elementType = persister.ElementType;
???????? if (elementType.IsAssociationType && !elementType.IsAnyType)
????????{
???????????? string entityName = (( IAssociationType) elementType).GetAssociatedEntityName( this);
???????????? ISet< string> roles;
???????????? if (!tmpEntityToCollectionRoleMap.TryGetValue(entityName, out roles))
????????????{
????????????????roles = new HashedSet< string>();
????????????????tmpEntityToCollectionRoleMap[entityName] = roles;
????????????}
????????????roles.Add(persister.Role);
????????}
????}
???? Dictionary< string, ICollectionMetadata> tmpcollectionMetadata = new Dictionary< string, ICollectionMetadata>(collectionPersisters.Count);
???? foreach ( KeyValuePair< string, ICollectionPersister> collectionPersister in collectionPersisters)
????{
????????tmpcollectionMetadata.Add(collectionPersister.Key, collectionPersister.Value.CollectionMetadata);
????}
????collectionMetadata = new UnmodifiableDictionary< string, ICollectionMetadata>(tmpcollectionMetadata);
????collectionRolesByEntityParticipant = new UnmodifiableDictionary< string, ISet< string>>(tmpEntityToCollectionRoleMap);
???? #endregion
???? #region Named Queries
????namedQueries = new Dictionary< string, NamedQueryDefinition>(cfg.NamedQueries);
????namedSqlQueries = new Dictionary< string, NamedSQLQueryDefinition>(cfg.NamedSQLQueries);
????sqlResultSetMappings = new Dictionary< string, ResultSetMappingDefinition>(cfg.SqlResultSetMappings);
???? #endregion
????imports = new Dictionary< string, string>(cfg.Imports);
???? #region after *all* persisters and named queries are registered
???? foreach ( IEntityPersister persister in entityPersisters.Values)
????{
????????persister.PostInstantiate();
????}
???? foreach ( ICollectionPersister persister in collectionPersisters.Values)
????{
????????persister.PostInstantiate();
????}
???? #endregion
???? #region Serialization info
????name = settings.SessionFactoryName;
???? try
????{
????????uuid = ( string) UuidGenerator.Generate( null, null);
????}
???? catch ( Exception)
????{
???????? throw new AssertionFailure( "Could not generate UUID");
????}
???? SessionFactoryObjectFactory.AddInstance(uuid, name, this, properties);
???? #endregion
????log.Debug( "Instantiated session factory");
???? #region Schema management
???? if (settings.IsAutoCreateSchema)
????{
???????? new SchemaExport(cfg).Create( false, true);
????}
???? if ( settings.IsAutoUpdateSchema )
????{
???????? new SchemaUpdate(cfg).Execute( false, true);
????}
???? if (settings.IsAutoValidateSchema)
????{
????????? new SchemaValidator(cfg, settings).Validate();
????}
???? if (settings.IsAutoDropSchema)
????{
????????schemaExport = new SchemaExport(cfg);
????}
???? #endregion
???? #region Obtaining TransactionManager
???? // not ported yet
???? #endregion
????currentSessionContext = BuildCurrentSessionContext();
???? if (settings.IsQueryCacheEnabled)
????{
????????updateTimestampsCache = new UpdateTimestampsCache(settings, properties);
????????queryCache = settings.QueryCacheFactory.GetQueryCache( null, updateTimestampsCache, settings, properties);
????????queryCaches = new ThreadSafeDictionary< string, IQueryCache>( new Dictionary< string, IQueryCache>());
????}
???? else
????{
????????updateTimestampsCache = null;
????????queryCache = null;
????????queryCaches = null;
????}
???? #region Checking for named queries
???? if (settings.IsNamedQueryStartupCheckingEnabled)
????{
???????? IDictionary< string, HibernateException> errors = CheckNamedQueries();
???????? if (errors.Count > 0)
????????{
???????????? StringBuilder failingQueries = new StringBuilder( "Errors in named queries: ");
???????????? foreach ( KeyValuePair< string, HibernateException> pair in errors)
????????????{
????????????????failingQueries.Append( '{').Append(pair.Key).Append( '}');
????????????????log.Error( "Error in named query: " + pair.Key, pair.Value);
????????????}
???????????? throw new HibernateException(failingQueries.ToString());
????????}
????}
???? #endregion
????Statistics.IsStatisticsEnabled = settings.IsStatisticsEnabled;
???? // EntityNotFoundDelegate
???? IEntityNotFoundDelegate enfd = cfg.EntityNotFoundDelegate;
???? if (enfd == null)
????{
????????enfd = new DefaultEntityNotFoundDelegate();
????}
????entityNotFoundDelegate = enfd;
}
这是类SessionFactoryImpl（它实现了ISessionFactoryImplementor接口）的构造函数，其目的时是通过Configuration以及Setting中的某些值，去初始化SessionFactoryImpl，然后构建该类的对象。坦白说，我从来没有看过如此“浩瀚无垠”的构造函数。幸好，Visual Studio提高了Region，否则，更让人头疼。（我在想，既然代码的编写者已经利用了Region来分割实现，为何不进一步将其分割为小的方法呢？）
看这样的代码，我们能够轻易读懂吗？
拙劣代码可谓遗患无穷。在《程序员修炼之道》一书中，提到了所谓“破窗效应”，即“没修复的破窗，导致更多的窗户被打破”。丑陋的代码如果只有一个小的片段，看似无关紧要，就像一幢大楼的一扇破窗一般容易让人忘记。随着时间的推移，当这些丑陋代码不知不觉蔓延到整个项目中时，我们才发现这一幢大楼已经满目疮痍了。“一屋不扫，何以扫天下”，程序员应该从小处着手，未来才可能写出优雅的代码。
本文转自wayfarer51CTO博客，原文链接：http://blog.51cto.com/wayfarer/310016，如需转载请自行联系原作者
