JDK中的设计模式

原文：http://stackoverflow.com/questions/1673841/examples-of-gof-design-patterns

创建型模式

抽象工厂

• javax.xml.parsers.DocumentBuilderFactory#newInstance()
• javax.xml.transform.TransformerFactory#newInstance()
• javax.xml.xpath.XPathFactory#newInstance()

Builder 

• java.lang.StringBuilder#append() (unsynchronized)
• java.lang.StringBuffer#append() (synchronized)
• java.nio.ByteBuffer#put() (also on CharBuffer, ShortBuffer, IntBuffer, LongBuffer,FloatBuffer and DoubleBuffer)
• javax.swing.GroupLayout.Group#addComponent()
• All implementations of java.lang.Appendable

工厂方法

• java.util.Calendar#getInstance()
• java.util.ResourceBundle#getBundle()
• java.text.NumberFormat#getInstance()
• java.nio.charset.Charset#forName()
• java.net.URLStreamHandlerFactory#createURLStreamHandler(String) (Returns singleton object per protocol)

原型

• java.lang.Object#clone() (the class has to implement java.lang.Cloneable)

单例

• java.lang.Runtime#getRuntime()
• java.awt.Desktop#getDesktop()

结构型模式

• 适配器 (把一种接口类型转换成另一种接口类型)

  • java.util.Arrays#asList()
  • java.io.InputStreamReader(InputStream) (returns a Reader)
  • java.io.OutputStreamWriter(OutputStream) (returns a Writer)
  • javax.xml.bind.annotation.adapters.XmlAdapter#marshal() and #unmarshal()

  组合

  • java.awt.Container#add(Component) (practically all over Swing thus)
  • javax.faces.component.UIComponent#getChildren() (practically all over JSF UI thus)

  装饰器

  • All subclasses of java.io.InputStream, OutputStream, Reader and Writer have a constructor taking an instance of same type.
  • java.util.Collections, the checkedXXX(), synchronizedXXX() and unmodifiableXXX()methods.
  • javax.servlet.http.HttpServletRequestWrapper and HttpServletResponseWrapper

  Facade (recognizeable by behavioral methods which internally uses instances of different independent abstract/interface types)

  • javax.faces.context.FacesContext, it internally uses among others the abstract/interface typesLifeCycle, ViewHandler, NavigationHandler and many more without that the enduser has to worry about it (which are however overrideable by injection).
  • javax.faces.context.ExternalContext, which internally uses ServletContext, HttpSession, HttpServletRequest, HttpServletResponse, etc.

  Flyweight (recognizeable by creational methods returning a cached instance, a bit the "multiton" idea)

  • java.lang.Integer#valueOf(int) (also on Boolean, Byte, Character, Short and Long)

  Proxy (recognizeable by creational methods which returns an implementation of given abstract/interface type which in turn delegates/uses a different implementation of given abstract/interface type)

  • java.lang.reflect.Proxy
  • java.rmi.*, the whole API actually.

  Behavioral patterns

  Chain of responsibility (recognizeable by behavioral methods which (indirectly) invokes the same method inanother implementation of same abstract/interface type in a queue)

  • java.util.logging.Logger#log()
  • javax.servlet.Filter#doFilter()

  Command (recognizeable by behavioral methods in an abstract/interface type which invokes a method in an implementation of a different abstract/interface type which has been encapsulated by the command implementation during its creation)

  • All implementations of java.lang.Runnable
  • All implementations of javax.swing.Action

  Interpreter (recognizeable by behavioral methods returning a structurally different instance/type of the given instance/type; note that parsing/formatting is not part of the pattern, determining the pattern and how to apply it is)

  • java.util.Pattern
  • java.text.Normalizer
  • All subclasses of java.text.Format
  • All subclasses of javax.el.ELResolver

  Iterator (recognizeable by behavioral methods sequentially returning instances of a different type from a queue)

  • All implementations of java.util.Iterator (thus among others also java.util.Scanner!).
  • All implementations of java.util.Enumeration

  Mediator (recognizeable by behavioral methods taking an instance of different abstract/interface type (usually using the command pattern) which delegates/uses the given instance)

  • java.util.Timer (all scheduleXXX() methods)
  • java.util.concurrent.Executor#execute()
  • java.util.concurrent.ExecutorService (the invokeXXX() and submit() methods)
  • java.util.concurrent.ScheduledExecutorService (all scheduleXXX() methods)
  • java.lang.reflect.Method#invoke()

  Memento (recognizeable by behavioral methods which internally changes the state of the whole instance)

  • java.util.Date (the setter methods do that, Date is internally represented by a long value)
  • All implementations of java.io.Serializable
  • All implementations of javax.faces.component.StateHolder

  Observer (or Publish/Subscribe) (recognizeable by behavioral methods which invokes a method on an instance of another abstract/interface type, depending on own state)

  • java.util.Observer/java.util.Observable (rarely used in real world though)
  • All implementations of java.util.EventListener (practically all over Swing thus)
  • javax.servlet.http.HttpSessionBindingListener
  • javax.servlet.http.HttpSessionAttributeListener
  • javax.faces.event.PhaseListener

  State (recognizeable by behavioral methods which changes its behaviour depending on the instance's state which can be controlled externally)

  • javax.faces.lifecycle.LifeCycle#execute() (controlled by FacesServlet, the behaviour is dependent on current phase (state) of JSF lifecycle)

  Strategy (recognizeable by behavioral methods in an abstract/interface type which invokes a method in an implementation of a different abstract/interface type which has been passed-in as method argument into the strategy implementation)

  • java.util.Comparator#compare(), executed by among others Collections#sort().
  • javax.servlet.http.HttpServlet, the service() and all doXXX() methods take HttpServletRequest and HttpServletResponse and the implementor has to process them (and not to get hold of them as instance variables!).
  • javax.servlet.Filter#doFilter()

  Template method (recognizeable by behavioral methods which already have a "default" behaviour definied by an abstract type)

  • All non-abstract methods of java.io.InputStream, java.io.OutputStream, java.io.Readerand java.io.Writer.
  • All non-abstract methods of java.util.AbstractList, java.util.AbstractSet and java.util.AbstractMap.
  • javax.servlet.http.HttpServlet, all the doXXX() methods by default sends a HTTP 405 "Method Not Allowed" error to the response. You're free to implement none or any of them.

  Visitor (recognizeable by two different abstract/interface types which has methods definied which takes each theother abstract/interface type; the one actually calls the method of the other and the other executes the desired strategy on it)

  • javax.lang.model.element.AnnotationValue and AnnotationValueVisitor
  • javax.lang.model.element.Element and ElementVisitor
  • javax.lang.model.type.TypeMirror and TypeVisitor