JDK源码中使用的设计模式

https://stackoverflow.com/questions/1673841/examples-of-gof-design-patterns-in-javas-core-libraries

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Creational patterns

Abstract factory (recognizeable by creational methods returning the factory itself which in turn can be used to create another abstract/interface type)

• javax.xml.parsers.DocumentBuilderFactory#newInstance()

• javax.xml.transform.TransformerFactory#newInstance()

• javax.xml.xpath.XPathFactory#newInstance()

Builder (recognizeable by creational methods returning the instance itself)

• java.lang.StringBuilder#append() (unsynchronized)--【https://blog.csdn.net/weixin_38246518/article/details/78756615】

• 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

• java.util.stream.Stream.Builder

Factory method (recognizeable by creational methods returning an implementation of an abstract/interface type)

• 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)

• java.util.EnumSet#of()

• javax.xml.bind.JAXBContext#createMarshaller() and other similar methods

Prototype (recognizeable by creational methods returning a different instance of itself with the same properties)

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

Singleton (recognizeable by creational methods returning the same instance (usually of itself) everytime)

• java.lang.Runtime#getRuntime()

• java.awt.Desktop#getDesktop()

• java.lang.System#getSecurityManager()

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Structural patterns

Adapter (recognizeable by creational methods taking an instance of different abstract/interface type and returning an implementation of own/another abstract/interface type which decorates/overrides the given instance)

• java.util.Arrays#asList()

• java.util.Collections#list()

• java.util.Collections#enumeration()

• java.io.InputStreamReader(InputStream) (returns a Reader)

• java.io.OutputStreamWriter(OutputStream) (returns a Writer)

• javax.xml.bind.annotation.adapters.XmlAdapter#marshal() and #unmarshal()

Bridge (recognizeable by creational methods taking an instance of different abstract/interface type and returning an implementation of own abstract/interface type which delegates/uses the given instance)

• None comes to mind yet. A fictive example would be new LinkedHashMap(LinkedHashSet, List) which returns an unmodifiable linked map which doesn't clone the items, but usesthem. The java.util.Collections#newSetFromMap() and singletonXXX() methods however comes close.

Composite (recognizeable by behavioral methods taking an instance of same abstract/interface type into a tree structure)

• java.awt.Container#add(Component) (practically all over Swing thus)

• javax.faces.component.UIComponent#getChildren() (practically all over JSF UI thus)

Decorator (recognizeable by creational methods taking an instance of same abstract/interface type which adds additional behaviour)

• 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

• javax.swing.JScrollPane

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 types LifeCycle, 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, Long and BigDecimal)

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.*

• javax.ejb.EJB (explanation here)

• javax.inject.Inject (explanation here)

• javax.persistence.PersistenceContext

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Behavioral patterns

Chain of responsibility (recognizeable by behavioral methods which (indirectly) invokes the same method in another 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 defined 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 defined 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

• java.nio.file.FileVisitor and SimpleFileVisitor

• javax.faces.component.visit.VisitContext and VisitCallback