首页 > 代码库 > 《JAVA与模式》之装修者模式
《JAVA与模式》之装修者模式
装饰者模式
动态地将责任附加到对象上。若要扩展功能,装饰者提供了比继承更有弹性的替代方案。
具体被装饰者和抽象装饰类都继承于抽象被装饰者类,继承的是类型,而不是行为。行为来自装饰者和基础组件,或与其他装饰者之间的组合关系。
装饰模式的角色
抽象构件角色(Component):给出一个抽象接口,以规范准备接收附加责任的对象。
具体构件角色(Concrete Component):定义将要接收附加责任的类。
装饰角色(Decorator):持有一个构件(Component)对象的引用,并定义一个与抽象构件接口一致的接口。
具体装饰角色(Concrete Decorator):负责给构件对象“贴上”附加的责任。
装饰模式的特点
装饰对象和真实对象有相同的接口。这样客户端对象就可以以和真实对象相同的方式和装饰对象交互。
装饰对象包含一个真实对象的引用(reference)。
装饰对象接收所有来自客户端的请求,它把这些请求转发给真实的对象。
装饰对象可以在转发这些请求之前或之后附加一些功能。
这样就确保了在运行时,不用修改给定对象的结构就可以在外部增加附加的功能。
代码
1 public class Zhuangxiuzhe { 2 public static void main(String[] args) { 3 Zhuangxiuzhe zhuangxiuzhe=new Zhuangxiuzhe(); 4 Component component=zhuangxiuzhe.new ConcreteComponent(); 5 Component decorator=zhuangxiuzhe.new ConcreteDecorator1(component); 6 decorator.doMethod(); 7 Component decorator2=zhuangxiuzhe.new ConcreteDecorator2(decorator); 8 decorator2.doMethod(); 9 10 }11 12 interface Component {13 14 public void doMethod();15 16 }17 18 class ConcreteComponent implements Component {19 20 public void doMethod() {21 System.out.println("一般操作");22 23 }24 25 }26 abstract class Decorator implements Component{27 28 protected Component component;29 public Decorator(Component component){30 this.component=component;31 }32 33 34 }35 class ConcreteDecorator1 extends Decorator{36 37 public ConcreteDecorator1(Component component) {38 super(component);39 40 }41 public void test1(){42 System.out.println("ConcreteDecorator1 额外操作");43 }44 45 public void doMethod() {46 super.component.doMethod();47 test1();48 }49 }50 class ConcreteDecorator2 extends Decorator{51 52 public ConcreteDecorator2(Component component) {53 super(component);54 55 }56 57 public void doMethod() {58 super.component.doMethod();59 test2();60 }61 62 public void test2(){63 System.out.println("ConcreteDecorator2 额外操作");64 }65 }66 67 68 }
执行结果
一般操作
ConcreteDecorator1 额外操作
一般操作
ConcreteDecorator1 额外操作
ConcreteDecorator2 额外操作
突然发现装修者模式跟责任链模式有点相同,自身都引用了抽象类,这样可以调用传入的包装类
区别在于功能上:责任链强调的是请求由谁来处理,而装修者模式则是对引入的对象的现有功能进行包装,增强改变
Java IO中的装饰模式
在IO中,具体构件角色是节点流,装饰角色是过滤流。
FilterInputStream和FilterOutputStream是装饰角色,而其他派生自它们的类则是具体装饰角色。
我们来看看代码
抽象角色类InputStream
1 public abstract class InputStream implements Closeable {2 3 4 //实现了read等方法5 public int read(byte b[]) throws IOException {6 return read(b, 0, b.length);7 }8 9 }
具体角色类FileInputStream
1 public2 class FileInputStream extends InputStream{3 4 5 }
抽象包装类FilterInputStream
1 public 2 class FilterInputStream extends InputStream { 3 /** 4 * The input stream to be filtered. 5 */ 6 protected volatile InputStream in; 7 8 9 protected FilterInputStream(InputStream in) {10 this.in = in;11 }12 13 public int read() throws IOException {14 return in.read();15 }16 17 18 }
具体包装类BufferedInputStream
1 public 2 class BufferedInputStream extends FilterInputStream { 3 4 public BufferedInputStream(InputStream in) { 5 this(in, defaultBufferSize); 6 } 7 8 //完成了设置抽象角色类的映射 9 public BufferedInputStream(InputStream in, int size) {10 super(in);11 if (size <= 0) {12 throw new IllegalArgumentException("Buffer size <= 0");13 }14 buf = new byte[size];15 }16 17 //read方法中调用fill()18 public synchronized int read() throws IOException {19 if (pos >= count) {20 fill();21 if (pos >= count)22 return -1;23 }24 return getBufIfOpen()[pos++] & 0xff;25 }26 private void fill() throws IOException {27 byte[] buffer = getBufIfOpen();28 if (markpos < 0)29 pos = 0; /* no mark: throw away the buffer */30 else if (pos >= buffer.length) /* no room left in buffer */31 if (markpos > 0) { /* can throw away early part of the buffer */32 int sz = pos - markpos;33 System.arraycopy(buffer, markpos, buffer, 0, sz);34 pos = sz;35 markpos = 0;36 } else if (buffer.length >= marklimit) {37 markpos = -1; /* buffer got too big, invalidate mark */38 pos = 0; /* drop buffer contents */39 } else { /* grow buffer */40 int nsz = pos * 2;41 if (nsz > marklimit)42 nsz = marklimit;43 byte nbuf[] = new byte[nsz];44 System.arraycopy(buffer, 0, nbuf, 0, pos);45 if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {46 // Can‘t replace buf if there was an async close.47 // Note: This would need to be changed if fill()48 // is ever made accessible to multiple threads.49 // But for now, the only way CAS can fail is via close.50 // assert buf == null;51 throw new IOException("Stream closed");52 }53 buffer = nbuf;54 }55 count = pos;56 int n = getInIfOpen().read(buffer, pos, buffer.length - pos);57 if (n > 0)58 count = n + pos;59 }60 61 62 }
fill()方法中除了自身操作外,我们看到了 int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
1 private InputStream getInIfOpen() throws IOException {2 InputStream input = in;3 if (input == null)4 throw new IOException("Stream closed");5 return input;6 }
在看看getInIfOpen()方法,我们就明白了 整个的过程
参考地址:
http://www.cnblogs.com/mengdd/archive/2013/02/12/2910302.html
http://blog.csdn.net/cai1213/article/details/8003445
http://xubindehao.iteye.com/blog/474636