点击这里查看更多设计模式

 

基本概念

运用共享技术有效的支持大量细粒度的对象，主要用于减少创建对象，提高资源利用。

应用场景列举

1. 系统中有大量相同或类似的对象，创建这些对象需要消耗大量内存资源；

2. 适用于有缓存需求的场景。

实现

如上图，享元模式有两个关键点：1. 享元类中需要维护内部状态，对于同一享元对象，内部状态是一致的；2. 享元工厂中需要维护一个享元对象的容器，客户端可直接通过工厂提供的方法获取享元对象。

/** * 抽象享元对象 */ @Data public abstract class Flyweight { /** * 内部状态，同一享元对象其内部状态相同 */ private String intrinsicState; public Flyweight(String intrinsicState) { this.intrinsicState = intrinsicState; } /** * @param extrinsicState 外部状态，根据外部状态进行具体操作 */ public abstract void operation(String extrinsicState); } /** * 具体Flyweight */ public class ConcreteFlyweight extends Flyweight { public ConcreteFlyweight(String intrinsicState) { super(intrinsicState); } @Override public void operation(String extrinsicState) { System.out.println("具体Flyweight外部状态：" + extrinsicState + "，内部状态：" + getIntrinsicState()); } } /** * 不共享Flyweight */ public class UnSharedFlyweight extends Flyweight { public UnSharedFlyweight(String intrinsicState) { super(intrinsicState); } @Override public void operation(String extrinsicState) { System.out.println("不共享Flyweight外部状态：" + extrinsicState + "，内部状态：" + getIntrinsicState()); } } public class FlyweightFactory { private static final Map<String, Flyweight> FLYWEIGHTS = new HashMap<>(); private FlyweightFactory() { } static { FLYWEIGHTS.put("A", new ConcreteFlyweight("A")); FLYWEIGHTS.put("B", new ConcreteFlyweight("B")); } public static Flyweight getFlyweight(String key) { return FLYWEIGHTS.get(key); } } public class Test { public static void main(String[] args) { Flyweight flyweight = FlyweightFactory.getFlyweight("A"); flyweight.operation("AO"); } }

 

举例

在一个文件系统中，通过文件MD5（相当于内部状态）来判断文件是否已经存在，若已经存在，则上传时，直接存储一个文件路径即可，不必真实上传文件，提高用户体验。

/** * 文件类，相当于享元类 */ @Data public class File { private String filename; private String content; /** * 文件md5，相当于内部状态 */ private String md5; public File(String filename, String content) { this.filename = filename; this.content = content; this.md5 = calMd5(); } private String calMd5() { // 计算MD5，这里为了方便演示，直接返回文件内容 return content; } } public class FileFactory { private static Map<String, File> FILE_MAP = new HashMap<>(); private static FileFactory fileFactory = new FileFactory(); public static FileFactory getInstance() { return fileFactory; } public void upload(File file) { if (FILE_MAP.containsKey(file.getMd5())) { System.out.println("文件已存在，直接将相关数据和存入数据库"); } else { System.out.println("上传文件，并将相关数据存入数据库"); FILE_MAP.put(file.getMd5(), file); } } } public class Test { public static void main(String[] args) { File file = new File("文件A", "内容A"); FileFactory.getInstance().upload(file); File file2 = new File("文件A", "内容A"); FileFactory.getInstance().upload(file2); } }

测试结果如下：