设计模式之 享元模式

享元模式 通过对象的复用来减少对象创建的次数和数量，以减少系统内存的使用和降低系统的负载。在系统需要一个对象时，享元模式首先在系统中查找并尝试重用现有的对象，如果未找到匹配的对象，则创建新对象并将其缓存在系统中以便下次使用。

（1）定义Memory

public class Memory{
    private int size;
    private boolean isused;
    private String id;
    public Memory(int size,boolean isused,String id){
        this.size = size;
        this.isused = isused;
        this.id = id;
    }
    
    public int getSize() {
        return size;
    }
    
    public void setSize(int size) {
        this.size = size;
    }
    
    public boolean isIsused() {
        return isused;
    }

    public void setIsused(boolean isused) {
        this.isused = isused;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }
}

（2）定义MemoryFactory工厂

public class MemoryFactory{
    private final static Log logger = LogFactory.getLog(this.getClass());

    private static List<Memory> memoryList = new ArrayList<>();
    public static Memory getMemory(int size){
        Memory memory = null;
        for (int i = 0; i<memoryList.size();i++){
            memory = memoryList.get(i);
            // 如果存在和需求size一样大小并且未使用的内存块，则直接使用
            if (memory.getSize() == size && memory.isIsused() == false){
                memory.setIsused(true);
                memoryList.set(i,memory);
                logger.info("get memory from memoryList");
                break;
            }
        }
        if (memory == null){
            memory = new Memory(32,false, UUID.randomUUID().toString());
            memoryList.add(memory);
        }

        return memory;
    }

    // 释放内存
    public static void releaseMemory(String id){
        for (int i = 0; i < memoryList.size(); i++) {
            Memory memory = memoryList.get(i);
            if (memory.getId().equals(id)){
                memory.setIsused(false);
                memoryList.set(i,memory);
                logger.info("release memory"+id);
                break;
            }
        }
    }
}

（3）使用享元模式

public static void main(String[] args){
    // 获取内存
    Memory memory = MemoryFactory.getMemory(32);
    // 释放内存
    MemoryFactory.releaseMemory(memory.getId());
    // 重新获取内存
    MemoryFactory.getMemory(32);
}

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