Java中的缓存池有哪些

package com.paic.zhangqi.cache;  
import java.util.Date; 
 
/** 
 * 缓存实体 
 * @author ZHANGQI947 
 */ 
public class CacheItem {  
 // 创建缓存时间 
 private Date createTime = new Date();   
 // 缓存期满时间 
 private long expireTime = 1;   
 // 缓存实体 
 private Object entity;    
 public CacheItem(Object obj, long expires) { 
  this.entity = obj; 
  this.expireTime = expires; 
 }   
 // 判断缓存是否超时 
 public boolean isExpired() { 
  return (expireTime != -1 && new Date().getTime() - createTime.getTime() > expireTime); 
 }  
 public Date getCreateTime() { 
  return createTime; 
 }  
 public void setCreateTime(Date createTime) { 
  this.createTime = createTime; 
 }  
 public Object getEntity() { 
  return entity; 
 }  
 public void setEntity(Object entity) { 
  this.entity = entity; 
 }  
 public long getExpireTime() { 
  return expireTime; 
 }  
 public void setExpireTime(long expireTime) { 
  this.expireTime = expireTime; 
 } 
} 

package com.paic.zhangqi.cache;  
import java.util.Date; 
import java.util.HashMap; 
import java.util.Map; 
/** 
 * 缓存池 
 * @author Administrator 
 */ 
public class CachePool { 
 // 缓存池唯一实例 
 private static CachePool instance; 
 // 缓存Map 
 private static Map<String, Object> cacheItems;   
 private CachePool() { 
  cacheItems = new HashMap<String, Object>(); 
 }   
 /** 
  * 获取唯一的实例 
  * @return instance 
  */ 
 public synchronized static CachePool getInstance() { 
  if (instance == null) { 
   instance = new CachePool(); 
  } 
  return instance; 
 }   
 /** 
  * 清除所有的Item缓存 
  */ 
 public synchronized void clearAllItems() { 
  cacheItems.clear(); 
 }   
 /** 
  * 获取缓存实例 
  * @param name 缓存名称 
  * @return 缓存实例 
  */ 
 public synchronized Object getCacheItem(String name) { 
  if (!cacheItems.containsKey(name)) { 
   return null; 
  } 
  CacheItem cacheItem = (CacheItem) cacheItems.get(name); 
  if (cacheItem.isExpired()) { 
   return null; 
  } 
  return cacheItem.getEntity(); 
 } 
 /** 
  * 存放缓存信息 
  * @param name 名称 
  * @param obj 实例对象 
  * @param expires 超时时长 
  */ 
 public synchronized void putCacheItem(String name, Object obj, long expires) { 
  // 判断该对象是否在在缓存池，不在直接put 
  if (!cacheItems.containsKey(name)) { 
   cacheItems.put(name, new CacheItem(obj, expires)); 
  } 
  // 获取缓存池中对象，更新对象信息 
  CacheItem cacheItem = (CacheItem) cacheItems.get(name); 
  cacheItem.setCreateTime(new Date()); 
  cacheItem.setEntity(obj); 
  cacheItem.setExpireTime(expires); 
 } 
 /** 
  * 移除缓存数据 
  * @param name 
  */ 
 public synchronized void removeCacheItem(String name) { 
  if (!cacheItems.containsKey(name)) { 
   return ; 
  } 
  cacheItems.remove(name); 
 }   
 /** 
  * 获取缓存数据的数量 
  * @return 
  */ 
 public int getSize() { 
  return cacheItems.size(); 
 }  
} 

package com.paic.zhangqi.cache; 
/** 
 * 学生类 
 * @author Administrator 
 */ 
public class Student {  
 private String name; 
 private String id; 
 private int age; 
 private int sal; 
 public Student() { 
   
 }   
 public Student(String name, String id, int age, int sal) { 
  this.name = name; 
  this.id = id; 
  this.age = age; 
  this.sal = sal; 
 }  
 public String getName() { 
  return name; 
 }  
 public void setName(String name) { 
  this.name = name; 
 }  
 public String getId() { 
  return id; 
 }  
 public void setId(String id) { 
  this.id = id; 
 }  
 public int getAge() { 
  return age; 
 }  
 public void setAge(int age) { 
  this.age = age; 
 }  
 public int getSal() { 
  return sal; 
 } 
 public void setSal(int sal) { 
  this.sal = sal; 
 } 
}

package com.paic.zhangqi.cache; 
/** 
 * 主测试类 
 * @author ZHANGQI947 
 */ 
public class MainTest { 
 
 /** 
  * @param args 
  * @throws InterruptedException 
  */ 
 public static void main(String[] args) throws InterruptedException { 
  // 获取缓存池 
  CachePool cachePool = CachePool.getInstance();    
  Student stu1 = new Student("l1", "stu001", 25, 40); 
  Student stu2 = new Student("l2", "stu002", 25, 40); 
  Student stu3 = new Student("l3", "stu003", 25, 40); 
  Student stu4 = new Student("l4", "stu004", 25, 40);    
  cachePool.putCacheItem("001", stu1, 122222); 
  cachePool.putCacheItem("002", stu2, 10); 
  cachePool.putCacheItem("003", stu3, 360002); 
  cachePool.putCacheItem("004", stu4, 1222222);    
  // 设置线程休眠，其中002对象会超时 
  Thread.sleep(200);    
  Student stu001 = (Student) cachePool.getCacheItem("001"); 
  if (null != stu001) { 
   System.out.println(stu001.getName()); 
  }    
  // 由于超时，这里取出的002对象为null 
  Student stu002 = (Student) cachePool.getCacheItem("002"); 
  if (null != stu002) { 
   System.out.println(stu002.getName()); 
  }    
  // 获取打印缓存池中对象数量 
  int cacheSize = cachePool.getSize(); 
  System.out.println(cacheSize);    
  // 删除对象002 
  cachePool.removeCacheItem("002");   
  // 打印缓存池数量 
  cacheSize = cachePool.getSize(); 
  System.out.println(cacheSize); 
 } 
}