package com.bdc.cache;
 

 import java.util.HashMap;
 
 import java.util.Map;
 
  
  
  
  
 
  
  
   
 public class CacheTest {
 
  
 
  
  
   
  
  
  
  private Map map = new HashMap();  
 
  
  
 
  
  
   
  
  
  
  public Object getValue(String key){ 
 
  
  
   
  
  
  
  
  
  
  
  Object obj = map.get(key);  
  
  
  
  //先从缓存里面取值 
 
  
  
   
  
  
  
  
  
  
  
  if(obj == null){  
   
  //判断缓存里面是否有值数据
 
  
  
   
  
  
  
  
  
  
   
  
  
   
 System.out.println("缓存中不存在，从数据库中取出");
 
  
  
   
  
  
  
  
  
  
  
  
  
  
  
  obj =“The Value You Put” //模拟从数据库读取数据
 
  
  
   
  
  
  
  
  
  
  
  
  
  
  
  map.put(key, obj); 
  //将取出的数据 放入缓存，以便下次从缓存取数据
 
  
  
   
  
  
  
  
  
  
  
  }else{
 
  
  
   
  
  
  
  
  
  
   
  
  
   
 System.out.println("缓存中存在此key的数据");
 
  
  
   
  
  
  
  
  
  
  
  }
 
  
  
   
  
  
  
  
  
  
  
  return obj;  
 
  
  
   
  
  
  
  } 
 
  
  
  
  
  
  
 
  
  
  
  
  
  
  
  
 
  
  
  
   
  
  
  public void 
  deleteCache(String key){
 
  
  
  
   
  
  
   
  
  
  if(map.get(key)!=null){
 
  
  
  
   
  
  
   
  
  
   
  
  
  map.remove(key);
 
  
  
  
   
  
  
   
  
  
  }
 
  
  
  
   
  
  
   
  
  
 
  
  
  
   
  
  
  }
 
  
  
  
   
  
  
 
  
  
  
   
  
  
 
  
  
  
   
  
  
  public void updateCache(String key){
 
  
  
  
   
  
  
   
  
  
  //模拟从数据库取出此数据
 
  
  
  
   
  
  
   
  
  
  Object obj = "GetDataFromDB";
 
  
  
  
   
  
  
   
  
  
  if(obj!=map.get(key)){
 
  
  
  
   
  
  
   
  
  
   
  
  
  map.remove(key);
 
  
  
  
   
  
  
   
  
  
   
  
  
  map.put(key, obj);
 
  
  
  
   
  
  
   
  
  
  }
 
  
  
  
   
  
  
  }
 
  
  
  
   
  
  
 

 }
 

 Junit测试-
 
 package com.bdc.test;
 

 import org.junit.Test;
 
 import com.bdc.cache.CacheTest;
 

 public class TestCache {
 
  
  
  
 
  
  
  
  @Test
 
  
  
  
  public void test(){
 
  
  
  
   
  
  
  CacheTest cache = new CacheTest();
 
  
  
  
   
  
  
  System.out.println("********************");
 
  
  
  
   
  
  
  long t1 = System.currentTimeMillis();
 
  
  
  
   
  
  
  String str1 = (String) cache.getValue("name");
 
  
  
  
   
  
  
  for(int i=0;i<=10000;i++){
 
  
  
  
   
  
  
   
  
  
  System.out.print("");
 
  
  
  
   
  
  
  }
 
  
  
  
   
  
  
  long t2 = System.currentTimeMillis();
 
  
  
  
   
  
  
  System.out.println("str1 is :"+str1);
 
  
  
  
   
  
  
  System.out.println("用时 :"+(t2-t1));
 
  
  
  
   
  
  
  System.out.println("********************");
 
  
  
  
   
  
  
  long t3 = System.currentTimeMillis();
 
  
  
  
   
  
  
  String str2 = (String) cache.getValue("name");
 
  
  
  
   
  
  
  for(int i=0;i<=10000;i++){
 
  
  
  
   
  
  
   
  
  
  System.out.print("");
 
  
  
  
   
  
  
  }
 
  
  
  
   
  
  
  long t4 = System.currentTimeMillis();
 
  
  
  
   
  
  
  System.out.println("str2 is :"+str2);
 
  
  
  
   
  
  
  System.out.println("用时 :"+(t4-t3));
 
  
  
  
   
  
  
  System.out.println("********************");
 
  
  
  
   
  
  
  long t5 = System.currentTimeMillis();
 
  
  
  
   
  
  
  String str3 = (String) cache.getValue("age");
 
  
  
  
   
  
  
  for(int i=0;i<=10000;i++){
 
  
  
  
   
  
  
   
  
  
  System.out.print("");
 
  
  
  
   
  
  
  }
 
  
  
  
   
  
  
  long t6 = System.currentTimeMillis();
 
  
  
  
   
  
  
  System.out.println("str3 is :"+str3);
 
  
  
  
   
  
  
  System.out.println("用时 :"+(t6-t5));
 
  
  
  
   
  
  
  System.out.println("********************");
 
  
  
  
  }
 

 }
 

 输出结果-
 
 ********************
 
 缓存中不存在，从数据库中取出
 
 str1 is :name baby
 
 用时 :3
 
 ********************
 
 缓存中存在
 
 str2 is :name baby
 
 用时 :1
 
 ********************
 
 缓存中不存在，从数据库中取出
 
 str3 is :age baby
 
 用时 :2
 
 ********************