Guava通過接口LoadingCache提供了一個非常強大的基於內存的LoadingCache<K，V>。在緩存中自動加載值，它提供了許多實用的方法，在有緩存需求時非常有用。

接口聲明

以下是forcom.google.common.cache.LoadingCache<K，V>接口的聲明：

@Beta
@GwtCompatible
public interface LoadingCache<K,V>
   extends Cache<K,V>, Function<K,V>

接口方法

S.N.	方法及說明
1	V apply(K key) 不推薦使用。提供滿足功能接口;使用get(K)或getUnchecked(K)代替。
2	ConcurrentMap<K,V> asMap() 返回存儲在該緩存作為一個線程安全的映射條目的視圖。
3	V get(K key) 返回一個鍵在這個高速緩存中，首先裝載如果需要該值相關聯的值。
4	ImmutableMap<K,V> getAll(Iterable<? extends K> keys) 返回一個鍵相關聯的值的映射，創建或必要時檢索這些值。
5	V getUnchecked(K key) 返回一個鍵在這個高速緩存中，首先裝載如果需要該值相關聯的值。
6	void refresh(K key) 加載鍵key，可能是異步的一個新值。

LoadingCache 示例

使用所選擇的編輯器創建下麵的java程序 C:/> Guava

GuavaTester.java

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import com.google.common.base.MoreObjects;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

public class GuavaTester {
   public static void main(String args[]){
      //create a cache for employees based on their employee id
      LoadingCache employeeCache = 
         CacheBuilder.newBuilder()
            .maximumSize(100) // maximum 100 records can be cached
            .expireAfterAccess(30, TimeUnit.MINUTES) // cache will expire after 30 minutes of access
            .build(new CacheLoader(){ // build the cacheloader
               @Override
               public Employee load(String empId) throws Exception {
                  //make the expensive call
                  return getFromDatabase(empId);
               }							
            });

      try {			
         //on first invocation, cache will be populated with corresponding
         //employee record
         System.out.println("Invocation #1");
         System.out.println(employeeCache.get("100"));
         System.out.println(employeeCache.get("103"));
         System.out.println(employeeCache.get("110"));
         //second invocation, data will be returned from cache
         System.out.println("Invocation #2");
         System.out.println(employeeCache.get("100"));
         System.out.println(employeeCache.get("103"));
         System.out.println(employeeCache.get("110"));

      } catch (ExecutionException e) {
         e.printStackTrace();
      }
   }

   private static Employee getFromDatabase(String empId){
      Employee e1 = new Employee("Mahesh", "Finance", "100");
      Employee e2 = new Employee("Rohan", "IT", "103");
      Employee e3 = new Employee("Sohan", "Admin", "110");

      Map database = new HashMap();
      database.put("100", e1);
      database.put("103", e2);
      database.put("110", e3);
      System.out.println("Database hit for" + empId);
      return database.get(empId);		
   }
}

class Employee {
   String name;
   String dept;
   String emplD;

   public Employee(String name, String dept, String empID){
      this.name = name;
      this.dept = dept;
      this.emplD = empID;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public String getDept() {
      return dept;
   }
   public void setDept(String dept) {
      this.dept = dept;
   }
   public String getEmplD() {
      return emplD;
   }
   public void setEmplD(String emplD) {
      this.emplD = emplD;
   }

   @Override
   public String toString() {
      return MoreObjects.toStringHelper(Employee.class)
      .add("Name", name)
      .add("Department", dept)
      .add("Emp Id", emplD).toString();
   }	
}

驗證結果

使用javac編譯器如下編譯類

C:\Guava>javac GuavaTester.java

現在運行GuavaTester看到的結果

C:\Guava>java GuavaTester

看看結果：

Invocation #1
Database hit for100
Employee{Name=Mahesh, Department=Finance, Emp Id=100}
Database hit for103
Employee{Name=Rohan, Department=IT, Emp Id=103}
Database hit for110
Employee{Name=Sohan, Department=Admin, Emp Id=110}
Invocation #2
Employee{Name=Mahesh, Department=Finance, Emp Id=100}
Employee{Name=Rohan, Department=IT, Emp Id=103}
Employee{Name=Sohan, Department=Admin, Emp Id=110}