[Google Guava]--缓存工具

亦凉 2022-05-29 12:22 236阅读 0赞

## 简介： ##

Guava通过接口LoadingCache提供了一个非常强大的基于内存的LoadingCache<K，V>。在缓存中自动加载值，它提供了许多实用的方法，在有缓存需求时非常有用。

## 接口声明 ##

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

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

## 接口方法 ##

<table style="border-collapse:collapse;border-spacing:0px;border-color:rgb(214,214,214);width:495.555572509766px;vertical-align:top;margin-top:8px;margin-bottom:8px;color:rgb(49,49,49);font-size:14.4444446563721px;line-height:22px;background-color:rgb(247,247,247);"> 
 <tbody> 
  <tr> 
   <th style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;width:38.8888893127441px;background:rgb(238,238,238);">S.N.</th> 
   <th style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;background:rgb(238,238,238);">方法及说明</th> 
  </tr> 
  <tr> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;">1</td> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;"><strong>V apply(K key)</strong><br>不推荐使用。提供满足功能接口;使用get(K)或getUnchecked(K)代替。</td> 
  </tr> 
  <tr> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;">2</td> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;"><strong>ConcurrentMap&lt;K,V&gt; asMap()</strong><br>返回存储在该缓存作为一个线程安全的映射条目的视图。</td> 
  </tr> 
  <tr> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;">3</td> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;"><strong>V get(K key)</strong><br>返回一个键在这个高速缓存中，首先装载如果需要该值相关联的值。</td> 
  </tr> 
  <tr> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;">4</td> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;"><strong>ImmutableMap&lt;K,V&gt; getAll(Iterable&lt;? extends K&gt; keys)</strong><br>返回一个键相关联的值的映射，创建或必要时检索这些值。</td> 
  </tr> 
  <tr> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;">5</td> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;"><strong>V getUnchecked(K key)</strong><br>返回一个键在这个高速缓存中，首先装载如果需要该值相关联的值。</td> 
  </tr> 
  <tr> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;">6</td> 
   <td style="border-collapse:collapse;border-color:rgb(214,214,214);padding:5px;"><strong>void refresh(K key)</strong><br>加载键key，可能是异步的一个新值。</td> 
  </tr> 
 </tbody> 
</table>

## LoadingCache 示例 ##

package com.koolearn.duobao.service;
    
    import com.google.common.base.MoreObjects;
    import com.google.common.cache.CacheBuilder;
    import com.google.common.cache.CacheLoader;
    import com.google.common.cache.LoadingCache;
    
    import java.util.HashMap;
    import java.util.Map;
    import java.util.concurrent.ExecutionException;
    import java.util.concurrent.TimeUnit;
    
    /**
     * @author Franco_Q
     * @date 2018/3/23 17:26
     */
    public class Test {
        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<String, Employee>(){
                                @Override
                                public Employee load(String empId) throws Exception {
                                    return getFromDatabase(empId);
                                } // build the cacheloader
                            });
    
            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 (Employee) 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();
        }
    }