一、背景

當業務實現上需要用到本地快取，來解決一些資料量相對較小但是頻繁訪問資料的場景，可以採用Google的CacheBuilder解決方案。

二、程式碼實現

1.首先在maven中引入下面的包

<dependency>  
    <groupId>com.google.guava</groupId>  
    <artifactId>guava</artifactId>  
    <version>19.0</version>  
</dependency>

2. 程式碼測試案例

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

import java.util.concurrent.TimeUnit;

public class LocalCacheTest {
    // 測試類
    public static void main(String[] args) throws Exception {
        CacheService us = new CacheService();
        
 
for (int i = 0; i < 6; i++) {
            System.out.println(us.getName("1001"));
            TimeUnit.SECONDS.sleep(1);
        }
    }

    // 實現類
    public static class CacheService {
        private final LoadingCache<String, String> cache;

        public CacheService() {
            /**
             * 建立本地快取，當本地快取不命中時，呼叫load方法，返回結果，再快取結果, 3秒自動過期
             
 
*/
            cache = CacheBuilder.newBuilder().expireAfterWrite(3, TimeUnit.SECONDS)
                    .build(new CacheLoader<String, String>() {
                public String load(String id) throws Exception {
                    System.out.println("load()method invoke, 執行查詢資料庫, 等其他複雜的邏輯");
                    TimeUnit.MILLISECONDS.sleep(100);
                    return "User:" + id;
                }
            });
        }

        public String getName(String id) throws Exception {
            long start = System.currentTimeMillis();
            String result = cache.get(id);
            System.out.println("查詢 "+id +" 耗時："+ (System.currentTimeMillis()-start) + " ms");
            return result;
        }
    }
}

3. 控制檯輸出

從控制檯輸出，可以看出，當本地快取不命中時，呼叫load方法，通過資料庫查詢結果，返回結果，再快取結果, 耗時較長。如果命中查詢速度非常快，可達0ms，3秒自動過期後，重複上述操作。

load()method invoke, 執行查詢資料庫, 等其他複雜的邏輯
查詢 1001 耗時：124 ms
User:1001
查詢 1001 耗時：0 ms
User:1001
查詢 1001 耗時：0 ms
User:1001
load()method invoke, 執行查詢資料庫, 等其他複雜的邏輯
查詢 1001 耗時：108 ms
User:1001
查詢 1001 耗時：0 ms
User:1001
查詢 1001 耗時：0 ms
User:1001

Process finished with exit code 0

4. 附工具類

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;

import java.util.concurrent.TimeUnit;

public final class JvmCacheUtil {

    public static final String JVM_CACHE_SPECIFY_GEO = "cache_specify_geo";

    public static final String JVM_CACHE_BUILD_SQL = "cache_build_sql";

    public static final int DEFAULT_CAPACITY = 50;

    public static final long DEFAULT_CACHE_EXP = 12L;

    public static final long DEFAULT_CACHE_ENTRY_EXP = 900L;
    
    /**
    * 12小時後過期
    */
    private static Cache<String,
        Cache> cacheManager = CacheBuilder.newBuilder()
            .maximumSize(DEFAULT_CAPACITY)
            .expireAfterAccess(12L, TimeUnit.HOURS)
            .expireAfterWrite(12L, TimeUnit.HOURS)
            .initialCapacity(10)
            .build();

    public static Cache getCache(String cacheName) {
        return getCache(cacheName, DEFAULT_CAPACITY, DEFAULT_CACHE_ENTRY_EXP, TimeUnit.SECONDS);
    }

    public static Cache getCache(String cacheName, long expire, TimeUnit timeUnit) {
        return getCache(cacheName, DEFAULT_CAPACITY, expire, timeUnit);
    }

    public static Cache getCache(String cacheName, int capacity, long expire, TimeUnit timeUnit) {
        Cache cache = cacheManager.getIfPresent(cacheName);
        if (null == cache) {
            cache = CacheBuilder.newBuilder()
                .maximumSize(DEFAULT_CAPACITY)
                .expireAfterAccess(expire, timeUnit)
                .expireAfterWrite(expire, timeUnit)
                .initialCapacity(capacity)
                .build();
            cacheManager.put(cacheName, cache);
        }
        return cache;
    }

    public static Object get(String cacheName, String key) {
        Cache cache = getCache(cacheName);
        return cache.getIfPresent(key);
    }

    public static void put(String cacheName, String key, Object val) {
        Cache cache = getCache(cacheName);
        cache.put(key, val);
    }

    public static void put(String cacheName, String key, Object val, long expire, TimeUnit timeUnit) {
        Cache cache = getCache(cacheName, expire, timeUnit);
        cache.put(key, val);
    }