结论：

refreshAfterWrite：可以不重写reload。如果缓存过期，则一个线程去获取数据，其他线程返回老数据。
expireAfterWrite：如果缓存过期，则阻塞所有线程，一个线程去获取数据。
expireAfterAccess：一段时间内没有访问则过期，如果有多个线程同时查询，则阻塞所有线程，一个线程去获取数据。

refreshAfterWrite + CacheLoader.asyncReloading：第一次加载数据是同步的，以后所有加载数据都是异步的。如果当前数据过期则异步线程去获取新的数据，所有线程都先返回。

生产代码

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import org.springframework.stereotype.Service;import java.util.concurrent.TimeUnit;@Component
@Slf4j
public class AsyncCacheExample {private static final Executor DEFAULT_REOLAD_EXECUTOR =new ThreadPoolExecutor(1, // 没必要多个4,60,TimeUnit.MILLISECONDS,new LinkedBlockingDeque<>(10), // 队列长度+非核心线程数>key的数量new ThreadFactoryBuilder().setNameFormat("default-reload-cache-task-pool-%d").build());private final LoadingCache<String, String> cache;public AsyncCacheExample() {this.cache = CacheBuilder.newBuilder().maximumSize(10) // 数量不超过key的数量.refreshAfterWrite(10, TimeUnit.MINUTES).recordStats()// 记录缓存统计信息.build(CacheLoader.asyncReloading(new CacheLoader<String, String>() {@Overridepublic String load(String key) {try {return loadData(key);}catch (Exception e){log.error(e.getMessage());// 异常处理}}}, DEFAULT_REOLAD_EXECUTOR));}private static String loadData(String key) {// 模拟从数据库加载数据return "json";}public String get(String key){try {return cache.get(key);} catch (ExecutionException e) {throw new RuntimeException(e);}}}

生产代码2

public class LocalCacheUtils{private static final Executor DEFAULT_REOLAD_EXECUTOR =new ThreadPoolExecutor(1,1,60,TimeUnit.MILLISECONDS,new LinkedBlockingDeque<>(1000),new ThreadFactoryBuilder().setNameFormat("default-reload-cache-task-pool-%d").build());public static <K, V> LoadingCache<K, V> buildAsyncReloadingCache(long duration, TimeUnit unit, Function<K, V> loader) {return CacheBuilder.newBuilder().maximumSize(50).refreshAfterWrite(duration, unit).build(CacheLoader.asyncReloading(new CacheLoader<K, V>() {@Overridepublic V load(K key) {return loader.apply(key);}}, DEFAULT_REOLAD_EXECUTOR));}}// 使用：private final LoadingCache<String, Map<String, List<String>> xxxyyyListMap = LocalCacheUtils.buildAsyncReloadingCache(5,TimeUnit.MINUTES,k->getData());private Map<String, List<String> getData(){return ...
}

测试expireAfterWrite：

package com.github.liyue2008.ipcount;import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;public class CacheMultiThreadTest {public static void main(String[] args) {AtomicInteger integer = new AtomicInteger(0);LoadingCache<String, String> cache = CacheBuilder.newBuilder().expireAfterWrite(1, TimeUnit.SECONDS).build(new CacheLoader<String, String>() {@Overridepublic String load(String key) throws Exception {// Simulating loading data from databaseSystem.out.println("Loading data for key: " + key);return "Data for key: " + key + ":" + integer.getAndIncrement();}});// Create a thread pool with 5 threadsExecutorService executorService = Executors.newFixedThreadPool(2);// Submit tasks to the thread poolfor (int i = 0; i < 10; i++) {final int taskId = i;executorService.submit(() -> {try {String data = cache.get("Key");System.out.println("Task " + taskId + " - Data: " + data);Thread.sleep(600);} catch (ExecutionException | InterruptedException e) {e.printStackTrace();}});}// Shutdown the executor serviceexecutorService.shutdown();}
}

测试refreshAfterWrite：

package com.github.liyue2008.ipcount;import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;public class CacheMultiThreadTest {public static void main(String[] args) {AtomicInteger integer = new AtomicInteger(0);LoadingCache<String, String> cache = CacheBuilder.newBuilder().refreshAfterWrite(1, TimeUnit.SECONDS).build(new CacheLoader<String, String>() {@Overridepublic String load(String key) throws Exception {// Simulating loading data from databaseSystem.out.println("Loading data for key: " + key);return "Data for key: " + key + ":" + integer.getAndIncrement();}});// Create a thread pool with 5 threadsExecutorService executorService = Executors.newFixedThreadPool(2);// Submit tasks to the thread poolfor (int i = 0; i < 10; i++) {final int taskId = i;executorService.submit(() -> {try {String data = cache.get("Key");System.out.println("Task " + taskId + " - Data: " + data);Thread.sleep(600);} catch (ExecutionException | InterruptedException e) {e.printStackTrace();}});}// Shutdown the executor serviceexecutorService.shutdown();}
}