Redis實現多級快取

<dependency>
     <groupId>com.github.ben-manes.caffeine</groupId>
     <artifactId>caffeine</artifactId>
     <version>3.0.5</version>
 </dependency>

package com.erick.cache;

import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;

import java.time.Duration;

public final class CacheUtil {
    private static int expireSeconds = 2;
    public static Cache<String, String> cacheWithExpireSeconds;

    private static int maxPairs = 1;
    public static Cache<String, String> cacheWithMaxPairs;

    static {
        /*過期策略，寫完60s後過期*/
        cacheWithExpireSeconds = Caffeine.newBuilder()
                .expireAfterWrite(Duration.ofSeconds(expireSeconds))
                .build();

        /*過期策略，達到最大值後刪除
         * 1. 並不會立即刪除，等一會兒才會刪除
         * 2. 會將之前儲存的資料刪除掉*/
        cacheWithMaxPairs = Caffeine.newBuilder()
                .maximumSize(maxPairs)
                .build();
    }

    /*從快取中獲取資料
     * 1. 如果快取中有，則直接從快取中返回
     * 2. 如果快取中沒有，則去資料查詢並返回結果*/
    public static String getKeyWithExpire(String key) {
        return cacheWithExpireSeconds.get(key, value -> {
            return getResultFromDB();
        });
    }

    public static String getKeyWithMaxPair(String key) {
        return cacheWithMaxPairs.get(key, value -> {
            return getResultFromDB();
        });
    }

    private static String getResultFromDB() {
        System.out.println("資料庫查詢");
        return "db result";
    }
}

package com.erick.cache;

import java.util.concurrent.TimeUnit;

public class Test {

    @org.junit.Test
    public void test01() throws InterruptedException {
        CacheUtil.cacheWithExpireSeconds.put("name", "erick");
        System.out.println(CacheUtil.getKeyWithExpire("name"));
        TimeUnit.SECONDS.sleep(3);
        System.out.println(CacheUtil.getKeyWithExpire("name"));
    }

    @org.junit.Test
    public void test02() throws InterruptedException {
        CacheUtil.cacheWithMaxPairs.put("name", "erick");
        CacheUtil.cacheWithMaxPairs.put("age", "12");

        System.out.println(CacheUtil.getKeyWithMaxPair("name"));
        System.out.println(CacheUtil.getKeyWithMaxPair("age"));

        TimeUnit.SECONDS.sleep(2);

        System.out.println(CacheUtil.getKeyWithMaxPair("name")); // 查詢不到了
        System.out.println(CacheUtil.getKeyWithMaxPair("age"));
    }
}