java-code-GuavaDemo

pom

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>27.0.1-jre</version>
</dependency>

User

package redis;

import java.io.Serializable;

public class User implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 7710153170636593560L;
    private String userName;
    private String userId;

    public User(String userName, String userId) {
        this.userName = userName;
        this.userId = userId;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    @Override
    public String toString() {
        return "User [userName=" + userName + ", userId=" + userId + "]";
    }
}

GuavaCacheDemo

package redis;

import com.google.common.cache.*;

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

public class GuavaCacheDemo {

    public static void main(String[] args) throws ExecutionException {
        //缓存接口这里是LoadingCache，LoadingCache在缓存项不存在时可以自动加载缓存
        LoadingCache<String, User> userCache
                //CacheBuilder的构造函数是私有的，只能通过其静态方法newBuilder()来获得CacheBuilder的实例
                = CacheBuilder.newBuilder()
                //设置并发级别为8，并发级别是指可以同时写缓存的线程数
                .concurrencyLevel(8)
                //设置写缓存后8秒钟过期
                .expireAfterWrite(8, TimeUnit.SECONDS)
                //设置写缓存后1秒钟刷新
                .refreshAfterWrite(1, TimeUnit.SECONDS)
                //设置缓存容器的初始容量为10
                .initialCapacity(10)
                //设置缓存最大容量为100，超过100之后就会按照LRU最近虽少使用算法来移除缓存项
                .maximumSize(100)
                //设置要统计缓存的命中率
                .recordStats()
                //设置缓存的移除通知
                .removalListener(new RemovalListener<Object, Object>() {
                    @Override
                    public void onRemoval(RemovalNotification<Object, Object> notification) {
                        System.out.println(notification.getKey() + " 被移除了，原因： " + notification.getCause());
                    }
                })
                //build方法中可以指定CacheLoader，在缓存不存在时通过CacheLoader的实现自动加载缓存
                .build(
                        new CacheLoader<String, User>() {
                            @Override
                            public User load(String key) throws Exception {
                                System.out.println("缓存没有时，从数据库加载" + key);
                                // TODO jdbc的代码~~忽略掉
                                return new User("cache" + key, key);
                            }
                        }
                );

        // 第一次读取
        for (int i = 0; i < 20; i++) {
            User user = userCache.get("uid" + i);
            System.out.println(user);
        }

        // 第二次读取
        for (int i = 0; i < 20; i++) {
            User user = userCache.get("uid" + i);
            System.out.println(user);
        }
        
        System.out.println("cache stats:");
        //最后打印缓存的命中率等 情况
        System.out.println(userCache.stats().toString());
    }
}