1、前言

Google Guava Cache是Google Guava库中的一个缓存框架，用于缓存计算结果、数据或资源，提高程序访问效率和响应速度。Guava Cache具有以下特点：

①可配置性：Guava Cache支持多种缓存参数的配置，例如缓存大小、过期时间、访问策略等，可以根据应用场景进行灵活配置。

②基于引用计数的回收策略：Guava Cache使用基于引用计数的回收策略，当缓存对象的引用计数为0时自动回收，避免了内存泄漏。

③多线程安全：Guava Cache是线程安全的，支持并发读写，保证多个线程能安全地访问和操作缓存数据。

④易于使用：Guava Cache提供简单易用的API，可以方便地进行缓存数据的读取、添加、删除和更新操作，降低了开发的难度和复杂度。

2、依赖引入

<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>32.1.2-jre</version>
</dependency>

3、缓存

3.1 LoadingCache

import com.google.common.cache.*;
import java.util.Locale;
import java.util.concurrent.TimeUnit;

public class LoadingCacheTest {

    private static final RemovalListener<String,String> listener = notification -> System.err.println("remove key:" + notification.getKey());

    private static LoadingCache<String, String> loadingCache = CacheBuilder
            .newBuilder()
            .maximumSize(2) // 缓存的个数
            .removalListener(listener) // 移除缓存时的监听事件
            .build(new CacheLoader<String, String>() {
                @Override
                public String load(String key) {  
                    return key.toUpperCase(Locale.ROOT);
                }
            });
    
    public static void main(String[] args) throws Exception {
        System.out.println("a的缓存：" + loadingCache.get("a"));
        System.out.println("b的缓存：" + loadingCache.get("b"));
        loadingCache.put("c", "C");
        System.out.println("c的缓存：" + loadingCache.get("c"));
    }

}

运行结果：

这里设置的最大缓存个数是2，当缓存第三个的时候，就会出发移除缓存的监听事件，因此结果打印了remove key。

可以设置缓存过期时间expireAfterWrite：

import com.google.common.cache.*;
import java.util.Locale;
import java.util.concurrent.TimeUnit;

public class LoadingCacheTest {

    private static final RemovalListener<String,String> listener = notification -> System.err.println("remove key:" + notification.getKey());

    private static LoadingCache<String, String> loadingCache = CacheBuilder
            .newBuilder()
            .maximumSize(5)
            .removalListener(listener)
            .expireAfterWrite(2,TimeUnit.SECONDS)
            .build(new CacheLoader<String, String>() {
                @Override
                public String load(String key) {
                    return key.toUpperCase(Locale.ROOT);
                }
            });

    public static void main(String[] args) throws Exception {
        System.out.println("a的缓存：" + loadingCache.get("a"));
        System.out.println("b的缓存：" + loadingCache.get("b"));
        Thread.sleep(3000);
        loadingCache.put("c", "C");
        System.out.println("c的缓存：" + loadingCache.get("c"));
    }

}

运行结果：

3.2 Cache

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import java.util.concurrent.ExecutionException;

public class CacheTest {

    private static Cache<String, String> cache = CacheBuilder.newBuilder().
            maximumSize(10).build();


    public static void main(String[] args) throws ExecutionException {
        cache.put("a", "A");
        System.out.println("cache key a value:" + cache.getIfPresent("a"));
        // 删除值
        cache.invalidate("a");
        System.out.println("invalidate后cache.getIfPresent(a)：" + cache.getIfPresent("a"));
        // 添加值
        cache.put("b", "B");
        System.out.println("put后cache.getIfPresent(b)：" + cache.getIfPresent("b"));
    }
}

运行结果：

Cachey也可以设置监听、过期时间等：

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

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

public class CacheTest {
    private static final RemovalListener<String,String> listener = notification -> System.err.println("remove key:" + notification.getKey());


    private static Cache<String, String> cache = CacheBuilder.newBuilder()
            .maximumSize(10)
            .expireAfterWrite(2, TimeUnit.SECONDS)
            .removalListener(listener)
            .build();


    public static void main(String[] args) throws ExecutionException, InterruptedException {
        cache.put("a", "A");
        System.out.println("cache key a value:" + cache.getIfPresent("a"));
        Thread.sleep(3000);
        // 添加值
        cache.put("b", "B");
        System.out.println("put后cache.getIfPresent(b)：" + cache.getIfPresent("b"));
    }
}

运行结果：