.NET 缓存：内存缓存 IMemoryCache、分布式缓存 IDistributedCache（Redis）

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.NET缓存里分了几类，主要学习内存缓存、分布式缓存

一、内存缓存 IMemoryCache

1、Program注入缓存

builder.Services.AddMemoryCache();

2、相关方法及参数

Get、TryGetValue、GetOrCreate、GetOrCreateAsync、Set、Remove，关键参数是过期时间，GetOrCreate、GetOrCreateAsync是通过委托类型的参数设置的，Set方法可以通过参数直接设置，或者使用MemoryCacheEntryOptions，类型有三种：（1）AbsoluteExpiration 绝对过期，到期删除（2）AbsoluteExpirationRelativeToNow 相对当前时间过期，到期删除（3）SlidingExpiration 滑动过期，时效内访问再延长，未访问到期删除

[Route("api/[controller]/[action]")]
[ApiController]
public class MemoryCacheController : ControllerBase
{
    private readonly IMemoryCache _memoryCache;
    private readonly string cacheKey = "cache";
    public MemoryCacheController(IMemoryCache memoryCache)
    {
        _memoryCache = memoryCache;
    }

    [HttpGet]
    public string Get()
    {
        var value = _memoryCache.Get(cacheKey);
        return value == null ? "null" : value.ToString();
    }

    [HttpGet]
    public string TryGetValue()
    {
        if (_memoryCache.TryGetValue(cacheKey, out string value))
            return value;
        return "null";
    }

    [HttpGet]
    public string GetOrCreate()
    {
        var value = _memoryCache.GetOrCreate(
            cacheKey,
            cacheEntry =>
             {
                 cacheEntry.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(3);
                 return "GetOrCreate：" + DateTime.Now.ToString("T");
             });
        return value;
    }

    [HttpGet]
    public async Task<string> GetOrCreateAsync()
    {
        var value = await _memoryCache.GetOrCreateAsync(
            cacheKey,
            cacheEntry =>
            {
                cacheEntry.SlidingExpiration = TimeSpan.FromSeconds(3);
                return Task.FromResult("GetOrCreateAsync：" + DateTime.Now.ToString("T"));
            });
        return value;
    }

    [HttpPost]
    public void Set()
    {
        string value = "Set：" + DateTime.Now.ToString("T");

        MemoryCacheEntryOptions op = new MemoryCacheEntryOptions();

        //绝对到期，到期删除
        op.AbsoluteExpiration = DateTimeOffset.Parse("2023-12-31 23:59:59");
        //_memoryCache.Set(cacheKey, value, DateTimeOffset.Parse("2023-12-31 23:59:59"));

        //相对当前时间过期，到期删除
        op.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(10);
        //_memoryCache.Set(cacheKey, value, TimeSpan.FromSeconds(10));

        //滑动过期，时效内访问再延长，未访问到期删除
        op.SlidingExpiration = TimeSpan.FromSeconds(10);

        _memoryCache.Set(cacheKey, value, op);
    }

    [HttpDelete]
    public void Remove()
    {
        _memoryCache.Remove(cacheKey);
    }
}

二、分布式缓存 IDistributedCache

工欲善其事，必先利其器——>Redis安装

1、Program注入缓存

（1）先安装Nuget：Microsoft.Extensions.Caching.StackExchangeRedis（2）appsettings.json配置Redis连接

"Redis": "39.107.109.17:6379,password=shenhuak1"

（3）Program注入

//Redis分布式缓存
builder.Services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = builder.Configuration["Redis"];
    options.InstanceName = "RedisInstance";//实例名，配置后实际的key=InstanceName+key
});

2、相关方法及参数

IDistributedCache 接口提供方法：Get、GetAsync、Set、SetAsync、Refresh、RefreshAsync、Remove、RemoveAsync以及拓展方法：GetString、GetStringAsync、SetString、SetStringAsync过期参数跟内存缓存差不多，直接看代码

[Route("api/[controller]/[action]")]
[ApiController]
public class DistributedController : ControllerBase
{
    private readonly IDistributedCache _distributedCache;
    private readonly string cacheKey = "cache";
    public DistributedController(IDistributedCache distributedCache)
    {
        _distributedCache = distributedCache;
    }

    [HttpGet]
    public string Get()
    {
        return _distributedCache.GetString(cacheKey);
    }

    [HttpGet]
    public async Task<string> GetAsync()
    {
        return await _distributedCache.GetStringAsync(cacheKey);
    }

    [HttpPost]
    public void Set()
    {
        DistributedCacheEntryOptions op = new DistributedCacheEntryOptions();

        //绝对过期，到期删除
        op.AbsoluteExpiration = DateTimeOffset.Parse("2023-12-31 23:59:59");//op.SetAbsoluteExpiration(DateTimeOffset.Parse("2023-12-31 23:59:59"));

        //相对当前时间过期，到期删除
        op.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(10);//op.SetAbsoluteExpiration(TimeSpan.FromSeconds(10));

        //滑动过期，时效内访问再延长，未访问到期删除
        op.SlidingExpiration = TimeSpan.FromSeconds(10);//op.SetSlidingExpiration(TimeSpan.FromSeconds(10));

        _distributedCache.SetString(cacheKey, DateTime.Now.ToString("T"), op);
    }

    [HttpPost]
    public async Task SetAsync()
    {
        await _distributedCache.SetStringAsync(cacheKey, DateTime.Now.ToString("T"));
    }

    [HttpPost]
    public void Refresh()
    {
        _distributedCache.Refresh(cacheKey);
    }

    [HttpPost]
    public async Task RefreshAsync()
    {
        await _distributedCache.RefreshAsync(cacheKey);
    }

    [HttpDelete]
    public void Remove()
    {
        _distributedCache.Remove(cacheKey);
    }

    [HttpDelete]
    public async void RemoveAsync()
    {
        await _distributedCache.RemoveAsync(cacheKey);
    }
}

3、总结

非拓展方法是都是通过byte[]字节数组来向Redis存取数据的不方便，大多情况都会自己封装一个helper类。拓展方法虽然用string类型操作，实际存储到Redis是用的Hash类型，无法操作Redis其他类型及功能。完整功能需要使用其他客户端：StackExchange.Redis、FreeRedis、NRedisStack 等

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