《ASP.NET Core技术内幕与项目实战》精简集-高级组件4.1：缓存Cache

//GetNow1未设置客户端缓存
//GetNow2通过特性标注设置了客户端缓存
//特性[ResponseCache(Duration = 60)]，告诉浏览器可以缓存数据60秒
//实质上是设置响应报文头的chche-control值为max-age=60，遵守HTTP的RFC7234规范
[ApiController]
[Route("api/[controller]/[action]")]
public class MyController: ControllerBase
{
    [HttpGet]
    public DateTime GetNow1()
    {
        return DateTime.Now;
    }

    [HttpGet]
    [ResponseCache(Duration = 60)]
    public DateTime GetNow2()
    {
        return DateTime.Now;
    }
}

//配置中间件UseResponseCaching，其它与客户端响应缓存一致
//注意中间件位置，在UseCors之后，在MapControllers之前

var app = builder.Build();
......
app.UseCors();

app.UseResponseCaching();

app.MapControllers();

app.Run();

 1 [ApiController]
 2 [Route("api/[controller]/[action]")]
 3 public class MyController: ControllerBase
 4 {
 5     private readonly MyDbContext ctx;
 6     private readonly ILogger<MyController> logger;
 7     private readonly IMemoryCache memoryCache;
 8 
 9     public MyController(MyDbContext ctx, ILogger<MyController> logger, IMemoryCache memoryCache)
10     {
11         this.ctx = ctx;
12         this.logger = logger;
13         this.memoryCache = memoryCache;
14     }
15 
16     [HttpGet]
17     public async Task<Book[]> GetBooks()
18     {
19         logger.LogInformation("开始执行GetBooks");
20         var books = await memoryCache.GetOrCreateAsync("AllBooks", async (e) =>
21         {
22             //绝对过期时间
23             e.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(30);
24             //滑动过期时间
25             e.SlidingExpiration = TimeSpan.FromSeconds(10); 
26 
27             logger.LogInformation("从数据库中读取数据");
28 
29             return await ctx.Books.ToArrayAsync();
30         });
31         logger.LogInformation("把数据返回给调用者");
32         return books;
33     }
34 }

//首先注册Redis缓存服务
builder.Services.AddStackExchangeRedisCache(opt => 
{
    opt.Configuration = "localhost"; //配置Redis数据库连接
    opt.InstanceName = "fun_"; //配置缓存键的前缀
});


//操作使用分布式缓存，和IMemoryCache相似
[ApiController]
[Route("api/[controller]/[action]")]
public class TestController : ControllerBase
{
    //注入IDistributedCache服务
    private readonly IDistributedCache disCache
    public TestController(IDistributedCache disCache)
    {
        this.disCache = disCache;
    }
    
    [HttpGet]
    public string Now()
    {
        //获取缓存键为“Now”的值
        string s = disCache.GetString("Now");
        //如果键值为空，则获取s值，并缓存数据，过期时间设置为30秒
        if(s == null)
        {
            s = DateTime.Now.ToString();
            //设置过期时间
            var opt = new DistributedCacheEntryOptions();
            opt.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(30);
            //缓存数据
            disCache.SetString("Now", s, opt);
        }
        return s;
    }
}