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解读ASP.NET 5 & MVC6系列教程(8):Session与Caching

2024-07-10 13:30:49
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在之前的版本中,Session存在于System.Web中,新版ASP.NET 5中由于不在依赖于System.Web.dll库了,所以相应的,Session也就成了ASP.NET 5中一个可配置的模块(middleware)了。

配置启用Session

ASP.NET 5中的Session模块存在于Microsoft.AspNet.Session类库中,要启用Session,首先需要在project.json中的dependencies节点中添加如下内容:

"Microsoft.AspNet.Session": "1.0.0-beta3"

然后在ConfigureServices中添加Session的引用(并进行配置):

services.AddCaching(); // 这两个必须同时添加,因为Session依赖于Cachingservices.AddSession();//services.ConfigureSession(null); 可以在这里配置,也可以再后面进行配置

最后在Configure方法中,开启使用Session的模式,如果在上面已经配置过了,则可以不再传入配置信息,否则还是要像上面的配置信息一样,传入Session的配置信息,代码如下:

app.UseInMemorySession(configure:s => { s.IdleTimeout = TimeSpan.FromMinutes(30); });//app.UseSession(o => { o.IdleTimeout = TimeSpan.FromSeconds(30); });//app.UseInMemorySession(null, null); //开启内存Session//app.UseDistributedSession(null, null);//开启分布式Session,也即持久化Session//app.UseDistributedSession(new RedisCache(new RedisCacheOptions() { Configuration = "localhost" }));

对于UseInMemorySession方法,接收2个可选参数,分别是:IMemoryCache可用于修改Session数据的默认保存地址;Action<SessionOptions>委托则可以让你修改默认选项,比如Session cookie的路径、默认的过期时间等。本例中,我们修改默认过期时间为30分钟。

注意:该方法必须在app.UseMvc之前调用,否则在Mvc里获取不到Session,而且会出错。

获取和设置Session

获取和设置Session对象,一般是在Controller的action里通过this.Context.Session来获取的,其获取的是一个基于接口ISessionCollection的实例。该接口可以通过索引、Set、TryGetValue等方法进行Session值的获取和设置,但我们发现在获取和设置Session的时候,我们只能使用byte[]类型,而不能像之前版本的Session一样可以设置任意类型的数据。原因是因为,新版本的Session要支持在远程服务器上存储,就需要支持序列化,所以才强制要求保存为byte[]类型。所以我们在保存Session的时候,需要将其转换为byte[]才能进行保存,并且获取以后要再次将byte[]转换为自己的原有的类型才行。这种形式太麻烦了,好在微软在Microsoft.AspNet.Http命名空间(所属Microsoft.AspNet.Http.Extensions.dll中)下,为我们添加了几个扩展方法,分别用于设置和保存byte[]类型、int类型、以及string类型,代码如下:

public static byte[] Get(this ISessionCollection session, string key);public static int? GetInt(this ISessionCollection session, string key);public static string GetString(this ISessionCollection session, string key);public static void Set(this ISessionCollection session, string key, byte[] value);public static void SetInt(this ISessionCollection session, string key, int value);public static void SetString(this ISessionCollection session, string key, string value);

所以,在Controller里引用Microsoft.AspNet.Http命名空间以后,我们就可以通过如下代码进行Session的设置和获取了:

Context.Session.SetString("Name", "Mike");Context.Session.SetInt("Age", 21);ViewBag.Name = Context.Session.GetString("Name");ViewBag.Age = Context.Session.GetInt("Age");

自定义类型的Session设置和获取

前面我们说了,要保存自定义类型的Session,需要将其类型转换成byte[]数组才行,在本例中,我们对bool类型的Session数据进行设置和获取的代码,示例如下:

public static class SessionExtensions{ public static bool? GetBoolean(this ISessionCollection session, string key) {  var data = session.Get(key);  if (data == null)  {   return null;  }  return BitConverter.ToBoolean(data, 0); }  public static void SetBoolean(this ISessionCollection session, string key, bool value) {  session.Set(key, BitConverter.GetBytes(value)); }}

 

定义bool类型的扩展方法以后,我们就可以像SetInt/GetInt那样进行使用了,示例如下:

Context.Session.SetBoolean("Liar", true);ViewBag.Liar = Context.Session.GetBoolean("Liar");

另外,ISessionCollection接口上还提供了Remove(string key)和Clear()两个方法分别用于删除某个Session值和清空所有的Session值的功能。但同时也需要注意,该接口并没提供之前版本中的Abandon方法功能。

基于Redis的Session管理

使用分布式Session,其主要工作就是将Session保存的地方从原来的内存换到分布式存储上,本节,我们以Redis存储为例来讲解分布式Session的处理。

先查看使用分布式Session的扩展方法,示例如下,我们可以看到,其Session容器需要是一个支持IDistributedCache的接口示例。

public static IApplicationBuilder UseDistributedSession([NotNullAttribute]this IApplicationBuilder app, IDistributedCache cache, Action<SessionOptions> configure = null);

该接口是缓存Caching的通用接口,也就是说,只要我们实现了缓存接口,就可以将其用于Session的管理。进一步查看该接口发现,该接口中定义的Set方法还需要实现一个ICacheContext类型的缓存上下文(以便在调用的时候让其它程序进行委托调用),接口定义分别如下:

public interface IDistributedCache{ void Connect(); void Refresh(string key); void Remove(string key); Stream Set(string key, object state, Action<ICacheContext> create); bool TryGetValue(string key, out Stream value);}public interface ICacheContext{ Stream Data { get; } string Key { get; } object State { get; } void SetAbsoluteExpiration(TimeSpan relative); void SetAbsoluteExpiration(DateTimeOffset absolute); void SetSlidingExpiration(TimeSpan offset);}

接下来,我们基于Redis来实现上述功能,创建RedisCache类,并继承IDistributedCache,引用StackExchange.Redis程序集,然后实现IDistributedCache接口的所有方法和属性,代码如下:

using Microsoft.Framework.Cache.Distributed;using Microsoft.Framework.OptionsModel;using StackExchange.Redis;using System;using System.IO;namespace Microsoft.Framework.Caching.Redis{ public class RedisCache : IDistributedCache {  // KEYS[1] = = key  // ARGV[1] = absolute-expiration - ticks as long (-1 for none)  // ARGV[2] = sliding-expiration - ticks as long (-1 for none)  // ARGV[3] = relative-expiration (long, in seconds, -1 for none) - Min(absolute-expiration - Now, sliding-expiration)  // ARGV[4] = data - byte[]  // this order should not change LUA script depends on it  private const string SetScript = (@"    redis.call('HMSET', KEYS[1], 'absexp', ARGV[1], 'sldexp', ARGV[2], 'data', ARGV[4])    if ARGV[3] ~= '-1' then     redis.call('EXPIRE', KEYS[1], ARGV[3])     end    return 1");  private const string AbsoluteExpirationKey = "absexp";  private const string SlidingExpirationKey = "sldexp";  private const string DataKey = "data";  private const long NotPresent = -1;  private ConnectionMultiplexer _connection;  private IDatabase _cache;  private readonly RedisCacheOptions _options;  private readonly string _instance;  public RedisCache(IOptions<RedisCacheOptions> optionsAccessor)  {   _options = optionsAccessor.Options;   // This allows partitioning a single backend cache for use with multiple apps/services.   _instance = _options.InstanceName ?? string.Empty;  }  public void Connect()  {   if (_connection == null)   {    _connection = ConnectionMultiplexer.Connect(_options.Configuration);    _cache = _connection.GetDatabase();   }  }  public Stream Set(string key, object state, Action<ICacheContext> create)  {   Connect();   var context = new CacheContext(key) { State = state };   create(context);   var value = context.GetBytes();   var result = _cache.ScriptEvaluate(SetScript, new RedisKey[] { _instance + key },    new RedisValue[]    {     context.AbsoluteExpiration?.Ticks ?? NotPresent,     context.SlidingExpiration?.Ticks ?? NotPresent,     context.GetExpirationInSeconds() ?? NotPresent,     value    });   // TODO: Error handling   return new MemoryStream(value, writable: false);  }  public bool TryGetValue(string key, out Stream value)  {   value = GetAndRefresh(key, getData: true);   return value != null;  }  public void Refresh(string key)  {   var ignored = GetAndRefresh(key, getData: false);  }  private Stream GetAndRefresh(string key, bool getData)  {   Connect();   // This also resets the LRU status as desired.   // TODO: Can this be done in one operation on the server side? Probably, the trick would just be the DateTimeOffset math.   RedisValue[] results;   if (getData)   {    results = _cache.HashMemberGet(_instance + key, AbsoluteExpirationKey, SlidingExpirationKey, DataKey);   }   else   {    results = _cache.HashMemberGet(_instance + key, AbsoluteExpirationKey, SlidingExpirationKey);   }   // TODO: Error handling   if (results.Length >= 2)   {    // Note we always get back two results, even if they are all null.    // These operations will no-op in the null scenario.    DateTimeOffset? absExpr;    TimeSpan? sldExpr;    MapMetadata(results, out absExpr, out sldExpr);    Refresh(key, absExpr, sldExpr);   }   if (results.Length >= 3 && results[2].HasValue)   {    return new MemoryStream(results[2], writable: false);   }   return null;  }  private void MapMetadata(RedisValue[] results, out DateTimeOffset? absoluteExpiration, out TimeSpan? slidingExpiration)  {   absoluteExpiration = null;   slidingExpiration = null;   var absoluteExpirationTicks = (long?)results[0];   if (absoluteExpirationTicks.HasValue && absoluteExpirationTicks.Value != NotPresent)   {    absoluteExpiration = new DateTimeOffset(absoluteExpirationTicks.Value, TimeSpan.Zero);   }   var slidingExpirationTicks = (long?)results[1];   if (slidingExpirationTicks.HasValue && slidingExpirationTicks.Value != NotPresent)   {    slidingExpiration = new TimeSpan(slidingExpirationTicks.Value);   }  }  private void Refresh(string key, DateTimeOffset? absExpr, TimeSpan? sldExpr)  {   // Note Refresh has no effect if there is just an absolute expiration (or neither).   TimeSpan? expr = null;   if (sldExpr.HasValue)   {    if (absExpr.HasValue)    {     var relExpr = absExpr.Value - DateTimeOffset.Now;     expr = relExpr <= sldExpr.Value ? relExpr : sldExpr;    }    else    {     expr = sldExpr;    }    _cache.KeyExpire(_instance + key, expr);    // TODO: Error handling   }  }  public void Remove(string key)  {   Connect();   _cache.KeyDelete(_instance + key);   // TODO: Error handling  } }}

在上述代码中,我们使用了自定义类RedisCacheOptions作为Redis的配置信息类,为了实现基于POCO的配置定义,我们还继承了IOptions接口,该类的定义如下:

public class RedisCacheOptions : IOptions<RedisCacheOptions>{ public string Configuration { get; set; } public string InstanceName { get; set; } RedisCacheOptions IOptions<RedisCacheOptions>.Options {  get { return this; } } RedisCacheOptions IOptions<RedisCacheOptions>.GetNamedOptions(string name) {  return this; }}

第三部,定义委托调用时使用的缓存上下文类CacheContext,具体代码如下:

using Microsoft.Framework.Cache.Distributed;using System;using System.IO;namespace Microsoft.Framework.Caching.Redis{ internal class CacheContext : ICacheContext {  private readonly MemoryStream _data = new MemoryStream();  internal CacheContext(string key)  {   Key = key;   CreationTime = DateTimeOffset.UtcNow;  }  /// <summary>  /// The key identifying this entry.  /// </summary>  public string Key { get; internal set; }  /// <summary>  /// The state passed into Set. This can be used to avoid closures.  /// </summary>  public object State { get; internal set; }  public Stream Data { get { return _data; } }  internal DateTimeOffset CreationTime { get; set; } // 可以让委托设置创建时间  internal DateTimeOffset? AbsoluteExpiration { get; private set; }  internal TimeSpan? SlidingExpiration { get; private set; }  public void SetAbsoluteExpiration(TimeSpan relative) // 可以让委托设置相对过期时间  {   if (relative <= TimeSpan.Zero)   {    throw new ArgumentOutOfRangeException("relative", relative, "The relative expiration value must be positive.");   }   AbsoluteExpiration = CreationTime + relative;  }  public void SetAbsoluteExpiration(DateTimeOffset absolute) // 可以让委托设置绝对过期时间  {   if (absolute <= CreationTime)   {    throw new ArgumentOutOfRangeException("absolute", absolute, "The absolute expiration value must be in the future.");   }   AbsoluteExpiration = absolute.ToUniversalTime();  }  public void SetSlidingExpiration(TimeSpan offset) // 可以让委托设置offset过期时间  {   if (offset <= TimeSpan.Zero)   {    throw new ArgumentOutOfRangeException("offset", offset, "The sliding expiration value must be positive.");   }   SlidingExpiration = offset;  }  internal long? GetExpirationInSeconds()  {   if (AbsoluteExpiration.HasValue && SlidingExpiration.HasValue)   {    return (long)Math.Min((AbsoluteExpiration.Value - CreationTime).TotalSeconds, SlidingExpiration.Value.TotalSeconds);   }   else if (AbsoluteExpiration.HasValue)   {    return (long)(AbsoluteExpiration.Value - CreationTime).TotalSeconds;   }   else if (SlidingExpiration.HasValue)   {    return (long)SlidingExpiration.Value.TotalSeconds;   }   return null;  }  internal byte[] GetBytes()  {   return _data.ToArray();  } }}

最后一步定义,RedisCache中需要的根据key键获取缓存值的快捷方法,代码如下:

using StackExchange.Redis;using System;namespace Microsoft.Framework.Caching.Redis{ internal static class RedisExtensions {  private const string HmGetScript = (@"return redis.call('HMGET', KEYS[1], unpack(ARGV))");  internal static RedisValue[] HashMemberGet(this IDatabase cache, string key, params string[] members)  {   var redisMembers = new RedisValue[members.Length];   for (int i = 0; i < members.Length; i++)   {    redisMembers[i] = (RedisValue)members[i];   }   var result = cache.ScriptEvaluate(HmGetScript, new RedisKey[] { key }, redisMembers);   // TODO: Error checking?   return (RedisValue[])result;  } }}

至此,所有的工作就完成了,将该缓存实现注册为Session的provider的代码方法如下:

app.UseDistributedSession(new RedisCache(new RedisCacheOptions(){ Configuration = "此处填写 redis的地址", InstanceName = "此处填写自定义实例名"}), options =>{ options.CookieHttpOnly = true;});

参考:http://www.mikesdotnetting.com/article/270/sessions-in-asp-net-5

关于Caching

默认情况下,本地缓存使用的是IMemoryCache接口的示例,可以通过获取该接口的示例来对本地缓存进行操作,示例代码如下:

var cache = app.ApplicationServices.GetRequiredService<IMemoryCache>();var obj1 = cache.Get("key1");bool obj2 = cache.Get<bool>("key2");

对于,分布式缓存,由于AddCaching,默认将IMemoryCache实例作为分布式缓存的provider了,代码如下:

public static class CachingServicesExtensions{ public static IServiceCollection AddCaching(this IServiceCollection collection) {  collection.AddOptions();  return collection.AddTransient<IDistributedCache, LocalCache>()   .AddSingleton<IMemoryCache, MemoryCache>(); }}

所以,要使用新的分布式Caching实现,我们需要注册自己的实现,代码如下:

services.AddTransient<IDistributedCache, RedisCache>();services.Configure<RedisCacheOptions>(opt =>{ opt.Configuration = "此处填写 redis的地址"; opt.InstanceName = "此处填写自定义实例名";});

基本的使用方法如下:

var cache = app.ApplicationServices.GetRequiredService<IDistributedCache>();cache.Connect();var obj1 = cache.Get("key1"); //该对象是流,需要将其转换为强类型,或自己再编写扩展方法var bytes = obj1.ReadAllBytes();


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