[Asp.net 5] Configuration-新一代的配置文件（接口定义与基础实现）

关于配置文件的目录：[Asp.net 5] Configuration-新一代的配置文件

本系列文章讲的是asp.net 5(Asp.net VNext)中的配置文件部分，工程下载地址为：https://github.com/aspnet/Configuration

本节讲的是Configuration解决方案中的Microsoft.Framework.Configuration和Microsoft.Framework.Configuration.Abstractions俩个工程。

Abstractions

首先我们看下Configuration.Abstractions这个工程的详情：

该工程中只定义了三个接口：IConfiguration、IConfigurationBuilder、IConfigurationSource，是完全为了抽象而设计的工程。

我们在依赖注入（DependencyInjection）篇中也接触过名字为“Abstractions”的工程（链接地址：http://www.cnblogs.com/watermoon2/p/4511269.html），也是只包含必须的接口定义，我们可以推测，微软的命名规则是对于XXXX类工程：

• Microsoft.Framework.XXXX.Abstractions：定义微软XXXX的必须的抽象
• Microsoft.Framework.XXXX：定义微软的XXXX的基础实现，内部类多实现Microsoft.Framework.XXXX.Abstractions中接口

配置文件中，肯定少不了配置文件类的基础接口定义：IConfiguration；我们知道新的配置文件实现，支持配置文件有多个来源，可以来自xml、可以来自json、也可以既有部分来自xml，又有部分来自json，所以接口中定义了“IConfigurationSource”接口，用于标示配置文件的来源；而IConfigurationBuilder是IConfiguration的构造器。

这个工程代码比较少，下面我就将接口定义罗列如下：

public interface IConfigurationSource
    {
        bool TryGet(string key, out string value);

        void Set(string key, string value);

        void Load();

        IEnumerable<string> ProduceConfigurationSections(
            IEnumerable<string> earlierKeys,
            string prefix,
            string delimiter);
    }
 public interface IConfigurationBuilder
    {
        string BasePath { get; }

        IEnumerable<IConfigurationSource> Sources { get; }

        IConfigurationBuilder Add(IConfigurationSource configurationSource);

        IConfiguration Build();
    }

public interface IConfiguration
    {
        string this[string key] { get; set; }

        string Get(string key);

        bool TryGet(string key, out string value);

        IConfiguration GetConfigurationSection(string key);

        IEnumerable<KeyValuePair<string, IConfiguration>> GetConfigurationSections();

        IEnumerable<KeyValuePair<string, IConfiguration>> GetConfigurationSections(string key);

        void Set(string key, string value);

        void Reload();
    }

接口定义

Configuration

我们还是将工程的详情列出：

工程中一共八个cs文件：

1，IConfigurationSource实现类：ConfigurationSource、MemoryConfigurationSource

2，IConfigurationBuilder实现类：ConfigurationBuilder；IConfigurationBuilder扩展方法：ConfigurationHelper

3，IConfiguration实现类：ConfigurationSection、ConfigurationFocus

4，帮助辅助类：ConfigurationKeyComparer、Constants。

一个约定：":"

我们知道配置文件不都是线性的，可能有层次结构（比如传统的配置文件、json的、xml的）。我们读取配置文件的key值就需要有一定的逻辑。现在的逻辑是:

• 根节点对象：“当前key”
• 非根节点对象：“前缀”+“分隔符”+“当前key"（前缀是当前节点父节点的key值）

所以对于如下的json格式{"root1":"r1","root2":{"sub1":"s2"}}，想要获取值是“s2”，所使用的key值是“root2:sub1”；“root2”是父节点的key，“:”是分隔符，“sub1”是当前key。

在这里的分隔符，其实就是定义在Constants类中，public static readonly string KeyDelimiter = ":"; 不过源文件中其他部分并未都直接使用该处定义，在IConfigurationSource的派生类也都是自己定义的“:”；所以想修改分隔符，在现有代码中不是能够只修改Constants中这个全局变量就可以的。所以在源码还有问题的时候，我们还是把分隔符=“:”，作为一个约定（不要试图把分隔符该城其他字符串）。

特殊的排序方式

由于当前key值得字符串可能是由存数字组成，我们希望key值为“1”，“2”，“10”的顺序是“1”，“2”，“10” 而不是“1”，“10”，“2”（字符串默认排序的顺序），所以系统在排序的时候使用了IComparer<string>接口。而IComparer<string>接口的实现类就是ConfigurationKeyComparer。

public class ConfigurationKeyComparer : IComparer<string>
    {
        private const char Separator = ':';

        public static ConfigurationKeyComparer Instance { get; } = new ConfigurationKeyComparer();

        public int Compare(string x, string y)
        {
            var xParts = x?.Split(Separator) ?? new string[];
            var yParts = y?.Split(Separator) ?? new string[];

            // Compare each part until we get two parts that are not equal
            for (int i = ; i < Math.Min(xParts.Length, yParts.Length); i++)
            {
                x = xParts[i];
                y = yParts[i];

                var value1 = ;
                var value2 = ;

                var xIsInt = x != null && int.TryParse(x, out value1);
                var yIsInt = y != null && int.TryParse(y, out value2);

                int result = ;

                if (!xIsInt && !yIsInt)
                {
                    // Both are strings
                    result = string.Compare(x, y, StringComparison.OrdinalIgnoreCase);
                }
                else if (xIsInt && yIsInt)
                {
                    // Both are int
                    result = value1 - value2;
                }
                else
                {
                    // Only one of them is int
                    result = xIsInt ? - : ;
                }

                if (result != )
                {
                    // One of them is different
                    return result;
                }
            }

            // If we get here, the common parts are equal.
            // If they are of the same length, then they are totally identical
            return xParts.Length - yParts.Length;
        }
    }

ConfigurationKeyComparer

前面的铺垫已经讲完，下面我们进入正文：
ConfigurationBuilder以及ConfigurationHelper

ConfigurationBuilder的功能主要有四点：

• 能够设置加载的IConfigurationSource源路径目录
• 能够管理的IConfigurationSource列表
• 能够加载IConfigurationSource
• 能够创建IConfiguration

代码中需要注意的也就只有一点：添加新的IConfigurationSource时，首先加载，之后再将IConfigurationSource对象添加到内部IConfigurationSource列表中。

ConfigurationHelper是ConfigurationBuilder的扩展，作用只有一个：

• 将如果传入路径是相对路径，将IConfigurationSource源路径目录和传入路径进行合并。

ConfigurationBuilder以及ConfigurationHelper源码如下：

public class ConfigurationBuilder : IConfigurationBuilder
    {
        private readonly IList<IConfigurationSource> _sources = new List<IConfigurationSource>();

        public ConfigurationBuilder(params IConfigurationSource[] sources)
            : this(null, sources)
        {
        }

        public ConfigurationBuilder(string basePath, params IConfigurationSource[] sources)
        {
            if (sources != null)
            {
                foreach (var singleSource in sources)
                {
                    Add(singleSource);
                }
            }

            BasePath = basePath;
        }

        public IEnumerable<IConfigurationSource> Sources
        {
            get
            {
                return _sources;
            }
        }

        public string BasePath
        {
            get;
        }

        public IConfigurationBuilder Add(IConfigurationSource configurationSource)
        {
            return Add(configurationSource, load: true);
        }

        public IConfigurationBuilder Add(IConfigurationSource configurationSource, bool load)
        {
            if (load)
            {
                configurationSource.Load();
            }
            _sources.Add(configurationSource);
            return this;
        }

        public IConfiguration Build()
        {
            return new ConfigurationSection(_sources);
        }
    }

ConfigurationBuilder

 public static class ConfigurationHelper
    {
        public static string ResolveConfigurationFilePath(IConfigurationBuilder configuration, string path)
        {
            if (!Path.IsPathRooted(path))
            {
                if (configuration.BasePath == null)
                {
                    throw new InvalidOperationException(Resources.FormatError_MissingBasePath(
                        path,
                        typeof(IConfigurationBuilder).Name,
                        nameof(configuration.BasePath)));
                }
                else
                {
                    path = Path.Combine(configuration.BasePath, path);
                }
            }

            return path;
        }
    }

ConfigurationHelper

ConfigurationSource和MemoryConfigurationSource

ConfigurationSource实现了IConfigurationSource接口，是其他具体的IConfigurationSource父类，该类是抽象类，不能直接实例化。

该类主要提供以下几个功能：

• 用字典表保存key，value；并且提供get/set方法
• 提供load方法（该类中是空的虚方法）
• 给定制定前缀，获取该前缀下的子key（如：对于key值包含如下{“p1”，“p1:p2”，“p1:p3:p4”，“s1”}，则通过“p1”可以获取到p2、p3）

MemoryConfigurationSource类继承自ConfigurationSource，提供了额外的方法：获取整个字典表。

[ConfigurationSource是扩展配置文件类型的基类，系统中就是通过继承自该类，实现xml以及json格式的配置文件类型]

public abstract class ConfigurationSource : IConfigurationSource
    {
        protected ConfigurationSource()
        {
            Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        }

        protected IDictionary<string, string> Data { get; set; }

        public virtual bool TryGet(string key, out string value)
        {
            return Data.TryGetValue(key, out value);
        }

        public virtual void Set(string key, string value)
        {
            Data[key] = value;
        }

        public virtual void Load()
        {
        }

        public virtual IEnumerable<string> ProduceConfigurationSections(
            IEnumerable<string> earlierKeys,
            string prefix,
            string delimiter)
        {
            return Data
                .Where(kv => kv.Key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
                .Select(kv => Segment(kv.Key, prefix, delimiter))
                .Concat(earlierKeys)
                .OrderBy(k => k, ConfigurationKeyComparer.Instance);
        }

        private static string Segment(string key, string prefix, string delimiter)
        {
            var indexOf = key.IndexOf(delimiter, prefix.Length, StringComparison.OrdinalIgnoreCase);
            return indexOf <  ? key.Substring(prefix.Length) : key.Substring(prefix.Length, indexOf - prefix.Length);
        }
    }

ConfigurationSource

public class MemoryConfigurationSource :
        ConfigurationSource,
        IEnumerable<KeyValuePair<string,string>>
    {
        public MemoryConfigurationSource()
        {
        }

        public MemoryConfigurationSource(IEnumerable<KeyValuePair<string, string>> initialData)
        {
            foreach (var pair in initialData)
            {
                Data.Add(pair.Key, pair.Value);
            }
        }

        public void Add(string key, string value)
        {
            Data.Add(key, value);
        }

        public IEnumerator<KeyValuePair<string, string>> GetEnumerator()
        {
            return Data.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
    }

MemoryConfigurationSource

ConfigurationSection和ConfigurationFocus

这两个类是双生类，使用了代理模式：通过GetConfigurationSection等获取IConfiguration方法返回的是ConfigurationFocus代理的ConfigurationSection(ConfigurationBuilder创建的是ConfigurationSection类)。简单的类关系图如下所示：(ConfigurationFocus不会和ConfigurationSource产生关联，会通过ConfigurationSection进行访问)

ConfigurationSection类实现的主要功能：

• 根据key值获取配置信息（包含key值的IConfigurationSource中，ConfigurationBuilder最后添加的IConfigurationSource对象的key值所对应的value值）
• 根据key值设置配置信息（所有IConfigurationSource文件都会被更新，最后信息不是保存在ConfigurationSection中，而是直接反应在IConfigurationSource上）
• 重新加载配置源（IConfigurationSource）
• 根据key值（可以为空）获取<string, IConfiguration>对应的字典表。（系统构建的IConfiguration就是ConfigurationFocus类型）

ConfigurationFocus实现的主要功能：

• 内部封装ConfigurationSection对象
• 内部封装当前的前缀信息
• 根据内部封装的前缀信息+key构造新的key值，之后通过ConfigurationSection获取新key值配置信息/设置新key配置信息
• 根据内部封装的前缀信息+key构造新的key值，之后通过ConfigurationSection获取新key配置信息。（当前配置信息下一级为key的配置信息）
• 根据内部封装的前缀信息+key构造新的key值，之后通过ConfigurationSection获取子<string, IConfiguration>对应的字典表。（当先配置信息下一级为key的配置信息的所有子配置信息）

public class ConfigurationSection : IConfiguration
    {
        private readonly IList<IConfigurationSource> _sources = new List<IConfigurationSource>();

        public ConfigurationSection(IList<IConfigurationSource> sources)
        {
            _sources = sources;
        }

        public string this[string key]
        {
            get
            {
                return Get(key);
            }
            set
            {
                Set(key, value);
            }
        }

        public IEnumerable<IConfigurationSource> Sources
        {
            get
            {
                return _sources;
            }
        }

        public string Get([NotNull] string key)
        {
            string value;
            return TryGet(key, out value) ? value : null;
        }

        public bool TryGet([NotNull] string key, out string value)
        {
            // If a key in the newly added configuration source is identical to a key in a
            // formerly added configuration source, the new one overrides the former one.
            // So we search in reverse order, starting with latest configuration source.
            foreach (var src in _sources.Reverse())
            {
                if (src.TryGet(key, out value))
                {
                    return true;
                }
            }
            value = null;
            return false;
        }

        public void Set([NotNull] string key, [NotNull] string value)
        {
            if (!_sources.Any())
            {
                throw new InvalidOperationException(Resources.Error_NoSources);
            }
            foreach (var src in _sources)
            {
                src.Set(key, value);
            }
        }

        public void Reload()
        {
            foreach (var src in _sources)
            {
                src.Load();
            }
        }

        public IConfiguration GetConfigurationSection(string key)
        {
            return new ConfigurationFocus(this, key + Constants.KeyDelimiter);
        }

        public IEnumerable<KeyValuePair<string, IConfiguration>> GetConfigurationSections()
        {
            return GetConfigurationSectionsImplementation(string.Empty);
        }

        public IEnumerable<KeyValuePair<string, IConfiguration>> GetConfigurationSections([NotNull] string key)
        {
            return GetConfigurationSectionsImplementation(key + Constants.KeyDelimiter);
        }

        private IEnumerable<KeyValuePair<string, IConfiguration>> GetConfigurationSectionsImplementation(string prefix)
        {
            var segments = _sources.Aggregate(
                Enumerable.Empty<string>(),
                (seed, source) => source.ProduceConfigurationSections(seed, prefix, Constants.KeyDelimiter));

            var distinctSegments = segments.Distinct();

            return distinctSegments.Select(segment => CreateConfigurationFocus(prefix, segment));
        }

        private KeyValuePair<string, IConfiguration> CreateConfigurationFocus(string prefix, string segment)
        {
            return new KeyValuePair<string, IConfiguration>(
                segment,
                new ConfigurationFocus(this, prefix + segment + Constants.KeyDelimiter));
        }
    }

ConfigurationSection

public class ConfigurationFocus : IConfiguration
    {
        private readonly string _prefix;
        private readonly IConfiguration _root;

        public ConfigurationFocus(IConfiguration root, string prefix)
        {
            _prefix = prefix;
            _root = root;
        }

        public string this[string key]
        {
            get
            {
                return Get(key);
            }
            set
            {
                Set(key, value);
            }
        }

        public string Get(string key)
        {
            // Null key indicates that the prefix passed to ctor should be used as a key
            if (key == null)
            {
                // Strip off the trailing colon to get a valid key
                var defaultKey = _prefix.Substring(, _prefix.Length - );
                return _root.Get(defaultKey);
            }

            return _root.Get(_prefix + key);
        }

        public bool TryGet(string key, out string value)
        {
            // Null key indicates that the prefix passed to ctor should be used as a key
            if (key == null)
            {
                // Strip off the trailing colon to get a valid key
                var defaultKey = _prefix.Substring(, _prefix.Length - );
                return _root.TryGet(defaultKey, out value);
            }
            return _root.TryGet(_prefix + key, out value);
        }

        public IConfiguration GetConfigurationSection(string key)
        {
            return _root.GetConfigurationSection(_prefix + key);
        }

        public void Set(string key, string value)
        {
            _root.Set(_prefix + key, value);
        }

        public IEnumerable<KeyValuePair<string, IConfiguration>> GetConfigurationSections()
        {
            return _root.GetConfigurationSections(_prefix.Substring(, _prefix.Length - ));
        }

        public IEnumerable<KeyValuePair<string, IConfiguration>> GetConfigurationSections(string key)
        {
            return _root.GetConfigurationSections(_prefix + key);
        }

        public void Reload()
        {
            throw new InvalidOperationException(Resources.Error_InvalidReload);
        }
    }

ConfigurationFocus

最后我们将ConfigurationSection和ConfigurationFocus的测试代码贴出，以便能够更好的理解俩个类的关系。

public void CanGetConfigurationSection()
        {
            // Arrange
            var dic1 = new Dictionary<string, string>()
                {
                    {"Data:DB1:Connection1", "MemVal1"},
                    {"Data:DB1:Connection2", "MemVal2"}
                };
            var dic2 = new Dictionary<string, string>()
                {
                    {"DataSource:DB2:Connection", "MemVal3"}
                };
            var dic3 = new Dictionary<string, string>()
                {
                    {"Data", "MemVal4"}
                };
            var memConfigSrc1 = new MemoryConfigurationSource(dic1);
            var memConfigSrc2 = new MemoryConfigurationSource(dic2);
            var memConfigSrc3 = new MemoryConfigurationSource(dic3);

            var builder = new ConfigurationBuilder();
            builder.Add(memConfigSrc1, load: false);
            builder.Add(memConfigSrc2, load: false);
            builder.Add(memConfigSrc3, load: false);

            var config = builder.Build();

            string memVal1, memVal2, memVal3, memVal4, memVal5;
            bool memRet1, memRet2, memRet3, memRet4, memRet5;

            // Act
            var configFocus = config.GetConfigurationSection("Data");

            memRet1 = configFocus.TryGet("DB1:Connection1", out memVal1);
            memRet2 = configFocus.TryGet("DB1:Connection2", out memVal2);
            memRet3 = configFocus.TryGet("DB2:Connection", out memVal3);
            memRet4 = configFocus.TryGet("Source:DB2:Connection", out memVal4);
            memRet5 = configFocus.TryGet(null, out memVal5);

            // Assert
            Assert.True(memRet1);
            Assert.True(memRet2);
            Assert.False(memRet3);
            Assert.False(memRet4);
            Assert.True(memRet5);

            Assert.Equal("MemVal1", memVal1);
            Assert.Equal("MemVal2", memVal2);
            Assert.Equal("MemVal4", memVal5);

            Assert.Equal("MemVal1", configFocus.Get("DB1:Connection1"));
            Assert.Equal("MemVal2", configFocus.Get("DB1:Connection2"));
            Assert.Null(configFocus.Get("DB2:Connection"));
            Assert.Null(configFocus.Get("Source:DB2:Connection"));
            Assert.Equal("MemVal4", configFocus.Get(null));

            Assert.Equal("MemVal1", configFocus["DB1:Connection1"]);
            Assert.Equal("MemVal2", configFocus["DB1:Connection2"]);
            Assert.Null(configFocus["DB2:Connection"]);
            Assert.Null(configFocus["Source:DB2:Connection"]);
            Assert.Equal("MemVal4", configFocus[null]);
        }