文件型配置基本内容
上一篇文章讨论了configuration的几个核心对象，本文继续讨论configuration中关于文件型配置的相关内容。相比较而言，文件型配置的使用场景更加广泛，用户自定义配置扩展也可以基于文件型配置进行扩展。如果需要查看上一篇文章，可以点击。
.net core文件型配置中我们提供了三种主要的实现，分别是json、xml、ini，请查看下图
由图可知，这三种配置的实现方式是一样的，当然了其他的配置比如命令行配置、环境变量配置等也是大同小异，理解了改配置类型的实现方式，后面我们再扩展基于consul或者zk的实现，就非常简单了。
文件型配置的抽象扩展
文件型配置的抽象扩展位于microsoft.extensions.configuration.fileextensions组件中，该扩展是一个基础实现。不过其命名空间是microsoft.extensions.configuration，而micros oft.extensions.configuration扩建本身又是整个.net core configuration的基础实现。将file扩展独立于外部，体验了.net core的模块化设计。
fileconfigurationsource
configuration.fileextensions组件中，fileconfigurationsource是继承于iconfigurationsource的一个抽象类，包含了一个iconfigurationprovider类型的抽象方法，如下所示
1: /// <summary>
2: /// builds the <see cref="iconfigurationprovider"/> for this source.
3: /// </summary>
4: /// <param name="builder">the <see cref="iconfigurationbuilder"/>.</param>
5: /// <returns>a <see cref="iconfigurationprovider"/></returns>
6: public abstract iconfigurationprovider build(iconfigurationbuilder builder);
该抽象类中还包括了几个比较重要的参数，分别用于配置性行为、文件内容访问以及异常处理。
string path：文件的路径
bool optional：标识加载的文件是否是可选的
bool reloadonchange：如果文件发生修改，是否重新加载配置源
int reloaddelay：加载延迟，单位是毫秒，默认是250毫秒
ifileprovider fileprovider：用于获取文件内容
action<fileloadexceptioncontext> onloadexception：文件加载异常处理
该类对fileprovider有特殊处理，就是如果没有提供fileprovider实例，则会基于绝对路径，在最近的现有目录中创建物理文件提供程序。源码如下，
1: /// <summary>
2: /// if no file provider has been set, for absolute path, this will creates a physical file provider
3: /// for the nearest existing directory.
4: /// </summary>
5: public void resolvefileprovider()
6: {
7: if (fileprovider == null &&
8: !string.isnullorempty(path) &&
9: system.io.path.ispathrooted(path))
10: {
11:
var directory = system.io.path.getdirectoryname(path);
12: var pathtofile = system.io.path.getfilename(path);
13: while (!string.isnullorempty(directory) && !directory.exists(directory))
14: {
15: pathtofile = system.io.path.combine(system.io.path.getfilename(directory), pathtofile);
16: directory = system.io.path.getdirectoryname(directory);
17: }
18: if (directory.exists(directory))
19: {
20: fileprovider = new physicalfileprovider(directory);
21: path = pathtofile;
22: }
23: }
24: }
fileconfigurationprovider
该类是继承于configurationprovider的抽象类，是从文件系统加载配置的基类，同时还继承了idisposable，其抽象方法是load方法，用于从当前的provider中以stream方式加载数据
1: /// <summary>
2: /// loads this provider's data from a stream.
3: /// </summary>
4: /// <param name="stream">the stream to read.</param>
5: public abstract void load(stream stream);
该类还重写了configurationprovider的load方法，并对文件加载中的异常做了处理，data属性在前文有提到过，此处不再做其他说明。方法源码如下所示：
1: private void load(bool reload)
2: {
3: var file = source.fileprovider?.getfileinfo(source.path);
4: if (file == null || !file.exists)
5: {
6: if (source.optional || reload) // always optional on reload
7: {
8: data = new dictionary<string, string>(stringcomparer.ordinalignorecase);
9: }
10: else
11: {
12: var error = new stringbuilder($"the configuration file '{source.path}' was not found and is not optional.");
13: if (!string.isnullorempty(file?.physicalpath))
14: {
15: error.append($" the physical path is '{file.physicalpath}'.");
16: }
17: handleexception(new filenotfoundexception(error.tostring()));
18: }
19: }
20: else
21: {
22: // always create new data on reload to drop old keys
23: if (reload)
24: {
25: data = new dictionary<string, string>(stringcomparer.ordinalignorecase);
26: }
27: using (var stream = file.createreadstream())
28: {
29: try
30: {
31: load(stream);
32: }
33: catch (exception e)
34: {
35: handleexception(e);
36: }
37: }
38: }
39: // review: should we raise this in the base as well / instead?，通过注释，我们可以知道onreload()方法可能会在新版中发生变化
40: onreload();
41: }
42:
43: /// <summary>
44: /// loads the contents of the file at <see cref="path"/>.
45: /// </summary>
46: /// <exception cref="filenotfoundexception">if optional is <c>false</c> on the source and a
47: /// file does not exist at specified path.</exception>
48: public override void load()
49: {
50: load(reload: false);
51: }
另外它还有一个特殊方法，就是参数类型为fileconfigurationsource的构造函数，其主要功能是监控文件，并在fileconfigurationsource.reloaddelay设置的时间里重新加载文件并返回一个idisposable类型的值，以下是该构造函数的源码：
1: /// <summary>
2: /// initializes a new instance with the specified source.
3: /// </summary>
4: /// <param name="source">the source settings.</param>
5: public fileconfigurationprovider(fileconfigurationsource source)
6: {
7: if (source == null)
8: {
9: throw new argumentnullexception(nameof(source));
10: }
11: source = source;
12:
13: if (source.reloadonchange && source.fileprovider != null)
14: {
15: _changetokenregistration = changetoken.onchange(
16: () => source.fileprovider.watch(source.path),
17: () => {
18: thread.sleep(source.reloaddelay);
19: load(reload: true);
20: });
21: }
22: }
fileconfigurationextensions
该类是一个静态类，其提供了的多个扩展方法，主要基于
- iconfigurationbuilder
- ifileprovider
- action<fileloadexceptioncontext>
包括主要用于设置或获取ifileprovider对象，前文有介绍过，是存储于字典之中，需要注意的是，在get的时候如果字典中并不存在ifileprovider对象，则会实例化一个physicalfileprovider对象出来，该类位于microsoft.extensions.fileproviders.physicalfileprovider
1: /// <summary>
2: /// sets the default <see cref="ifileprovider"/> to be used for file-based providers.
3: /// </summary>
4: /// <param name="builder">the <see cref="iconfigurationbuilder"/> to add to.</param>
5: /// <param name="fileprovider">the default file provider instance.</param>
6: /// <returns>the <see cref="iconfigurationbuilder"/>.</returns>
7: public static iconfigurationbuilder setfileprovider(this iconfigurationbuilder builder, ifileprovider fileprovider)
8: {
9: if (builder == null)
10: {
11: throw new argumentnullexception(nameof(builder));
12: }
13:
14: builder.properties[fileproviderkey] = fileprovider ?? throw new argumentnullexception(nameof(fileprovider));
15: return builder;
16: }
17:
18: /// <summary>
19: /// gets the default <see cref="ifileprovider"/> to be used for file-based providers.
20: /// </summary>
21: /// <param name="builder">the <see cref="iconfigurationbuilder"/>.</param>
22: /// <returns>the <see cref="iconfigurationbuilder"/>.</returns>
23: public static ifileprovider getfileprovider(this iconfigurationbuilder builder)
24: {
25: if (builder == null)
26: {
27: throw new argumentnullexception(nameof(builder));
28: }
29:
30: if (builder.properties.trygetvalue(fileproviderkey, out object provider))
31: {
32: return provider as ifileprovider;
33: }
34:
35: return new physicalfileprovider(appcontext.basedirectory ?? string.empty);
36: }
为指定路径的物理文件设置文件型provider，该方法同样基于physicalfileprovider，并返回iconfigurationbuilder对象
1: /// <summary>
2: /// sets the fileprovider for file-based providers to a physicalfileprovider with the base path.
3: /// </summary>
4: /// <param name="builder">the <see cref="iconfigurationbuilder"/> to add to.</param>
5: /// <param name="basepath">the absolute path of file-based providers.</param>
6: /// <returns>the <see cref="iconfigurationbuilder"/>.</returns>
7: public static iconfigurationbuilder setbasepath(this iconfigurationbuilder builder, string basepath)
8: {
9: if (builder == null)
10: {
11: throw new argumentnullexception(nameof(builder));
12: }
13:
14: if (basepath == null)
15: {
16: throw new argumentnullexception(nameof(basepath));
17: }
18:
19: return builder.setfileprovider(new physicalfileprovider(basepath));
20: }
以及异常处理，可以看到其异常处理也会存放于字典中，如果字典中找不到，就会返回空，这个地方如果直接使用，需要注意空指针问题。
1: /// <summary>
2: /// sets a default action to be invoked for file-based providers when an error occurs.
3: /// </summary>
4: /// <param name="builder">the <see cref="iconfigurationbuilder"/> to add to.</param>
5: /// <param name="handler">the action to be invoked on a file load exception.</param>
6: /// <returns>the <see cref="iconfigurationbuilder"/>.</returns>
7: public static iconfigurationbuilder setfileloadexceptionhandler(this iconfigurationbuilder builder, action<fileloadexceptioncontext> handler)
8: {
9: if (builder == null)
10: {
11: throw new argumentnullexception(nameof(builder));
12: }
13:
14: builder.properties[fileloadexceptionhandlerkey] = handler;
15: return builder;
16: }
17:
18: /// <summary>
19: /// gets the default <see cref="ifileprovider"/> to be used for file-based providers.
20: /// </summary>
21: /// <param name="builder">the <see cref="iconfigurationbuilder"/>.</param>
22: /// <returns>the <see cref="iconfigurationbuilder"/>.</returns>
23: public static action<fileloadexceptioncontext> getfileloadexceptionhandler(this iconfigurationbuilder builder)
24: {
25: if (builder == null)
26: {
27: throw new argumentnullexception(nameof(builder));
28: }
29:
30: if (builder.properties.trygetvalue(fileloadexceptionhandlerkey, out object handler))
31: {
32: return handler as action<fileloadexceptioncontext>;
33: }
34:
return null;
35: }
该类还有两个静态私有变量，指定了文件provider的key以及文件加载异常处理key。
1: private static string fileproviderkey = "fileprovider";
2: private static string fileloadexceptionhandlerkey = "fileloadexceptionhandler";
总结
文件型配置还依赖于.net core的其他组件microsoft.extensions.fileproviders和microsoft.extensions.primitives。
fileproviders组件提供了文件处理的一般方法，primitives组件提供了监控机制，同时还包括两个比较重要的结构体stringvalues和stringsegment，本文暂时不做讨论，有兴趣的朋友，可以自行查看该组件源码。
