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[译]ASP.NET Core 2.0 本地文件操作

问题

如何在ASP.NET Core 2.0中受限地访问本地目录和文件信息？

答案

新建一个空项目，修改Startup类，添加访问本地文件所需的服务：

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IFileProvider>(
        new PhysicalFileProvider(Directory.GetCurrentDirectory()));
}

创建一个中间件，读取根目录下的所有文件，输出文件名：

public class HelloFileProviderMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IFileProvider _fileProvider;
 
    public HelloFileProviderMiddleware(RequestDelegate next, IFileProvider fileProvider)
    {
        _next = next;
        _fileProvider = fileProvider;
    }
 
    public async Task Invoke(HttpContext context)
    {
        var output = new StringBuilder("");
        IDirectoryContents dir = _fileProvider.GetDirectoryContents("");
        foreach (IFileInfo item in dir)
        {
            output.AppendLine(item.Name);
        }
        await context.Response.WriteAsync(output.ToString());
    }
}
 
public static class UseHelloFileProviderExtensions
{
    public static IApplicationBuilder UseHelloFileProvider(this IApplicationBuilder app)
    {
        return app.UseMiddleware<HelloFileProviderMiddleware>();
    }
}

运行，此时页面效果：

当然，我们也可以通过IFileProvider接口读取单个文件信息：

public class HelloFileProviderMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IFileProvider _fileProvider;
 
    public HelloFileProviderMiddleware(RequestDelegate next, IFileProvider fileProvider)
    {
        _next = next;
        _fileProvider = fileProvider;
    }
 
    public async Task Invoke(HttpContext context)
    {
        IFileInfo file = _fileProvider.GetFileInfo("Startup.cs");
        using (var stream = file.CreateReadStream())
        {
            using (var reader = new StreamReader(stream))
            {
                var output = await reader.ReadToEndAsync();
                await context.Response.WriteAsync(output.ToString());
            }
        }
    }
}

运行，此时页面效果：

讨论

ASP.NET Core 2.0提供了继承自接口IFileProvider的PhysicalFileProvider类型，用于受限地访问本地文件系统，它是对System.IO.File的一个封装。

我们可以在Startup的Configure()方法内将IFileProvider配置为一个服务，然后通过构造函数注入添加到中间件或者控制器中。这样可以在一个地方控制文件的访问路径（也就是应用程序启动的时候）。

IFileProvider有两个重要的方法：

1. GetDirectoryContents：返回IDirectoryContents接口。可用于遍历某个目录中的全部文件或目录。

2. GetFileInfo：返回IFileInfo接口。通过其CreateReadSteam方法可以读取文件内容。

====start by sanshi=========================

下面通过递归来遍历根目录下全部文件和目录，修改中间件代码：

public class HelloFileProviderMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IFileProvider _fileProvider;
 
    public HelloFileProviderMiddleware(RequestDelegate next, IFileProvider fileProvider)
    {
        _next = next;
        _fileProvider = fileProvider;
    }
 
    public async Task Invoke(HttpContext context)
    {
        var output = new StringBuilder("");
        ResolveDirectory(output, "", "");
 
        await context.Response.WriteAsync(output.ToString());
    }
 
    private void ResolveDirectory(StringBuilder output, string path, string prefix)
    {
        IDirectoryContents dir = _fileProvider.GetDirectoryContents(path);
        foreach (IFileInfo item in dir)
        {
            if (item.IsDirectory)
            {
                output.AppendLine(prefix + "[" + item.Name + "]");
 
                ResolveDirectory(output, 
                    item.PhysicalPath.Substring(Directory.GetCurrentDirectory().Length), 
                    prefix + "    ");
            } else
            {
                output.AppendLine(prefix + item.Name);
            }
        }
    }
}　　