Question

我有一个非常大的XML文档（大约120M），我不想立刻将它加载到内存中。我的目的是检查此文件是否使用有效的UTF-8编码。

任何想法都可以快速检查，而不会以byte[]的形式将整个文件读入内存？

我正在使用VSTS 2008和C＃。

当使用XMLDocument加载包含无效字节序列的XML文档时，有一个例外，但是当将所有内容读入字节数组然后检查UTF-8时，没有例外，任何想法？

以下是显示我的XML文件内容的屏幕截图，或者您可以从here

下载该文件的副本

编辑1：

class Program
{
    public static byte[] RawReadingTest(string fileName)
    {
        byte[] buff = null;

        try
        {
            FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
            BinaryReader br = new BinaryReader(fs);
            long numBytes = new FileInfo(fileName).Length;
            buff = br.ReadBytes((int)numBytes);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }

        return buff;
    }

    static void XMLTest()
    {
        try
        {
            XmlDocument xDoc = new XmlDocument();
            xDoc.Load("c:\\abc.xml");
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
    }

    static void Main()
    {
        try
        {
            XMLTest();
            Encoding ae = Encoding.GetEncoding("utf-8");
            string filename = "c:\\abc.xml";
            ae.GetString(RawReadingTest(filename));
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }

        return;
    }
}

编辑2：使用new UTF8Encoding(true, true)时会出现异常，但使用new UTF8Encoding(false, true)时，不会抛出异常。我很困惑，因为它应该是控制是否抛出异常的第二个参数（如果有无效的字节序列），为什么第一个参数很重要？

    public static void TestTextReader2()
    {
        try
        {
            // Create an instance of StreamReader to read from a file.
            // The using statement also closes the StreamReader.
            using (StreamReader sr = new StreamReader(
                "c:\\a.xml",
                new UTF8Encoding(true, true)
                ))
            {
                int bufferSize = 10 * 1024 * 1024; //could be anything
                char[] buffer = new char[bufferSize];
                // Read from the file until the end of the file is reached.
                int actualsize = sr.Read(buffer, 0, bufferSize);
                while (actualsize > 0)
                {
                    actualsize = sr.Read(buffer, 0, bufferSize);
                }
            }
        }
        catch (Exception e)
        {
            // Let the user know what went wrong.
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
        }

    }

Answer 1

var buffer = new char[32768] ;

using (var stream = new StreamReader (pathToFile, 
    new UTF8Encoding (true, true)))
{
    while (true)
    try
    {
        if (stream.Read (buffer, 0, buffer.Length) == 0)
            return GoodUTF8File ;
    }
    catch (ArgumentException)
    {
        return BadUTF8File ;
    }
}

Answer 2

@ George2我认为它们意味着像下面这样的解决方案（我没有测试过）。

处理缓冲区之间的转换（即在读取之间缓存额外字节/部分字符）是StreamReader实现的责任和内部实现细节。

using System;
using System.IO;
using System.Text;

class Test 
{
    public static void Main() 
    {
        try 
        {
            // Create an instance of StreamReader to read from a file.
            // The using statement also closes the StreamReader.
            using (StreamReader sr = new StreamReader(
                "TestFile.txt",
                Encoding.UTF8
                ))
            {
                const int bufferSize = 1000; //could be anything
                char[] buffer = new char[bufferSize];
                // Read from the file until the end of the file is reached.
                while (bufferSize == sr.Read(buffer, bufferSize, 0)) 
                {
                    //successfuly decoded another buffer's-worth of data
                }
            }
        }
        catch (Exception e) 
        {
            // Let the user know what went wrong.
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
        }
    }
}

Answer 3

这不起作用吗？

StreamReader reader = new StreamReader(file);

Console.WriteLine(reader.CurrentEncoding.ToString()); //You get the default encoding
reader.Read();

Console.WriteLine(reader.CurrentEncoding.ToString()); //You get the right encoding. 
reader.Close();

如果没有，有人可以帮忙解释原因吗？

使用UTF-8解码文件流

3 个答案: