ASP.NET MVC应用中XML异常无法捕获且代码重复执行问题求助

问题现象 #

为ASP.NET MVC应用编写的设置处理单例类，在测试格式错误/缺失的XML文件时，出现以下问题：

• 抛出的XmlException看似无法被捕获，代码无限重复执行同一代码段
• 异常发生前后的断点被反复触发，异常抛出后的断点无法命中
• 已禁用Visual Studio调试对话框弹窗，且无手动循环调用属性的逻辑，异常后的默认处理逻辑未生效

原代码 #

设置容器属性 #

private static Settings _singletonSettings;

public static Settings SettingsContainer 
{
    get
    {
        if (_singletonSettings == null)
        {
            _singletonSettings = new Settings();
            _singletonSettings.LoadSettings();
        }
        return _singletonSettings;
    }
    private set 
    {
        _singletonSettings = value;
    }
}

LoadSettings函数 #

public void LoadSettings() 
{
    string filePath = "Config/Settings.txt";

    if (!Directory.Exists(Path.GetDirectoryName(filePath)))
    {
        Directory.CreateDirectory(Path.GetDirectoryName(filePath));
    }

    if (File.Exists(filePath))
    {
        try
        {
            SettingsContainer = LoadViaDataContractSerialization<Settings>(filePath);   // 尝试捕获异常
        }
        catch (Exception ex)
        {
            Log.GlobalLog.WriteError("LoadViaDataContractSerialization() error:\n" + ex.Message + "\nStackTrace: \n" + ex.StackTrace);
        }
    }
    else
    {
        File.Create(filePath);
    }

    if (SettingsContainer == null)
    {
        SettingsContainer = new Settings();
    }
}

LoadViaDataContractSerialization函数 #

public static T LoadViaDataContractSerialization<T>(string filepath)
{
    try
    {
        T serializableObject;

        using (var fileStream = new FileStream(filepath, FileMode.Open))
        {
            try
            {
                using (var reader = XmlDictionaryReader.CreateTextReader(fileStream, new XmlDictionaryReaderQuotas())) // 所有执行在此处停止
                {
                    var serializer = new DataContractSerializer(typeof(T));
                    serializableObject = (T)serializer.ReadObject(reader, true);
                    reader.Close();
                }
            }
            catch (XmlException ex)
            {
                Log.GlobalLog.WriteError("LoadViaDataContractSerialization() XML Fail: Message: " + ex.Message + "\n StackTrace: " + ex.StackTrace);
                return default(T);
            }

            fileStream.Close();
        }

        return serializableObject;
    }
    catch (Exception ex)
    {
        Log.GlobalLog.WriteError("LoadViaDataContractSerialization() Fail: Message: " + ex.Message + "\n StackTrace: " + ex.StackTrace);
        return default(T);
    }
}

问题根因 #

1. 无限循环触发逻辑：当XML反序列化失败，LoadViaDataContractSerialization返回default(T)（即null），执行SettingsContainer = null后，LoadSettings中的if (SettingsContainer == null)会访问SettingsContainer的getter。此时_singletonSettings已被设为null，getter会重新创建Settings实例并调用LoadSettings，形成无限循环。
2. 异常看似未捕获：实际异常已被LoadViaDataContractSerialization的catch块捕获，但循环反复触发异常抛出逻辑，导致视觉上异常一直在重复出现。

修复方案 #

核心修改：避免触发属性getter的循环初始化 #

修改LoadSettings方法，直接操作私有字段_singletonSettings，而非通过SettingsContainer属性访问，同时修复File.Create的句柄泄漏问题：

public void LoadSettings() 
{
    string filePath = "Config/Settings.txt";

    if (!Directory.Exists(Path.GetDirectoryName(filePath)))
    {
        Directory.CreateDirectory(Path.GetDirectoryName(filePath));
    }

    Settings loadedSettings = null;
    if (File.Exists(filePath))
    {
        try
        {
            loadedSettings = LoadViaDataContractSerialization<Settings>(filePath);
        }
        catch (Exception ex)
        {
            Log.GlobalLog.WriteError("LoadViaDataContractSerialization() error:\n" + ex.Message + "\nStackTrace: \n" + ex.StackTrace);
        }
    }
    else
    {
        // 用using块释放File.Create返回的文件流，避免后续文件访问异常
        using (File.Create(filePath)) {}
    }

    // 直接操作私有字段，跳过SettingsContainer的getter逻辑
    _singletonSettings = loadedSettings ?? new Settings();
}

进阶优化：使用Lazy实现安全单例 #

替换手动单例逻辑为Lazy<T>，自动实现线程安全的延迟初始化，彻底避免循环调用问题：

// 替换原有的_singletonSettings字段和SettingsContainer属性
private static readonly Lazy<Settings> _lazySettings = new Lazy<Settings>(() =>
{
    var settings = new Settings();
    settings.LoadSettings();
    return settings;
});

public static Settings SettingsContainer => _lazySettings.Value;

内容的提问来源于stack exchange，提问作者Joshua Walker