Logging Leave feedback

By default, logging is disabled when rendering documents. You can log to the console or a file.

To log, use the ILogger interface. It defines the methods required to instantiate and release the output file stream. Also, use the following classes:

The ConsoleLogger class defines the methods required to log to the console.
The FileLogger class defines the methods required to log to a file.

The log contains the following three types of messages:

Error means unrecoverable exceptions
Warning means recoverable/expected exceptions
Trace means general information

Logging to a file

The following code snippet shows how to log to a file using the FileLogger class:

using GroupDocs.Viewer;
using GroupDocs.Viewer.Logging;
using GroupDocs.Viewer.Options;
// ...

// Create logger and specify the output file.
FileLogger fileLogger = new FileLogger("output.log");

// Create ViewerSettings and specify FileLogger.
ViewerSettings viewerSettings = new ViewerSettings(fileLogger);

// Render a document.
using (Viewer viewer = new Viewer("sample.docx",viewerSettings))
{
    ViewOptions viewOptions = HtmlViewOptions.ForEmbeddedResources("result.html");
    viewer.View(viewOptions);
}

VB.NET

Imports GroupDocs.Viewer
Imports GroupDocs.Viewer.Logging
Imports GroupDocs.Viewer.Options
' ...

Module Program
    Sub Main(args As String())
        ' Create logger and specify the output file.
        Dim fileLogger As FileLogger = New FileLogger("output.log")
    
        ' Create ViewerSettings and specify FileLogger.
        Dim viewerSettings As ViewerSettings = New ViewerSettings(fileLogger)
    
        ' Render a document.
        Using viewer As Viewer = New Viewer("sample.docx", viewerSettings)
            Dim viewOptions As ViewOptions = HtmlViewOptions.ForEmbeddedResources("result.html")
            viewer.View(viewOptions)
        End Using
    End Sub
End Module

The following image shows the output.log file:

Logging to the console

The following code snippet shows how to log to the console using the ConsoleLogger class:

using GroupDocs.Viewer;
using GroupDocs.Viewer.Logging;
using GroupDocs.Viewer.Options;
// ...

// Create console logger.
ConsoleLogger consoleLogger = new ConsoleLogger();

// Create ViewerSettings and specify FileLogger.
ViewerSettings viewerSettings = new ViewerSettings(consoleLogger);

// Render a document.
using (Viewer viewer = new Viewer("sample.docx", viewerSettings))
{
    ViewOptions viewOptions = HtmlViewOptions.ForEmbeddedResources();
    viewer.View(viewOptions);
}

VB.NET

Imports GroupDocs.Viewer
Imports GroupDocs.Viewer.Logging
Imports GroupDocs.Viewer.Options
' ...

Module Program
    Sub Main(args As String())
        ' Create console logger.
        Dim consoleLogger As ConsoleLogger = New ConsoleLogger()
    
        ' Create ViewerSettings and specify FileLogger.
        Dim viewerSettings As ViewerSettings = New ViewerSettings(consoleLogger)
    
        ' Render a document.
        Using viewer As Viewer = New Viewer("sample.docx", viewerSettings)
            Dim viewOptions As ViewOptions = HtmlViewOptions.ForEmbeddedResources()
            viewer.View(viewOptions)
        End Using
    End Sub
End Module

The following image shows a sample console output:

Implementing custom logger

To create a logger, implement the ILogger interface:

For trace messages, implement the public void Trace(string message) method.
For warning messages, implement the public void Warning(string message) method.
For error messages, implement the public void Error(string message) method.

The following code snippet shows how to implement a simple file logger:

using System;
using System.IO;
using GroupDocs.Viewer;
using GroupDocs.Viewer.Logging;
using GroupDocs.Viewer.Options;
// ...

// Create logger and specify the output file.
CustomLogger customLogger = new CustomLogger("output.log");

// Create ViewerSettings and specify CustomLogger.
ViewerSettings viewerSettings = new ViewerSettings(customLogger);

// Render a document.
using (Viewer viewer = new Viewer("sample.docx",viewerSettings))
{
    ViewOptions viewOptions = HtmlViewOptions.ForEmbeddedResources("result.html");

    viewer.View(viewOptions);
}

/// <summary>
/// Writes log messages to a file.
/// </summary>
public class CustomLogger : ILogger
{
    private readonly string _fileName;

    private CustomLogger() { }

    /// <summary>
    /// Create logger to a file.
    /// </summary>
    /// <param name="fileName">Full file name with path</param>
    public CustomLogger(string fileName)
    {
        _fileName = fileName;
    }

    /// <summary>
    /// Writes trace message to the file.
    /// Trace log messages provide generally useful information about application flow.
    /// </summary>
    /// <param name="message">The trace message.</param>
    /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="message"/> is null.</exception>
    public void Trace(string message)
    {
        if (message == null)
            throw new ArgumentNullException(nameof(message));

        using (StreamWriter wr = new StreamWriter(_fileName, true))
        {
            wr.WriteLine($"[TRACE] {message}");
        }
    }

    /// <summary>
    /// Writes warning message to the file;
    /// Warning log messages provide information about the unexpected and recoverable events in application flow.
    /// </summary>
    /// <param name="message">The warning message.</param>
    /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="message"/> is null.</exception>
    public void Warning(string message)
    {
        if (message == null)
            throw new ArgumentNullException(nameof(message));

        using (StreamWriter wr = new StreamWriter(_fileName, true))
        {
            wr.WriteLine($"[WARN] {message}");
        }
    }

    /// <summary>
    /// Writes an error message to the file.
    /// Error log messages provide information about unrecoverable events in application flow.
    /// </summary>
    /// <param name="message">The error message.</param>
    /// <param name="exception">The exception.</param>
    /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="message"/> is null.</exception>
    /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="exception"/> is null.</exception>
    public void Error(string message, Exception exception)
    {
        if (message == null)
            throw new ArgumentNullException(nameof(message));
        if (exception == null)
            throw new ArgumentNullException(nameof(exception));

        using (StreamWriter wr = new StreamWriter(_fileName, true))
        {
            wr.WriteLine($"[ERROR] {message}, exception: {exception}");
        }
    }
}

VB.NET

Imports System
Imports System.IO
Imports GroupDocs.Viewer
Imports GroupDocs.Viewer.Logging
Imports GroupDocs.Viewer.Options
' ...

Module Program
    Sub Main(args As String())
        ' Create logger and specify the output file.
        Dim customLogger As CustomLogger = New CustomLogger("output.log")

        ' Create ViewerSettings and specify CustomLogger.
        Dim viewerSettings As ViewerSettings = New ViewerSettings(customLogger)

        ' Render a document.
        Using viewer As Viewer = New Viewer("sample.docx", viewerSettings)
            Dim viewOptions As ViewOptions = HtmlViewOptions.ForEmbeddedResources("result.html")
            viewer.View(viewOptions)
        End Using
    End Sub

    ' <summary>
    ' Writes log messages to a file.
    ' </summary>
    Public Class CustomLogger
        Implements ILogger

        Private ReadOnly _fileName As String

        Private Sub New()
        End Sub

        ''' <summary>
        ''' Create logger to a file.
        ''' </summary>
        ''' <param name="fileName">Full file name with path</param>
        Public Sub New(fileName As String)
            _fileName = fileName
        End Sub

        ''' <summary>
        ''' Writes warning message to the file;
        ''' Warning log messages provide information about the unexpected and recoverable events in application flow.
        ''' </summary>
        ''' <param name="message">The warning message.</param>
        ''' <exception cref="System.ArgumentNullException">Thrown when <paramref name="message"/> is null.</exception>
        Public Sub ILogger_Warning(message As String) Implements ILogger.Warning
            If message Is Nothing Then
                Throw New ArgumentNullException(NameOf(message))
            End If

            Using wr As New StreamWriter(_fileName, True)
                wr.WriteLine($"[WARN] {message}")
            End Using
        End Sub

        ''' <summary>
        ''' Writes trace message to the file.
        ''' Trace log messages provide generally useful information about application flow.
        ''' </summary>
        ''' <param name="message">The trace message.</param>
        ''' <exception cref="System.ArgumentNullException">Thrown when <paramref name="message"/> is null.</exception>
        Public Sub ILogger_Trace(message As String) Implements ILogger.Trace
            If message Is Nothing Then
                Throw New ArgumentNullException(NameOf(message))
            End If

            Using wr As New StreamWriter(_fileName, True)
                wr.WriteLine($"[TRACE] {message}")
            End Using
        End Sub

        ''' <summary>
        ''' Writes an error message to the file.
        ''' Error log messages provide information about unrecoverable events in application flow.
        ''' </summary>
        ''' <param name="message">The error message.</param>
        ''' <param name="exception">The exception.</param>
        ''' <exception cref="System.ArgumentNullException">Thrown when <paramref name="message"/> is null.</exception>
        ''' <exception cref="System.ArgumentNullException">Thrown when <paramref name="exception"/> is null.</exception>
        Public Sub [Error](message As String, exception As Exception) Implements ILogger.[Error]
            If message Is Nothing Then
                Throw New ArgumentNullException(NameOf(message))
            End If
            If exception Is Nothing Then
                Throw New ArgumentNullException(NameOf(exception))
            End If

            Using wr As New StreamWriter(_fileName, True)
                wr.WriteLine($"[ERROR] {message}, exception: {exception}")
            End Using
        End Sub
    End Class
End Module

The following image shows the output.log file:

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Logging Leave feedback

Logging to a file

Logging to the console

Implementing custom logger

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