使用log4net时记录异常的最佳方法是什么

Question

What should I be logging in my exceptions so I can all the details?

catch(Exception ex)
{
  Logger.Error("Users.GetUser " + ex.??????);
}

Should I be passing just the variable ex or should I be doing:

ex.InnerException + ex.Message + ex.Source

Answer 1

Error has a overload that takes in a exception as one of the parameters. So your logger should be in the form

catch(Exception ex)
{
  Logger.Error("Users.GetUser", ex);
}

It is then your responsibility to make sure your appender is also set up to record the information from the exception. If you look at their appender examples they have a MS SQL appeneder that puts the exception info in to its own column.

<appender name="AdoNetAppender" type="log4net.Appender.AdoNetAppender">
    <bufferSize value="100" />
    <connectionType value="System.Data.SqlClient.SqlConnection, System.Data, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
    <connectionString value="data source=[database server];initial catalog=[database name];integrated security=false;persist security info=True;User ID=[user];Password=[password]" />
    <commandText value="INSERT INTO Log ([Date],[Thread],[Level],[Logger],[Message],[Exception]) VALUES (@log_date, @thread, @log_level, @logger, @message, @exception)" />
    <parameter>
        <parameterName value="@log_date" />
        <dbType value="DateTime" />
        <layout type="log4net.Layout.RawTimeStampLayout" />
    </parameter>
    <parameter>
        <parameterName value="@thread" />
        <dbType value="String" />
        <size value="255" />
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%thread" />
        </layout>
    </parameter>
    <parameter>
        <parameterName value="@log_level" />
        <dbType value="String" />
        <size value="50" />
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%level" />
        </layout>
    </parameter>
    <parameter>
        <parameterName value="@logger" />
        <dbType value="String" />
        <size value="255" />
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%logger" />
        </layout>
    </parameter>
    <parameter>
        <parameterName value="@message" />
        <dbType value="String" />
        <size value="4000" />
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%message" />
        </layout>
    </parameter>
    <parameter>
        <parameterName value="@exception" />
        <dbType value="String" />
        <size value="2000" />
        <layout type="log4net.Layout.ExceptionLayout" />
    </parameter>
</appender>

Answer 2

I usually do this is my global.asax:

  Exception lastErrorWrapper = Server.GetLastError();
        Log.Error(lastErrorWrapper);       

Answer 3

You should use the ILog.Error(string, exception) method to log errors. This will give you all pertinent exception information - the exception type, message and stack trace will all be displayed:

log.Error("Construction of Foo failed due to the following exception", ex);

If you ever want to build a custom log entry depending on values in code, use the ILog.*Format(string, params object[] args) methods:

int i = 20; int y = 25
log.InfoFormat("The value of i is {0}, and the value of x is {1}", i, x);

Answer 4

If you are catching a general Exception then just use .ToString() because you don't know anything more about the exception unless you specifically write code to find out. .ToString() will give you the stack trace allowing you to see where the problem occurred.

catch(Exception ex)
{
  Logger.Error("Users.GetUser " + ex.ToString());
}

If you are catching specific exception types then you way want to log certain details within that exception which you will need to diagnose a problem. Take a WebException for example. You might want to know what the content type is. This information wouldn't be available in a normal .ToString() log.

catch(WebException webex)
{
    Logger.Error(webex.Response.ContentType);
}

Basically it all depends on the exception and what you want to know.

The question you need to ask yourself is : "If an error occurs what do I need in order to diagnose the problem."