Default log4j MDC value

Question

Does anyone know how to specify a default value for a missing entry in the MDC using log4j's config xml? I have an appender defined in my XML file like so:

<appender name="DBAppender" class="org.apache.log4j.jdbc.JDBCAppender"> 
    <param name="URL" value="jdbc:sqlserver://phenom\\MSSQLSERVER_2012\;databaseName=pickmax_express" /> 
    <param name="Driver" value="com.microsoft.sqlserver.jdbc.SQLServerDriver" /> 
    <param name="User" value="user" /> 
    <param name="Password" value="password" /> 
    <layout class="org.apache.log4j.PatternLayout"> 
        <param name="ConversionPattern" 
          value="INSERT INTO LOG (source, message, order_id, log_level) VALUES ( 'TESTSOURCE','%m', %X{orderID}, 0)" 
        /> 
    </layout> 
</appender> 

The part in question is the order ID from the MDC (%X{orderID}). I searched around and only found duplicates of the same thread saying something along the lines of $${orderID:-DefaultValue}, but this doesnt work in this context. I need to be able to default the value to 0 or -1 or some other sentinal value when log messages are received in contexts which wont have an order ID

Gilford

Answer 1

If you access the MDC object in your java code, you can initialize the value for orderId by adding the following in some startup area (for example, a servlet init() method):

import org.apache.log4j.MDC;

public void blammyStartupMethod()
{
    MDC.put("orderId", "sentinal value");
}

Edit: It seems likely that you will need to set this default every time you write a log message that does not have an orderId value and after each MDC.remove(). AOP seems like an option here.

Virginium

Thanks for this. While this wont work my problem, after playing around with it I learned a bit more about the MDC, so +1. – Gilford

Answer 2

Also you can define default value in the layout pattern like %X{orderID:-Def value}

<param name="ConversionPattern" 
          value="INSERT INTO LOG (source, message, order_id, log_level) VALUES ( 'TESTSOURCE','%m', %X{orderID:-Def value}, 0)" 
        />

Teneshatenesmus