How to specify log directory of log4j2 in java code?

Question

My application has logging system created by me. However i would like to replace it by log4j2. But i've met a problem with configuration of logging directory in log4j2. Yes, i know there is possibility to log into fixed directory described in config file:

    <RandomAccessFile  name="FILE" fileName="l4j2/${date:yyyy-MM-dd_hh-mm-ss}.log" append="true"  immediateFlush="false">
        <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss}  %-6p  %C{1}.%t:%L  >>> %m%n"/>
    </RandomAccessFile >

But i want to log data in users "My document" directory which can be specific during launching of java app. Is it even possible?

Answer 1

You can use a system property in the file name. See the system properties section of the Lookup manual page.

Example:

<RandomAccessFile  name="FILE" 
    fileName="${sys:logFolder}/l4j2/${date:yyyy-MM-dd_hh-mm-ss}.log"
    append="true"  immediateFlush="false"> ...

You can even specify a default in case the system property is not defined. The syntax is ${sys:KEY:-DEFAULT} . For example:

${sys:logFolder:-/var/tmp}

Answer 2

I've figured it out.

Modify log4j2.xml from

<RandomAccessFile  name="FILE" fileName="l4j2/${date:yyyy-MM-dd_hh-mm-ss}.log" append="true"  immediateFlush="false">

to:

<RandomAccessFile  name="FILE" fileName="${sys:log4j.saveDirectory}/${date:yyyy-MM-dd_hh-mm-ss}.logd" append="true" immediateFlush="false">

Add to java code:

 System.setProperty("log4j.saveDirectory", getMyDocuments());

You can estimate user's "My document" with this method:

String getMyDocuments()
{
    String out = ".\\";
    try
    {
        Process process = Runtime.getRuntime().exec("reg query \"HKCU\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\" /v personal");
        process.waitFor();
        StringWriter sw = new StringWriter();
        int c;
        while ((c = process.getInputStream().read()) != -1)
        {
            sw.write(c);
        }
        String output = sw.toString().replaceAll("\t", "    ");
        String[] parsed = output.split("\\t|\\s{2,}");
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    return out;
}

Answer 3

In the case of log4j2, you can use,

# May change log file path as per the need
property.filename = ${sys:user.dir}/logs/debug.log