7.2 Trace (Logging)

The SpringSource dm Server’s logging (trace) support serves two main purposes:

By default, the dm Server trace file is called $SERVER_HOME/serviceability/logs/dm-server/log_i.log, and, again by default, the application trace files are called $SERVER_HOME/serviceability/logs/application_name/log_i.log, where application_name is automatically set by dm Server for each application artifact installed and run (it is a combination of the artifact name and the version).

The index i varies from 1 to 4, on a rolling basis, as each log file exceeds 10Mb.

Entries in trace files are by default of the form <timestamp> <thread-name> <source> <level> <entry-text>. For example:

[2008-05-15 09:09:46.940] server-dm-2 org.apache.coyote.http11.Http11Protocol I Initializing Coyote HTTP/1.1 on http-48080

although this format is completely determined by the Logback configuration file serviceability.xml.

Application Output

SpringSource dm Server provides advanced support for capturing and tracing application-generated output by automatically separating trace output on a per-application basis and will also capture any System.out and System.err output.

Per-application trace

SpringSource dm Server uses SLF4J interfaces to Logback, and the root logger (by default) captures all logging output and appends it to the application-specific trace files as described above. To modify this, define application-specific loggers in the serviceability.xml file in the normal way.

System.out and System.err

System.out and System.err output from applications is, by default, captured in the application’s trace file. This happens because the output streams are intercepted and written to the loggers named System.out and System.err respectively. Since there are no explicit loggers defined with these names in the serviceability.xml file, this output is logged by the root logger (which captures INFO level and above).

The capture of System.out and System.err output is configured in the config/com.springsource.osgi.medic.properties file by the log.wrapSysOut and log.wrapSysErr properties. By default the properties have a value of true and capture is enabled. Capture can be disabled by configuring the properties with a value of false.

The trace entries for System.out and System.err output are of the form:

[2008-05-16 09:28:45.874] server-tomcat-thread-1 System.out Hello world!
[2008-05-16 09:28:45.874] server-tomcat-thread-1 System.err Hello world!

The third column indicates where the output came from (System.out or System.err).

To over-ride this behaviour, simply define explicit loggers named System.out and/or System.err in the configuration file to send this output to an appender of your choice. Be aware that all applications’ output streams will be caught by these loggers, and that a sifting appender might be useful to separate them.