Where does system.out.println print from a JSP?

问题:

Where does tomcat put the System.out.println output ?

I'm not interested in out.println. I'm using a system that uses system.out to log issues, like login success/fail, and I need to look to that generated "log".

回答1:

It usually prints to catalina.out.

It is highly unrecommended to log using system.out.println() from several reasons:

• you cannot control which messages are logged and which aren't unless you change the code
• catalina.out just grow all the time, and you cannot move it so that tomcat will create another one.

A better solution is to use one of the popular (and mature) logging frameworks:

• java.util.logging (actually used by tomcat itself and you have no third party dependencies)
• Log4j
• Logback

A good solution which is backed by log4j, is to use Jakarta's log tag library, where you can have your logging messages in any of this forms

<log:info message="this is a message"/>

<log:info category="foo.bar" message="this is a message"/>

<log:info category="foo.bar">
  this is a message
</log:info>

回答2:

CATALINA_HOME/logs/stdout_YYYYMMDD.log

is the default, where CATALINA_HOME is your base Tomcat directory. There are various ways to change this programatically and via configuration.