Log4j 没有为异常打印堆栈跟踪

小开

Using your code sample:

private static final Logger _log = Logger.getLogger(MyClass.class);
...
try{...} catch (Exception e) {
//Change
//_log.error("Error refreshing all prices", e);


//To
_log.error("Error refreshing all prices", e.fillInStackTrace());
}

You'll see all the stack trace displayed.

PS. Make Logger a singleton...(check my declaration) just after declaring public class MyClass {

小开

I don't see anything wrong with your config, so try to upgrade log4j to a newer (not necessarily the latest) version.

Though not the problem in this case, you'd better make your loggers private static final

小开

I haven't used the fillStackTrace call, so I cannot comment if that will work. Another approach is to use a little method that returns the formatted text from an Exception.

public static String getStackTrace(Exception e)
{
StringWriter sWriter = new StringWriter();
PrintWriter pWriter = new PrintWriter(sWriter);
e.printStackTrace(pWriter);
return sWriter.toString();
}

In your logging code, you could write:

logger.error("An exception occurred: " + Utils.getStackTrace(e));

小开

What you have posted should display the stack trace as stated in the javadoc.

Note that if you don't include a message (and just call logger.error(ex)) then the stack trace is not logged.

小开

最佳答案

Actually, it's probably due to a hotspot optimization: after a certain number of the same exception being thrown it stops printing out trace. This can be turned off with a VM arg, see:

From http://www.oracle.com/technetwork/java/javase/relnotes-139183.html :

The compiler in the server VM now provides correct stack backtraces for all "cold" built-in exceptions. For performance purposes, when such an exception is thrown a few times, the method may be recompiled. After recompilation, the compiler may choose a faster tactic using preallocated exceptions that do not provide a stack trace. To disable completely the use of preallocated exceptions, use this new flag: -XX:-OmitStackTraceInFastThrow.

More here:

http://jawspeak.com/2010/05/26/hotspot-caused-exceptions-to-lose-their-stack-traces-in-production-and-the-fix/

小开

Like answered by @Luhar above, I struggled with same thing and finally this worked for me; Good thing about this approach is we don't have to tinker with system level settings like JVM, Log4J since we never know it may lead to new unexpected surprise !

try {


...
..


} catch (Exception er) {
ByteArrayOutputStream os = new ByteArrayOutputStream();
er.printStackTrace(new PrintStream(os));
LOGGER.error(new String(os.toByteArray()));
//LOGGER.error(er);
}

小开

You can add these lines of code in your catch block.

catch (SQLException e) {
CharArrayWriter cw = new CharArrayWriter();
PrintWriter w = new PrintWriter(cw);
e.printStackTrace(w);
w.close();
String trace = cw.toString();


log.error("This is complete stacktrace", trace);
}

小开

There are two overloaded methods for error method.

logger.error(ex);
logger.error("some oops string ", ex);

if you use 1st method , which will only print the name of the Exception. if you use 2nd method, some message along with exception which will print complete stack trace similar to e.printStackTrace() method.