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Message-Id: <48104D25.1915.0068.0@mdinsurance.state.md.us>
Date: Thu, 24 Apr 2008 09:04:39 -0400
From: "Robert Pepersack" <RPepersack@mdinsurance.state.md.us>
To: "Log4J Users List" <log4j-user@logging.apache.org>
Subject: Re: FileAppender Truncates Stack Trace
References: <480F6211.1915.0068.0@mdinsurance.state.md.us>
 <d54c36420804231328i6da71405q826318eb95ff3298@mail.gmail.com>
 <9DABEA5B-3058-47C0-B1C0-F589C26748C3@apache.org>
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Thanks for your reply.

I've seen this behavior with many different exception classes, so I think =
it's the VM.

I've written a couple of appenders before.  For example, I wrote a =
SystemOutAppender that solves this problem when printing to the console.  =
The source code for SystemOutAppender is below.  How would I adapt this to =
work as DailyRollingFileAppender and FileAppender?

// SystemOutAppender.java

package myapp;

import org.apache.log4j.Layout;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.spi.ThrowableInformation;
import org.apache.log4j.AppenderSkeleton;


/**
 * SystemOutAppender is a custom log4j appender
 * that writes to the console using System.out.
 * Its output includes nested exceptions and their
 * stack traces.
 */
public class SystemOutAppender extends AppenderSkeleton
{

    /**
     * Default constructor.
     */
    public SystemOutAppender(){}


    /**
     * Construct an appender with the specified
     * Layout.
     */
    public SystemOutAppender(Layout layout)
    {
        this.layout =3D layout;
    }


    /**
     * Implement the abstract append method
     * inherited from AppenderSkeleton, which
     * AppenderSkeleton calls from doAppend().
     */
    public void append(LoggingEvent event)
    {
        ThrowableInformation throwableInfo =3D null;
        Throwable throwable =3D null;
        Throwable cause =3D null;
        String exceptionId =3D null;
        StackTraceElement[] stackTrace =3D null;
        String smallIndent =3D "      ";
        String largeIndent =3D "          at ";
        StringBuffer stringBuffer =3D new StringBuffer();

        // Print the information indicated by the
        // Layout.
        stringBuffer.append(this.layout.format(event));

        // Check to see if this LoggingEvent has
        // ThrowableInformation.
        if ((throwableInfo =3D event.getThrowableInformation()) !=3D null)
        {
            // Check to see if there is a Throwable.
            // If there is a Throwable, check to see
            // if it is RuntimeApplicationException.  If
            // so, then get its exception ID.
            if ((throwable =3D throwableInfo.getThrowable()) !=3D null)
            {
                cause =3D throwable;

                // Drill down to the point where there is
                // no cause encapsulated by the current
                // cause.
                while(cause !=3D null)
                {
                    stringBuffer.append(smallIndent);

                    // "Caused by: " is unnecessary for the
                    // outermost Throwable.
                    if (cause !=3D throwable)
                    {
                        stringBuffer.append("Caused by: ");
                    }

                    stringBuffer.append(cause.toString() + "\n");


                    // Get the StackTraceElements for this cause.
                    stackTrace =3D cause.getStackTrace();

                    // Loop through all of the StackTraceElements
                    // for this cause and append them to the
                    // StringBuffer.
                    for(int i =3D 0; i < stackTrace.length; i++)
                    {
                        stringBuffer.append(largeIndent +
                                            stackTrace[i] +
                                            "\n");
                    }

                    cause =3D cause.getCause();
                }
            }
        }

        // Print the contents of the StringBuffer.
        System.out.println(stringBuffer.toString());
    }


    public boolean requiresLayout()
    {
        return true;
    }


    public void close()
    {
        if (this.closed)
        {
            return;
        }

        this.closed =3D true;
    }

}

Thanks,

Bob

>>> Curt Arnold <carnold@apache.org> 04/23/2008 6:19 PM >>>
Okay, I'm assuming that somewhere this exception is passed to log4j in =20
something like:

try {
      ///
} catch(Exception ex) {
     logger.info("Some app message", ex);
}

Using a standard layout, the stack trace will get rendered by =20
WriterAppender.subAppend.

     this.qw.write(this.layout.format(event));

     if(layout.ignoresThrowable()) {
       String[] s =3D event.getThrowableStrRep();
       if (s !=3D null) {
	int len =3D s.length;
	for(int i =3D 0; i < len; i++) {
	  this.qw.write(s[i]);
	  this.qw.write(Layout.LINE_SEP);
	}
       }
     }


Most appenders will return ignoreThrowable to true which will result =20
in org.apache.log4j.spi.LoggingEvent;getThrowableStrRep() to render =20
the exception which will eventually end up at =20
org.apache.log4j.spi.ThrowableInformation.getThrowableStrRep() which =20
will then call the printStackTrace() method of the exception.  The =20
SymSQLException.printStackTrace() implementation (or the underlying =20
JVM) is most likely the source of the ".. 14 more".

At least as I understand the situation, OnlyOnceErrorHandler would not =20
be involved.  It would only be involved if the appender was raising =20
exceptions and you mentioned using a FileAppender and a file appender =20
should not be raising SQL exceptions.

A custom object renderer would not be useful unless the exception was =20
used as the message parameter, which is probably not the case.

The best way to add a custom rendering of the stack trace would be to =20
write a custom appender (likely either wrapping or extending =20
PatternLayout) which returns false ignoresThrowable() and then appends =20
your custom equivalent to printStackTrace() the the result of the =20
PatternLayout.format.


On Apr 23, 2008, at 3:28 PM, Matthew Kemp wrote:

> You can create your own custom object renderer that will properly =20
> render the
> whole stack trace. This renderer will need to be included in the log4j
> config and be available on the classpath when log4j initializes.
>
>
> On Wed, Apr 23, 2008 at 3:19 PM, Robert Pepersack <
> RPepersack@mdinsurance.state.md.us> wrote:
>
>> Hello,
>>
>> I'm using FileAppender to log to a log file.  When an exception gets
>> caught and printed, the stack trace is truncated as it usually is by
>> default:
>>
>> Caused by: com.sybase.jdbc3.jdbc.SybSQLException: Attempt to insert =20
>> NULL
>> value into column 'id', table 'table'; column does not allow nulls. =20
>> Update
>> fails.
>>
>>       at com.sybase.jdbc3.tds.Tds.a(Unknown Source)
>>       at com.sybase.jdbc3.tds.Tds.nextResult(Unknown Source)
>>       at com.sybase.jdbc3.jdbc.ResultGetter.nextResult(Unknown =20
>> Source)
>>       at com.sybase.jdbc3.jdbc.SybStatement.nextResult(Unknown =20
>> Source)
>>       at com.sybase.jdbc3.jdbc.SybStatement.nextResult(Unknown =20
>> Source)
>>       at com.sybase.jdbc3.jdbc.SybStatement.queryLoop(Unknown Source)
>>       at =20
>> com.sybase.jdbc3.jdbc.SybCallableStatement.executeQuery(Unknown
>> Source)
>>       at miaJs.jdbc.JdbcFacade.executeQuery(JdbcFacade.java:977)
>>       ... 14 more
>>
>> Instead of  the "... 14 more" at the bottom, I would like to see the
>> entire stack trace.  I know how to get Java to do this by using
>> Throwable.getStackTrace(), and then loop through the array of
>> StackTraceElements.  I looked in the log4j source code.  I think that
>> FileAppender uses the OnlyOnceErrorHandler in its super, superclass
>> AppenderSkeleton.  It looks like OnlyOnceErrorHandler uses LogLog.  =20
>> But, I'm
>> not sure how to get log4j to print the entire stack trace.
>>
>> Thanks,
>>
>> Bob
>>
>>
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