tomcat console does not appear after printing problems

My program is running more than a dozen hours later, suddenly the console does not print , and then run a few minutes all threads are suspended, only the main thread is normal, began to suspect that the database connection pool settings have a problem , look after the database connection not a problem , seeking expert analyze the reasons , grateful
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facie tomcat log directory log files , some error log messages are in that
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you You can manually break out ah can also use log4j.
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I find the reason is because when printing with a lot of strings behind the null so a long time so the console a problem ; processing a moment there is no longer out , as to why the strings behind many will follow as a special case null bad description
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I also put all the syso all changed to log4j bottom of this problem was found
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problem has been solved points bisects it