Passing message arguments that require further evaluation into a Guava com.google.common.base.Preconditions
check can result in a
performance penalty. That's because whether or not they're needed, each argument must be resolved before the method is actually called.
Similarly, passing concatenated strings into a logging method can also incur a needless performance hit because the concatenation will be performed every time the method is called, whether or not the log level is low enough to show the message.
Instead, you should structure your code to pass static or pre-computed values into Preconditions
conditions check and logging
calls.
Specifically, the built-in string formatting should be used instead of string concatenation, and if the message is the result of a method call,
then Preconditions
should be skipped altoghether, and the relevant exception should be conditionally thrown instead.
logger.log(Level.DEBUG, "Something went wrong: " + message); // Noncompliant; string concatenation performed even when log level too high to show DEBUG messages logger.fine("An exception occurred with message: " + message); // Noncompliant LOG.error("Unable to open file " + csvPath, e); // Noncompliant Preconditions.checkState(a > 0, "Arg must be positive, but got " + a); // Noncompliant. String concatenation performed even when a > 0 Preconditions.checkState(condition, formatMessage()); // Noncompliant. formatMessage() invoked regardless of condition Preconditions.checkState(condition, "message: %s", formatMessage()); // Noncompliant
logger.log(Level.SEVERE, "Something went wrong: {0} ", message); // String formatting only applied if needed logger.fine("An exception occurred with message: {}", message); // SLF4J, Log4j logger.log(Level.SEVERE, () -> "Something went wrong: " + message); // since Java 8, we can use Supplier , which will be evaluated lazily LOG.error("Unable to open file {0}", csvPath, e); if (LOG.isDebugEnabled() { LOG.debug("Unable to open file " + csvPath, e); // this is compliant, because it will not evaluate if log level is above debug. } Preconditions.checkState(arg > 0, "Arg must be positive, but got %d", a); // String formatting only applied if needed if (!condition) { throw new IllegalStateException(formatMessage()); // formatMessage() only invoked conditionally } if (!condition) { throw new IllegalStateException("message: " + formatMessage()); }
catch
blocks are ignored, because the performance penalty is unimportant on exceptional paths (catch block should not be a part of
standard program flow). Getters are ignored. This rule accounts for explicit test-level testing with SLF4J methods isXXXEnabled
and
ignores the bodies of such if
statements.