ThrowablesExplained

Throwables

Guava's Throwables utility can frequently simplify dealing with exceptions.

Propagation

Sometimes, when you catch an exception, you want to throw it back up to the next try/catch block. This is frequently the case for RuntimeException or Error instances, which do not require try/catch blocks, but can be caught by try/catch blocks when you don't mean them to.

Guava provides several utilities to simplify propagating exceptions. For example:

try {
  someMethodThatCouldThrowAnything();
} catch (IKnowWhatToDoWithThisException e) {
  handle(e);
} catch (Throwable t) {
  Throwables.throwIfInstanceOf(t, IOException.class);
  Throwables.throwIfInstanceOf(t, SQLException.class);
  Throwables.throwIfUnchecked(t);
  throw new RuntimeException(t);
}

Here are quick summaries of the propagation methods provided by Guava:

Signature	Explanation
void propagateIfPossible(Throwable, Class<X extends Throwable>) throws X	Throws throwable as-is only if it is a RuntimeException, an Error, or an X.
void throwIfInstanceOf(Throwable, Class<X extends Exception>) throws X	Propagates the throwable as-is, if and only if it is an instance of X.
void throwIfUnchecked(Throwable)	Throws throwable as-is only if it is a RuntimeException or an Error.

NOTE: We deprecated Throwables.propagate(Throwable) in v20.0. Read about why.

Causal Chain

Guava makes it somewhat simpler to study the causal chain of an exception, providing three useful methods whose signatures are self-explanatory:

• Throwable getRootCause(Throwable)
• List<Throwable> getCausalChain(Throwable)
• String getStackTraceAsString(Throwable)