Exception Handling - Beginning Java 8 Fundamentals - page 369

Creating MyResource. Level = 2
Using MyResource level 2
Using MyResource level 1
Closing MyResource...
When a resource is being closed automatically, an exception may be thrown. If a try-with-resources block
completes without throwing an exception and the call to the close() method throws the exception, the runtime
reports the exception thrown from the close() method. If a try-with-resources block throws an exception and the
call to the close() method also throws an exception, the runtime suppresses the exception thrown from the close()
method and reports the exception thrown from the try-with-resources block. The following snippet of code
demonstrates this rule:
// Create a resource of MyResource type with two levels, which can throw exception on closing
// and use it thrice so that its use() method throws an exception
try (MyResource mr = new MyResource (2, true) ) {
mr.use();
mr.use();
mr.use(); // Will throw a RuntimeException
}
catch(Exception e) {
System.out.println(e.getMessage());
}
Creating MyResource. Level = 2
Using MyResource level 2
Using MyResource level 1
Low in level.
The third call to the use() method throws an exception. In the above snippet of code, the automatic close()
method call will throw a RuntimeException because you pass true as the second argument when you create the
resource. The output shows that the catch block received the RuntimeException that was thrown from the use()
method, not from the close() method.
You can retrieve the suppressed exceptions by using the getSuppressed() method of the Throwable class. The
method was added in Java 7. It returns an array of Throwable objects. Each object in the array represents a suppressed
exception. The following snippet of code demonstrates the use of the getSuppressed() method to retrieve the
suppressed exceptions:
try (MyResource mr = new MyResource (2, true) ) {
mr.use();
mr.use();
mr.use(); // Throws an exception
}
catch(Exception e) {
System.out.println(e.getMessage());
// Display messages of supressed exceptions
System.out.println("Suppressed exception messages are...");
for(Throwable t : e.getSuppressed()) {
System.out.println(t.getMessage());
}
}