Change to use try-with-resources on test

[kazuki43zoo]

In current implementation, close a external resource explicitly.

Before:
e.g.

Connection connection = ....;
try {
    // ...
} finally {
    connection.close();
}

or

Reader reader = ....;
// ...
reader.close();  // If an exception is occurred, there is possible that an external resource does not close 

I've modified to use the try-with-resources supported by JDK 7 as follow:

After:

try (Connection connection = ....) {
    // ...
}