Is it possible to declare that a Supplier<T> needs to throw an Exception?
functional-interface, java, java-8
Solution
Edit
As pointed many times, you don't need any custom class, use Callable and Runnable instead
Wrong, outdated solution
Consider this generic solution:
// We need to describe supplier which can throw exceptions
@FunctionalInterface
public interface ThrowingSupplier<T> {
T get() throws Exception;
}
// Now, wrapper
private <T> T callMethod(ThrowingSupplier<T> supplier) {
try {
return supplier.get();
} catch (Exception e) {
throw new RuntimeException(e);
}
return null;
}
// And usage example
String methodThrowsException(String a, String b, String c) throws Exception {
// do something
}
String result = callMethod(() -> methodThrowsException(x, y, z));
Problem
So I am trying to refactor the following code: ``` /** * Returns the duration from the config file. * * @return The duration. */ private Duration durationFromConfig() { try { return durationFromConfigInner(); } catch (IOException ex) { throw new IllegalStateException("The config file (\"" + configFile + "\") has not been found."); } } /** * Returns the duration from the config file. * * Searches the log file for the first line indicating the config entry for this instance. * * @return The duration. * @throws FileNotFoundException If the config file has not been found. */ private Duration durationFromConfigInner() throws IOException { String entryKey = subClass.getSimpleName(); configLastModified = Files.getLastModifiedTime(configFile); String entryValue = ConfigFileUtils.readFileEntry(configFile, entryKey); return Duration.of(entryValue); } ``` I came up with the following to start of with: ``` private <T> T getFromConfig(final Supplier<T> supplier) { try { return supplier.get(); } catch (IOException ex) { throw new IllegalStateException("The config file (\"" + configFile + "\") has not been found."); } } ``` However, it does not compile (obviously), as `Supplier` cannot throw an `IOException`. Is there any way I can add that to the method declaration of `getFromConfig`? Or is the only way to do it like the following? ``` @FunctionalInterface public interface SupplierWithIO<T> extends Supplier<T> { @Override @Deprecated default public T get() { throw new UnsupportedOperationException(); } public T getWithIO() throws IOException; } ``` Update, I just realised that the `Supplier` interface is a really simple one, as in it has only the `get()` method. The original reason why I extended `Supplier` is to preverse the basic functionality, like the default methods for example.