final Consumer<String> consumer = aps -> {
try {
// maybe some other code here...
throw new Exception("asdas");
} catch (final Exception ex) {
System.out.println("handling an exception...");
}
};
list.forEach(consumer);
但是有了这个新接口,你可以用lambda表达式实例化它,编译器不会报错:
final ThrowingConsumer<String> throwingConsumer = aps -> {
// maybe some other code here...
throw new Exception("asdas");
};
list.forEach(throwingConsumer);
或者甚至只是转换它更简洁!:
list.forEach((ThrowingConsumer<String>) aps -> {
// maybe some other code here...
throw new Exception("asda");
});
// Do this once
ExceptionTranslator et = ET.newConfiguration().done();
...
// if your method returns something
Function<String, Integer> f = (t) -> et.withReturningTranslation(() -> myMethod(t));
// if your method returns nothing
Consumer<String> c = (t) -> et.withTranslation(() -> myMethod(t));
acceptMyMethod(s -> {
try {
Integer i = doSomeOperation(s);
return i;
} catch (IOException e) {
// try catch block because of throws clause
// in functional method, even though doSomeOperation
// might not be throwing any exception at all.
e.printStackTrace();
}
return null;
});
public static interface CheckedValueSupplier<V> {
public V get () throws Exception;
}
CheckedValue
public class CheckedValue<V> {
private final V v;
private final Optional<Exception> opt;
public Value (V v) {
this.v = v;
}
public Value (Exception e) {
this.opt = Optional.of(e);
}
public V get () throws Exception {
if (opt.isPresent()) {
throw opt.get();
}
return v;
}
public Optional<Exception> getException () {
return opt;
}
public static <T> CheckedValue<T> returns (T t) {
return new CheckedValue<T>(t);
}
public static <T> CheckedValue<T> rethrows (Exception e) {
return new CheckedValue<T>(e);
}
public static <V> CheckedValue<V> from (CheckedValueSupplier<V> sup) {
try {
return CheckedValue.returns(sup.get());
} catch (Exception e) {
return Result.rethrows(e);
}
}
public static <V> CheckedValue<V> escalates (CheckedValueSupplier<V> sup) {
try {
return CheckedValue.returns(sup.get());
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
使用
// Don't use this pattern with FileReader, it's meant to be an
// example. FileReader is a Closeable resource and as such should
// be managed in a try-with-resources block or in another safe
// manner that will make sure it is closed properly.
// This will not compile as the FileReader constructor throws
// an IOException.
Function<String, FileReader> sToFr =
(fn) -> new FileReader(Paths.get(fn).toFile());
// Alternative, this will compile.
Function<String, CheckedValue<FileReader>> sToFr = (fn) -> {
return CheckedValue.from (
() -> new FileReader(Paths.get("/home/" + f).toFile()));
};
// Single record usage
// The call to get() will propagate the checked exception if it exists.
FileReader readMe = pToFr.apply("/home/README").get();
// List of records usage
List<String> paths = ...; //a list of paths to files
Collection<CheckedValue<FileReader>> frs =
paths.stream().map(pToFr).collect(Collectors.toList());
// Find out if creation of a file reader failed.
boolean anyErrors = frs.stream()
.filter(f -> f.getException().isPresent())
.findAny().isPresent();
public final class Throwing {
private Throwing() {}
@Nonnull
public static <T> Consumer<T> rethrow(@Nonnull final ThrowingConsumer<T> consumer) {
return consumer;
}
/**
* The compiler sees the signature with the throws T inferred to a RuntimeException type, so it
* allows the unchecked exception to propagate.
*
* http://www.baeldung.com/java-sneaky-throws
*/
@SuppressWarnings("unchecked")
@Nonnull
public static <E extends Throwable> void sneakyThrow(@Nonnull Throwable ex) throws E {
throw (E) ex;
}
}
public class UncheckedExceptions {
/**
* throws {@code exception} as unchecked exception, without wrapping exception.
*
* @return will never return anything, return type is set to {@code exception} only to be able to write <code>throw unchecked(exception)</code>
* @throws T {@code exception} as unchecked exception
*/
@SuppressWarnings("unchecked")
public static <T extends Throwable> T unchecked(Exception exception) throws T {
throw (T) exception;
}
@FunctionalInterface
public interface UncheckedFunction<R> {
R call() throws Exception;
}
/**
* Executes given function,
* catches and rethrows checked exceptions as unchecked exceptions, without wrapping exception.
*
* @return result of function
* @see #unchecked(Exception)
*/
public static <R> R unchecked(UncheckedFunction<R> function) {
try {
return function.call();
} catch (Exception e) {
throw unchecked(e);
}
}
@FunctionalInterface
public interface UncheckedMethod {
void call() throws Exception;
}
/**
* Executes given method,
* catches and rethrows checked exceptions as unchecked exceptions, without wrapping exception.
*
* @see #unchecked(Exception)
*/
public static void unchecked(UncheckedMethod method) {
try {
method.call();
} catch (Exception e) {
throw unchecked(e);
}
}
}
unchecked(() -> new File("hello.txt").createNewFile());
boolean fileWasCreated = unchecked(() -> new File("hello.txt").createNewFile());
myFiles.forEach(unchecked(file -> new File(file.path).createNewFile()));
支持工具
public class UncheckedUtils {
@FunctionalInterface
public interface ThrowingConsumer<T> {
void accept(T t) throws Exception;
}
@FunctionalInterface
public interface ThrowingSupplier<T> {
T get() throws Exception;
}
@FunctionalInterface
public interface ThrowingRunnable {
void run() throws Exception;
}
public static <T> Consumer<T> unchecked(
ThrowingConsumer<T> throwingConsumer
) {
return i -> {
try {
throwingConsumer.accept(i);
} catch (Exception ex) {
throw new RuntimeException(ex);
}
};
}
public static <T> T unchecked(
ThrowingSupplier<T> throwingSupplier
) {
try {
return throwingSupplier.get();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
public static void unchecked(
ThrowingRunnable throwing
) {
try {
throwing.run();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
}