我知道如何创建一个有String参数并返回int的方法的引用,它是:

Function<String, Integer>

然而,如果函数抛出异常,比如它被定义为:

Integer myMethod(String s) throws IOException

我该如何定义这个引用呢?


当前回答

可以使用取消抛出包装器

Function<String, Integer> func1 = s -> Unthrow.wrap(() -> myMethod(s));

or

Function<String, Integer> func2 = s1 -> Unthrow.wrap((s2) -> myMethod(s2), s1);

其他回答

实际上,您可以使用一个处理异常的新接口来扩展Consumer(和Function等)——使用Java 8的默认方法!

考虑这个接口(扩展Consumer):

@FunctionalInterface
public interface ThrowingConsumer<T> extends Consumer<T> {

    @Override
    default void accept(final T elem) {
        try {
            acceptThrows(elem);
        } catch (final Exception e) {
            // Implement your own exception handling logic here..
            // For example:
            System.out.println("handling an exception...");
            // Or ...
            throw new RuntimeException(e);
        }
    }

    void acceptThrows(T elem) throws Exception;

}

然后,例如,如果你有一个列表:

final List<String> list = Arrays.asList("A", "B", "C");

如果你想消费它(例如。使用forEach)和一些抛出异常的代码,你通常会设置一个try/catch块:

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");
});

更新

看起来榴莲有一个非常好的实用程序库,叫做Errors,可以用来解决这个问题,具有更大的灵活性。例如,在上面的实现中,我显式地定义了错误处理策略(System.out…或者抛出RuntimeException),而Durian的Errors允许您通过一套大型实用程序方法动态应用策略。感谢分享,@NedTwigg!

示例用法:

list.forEach(Errors.rethrow().wrap(c -> somethingThatThrows(c)));

我是一个小库的作者,它具有一些通用的魔法,可以在任何地方抛出任何Java异常,而不需要捕获它们,也不需要将它们包装到RuntimeException中。

用法: unchecked(() -> methodThrowingCheckedException())

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);
        }
    }
}

来源:https://github.com/qoomon/unchecked-exceptions-java

使用Function包装器的另一种解决方案是返回结果包装器的实例,如果一切正常,则返回成功,或者返回失败。

一些代码来澄清事情:

public interface ThrowableFunction<A, B> {
    B apply(A a) throws Exception;
}

public abstract class Try<A> {

    public static boolean isSuccess(Try tryy) {
        return tryy instanceof Success;
    }

    public static <A, B> Function<A, Try<B>> tryOf(ThrowableFunction<A, B> function) {
        return a -> {
            try {
                B result = function.apply(a);
                return new Success<B>(result);
            } catch (Exception e) {
                return new Failure<>(e);
            }
        };
    }

    public abstract boolean isSuccess();

    public boolean isError() {
        return !isSuccess();
    }

    public abstract A getResult();

    public abstract Exception getError();
}

public class Success<A> extends Try<A> {

    private final A result;

    public Success(A result) {
        this.result = result;
    }

    @Override
    public boolean isSuccess() {
        return true;
    }

    @Override
    public A getResult() {
        return result;
    }

    @Override
    public Exception getError() {
        return new UnsupportedOperationException();
    }

    @Override
    public boolean equals(Object that) {
        if(!(that instanceof Success)) {
            return false;
        }
        return Objects.equal(result, ((Success) that).getResult());
    }
}

public class Failure<A> extends Try<A> {

    private final Exception exception;

    public Failure(Exception exception) {
        this.exception = exception;
    }

    @Override
    public boolean isSuccess() {
        return false;
    }

    @Override
    public A getResult() {
        throw new UnsupportedOperationException();
    }

    @Override
    public Exception getError() {
        return exception;
    }
}

一个简单的用例:

List<Try<Integer>> result = Lists.newArrayList(1, 2, 3).stream().
    map(Try.<Integer, Integer>tryOf(i -> someMethodThrowingAnException(i))).
    collect(Collectors.toList());

使用Jool库或JOOQ中的jOOλ库。它不仅提供了未经检查的异常处理接口,还为Seq类提供了许多有用的方法。

此外,它包含多达16个参数的功能接口。此外,它还提供了用于不同场景的Tuple类。

乔尔去链接

特别是在org.jooq.lambda.fi.util.function包的库查找中。它包含Java-8中所有带有前置Checked的接口。参考如下:-

Sneaky throw成语允许绕过Lambda表达式的CheckedException。将CheckedException包装在RuntimeException中不利于严格的错误处理。

它可以用作Java集合中使用的Consumer函数。

下面是jib答案的一个简单改进版本。

import static Throwing.rethrow;

@Test
public void testRethrow() {
    thrown.expect(IOException.class);
    thrown.expectMessage("i=3");

    Arrays.asList(1, 2, 3).forEach(rethrow(e -> {
        int i = e.intValue();
        if (i == 3) {
            throw new IOException("i=" + i);
        }
    }));
}

这只是在重新抛出中包装lambda。它使CheckedException重新抛出在lambda中抛出的任何异常。

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;
    }

}

在这里找到完整的代码和单元测试。