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

如果你不介意使用第三方自由库(Vavr),你可以写

CheckedFunction1<String, Integer> f = this::myMethod;

它也有所谓的Try单子来处理错误:

Try(() -> f.apply("test")) // results in a Success(Integer) or Failure(Throwable)
        .map(i -> ...) // only executed on Success
        ...

请在这里阅读更多。

声明:我是Vavr的创造者。

如果您不介意使用第三方库,使用cyclops-react(我贡献的一个库),您可以使用FluentFunctions API来编写

 Function<String, Integer> standardFn = FluentFunctions.ofChecked(this::myMethod);

ofChecked接受jOOλ CheckedFunction,并将软化后的引用返回到标准(未选中)JDK java.util.function.Function。

或者,你可以通过FluentFunctions api继续使用捕获的函数!

例如,要执行你的方法,最多重试5次,并记录你可以写入的状态

  FluentFunctions.ofChecked(this::myMethod)
                 .log(s->log.debug(s),e->log.error(e,e.getMessage())
                 .try(5,1000)
                 .apply("my param");

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

您需要执行以下操作之一。

If it's your code, then define your own functional interface that declares the checked exception: @FunctionalInterface public interface CheckedFunction<T, R> { R apply(T t) throws IOException; } and use it: void foo (CheckedFunction f) { ... } Otherwise, wrap Integer myMethod(String s) in a method that doesn't declare a checked exception: public Integer myWrappedMethod(String s) { try { return myMethod(s); } catch(IOException e) { throw new UncheckedIOException(e); } } and then: Function<String, Integer> f = (String t) -> myWrappedMethod(t); or: Function<String, Integer> f = (String t) -> { try { return myMethod(t); } catch(IOException e) { throw new UncheckedIOException(e); } };

默认情况下,Java 8函数不允许抛出异常,正如在多个回答中所建议的那样,有许多方法来实现它,其中一种方法是:

@FunctionalInterface
public interface FunctionWithException<T, R, E extends Exception> {
    R apply(T t) throws E;
}

定义为:

private FunctionWithException<String, Integer, IOException> myMethod = (str) -> {
    if ("abc".equals(str)) {
        throw new IOException();
    }
  return 1;
};

并在调用者方法中添加抛出或尝试/捕获相同的异常。