我认为这种方法是正确的:

public List<Class> getClasses() throws ClassNotFoundException {
    List<Class> classes;
    try {
        classes = Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String").map(className -> {
            try {
                return Class.forName(className);
            } catch (ClassNotFoundException e) {
                throw new UndeclaredThrowableException(e);
            }
        }).collect(Collectors.toList());
    } catch (UndeclaredThrowableException e) {
        if (e.getCause() instanceof ClassNotFoundException) {
            throw (ClassNotFoundException) e.getCause();
        } else {
            // this should never happen
            throw new IllegalStateException(e.getMessage(), e);
        }
    }
    return classes;
}

将检查过的异常包装在一个unclaredthrowableexception(这是该异常的用例)的Callable内部，并在外部将其展开。

是的，我觉得它很难看，我建议在这种情况下不要使用lambdas，而是退回到一个好的旧循环，除非您正在使用并行流，并且并行化带来了客观的好处，可以证明代码的不可读性是正确的。

正如许多人所指出的那样，有解决这种情况的解决方案，我希望其中一个解决方案能够出现在Java的未来版本中。

只要使用Lombok的@SneakyThrows就可以了。

Christian Hujer已经详细解释了为什么严格来说，由于Java的限制，从流中抛出受控异常是不可能的。

其他一些回答解释了一些技巧，可以绕过语言的限制，但仍然能够满足抛出“检查异常本身，并且不向流中添加丑陋的try/catch”的要求，其中一些需要额外的数十行样板文件。

我要强调的是另一个选项，在我看来，这个选项比其他选项干净得多:Lombok的@SneakyThrows。这个问题在其他答案中也提到过，但有很多不必要的细节。

生成的代码非常简单:

public List<Class> getClasses() throws ClassNotFoundException {
    List<Class> classes =
        Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
                .map(className -> getClass(className))
                .collect(Collectors.toList());
    return classes;
}

@SneakyThrows                                 // <= this is the only new code
private Class<?> getClass(String className) {
    return Class.forName(className);
}

我们只需要一个提取方法重构(由IDE完成)和一行额外的@SneakyThrows。注释负责添加所有样板文件，以确保您可以抛出检查过的异常，而无需将其包装在RuntimeException中，也无需显式声明它。

这是原来问题的不同观点或解决方案。在这里，我展示了我们有一个选项来编写只处理有效值子集的代码，并有一个选项来检测和处理抛出异常时的情况。

    @Test
    public void getClasses() {

        String[] classNames = {"java.lang.Object", "java.lang.Integer", "java.lang.Foo"};
        List<Class> classes =
                Stream.of(classNames)
                        .map(className -> {
                            try {
                                return Class.forName(className);
                            } catch (ClassNotFoundException e) {
                                // log the error
                                return null;
                            }
                        })
                        .filter(c -> c != null)
                        .collect(Collectors.toList());

        if (classes.size() != classNames.length) {
            // add your error handling here if needed or process only the resulting list
            System.out.println("Did not process all class names");
        }

        classes.forEach(System.out::println);
    }

这个LambdaExceptionUtil帮助类允许你在Java流中使用任何受控异常，像这样:

Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
      .map(rethrowFunction(Class::forName))
      .collect(Collectors.toList());

注意:Class::forName抛出ClassNotFoundException，该异常被检查。流本身也会抛出ClassNotFoundException和NOT一些未检查的包装异常。

public final class LambdaExceptionUtil {

@FunctionalInterface
public interface Consumer_WithExceptions<T, E extends Exception> {
    void accept(T t) throws E;
    }

@FunctionalInterface
public interface BiConsumer_WithExceptions<T, U, E extends Exception> {
    void accept(T t, U u) throws E;
    }

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

@FunctionalInterface
public interface Supplier_WithExceptions<T, E extends Exception> {
    T get() throws E;
    }

@FunctionalInterface
public interface Runnable_WithExceptions<E extends Exception> {
    void run() throws E;
    }

/** .forEach(rethrowConsumer(name -> System.out.println(Class.forName(name)))); or .forEach(rethrowConsumer(ClassNameUtil::println)); */
public static <T, E extends Exception> Consumer<T> rethrowConsumer(Consumer_WithExceptions<T, E> consumer) throws E {
    return t -> {
        try { consumer.accept(t); }
        catch (Exception exception) { throwAsUnchecked(exception); }
        };
    }

public static <T, U, E extends Exception> BiConsumer<T, U> rethrowBiConsumer(BiConsumer_WithExceptions<T, U, E> biConsumer) throws E {
    return (t, u) -> {
        try { biConsumer.accept(t, u); }
        catch (Exception exception) { throwAsUnchecked(exception); }
        };
    }

/** .map(rethrowFunction(name -> Class.forName(name))) or .map(rethrowFunction(Class::forName)) */
public static <T, R, E extends Exception> Function<T, R> rethrowFunction(Function_WithExceptions<T, R, E> function) throws E {
    return t -> {
        try { return function.apply(t); }
        catch (Exception exception) { throwAsUnchecked(exception); return null; }
        };
    }

/** rethrowSupplier(() -> new StringJoiner(new String(new byte[]{77, 97, 114, 107}, "UTF-8"))), */
public static <T, E extends Exception> Supplier<T> rethrowSupplier(Supplier_WithExceptions<T, E> function) throws E {
    return () -> {
        try { return function.get(); }
        catch (Exception exception) { throwAsUnchecked(exception); return null; }
        };
    }

/** uncheck(() -> Class.forName("xxx")); */
public static void uncheck(Runnable_WithExceptions t)
    {
    try { t.run(); }
    catch (Exception exception) { throwAsUnchecked(exception); }
    }

/** uncheck(() -> Class.forName("xxx")); */
public static <R, E extends Exception> R uncheck(Supplier_WithExceptions<R, E> supplier)
    {
    try { return supplier.get(); }
    catch (Exception exception) { throwAsUnchecked(exception); return null; }
    }

/** uncheck(Class::forName, "xxx"); */
public static <T, R, E extends Exception> R uncheck(Function_WithExceptions<T, R, E> function, T t) {
    try { return function.apply(t); }
    catch (Exception exception) { throwAsUnchecked(exception); return null; }
    }

@SuppressWarnings ("unchecked")
private static <E extends Throwable> void throwAsUnchecked(Exception exception) throws E { throw (E)exception; }

}

许多其他关于如何使用它的例子(在静态导入LambdaExceptionUtil之后):

@Test
public void test_Consumer_with_checked_exceptions() throws IllegalAccessException {
    Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
          .forEach(rethrowConsumer(className -> System.out.println(Class.forName(className))));

    Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
          .forEach(rethrowConsumer(System.out::println));
    }

@Test
public void test_Function_with_checked_exceptions() throws ClassNotFoundException {
    List<Class> classes1
          = Stream.of("Object", "Integer", "String")
                  .map(rethrowFunction(className -> Class.forName("java.lang." + className)))
                  .collect(Collectors.toList());

    List<Class> classes2
          = Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
                  .map(rethrowFunction(Class::forName))
                  .collect(Collectors.toList());
    }

@Test
public void test_Supplier_with_checked_exceptions() throws ClassNotFoundException {
    Collector.of(
          rethrowSupplier(() -> new StringJoiner(new String(new byte[]{77, 97, 114, 107}, "UTF-8"))),
          StringJoiner::add, StringJoiner::merge, StringJoiner::toString);
    }

@Test    
public void test_uncheck_exception_thrown_by_method() {
    Class clazz1 = uncheck(() -> Class.forName("java.lang.String"));

    Class clazz2 = uncheck(Class::forName, "java.lang.String");
    }

@Test (expected = ClassNotFoundException.class)
public void test_if_correct_exception_is_still_thrown_by_method() {
    Class clazz3 = uncheck(Class::forName, "INVALID");
    }    

截至2015年11月，代码在@PaoloC的帮助下得到了改进，请检查下面他的回答并投票。他帮助解决了最后一个问题:现在编译器会要求您添加抛出子句，一切就好像您可以在Java 8流上本机抛出检查异常一样。

注1:上面LambdaExceptionUtil类的重抛出方法可以毫无顾虑地使用，并且可以在任何情况下使用。

注2:上面LambdaExceptionUtil类的取消检查方法是额外的方法，如果你不想使用它们，可以安全地从类中删除它们。如果你确实使用了它们，请谨慎使用，在了解以下用例、优点/缺点和限制之前不要使用:

•如果你调用的方法永远不会抛出它声明的异常，你可以使用uncheck方法。例如:new String(byteArr， "UTF-8")抛出UnsupportedEncodingException，但Java规范保证UTF-8始终存在。在这里，throws声明是一个麻烦，任何用最小样板文件来沉默它的解决方案都是受欢迎的:String text = uncheck(() -> new String(byteArr， "UTF-8"));

•如果你正在实现一个严格的接口，你没有添加throws声明的选项，但抛出一个异常是完全合适的，你可以使用uncheck方法。包装一个异常只是为了获得抛出它的特权，结果是一个带有虚假异常的堆栈跟踪，这些异常没有提供关于实际错误的信息。一个很好的例子是Runnable.run()，它不会抛出任何受控异常。

• In any case, if you decide to use the uncheck methods, be aware of these 2 consequences of throwing CHECKED exceptions without a throws clause: 1) The calling-code won't be able to catch it by name (if you try, the compiler will say: Exception is never thrown in body of corresponding try statement). It will bubble and probably be caught in the main program loop by some "catch Exception" or "catch Throwable", which may be what you want anyway. 2) It violates the principle of least surprise: it will no longer be enough to catch RuntimeException to be able to guarantee catching all possible exceptions. For this reason, I believe this should not be done in framework code, but only in business code that you completely control.

引用:

http://www.philandstuff.com/2012/04/28/sneakily-throwing-checked-exceptions.html http://www.mail-archive.com/javaposse@googlegroups.com/msg05984.html Project Lombok注释:@SneakyThrows Brian Goetz的观点(反对):我如何在Java 8流中抛出CHECKED异常? https://softwareengineering.stackexchange.com/questions/225931/workaround-for-java-checked-exceptions?newreg=ddf0dd15e8174af8ba52e091cf85688e *

你可以!

扩展@marcg的UtilException并在必要的地方添加抛出E:这样，编译器会要求你添加抛出子句，一切就像你可以在java 8的流上本机抛出检查异常一样。

说明:只需复制/粘贴LambdaExceptionUtil在您的IDE，然后使用它，如下面的LambdaExceptionUtilTest所示。

public final class LambdaExceptionUtil {

    @FunctionalInterface
    public interface Consumer_WithExceptions<T, E extends Exception> {
        void accept(T t) throws E;
    }

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

    /**
     * .forEach(rethrowConsumer(name -> System.out.println(Class.forName(name))));
     */
    public static <T, E extends Exception> Consumer<T> rethrowConsumer(Consumer_WithExceptions<T, E> consumer) throws E {
        return t -> {
            try {
                consumer.accept(t);
            } catch (Exception exception) {
                throwActualException(exception);
            }
        };
    }

    /**
     * .map(rethrowFunction(name -> Class.forName(name))) or .map(rethrowFunction(Class::forName))
     */
    public static <T, R, E extends Exception> Function<T, R> rethrowFunction(Function_WithExceptions<T, R, E> function) throws E  {
        return t -> {
            try {
                return function.apply(t);
            } catch (Exception exception) {
                throwActualException(exception);
                return null;
            }
        };
    }

    @SuppressWarnings("unchecked")
    private static <E extends Exception> void throwActualException(Exception exception) throws E {
        throw (E) exception;
    }

}

一些测试显示使用和行为:

public class LambdaExceptionUtilTest {

    @Test(expected = MyTestException.class)
    public void testConsumer() throws MyTestException {
        Stream.of((String)null).forEach(rethrowConsumer(s -> checkValue(s)));
    }

    private void checkValue(String value) throws MyTestException {
        if(value==null) {
            throw new MyTestException();
        }
    }

    private class MyTestException extends Exception { }

    @Test
    public void testConsumerRaisingExceptionInTheMiddle() {
        MyLongAccumulator accumulator = new MyLongAccumulator();
        try {
            Stream.of(2L, 3L, 4L, null, 5L).forEach(rethrowConsumer(s -> accumulator.add(s)));
            fail();
        } catch (MyTestException e) {
            assertEquals(9L, accumulator.acc);
        }
    }

    private class MyLongAccumulator {
        private long acc = 0;
        public void add(Long value) throws MyTestException {
            if(value==null) {
                throw new MyTestException();
            }
            acc += value;
        }
    }

    @Test
    public void testFunction() throws MyTestException {
        List<Integer> sizes = Stream.of("ciao", "hello").<Integer>map(rethrowFunction(s -> transform(s))).collect(toList());
        assertEquals(2, sizes.size());
        assertEquals(4, sizes.get(0).intValue());
        assertEquals(5, sizes.get(1).intValue());
    }

    private Integer transform(String value) throws MyTestException {
        if(value==null) {
            throw new MyTestException();
        }
        return value.length();
    }

    @Test(expected = MyTestException.class)
    public void testFunctionRaisingException() throws MyTestException {
        Stream.of("ciao", null, "hello").<Integer>map(rethrowFunction(s -> transform(s))).collect(toList());
    }

}

只要使用任何一个NoException(我的项目)，jOOλ的Unchecked, throw -lambdas, Throwable接口或Faux Pas。

// NoException
stream.map(Exceptions.sneak().function(Class::forName));

// jOOλ
stream.map(Unchecked.function(Class::forName));

// throwing-lambdas
stream.map(Throwing.function(Class::forName).sneakyThrow());

// Throwable interfaces
stream.map(FunctionWithThrowable.aFunctionThatUnsafelyThrowsUnchecked(Class::forName));

// Faux Pas
stream.map(FauxPas.throwingFunction(Class::forName));