如何从Java8流内部抛出已检查的异常？
如何从Java8 streams/lambdas内部抛出已检查的异常 换句话说，我想编译如下代码：如何从Java8流内部抛出已检查的异常？,java,lambda,java-8,java-stream,checked-exceptions,Java,Lambda,Java 8,Java Stream,Checked Exceptions,如何从Java8 streams/lambdas内部抛出已检查的异常 换句话说，我想编译如下代码： public List<Class> getClasses() throws ClassNotFoundException { List<Class> classes = Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
public List<Class> getClasses() throws ClassNotFoundException {
List<Class> classes =
Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
.map(className -> Class.forName(className))
.collect(Collectors.toList());
return classes;
}
public List getClasses（）抛出ClassNotFoundException{
列表类=
Stream.of（“java.lang.Object”、“java.lang.Integer”、“java.lang.String”）
.map（className->Class.forName（className））
.collect（Collectors.toList（））；
返回类；
}
Class.forName（）ClassNotFoundException请注意，我不想将选中的异常包装到运行时异常中，而是抛出包装好的未选中异常我想抛出选中的异常本身，在不向流中添加丑陋的
的情况下，尝试捕获LambdaExceptionUtilStream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
.map(rethrowFunction(Class::forName))
.collect(Collectors.toList());
Class:：forNameClassNotFoundExceptionClassNotFoundExceptionpublic 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; }
}
LambdaExceptionUtilrethrow注2:上述
LambdaExceptionUtil取消选中的方法是额外的方法，如果您不想使用它们，可以安全地将它们从类中删除。如果您确实使用了它们，请在理解以下用例、优点/缺点和局限性之前小心使用：
•如果调用的方法不能抛出它声明的异常，则可以使用取消选中方法。例如：新字符串（byteArr，“UTF-8”）抛出UnsupportedEncodingException，但Java规范保证UTF-8始终存在。在这里，throws声明是一个讨厌的东西，任何用最少的样板文件使其静音的解决方案都是受欢迎的：stringtext=uncheck（（）->newstring（byteArr，“UTF-8”）
•如果您正在实现一个严格的接口，而您没有添加抛出声明的选项，并且抛出异常是完全合适的，那么您可以使用取消选中
方法。包装一个异常只是为了获得抛出它的特权，结果会产生一个带有虚假异常的stacktrace，这些异常不会提供关于实际出错的信息。一个很好的例子是Runnable.run（），它不会抛出任何已检查的异常
•在任何情况下，如果您决定使用取消选中方法，
请注意在没有throws子句的情况下抛出已检查异常的这两个后果：1）调用代码将无法按名称捕获它（如果您尝试，编译器将说：在相应try语句的主体中永远不会抛出异常）。它将冒泡，并可能被一些“catch Exception”或“catch Throwable”捕获到主程序循环中，这可能是您想要的。2） 它违反了最小意外原则：捕获RuntimeException
以保证捕获所有可能的异常将不再足够。出于这个原因，我认为这不应该在框架代码中完成，而应该只在您完全控制的业务代码中完成
- 参考资料：
- Lombok项目注释：@sleekythrows
- Brian Goetz的意见（反对）如下：
- *
你不能安全地这样做。你可以作弊，但随后你的程序被破坏了，这将不可避免地再次伤害到某人（应该是你，但我们的作弊通常会伤害到其他人）
这里有一个稍微安全一点的方法（但我还是不推荐这样做）
在这里，您要做的是捕获lambda中的异常，从流管道中抛出一个指示计算异常失败的信号，捕获该信号，并对该信号执行操作以抛出底层异常。关键是您总是捕获合成异常，而不是允许已检查的异常泄漏而不声明抛出该异常 你的问题的简单答案是：你不能，至少不能直接回答。这不是你的错。甲骨文把事情搞砸了。他们坚持检查异常的概念，但在设计功能接口、流、lambda等时却始终忘记了检查异常。这是像Robert C.Martin这样称检查异常为失败实验的专家们最担心的
在我看来，这是API中的一个大错误，也是语言规范中的一个小错误
API中的错误在于，它没有提供转发已检查异常的功能，而这实际上对函数式编程非常有意义。正如我将在下面演示的那样，这样的设施是很容易实现的
语言规范中的缺陷在于，它不允许类型参数推断类型列表而不是单个类型，只要类型参数仅在允许类型列表的情况下使用（
throws
子句）
作为Java程序员，我们期望编译以下代码：
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;
public class CheckedStream {
// List variant to demonstrate what we actually had before refactoring.
public List<Class> getClasses(final List<String> names) throws ClassNotFoundException {
final List<Class> classes = new ArrayList<>();
for (final String name : names)
classes.add(Class.forName(name));
return classes;
}
// The Stream function which we want to compile.
public Stream<Class> getClasses(final Stream<String> names) throws ClassNotFoundException {
return names.map(Class::forName);
}
}
函数接口的定义方式目前阻止编译器转发异常-没有声明告诉Stream.map（）
如果Function.apply（）抛出Eclass WrappedException extends RuntimeException {
Throwable cause;
WrappedException(Throwable cause) { this.cause = cause; }
}
static WrappedException throwWrapped(Throwable t) {
throw new WrappedException(t);
}
try
source.stream()
.filter(e -> { ... try { ... } catch (IOException e) { throwWrapped(e); } ... })
...
}
catch (WrappedException w) {
throw (IOException) w.cause;
}
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;
public class CheckedStream {
// List variant to demonstrate what we actually had before refactoring.
public List<Class> getClasses(final List<String> names) throws ClassNotFoundException {
final List<Class> classes = new ArrayList<>();
for (final String name : names)
classes.add(Class.forName(name));
return classes;
}
// The Stream function which we want to compile.
public Stream<Class> getClasses(final Stream<String> names) throws ClassNotFoundException {
return names.map(Class::forName);
}
}
cher@armor1:~/playground/Java/checkedStream$ javac CheckedStream.java
CheckedStream.java:13: error: incompatible thrown types ClassNotFoundException in method reference
return names.map(Class::forName);
^
1 error
import java.io.IOException;
interface Function<T, R, E extends Throwable> {
// Declare you throw E, whatever that is.
R apply(T t) throws E;
}
interface Stream<T> {
// Pass through E, whatever mapper defined for E.
<R, E extends Throwable> Stream<R> map(Function<? super T, ? extends R, E> mapper) throws E;
}
class Main {
public static void main(final String... args) throws ClassNotFoundException {
final Stream<String> s = null;
// Works: E is ClassNotFoundException.
s.map(Class::forName);
// Works: E is RuntimeException (probably).
s.map(Main::convertClass);
// Works: E is ClassNotFoundException.
s.map(Main::throwSome);
// Doesn't work: E is Exception.
s.map(Main::throwSomeMore); // error: unreported exception Exception; must be caught or declared to be thrown
}
public static Class convertClass(final String s) {
return Main.class;
}
static class FooException extends ClassNotFoundException {}
static class BarException extends ClassNotFoundException {}
public static Class throwSome(final String s) throws FooException, BarException {
throw new FooException();
}
public static Class throwSomeMore(final String s) throws ClassNotFoundException, IOException {
throw new FooException();
}
}
import static com.github.fge.lambdas.functions.Functions.wrap;
final ThrowingFunction<String, Class<?>> f = wrap(Class::forName);
List<Class> classes =
Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
.map(f.orThrow(MyException.class))
.collect(Collectors.toList());
@FunctionalInterface
public interface UseInstance<T, X extends Throwable> {
void accept(T instance) throws X;
}
import java.io.FileWriter;
import java.io.IOException;
//lambda expressions and the execute around method (EAM) pattern to
//manage resources
public class FileWriterEAM {
private final FileWriter writer;
private FileWriterEAM(final String fileName) throws IOException {
writer = new FileWriter(fileName);
}
private void close() throws IOException {
System.out.println("close called automatically...");
writer.close();
}
public void writeStuff(final String message) throws IOException {
writer.write(message);
}
//...
public static void use(final String fileName, final UseInstance<FileWriterEAM, IOException> block) throws IOException {
final FileWriterEAM writerEAM = new FileWriterEAM(fileName);
try {
block.accept(writerEAM);
} finally {
writerEAM.close();
}
}
public static void main(final String[] args) throws IOException {
FileWriterEAM.use("eam.txt", writerEAM -> writerEAM.writeStuff("sweet"));
FileWriterEAM.use("eam2.txt", writerEAM -> {
writerEAM.writeStuff("how");
writerEAM.writeStuff("sweet");
});
FileWriterEAM.use("eam3.txt", FileWriterEAM::writeIt);
}
void writeIt() throws IOException{
this.writeStuff("How ");
this.writeStuff("sweet ");
this.writeStuff("it is");
}
}
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;
}
}
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());
}
}
public List<Class> getClasses() throws ClassNotFoundException {
Stream<String> classNames =
Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String");
return ThrowingStream.of(classNames, ClassNotFoundException.class)
.map(Class::forName)
.collect(Collectors.toList());
}
CompletableFuture<List<Class<?>>> classes =
Stream.of("java.lang.String", "java.lang.Integer", "java.lang.Double")
.map(MonadUtils.applyOrDie(Class::forName))
.map(cfc -> cfc.thenApply(Class::getSuperclass))
.collect(MonadUtils.cfCollector(ArrayList::new,
List::add,
(List<Class<?>> l1, List<Class<?>> l2) -> { l1.addAll(l2); return l1; },
x -> x));
classes.thenAccept(System.out::println)
.exceptionally(t -> { System.out.println("unable to get class: " + t); return null; });
[class java.lang.Object, class java.lang.Number, class java.lang.Number]
Stream.of("java.lang.Object", "java.lang.Integer", "java.lang.String")
.map(Try.<String, Class<?>>safe(Class::forName)
.handle(System.out::println)
.unsafe())
.collect(toList());
final class Try {
public static <T> CheckedBuilder<Supplier<T>, CheckedSupplier<T>, T>
safe(CheckedSupplier<T> supplier) {
return new CheckedWrapper<>(supplier,
(current, next, handler, orResult) -> () -> {
try { return current.get(); } catch (Exception ex) {
handler.accept(ex);
return next.isPresent() ? next.get().get() : orResult.apply(ex);
}
});
}
public static <T> Supplier<T> unsafe(CheckedSupplier<T> supplier) {
return supplier;
}
public static <T> CheckedBuilder<Consumer<T>, CheckedConsumer<T>, Void>
safe(CheckedConsumer<T> consumer) {
return new CheckedWrapper<>(consumer,
(current, next, handler, orResult) -> t -> {
try { current.accept(t); } catch (Exception ex) {
handler.accept(ex);
if (next.isPresent()) {
next.get().accept(t);
} else {
orResult.apply(ex);
}
}
});
}
public static <T> Consumer<T> unsafe(CheckedConsumer<T> consumer) {
return consumer;
}
public static <T, R> CheckedBuilder<Function<T, R>, CheckedFunction<T, R>, R>
safe(CheckedFunction<T, R> function) {
return new CheckedWrapper<>(function,
(current, next, handler, orResult) -> t -> {
try { return current.applyUnsafe(t); } catch (Exception ex) {
handler.accept(ex);
return next.isPresent() ? next.get().apply(t) : orResult.apply(ex);
}
});
}
public static <T, R> Function<T, R> unsafe(CheckedFunction<T, R> function) {
return function;
}
@SuppressWarnings ("unchecked")
static <T, E extends Throwable> T throwAsUnchecked(Throwable exception) throws E {
throw (E) exception;
}
}
@FunctionalInterface interface CheckedConsumer<T> extends Consumer<T> {
void acceptUnsafe(T t) throws Exception;
@Override default void accept(T t) {
try { acceptUnsafe(t); } catch (Exception ex) {
Try.throwAsUnchecked(ex);
}
}
}
@FunctionalInterface interface CheckedFunction<T, R> extends Function<T, R> {
R applyUnsafe(T t) throws Exception;
@Override default R apply(T t) {
try { return applyUnsafe(t); } catch (Exception ex) {
return Try.throwAsUnchecked(ex);
}
}
}
@FunctionalInterface interface CheckedSupplier<T> extends Supplier<T> {
T getUnsafe() throws Exception;
@Override default T get() {
try { return getUnsafe(); } catch (Exception ex) {
return Try.throwAsUnchecked(ex);
}
}
}
interface ReduceFunction<TSafe, TUnsafe, R> {
TSafe wrap(TUnsafe current, Optional<TSafe> next,
Consumer<Throwable> handler, Function<Throwable, R> orResult);
}
interface CheckedBuilder<TSafe, TUnsafe, R> {
CheckedBuilder<TSafe, TUnsafe, R> orTry(TUnsafe next);
CheckedBuilder<TSafe, TUnsafe, R> handle(Consumer<Throwable> handler);
<E extends Throwable> CheckedBuilder<TSafe, TUnsafe, R> handle(
Class<E> exceptionType, Consumer<E> handler);
CheckedBuilder<TSafe, TUnsafe, R> handleLast(Consumer<Throwable> handler);
<E extends Throwable> CheckedBuilder<TSafe, TUnsafe, R> handleLast(
Class<E> exceptionType, Consumer<? super E> handler);
TSafe unsafe();
TSafe rethrow(Function<Throwable, Exception> transformer);
TSafe suppress();
TSafe orElse(R value);
TSafe orElseGet(Supplier<R> valueProvider);
}
final class CheckedWrapper<TSafe, TUnsafe, R>
implements CheckedBuilder<TSafe, TUnsafe, R> {
private final TUnsafe function;
private final ReduceFunction<TSafe, TUnsafe, R> reduceFunction;
private final CheckedWrapper<TSafe, TUnsafe, R> root;
private CheckedWrapper<TSafe, TUnsafe, R> next;
private Consumer<Throwable> handlers = ex -> { };
private Consumer<Throwable> lastHandlers = ex -> { };
CheckedWrapper(TUnsafe function,
ReduceFunction<TSafe, TUnsafe, R> reduceFunction) {
this.function = function;
this.reduceFunction = reduceFunction;
this.root = this;
}
private CheckedWrapper(TUnsafe function,
CheckedWrapper<TSafe, TUnsafe, R> prev) {
this.function = function;
this.reduceFunction = prev.reduceFunction;
this.root = prev.root;
prev.next = this;
}
@Override public CheckedBuilder<TSafe, TUnsafe, R> orTry(TUnsafe next) {
return new CheckedWrapper<>(next, this);
}
@Override public CheckedBuilder<TSafe, TUnsafe, R> handle(
Consumer<Throwable> handler) {
handlers = handlers.andThen(handler);
return this;
}
@Override public <E extends Throwable> CheckedBuilder<TSafe, TUnsafe, R>
handle(Class<E> exceptionType, Consumer<E> handler) {
handlers = handlers.andThen(ex -> {
if (exceptionType.isInstance(ex)) {
handler.accept(exceptionType.cast(ex));
}
});
return this;
}
@Override public CheckedBuilder<TSafe, TUnsafe, R> handleLast(
Consumer<Throwable> handler) {
lastHandlers = lastHandlers.andThen(handler);
return this;
}
@Override public <E extends Throwable> CheckedBuilder<TSafe, TUnsafe, R>
handleLast(Class<E> exceptionType, Consumer<? super E> handler) {
lastHandlers = lastHandlers.andThen(ex -> {
if (exceptionType.isInstance(ex)) {
handler.accept(exceptionType.cast(ex));
}
});
return this;
}
@Override public TSafe unsafe() {
return root.reduce(ex -> Try.throwAsUnchecked(ex));
}
@Override
public TSafe rethrow(Function<Throwable, Exception> transformer) {
return root.reduce(ex -> Try.throwAsUnchecked(transformer.apply(ex)));
}
@Override public TSafe suppress() {
return root.reduce(ex -> null);
}
@Override public TSafe orElse(R value) {
return root.reduce(ex -> value);
}
@Override public TSafe orElseGet(Supplier<R> valueProvider) {
Objects.requireNonNull(valueProvider);
return root.reduce(ex -> valueProvider.get());
}
private TSafe reduce(Function<Throwable, R> orResult) {
return reduceFunction.wrap(function,
Optional.ofNullable(next).map(p -> p.reduce(orResult)),
this::handle, orResult);
}
private void handle(Throwable ex) {
for (CheckedWrapper<TSafe, TUnsafe, R> current = this;
current != null;
current = current.next) {
current.handlers.accept(ex);
}
lastHandlers.accept(ex);
}
}
public class CheckedExceptionWrapper extends RuntimeException {
...
public <T extends Exception> CheckedExceptionWrapper rethrow() throws T {
throw (T) getCause();
}
}
void method() throws IOException, ServletException {
try {
list.stream().forEach(object -> {
...
throw new CheckedExceptionWrapper(e);
...
});
} catch (CheckedExceptionWrapper e){
e.<IOException>rethrow();
e.<ServletExcepion>rethrow();
}
}
List test = new ArrayList();
try {
test.forEach(obj -> {
//let say some functionality throws an exception
try {
throw new IOException("test");
}
catch(Exception e) {
throw new RuntimeException(e);
}
});
}
catch (RuntimeException re) {
if(re.getCause() instanceof IOException) {
//do your logic for catching checked
}
else
throw re; // it might be that there is real runtime exception
}
// 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));
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;
}
interface CheckedFunction<I, O> {
O apply(I i) throws Exception; }
static <I, O> Function<I, O> unchecked(CheckedFunction<I, O> f) {
return i -> {
try {
return f.apply(i);
} catch(Exception ex) {
throw new RuntimeException(ex);
}
} }
fileNamesToRead.map(unchecked(file -> Files.readAllLines(file)))
@SuppressWarnings("unchecked")
private static <T, E extends Exception> T throwUnchecked(Exception e) throws E {
throw (E) e;
}
static <I, O> Function<I, O> unchecked(CheckedFunction<I, O> f) {
return arg -> {
try {
return f.apply(arg);
} catch(Exception ex) {
return throwUnchecked(ex);
}
};
}
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);
}
private void run() {
List<String> list = Stream.of(1, 2, 3, 4).map(wrapper(i ->
String.valueOf(++i / 0), i -> String.valueOf(++i))).collect(Collectors.toList());
System.out.println(list.toString());
}
private <T, R, E extends Exception> Function<T, R> wrapper(ThrowingFunction<T, R, E> function,
Function<T, R> onException) {
return i -> {
try {
return function.apply(i);
} catch (ArithmeticException e) {
System.out.println("Exception: " + i);
return onException.apply(i);
} catch (Exception e) {
System.out.println("Other: " + i);
return onException.apply(i);
}
};
}
@FunctionalInterface
interface ThrowingFunction<T, R, E extends Exception> {
R apply(T t) throws E;
}
@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);
}