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[英]Why does Scanner#nextInt inside for loop keep throwing an exception?
[英]Throwing exception inside lambda does not work
我在 lambda 中抛出异常时遇到了一些问题,请考虑以下代码:
public interface StoreTransactionalExecutable {
void execute(@NotNull final StoreTransaction txn);
}
还有一个经理 class:
public final class DatabaseManager {
// ...
@Override
public void transactPersistentEntityStore(String dir, StoreTransactionalExecutable txn) {
final PersistentEntityStore entityStore =
getPersistentEntityStore(dir, isReadOnly);
entityStore.executeInTransaction(txn);
}
// ...
}
当像下面这样访问管理器 class 方法transactPersistentEntityStore
时,它可以工作:
public class Service {
databaseManager.transactPersistentEntityStore("/dbPath", txn -> {
txn.find(); // do stuff (throws and works)
});
}
但是,如果这样,它会引发编译时错误
public class Service {
databaseManager.transactPersistentEntityStore("/dbPath", rethrow(
transaction -> {
StoreTransaction txn = (StoreTransaction) transaction;
txn.find(); // do stuff
}
));
}
这是扔的东西
[ERROR] method com.myproject.store.DatabaseManager.transactPersistentEntityStore(java.lang.String,jetbrains.exodus.entitystore.StoreTransactionalExecutable) is not applicable
[ERROR] (argument mismatch; no instance(s) of type variable(s) T exist so that java.util.function.Consumer<T> conforms to jetbrains.exodus.entitystore.StoreTransactionalExecutable)
[ERROR] method com.myproject.store.DatabaseManager.<T,B>transactPersistentEntityStore(java.lang.String,java.util.Map<java.lang.Class<T>,B>,jetbrains.exodus.entitystore.StoreTransactionalExecutable) is not applicable
[ERROR] (cannot infer type-variable(s) T,B
[ERROR] (actual and formal argument lists differ in length))
rethrow
和ThrowingConsumer
的代码是这样的:
public final class Throwing {
private Throwing() {}
@Nonnull
public static <T> Consumer<T> rethrow(@Nonnull final ThrowingConsumer<T> consumer) {
return consumer;
}
@SuppressWarnings("unchecked")
@Nonnull
public static <E extends Throwable> void sneakyThrow(@Nonnull Throwable ex) throws E {
throw (E) ex;
}
}
和
@FunctionalInterface
public interface ThrowingConsumer<T> extends Consumer<T>{
@Override
default void accept(final T e) {
try {
accept0(e);
} catch (Throwable ex) {
Throwing.sneakyThrow(ex);
}
}
void accept0(T t) throws Throwable;
}
我真的很想知道这里有什么问题? 任何提示将不胜感激。
关于第一个编译器错误:
如果您仔细阅读错误“参数不匹配;不存在类型变量 T 的实例,因此 java.util.function.Consumer 符合 jetbrains.exodus.entitystore.Sto reTransactionalExecutable”
你会注意到一些事情:
execute
方法 not accept
。 所以在entityStore.executeInTransaction(txn);
里面的代码调用execute
方法而不accept
因此,当您将 Consumer object 传递给transactPersistentEntityStore
方法时,编译器会抱怨。
如果我错了,请纠正我。
一种“偷偷摸摸”的方式来抛出这个(但有一个try-catch)是做一个:
public class UncheckedException extends RuntimeException {
public UncheckedException(Throwable cause) {
super(cause);
}
}
然后像这样使用:
class Scratch {
public static void main(String[] args) {
databaseManager.transactPersistentEntityStore("/dbPath", txn -> {
try {
somethingThatThrows();
} catch (Exception e) {
throw new UnchecekdServiceException(e);
}
});
}
}
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