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?
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
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:-
其他回答
我所做的是允许用户在异常情况下给出他实际想要的值。 我有一个像这样的东西
public static <T, R> Function<? super T, ? extends R> defaultIfThrows(FunctionThatThrows<? super T, ? extends R> delegate, R defaultValue) {
return x -> {
try {
return delegate.apply(x);
} catch (Throwable throwable) {
return defaultValue;
}
};
}
@FunctionalInterface
public interface FunctionThatThrows<T, R> {
R apply(T t) throws Throwable;
}
这个可以被称为:
defaultIfThrows(child -> child.getID(), null)
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);
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
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。
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());