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handle NPE within a Failure
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@lambdista
lambdista committed Jul 22, 2015
1 parent 1cc753e commit 8d6be77
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Showing 2 changed files with 20 additions and 41 deletions.
45 changes: 11 additions & 34 deletions src/main/java/com/lambdista/util/Try.java
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,6 @@
package com.lambdista.util;

import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;
Expand All @@ -26,15 +25,15 @@
* <p>The {@code Try} type represents a computation that may fail. If the computation is successful returns
* the value wrapped in a {@link Success} otherwise returns the
* {@link java.lang.Exception} wrapped in a {@link Failure}.</p>
*
* <p>
* <p>To use {@code Try} you need to call the {@link Try#apply(FailableSupplier)} method passing in a lambda with
* the same signature used for a common {@link java.util.function.Supplier}.
* Indeed {@link FailableSupplier} is just a {@link java.util.function.Supplier} with a
* {@code 'throws Throwable'} added to its {@code 'get'} method.</p>
*
* <p>
* <p>For example, {@code Try} can be used to perform division on a user-defined input, without the need to do explicit
* exception-handling in all of the places that an exception might occur.</p>
*
* <p>
* <p>An important property of {@code Try} shown in the {@link com.lambdista.example.SumAndDivide#divideWithTry()} method is its ability
* to <i>pipeline (chain if you prefer)</i> operations,
* catching exceptions along the way thanks to its {@link Try#flatMap(java.util.function.Function)} method. If you
Expand All @@ -46,11 +45,11 @@
* {@code flatMap} calls and a last call to {@code map}. E.g.: Suppose you have 3 variables (x, y and z) being
* of type {@code Try<Integer>} and you just wanto to sum them up. The code you need for doing that is the
* following:</p>
*
* <p>
* <pre>
* x.flatMap(a -> y.flatMap(b -> z.map(c -> a + b + c)))
* </pre>
*
* <p>
* Apart from {@code map} and {@code flatMap}, {@code Try} has many other useful methods. See the {@code TryTest}
* class for a thorough coverage of all {@code Try}'s methods.
*
Expand Down Expand Up @@ -200,7 +199,7 @@ public abstract <U> Try<U> transform(Function<? super T, ? extends Try<U>> succe
/**
* Converts a {@link Function} expecting an {@link java.lang.AutoCloseable} into a
* {@code Function} which closes the {@code AutoCloseable} after execution.
*
* <p>
* <p>
* This is equivalent to the <a href=
* "https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html"
Expand All @@ -212,8 +211,6 @@ public abstract <U> Try<U> transform(Function<? super T, ? extends Try<U>> succe
* @see #apply(FailableSupplier)
*/
public static <T extends AutoCloseable, R> Function<T, Try<R>> apply(Function<T, R> consumer) {
Objects.requireNonNull(consumer);

return closeable -> Try.apply(() -> {
try (T in = closeable) {
return consumer.apply(in);
Expand All @@ -232,8 +229,6 @@ public static <T extends AutoCloseable, R> Function<T, Try<R>> apply(Function<T,
* @return a {@code Try} object (an instance of either {@link Success} or {@link Failure}
*/
public static <T> Try<T> apply(FailableSupplier<T> supplier) {
Objects.requireNonNull(supplier);

try {
return new Success<>(supplier.get());
} catch (Throwable e) {
Expand All @@ -245,14 +240,13 @@ public static <T> Try<T> apply(FailableSupplier<T> supplier) {
/**
* Converts a {@code Try<Try<T>>} to a {@code Try<T>}.
*
* @param t the {@code Try<Try<T>>} to be flattened.
* @param t the {@code Try<Try<T>>} to be flattened.
* @param <T> the type wrapped by {@code Try}
* @return a {@code Try<T>}
*/
public static <T> Try<T> join(Try<Try<T>> t) {
Objects.requireNonNull(t);

if (t instanceof Failure<?>) return ((Try<T>) t);
if (t == null) return ((Try<T>) new Failure<>(new NullPointerException("t is null")));
else if (t instanceof Failure<?>) return ((Try<T>) t);
else return t.get();
}

Expand Down Expand Up @@ -291,29 +285,21 @@ public T checkedGet() {

@Override
public void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);

action.accept(value);
}

@Override
public <U> Try<U> map(Function<? super T, ? extends U> mapper) {
Objects.requireNonNull(mapper);

return Try.apply(() -> mapper.apply(value));
}

@Override
public <U> Try<U> flatMap(Function<? super T, ? extends Try<U>> mapper) {
Objects.requireNonNull(mapper);

return Try.join(Try.apply(() -> mapper.apply(value)));
}

@Override
public Try<T> filter(Predicate<? super T> predicate) {
Objects.requireNonNull(predicate);

return Try.join(Try.apply(() ->
{
if (predicate.test(value)) {
Expand Down Expand Up @@ -360,9 +346,7 @@ public Try<T> orElse(Try<T> defaultValue) {
@Override
public <U> Try<U> transform(Function<? super T, ? extends Try<U>> successFunc,
Function<Throwable, ? extends Try<U>> failureFunc) {
Objects.requireNonNull(successFunc);

return successFunc.apply(value);
return Try.join(Try.apply(() -> successFunc.apply(value)));
}

@Override
Expand All @@ -373,7 +357,6 @@ public boolean equals(Object o) {
Success success = (Success) o;

return value.equals(success.value);

}

@Override
Expand Down Expand Up @@ -447,15 +430,11 @@ public Try<T> filter(Predicate<? super T> predicate) {

@Override
public <U> Try<U> recover(Function<? super Throwable, ? extends U> recoverFunc) {
Objects.requireNonNull(recoverFunc);

return Try.apply(() -> recoverFunc.apply(exception));
}

@Override
public <U> Try<U> recoverWith(Function<? super Throwable, ? extends Try<U>> recoverFunc) {
Objects.requireNonNull(recoverFunc);

return Try.join(Try.apply(() -> recoverFunc.apply(exception)));
}

Expand All @@ -482,9 +461,7 @@ public Try<T> orElse(Try<T> defaultValue) {
@Override
public <U> Try<U> transform(Function<? super T, ? extends Try<U>> successFunc,
Function<Throwable, ? extends Try<U>> failureFunc) {
Objects.requireNonNull(failureFunc);

return failureFunc.apply(exception);
return Try.join(Try.apply(() -> failureFunc.apply(exception)));
}

@Override
Expand Down
16 changes: 9 additions & 7 deletions src/test/java/com/lambdista/util/TryTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -399,11 +399,12 @@ public void testErrorMustNotBeCaught() throws Throwable {
);
}

@Test(expected = NullPointerException.class)
public void testSuppliedFailableSupplierIsNullShouldThrow() {
@Test
public void testSuppliedFailableSupplierIsNullShouldBeAFailure() {
FailableSupplier<Integer> s = null;

Try.apply(s);
Try<Integer> out = Try.apply(s);
assertEquals("out must be a Failure", out.isFailure(), true);
}

@Test
Expand All @@ -422,11 +423,12 @@ public void testInputStreamShouldBeClosedAfterConsumption() throws IOException{
assertThat(result, is(equalTo("Hello World!")));
}

@Test(expected = NullPointerException.class)
public void testSuppliedFunctionIsNullShouldThrow() throws IOException{
@Test
public void testSuppliedFunctionIsNullShouldBeAFailure() throws IOException{
verify(inputStreamMock, never()).close();
Try.apply((Function<InputStream, String>) null).apply(inputStreamMock);
verify(inputStreamMock).close();
Try<String> out = Try.apply((Function<InputStream, String>) null).apply(inputStreamMock);
assertEquals("out must be a Failure", out.isFailure(), true);
verify(inputStreamMock).close();
}

@Test
Expand Down

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