I have below piece of code in my spring boot app, which validates email addresses
class EmailValidation {
public static void validate(List<String> s){
try {
for (String address : s) {
if (s == null || s.indexOf("#") < 0) {
throw new InvalidEmailAddressException("Email address is invalid ");
}
new InternetAddress(s);
}
} catch(AddressException e){
LOGGER.Error("Please validate email addresses");
}
catch(InvalidEmailAddressesException e){
LOGGER.error(e.getMessage());
}
}
class InvalidEmailAddressException extends Exception {
public InvalidEmailAddressException(String message) {
super(message)
}
}
}
I want to write a Junit test which will verify that that InvalidEmailAddressesException was thrown and CAUGHT. How can I do that in JUnit?
In general I agree with the comments that such a test is probably unnecessary.
However, if I wanted to test something like that I would test the two cases separately and that requires a small modification to your code.
Firstly I would construct a method that only throws the exception if there is one.
public static void checkAddresses(List<String> s) throws AddressException, InvalidEmailAddressException {
for (String address : s) {
if (s == null || s.indexOf("#") < 0) {
throw new InvalidEmailAddressException("Email address is invalid ");
}
new InternetAddress(s);
}
}
then I would use it in your code like that:
class EmailValidation {
public static void validate(List<String> s){
try {
checkAddresses(s); // a wrapper method that throws the expected exceptions
} catch(AddressException e){
LOGGER.Error("Please validate email addresses");
}
catch(InvalidEmailAddressesException e){
LOGGER.error(e.getMessage());
}
}
// add checkAddresses here or somewhere appropriately
class InvalidEmailAddressException extends Exception {
public InvalidEmailAddressException(String message) {
super(message)
}
}
}
Then, I would write separate tests for checkAddresses that tests both if an exception is expected or not and separate tests for validate, (possibly with the same input that was given to checkAddresses) that should pass if an exception isn't thrown.
Also, if you would like to verify your logs may be you could try something like that.
Indeed using java Exception for common cause is considered a bad practice, and as #Michael said, Exceptions must be exceptional, because
they break flow control
they are slow (more details here How slow are Java exceptions?)
they do not mix with functional paradigm (where Java is in part going to with the addition of lamda-expressions
However, creating a custom object for wrapping validation data is a good thing and InvalidEmailAddressException can be turned into CheckedEmail:
import java.util.List;
import java.util.stream.Collectors;
public class EmailValidator {
public List<CheckedEmail> validate(List<String> emailAddresses) {
return emailAddresses.stream().map(this::validate).collect(Collectors.toList());
}
public CheckedEmail validate(String emailAddress) {
String[] emailParts = emailAddress.toString().split( "#", 3 );
final boolean valid;
if ( emailParts.length != 2 ) {
valid = false;
} else {
// More validation can go here using one or more regex
valid = true;
}
return new CheckedEmail(emailAddress, valid);
}
public static final class CheckedEmail {
private final String emailAddress;
private final boolean valid;
private CheckedEmail(String emailAddress, boolean valid) {
this.emailAddress = emailAddress;
this.valid = valid;
}
public String getEmailAddress() {
return emailAddress;
}
public boolean isValid() {
return valid;
}
}
}
This in turn can be tested quite easily (and improved with a parameterized test):
import static org.assertj.core.api.Assertions.assertThat;
import java.util.Arrays;
import java.util.List;
import org.junit.Test;
public class EmailValidatorTest {
private final EmailValidator emailValidator = new EmailValidator();
#Test
public void invalid_email() {
EmailValidator.CheckedEmail checkedEmail = emailValidator.validate("missing.an.at.symbol");
assertThat(checkedEmail.isValid()).isFalse();
}
#Test
public void valid_email() {
EmailValidator.CheckedEmail checkedEmail = emailValidator.validate("at.symbol#present");
assertThat(checkedEmail.isValid()).isTrue();
}
#Test
public void multiple_email_addresses() {
List<String> emailAddresses = Arrays.asList("missing.an.at.symbol", "at.symbol#present");
List<EmailValidator.CheckedEmail> checkedEmails = emailValidator.validate(emailAddresses);
assertThat(checkedEmails)
.extracting(ce -> ce.getEmailAddress() + " " + ce.isValid())
.containsExactly(
"missing.an.at.symbol false",
"at.symbol#present true");
}
}
If somewhere the point is just to log this, then:
List<EmailValidator.CheckedEmail> checkedEmails = emailValidator.validate(emailAddresses);
checkedEmails.stream()
.filter(ce -> !ce.isValid())
.map(ce -> String.format("Email address [%s] is invalid", ce.getEmailAddress()))
.forEach(logger::error);
Hope this helps !
Don't approach testing that way. You should test only the specified behaviour of your code, not its implementation details.
If the method you are testing delegates to a method that throws a checked exception, and the method you are testing does not also declare that it throws that checked exception, the compiler will enforce that the method catches the exception. So in that case a unit test is unnecessary.
If the method you are testing delegates to a method that throws an unchecked exception, consult the specification of the method to determine whether it is acceptable for the method under test to also throw (propagate) that exception. If it is not acceptable for it to propagate the exception, then you should create a test case that causes the the method delegated to to throw that unchecked exception. If the method propagates the exception, the test case will fail. How to do that? That depends on the method being delegated to, but in most cases you will need to use Dependency Injection to supply a mock object that throws the exception.
I know how to create a reference to a method that has a String parameter and returns an int, it's:
Function<String, Integer>
However, this doesn't work if the function throws an exception, say it's defined as:
Integer myMethod(String s) throws IOException
How would I define this reference?
You'll need to do one of the following.
If it's your code, then define your own functional interface that declares the checked exception:
#FunctionalInterface
public interface CheckedFunction<T, R> {
R apply(T t) throws IOException;
}
and use it:
void foo (CheckedFunction f) { ... }
Otherwise, wrap Integer myMethod(String s) in a method that doesn't declare a checked exception:
public Integer myWrappedMethod(String s) {
try {
return myMethod(s);
}
catch(IOException e) {
throw new UncheckedIOException(e);
}
}
and then:
Function<String, Integer> f = (String t) -> myWrappedMethod(t);
or:
Function<String, Integer> f =
(String t) -> {
try {
return myMethod(t);
}
catch(IOException e) {
throw new UncheckedIOException(e);
}
};
You can actually extend Consumer (and Function etc.) with a new interface that handles exceptions -- using Java 8's default methods!
Consider this interface (extends Consumer):
#FunctionalInterface
public interface ThrowingConsumer<T> extends Consumer<T> {
#Override
default void accept(final T elem) {
try {
acceptThrows(elem);
} catch (final Exception e) {
// Implement your own exception handling logic here..
// For example:
System.out.println("handling an exception...");
// Or ...
throw new RuntimeException(e);
}
}
void acceptThrows(T elem) throws Exception;
}
Then, for example, if you have a list:
final List<String> list = Arrays.asList("A", "B", "C");
If you want to consume it (eg. with forEach) with some code that throws exceptions, you would traditionally have set up a try/catch block:
final Consumer<String> consumer = aps -> {
try {
// maybe some other code here...
throw new Exception("asdas");
} catch (final Exception ex) {
System.out.println("handling an exception...");
}
};
list.forEach(consumer);
But with this new interface, you can instantiate it with a lambda expression and the compiler will not complain:
final ThrowingConsumer<String> throwingConsumer = aps -> {
// maybe some other code here...
throw new Exception("asdas");
};
list.forEach(throwingConsumer);
Or even just cast it to be more succinct!:
list.forEach((ThrowingConsumer<String>) aps -> {
// maybe some other code here...
throw new Exception("asda");
});
Update
Looks like there's a very nice utility library part of Durian called Errors which can be used to solve this problem with a lot more flexibility. For example, in my implementation above I've explicitly defined the error handling policy (System.out... or throw RuntimeException), whereas Durian's Errors allow you to apply a policy on the fly via a large suite of utility methods. Thanks for sharing it, #NedTwigg!.
Sample usage:
list.forEach(Errors.rethrow().wrap(c -> somethingThatThrows(c)));
I think Durian's Errors class combines many of the pros of the various suggestions above.
Wrap a throwing function to a standard Java 8 functional interface.
Easily specify various policies for handling errors
When wrapping a method that returns a value, there is an important distinction between specifying a default value or rethrowing a RuntimeException.
Throwing versions of Java 8's functional interfaces
Similar to fge's answer
Standard interfaces for throwing specific exceptions
Which addresses Zoltán's concern
To include Durian in your project, you can either:
grab it from jcenter or maven central at com.diffplug.durian:durian:3.3.0
or just copy paste just two small classes into your code: Throwing.java and Errors.java
This is not specific to Java 8. You are trying to compile something equivalent to:
interface I {
void m();
}
class C implements I {
public void m() throws Exception {} //can't compile
}
Disclaimer: I haven't used Java 8 yet, only read about it.
Function<String, Integer> doesn't throw IOException, so you can't put any code in it that throws IOException. If you're calling a method that expects a Function<String, Integer>, then the lambda that you pass to that method can't throw IOException, period. You can either write a lambda like this (I think this is the lambda syntax, not sure):
(String s) -> {
try {
return myMethod(s);
} catch (IOException ex) {
throw new RuntimeException(ex);
// (Or do something else with it...)
}
}
Or, if the method you're passing the lambda to is one you wrote yourself, you can define a new functional interface and use that as the parameter type instead of Function<String, Integer>:
public interface FunctionThatThrowsIOException<I, O> {
O apply(I input) throws IOException;
}
If you don't mind to use a 3rd party lib (Vavr) you could write
CheckedFunction1<String, Integer> f = this::myMethod;
It also has the so-called Try monad which handles errors:
Try(() -> f.apply("test")) // results in a Success(Integer) or Failure(Throwable)
.map(i -> ...) // only executed on Success
...
Please read more here.
Disclaimer: I'm the creator of Vavr.
Sneaky throw idiom enables bypassing CheckedException of Lambda expression. Wrapping a CheckedException in a RuntimeException is not good for strict error handling.
It can be used as a Consumer function used in a Java collection.
Here is a simple and improved version of jib's answer.
import static Throwing.rethrow;
#Test
public void testRethrow() {
thrown.expect(IOException.class);
thrown.expectMessage("i=3");
Arrays.asList(1, 2, 3).forEach(rethrow(e -> {
int i = e.intValue();
if (i == 3) {
throw new IOException("i=" + i);
}
}));
}
This just wrapps the lambda in a rethrow. It makes CheckedException rethrow any Exception that was thrown in your lambda.
public final class Throwing {
private Throwing() {}
#Nonnull
public static <T> Consumer<T> rethrow(#Nonnull final ThrowingConsumer<T> consumer) {
return consumer;
}
/**
* The compiler sees the signature with the throws T inferred to a RuntimeException type, so it
* allows the unchecked exception to propagate.
*
* http://www.baeldung.com/java-sneaky-throws
*/
#SuppressWarnings("unchecked")
#Nonnull
public static <E extends Throwable> void sneakyThrow(#Nonnull Throwable ex) throws E {
throw (E) ex;
}
}
Find a complete code and unit tests here.
You could however create your own FunctionalInterface that throws as below..
#FunctionalInterface
public interface UseInstance<T, X extends Throwable> {
void accept(T instance) throws X;
}
then implement it using Lambdas or references as shown below.
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");
}
}
You can use unthrow wrapper
Function<String, Integer> func1 = s -> Unthrow.wrap(() -> myMethod(s));
or
Function<String, Integer> func2 = s1 -> Unthrow.wrap((s2) -> myMethod(s2), s1);
You can.
Extending #marcg 's UtilException and adding generic <E extends Exception> where necessary: this way, the compiler will force you again to add throw clauses and everything's as if you could throw checked exceptions natively on java 8's streams.
public final class LambdaExceptionUtil {
#FunctionalInterface
public interface Function_WithExceptions<T, R, E extends Exception> {
R apply(T t) throws E;
}
/**
* .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
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();
}
private static class MyTestException extends Exception { }
}
I had this problem with Class.forName and Class.newInstance inside a lambda, so I just did:
public Object uncheckedNewInstanceForName (String name) {
try {
return Class.forName(name).newInstance();
}
catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
throw new RuntimeException(e);
}
}
Inside the lambda, instead of calling Class.forName("myClass").newInstance() I just called uncheckedNewInstanceForName ("myClass")
Create a custom return type that will propagate the checked exception. This is an alternative to creating a new interface that mirrors the existing functional interface with the slight modification of a "throws exception" on the functional interface's method.
Definition
CheckedValueSupplier
public static interface CheckedValueSupplier<V> {
public V get () throws Exception;
}
CheckedValue
public class CheckedValue<V> {
private final V v;
private final Optional<Exception> opt;
public Value (V v) {
this.v = v;
}
public Value (Exception e) {
this.opt = Optional.of(e);
}
public V get () throws Exception {
if (opt.isPresent()) {
throw opt.get();
}
return v;
}
public Optional<Exception> getException () {
return opt;
}
public static <T> CheckedValue<T> returns (T t) {
return new CheckedValue<T>(t);
}
public static <T> CheckedValue<T> rethrows (Exception e) {
return new CheckedValue<T>(e);
}
public static <V> CheckedValue<V> from (CheckedValueSupplier<V> sup) {
try {
return CheckedValue.returns(sup.get());
} catch (Exception e) {
return Result.rethrows(e);
}
}
public static <V> CheckedValue<V> escalates (CheckedValueSupplier<V> sup) {
try {
return CheckedValue.returns(sup.get());
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
Usage
// Don't use this pattern with FileReader, it's meant to be an
// example. FileReader is a Closeable resource and as such should
// be managed in a try-with-resources block or in another safe
// manner that will make sure it is closed properly.
// This will not compile as the FileReader constructor throws
// an IOException.
Function<String, FileReader> sToFr =
(fn) -> new FileReader(Paths.get(fn).toFile());
// Alternative, this will compile.
Function<String, CheckedValue<FileReader>> sToFr = (fn) -> {
return CheckedValue.from (
() -> new FileReader(Paths.get("/home/" + f).toFile()));
};
// Single record usage
// The call to get() will propagate the checked exception if it exists.
FileReader readMe = pToFr.apply("/home/README").get();
// List of records usage
List<String> paths = ...; //a list of paths to files
Collection<CheckedValue<FileReader>> frs =
paths.stream().map(pToFr).collect(Collectors.toList());
// Find out if creation of a file reader failed.
boolean anyErrors = frs.stream()
.filter(f -> f.getException().isPresent())
.findAny().isPresent();
What's going on?
A single functional interface that throws a checked exception is created (CheckedValueSupplier). This will be the only functional interface which allows checked exceptions. All other functional interfaces will leverage the CheckedValueSupplier to wrap any code that throws a checked exception.
The CheckedValue class will hold the result of executing any logic that throws a checked exception. This prevents propagation of a checked exception until the point at which code attempts to access the value that an instance of CheckedValue contains.
The problems with this approach.
We are now throwing "Exception" effectively hiding the specific type originally thrown.
We are unaware that an exception occurred until CheckedValue#get() is called.
Consumer et al
Some functional interfaces (Consumer for example) must be handled in a different manner as they don't provide a return value.
Function in lieu of Consumer
One approach is to use a function instead of a consumer, which applies when handling streams.
List<String> lst = Lists.newArrayList();
// won't compile
lst.stream().forEach(e -> throwyMethod(e));
// compiles
lst.stream()
.map(e -> CheckedValueSupplier.from(
() -> {throwyMethod(e); return e;}))
.filter(v -> v.getException().isPresent()); //this example may not actually run due to lazy stream behavior
Escalate
Alternatively, you can always escalate to a RuntimeException. There are other answers that cover escalation of a checked exception from within a Consumer.
Don't consume.
Just avoid functional interfaces all together and use a good-ole-fashioned for loop.
Another solution using a Function wrapper would be to return either an instance of a wrapper of your result, say Success, if everything went well, either an instance of, say Failure.
Some code to clarify things :
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;
}
}
A simple use case :
List<Try<Integer>> result = Lists.newArrayList(1, 2, 3).stream().
map(Try.<Integer, Integer>tryOf(i -> someMethodThrowingAnException(i))).
collect(Collectors.toList());
This problem has been bothering me as well; this is why I have created this project.
With it you can do:
final ThrowingFunction<String, Integer> f = yourMethodReferenceHere;
There are a totla of 39 interfaces defined by the JDK which have such a Throwing equivalent; those are all #FunctionalInterfaces used in streams (the base Stream but also IntStream, LongStream and DoubleStream).
And as each of them extend their non throwing counterpart, you can directly use them in lambdas as well:
myStringStream.map(f) // <-- works
The default behavior is that when your throwing lambda throws a checked exception, a ThrownByLambdaException is thrown with the checked exception as the cause. You can therefore capture that and get the cause.
Other features are available as well.
There are a lot of great responses already posted here. Just attempting to solve the problem with a different perspective. Its just my 2 cents, please correct me if I am wrong somewhere.
Throws clause in FunctionalInterface is not a good idea
I think this is probably not a good idea to enforce throws IOException because of following reasons
This looks to me like an anti-pattern to Stream/Lambda. The whole idea is that the caller will decide what code to provide and how to handle the exception. In many scenarios, the IOException might not be applicable for the client. For example, if the client is getting value from cache/memory instead of performing actual I/O.
Also, the exceptions handling in streams becomes really hideous. For example, here is my code will look like if I use your API
acceptMyMethod(s -> {
try {
Integer i = doSomeOperation(s);
return i;
} catch (IOException e) {
// try catch block because of throws clause
// in functional method, even though doSomeOperation
// might not be throwing any exception at all.
e.printStackTrace();
}
return null;
});
Ugly isn't it? Moreover, as I mentioned in my first point, that the doSomeOperation method may or may not be throwing IOException (depending on the implementation of the client/caller), but because of the throws clause in your FunctionalInterface method, I always have to write the try-catch.
What do I do if I really know this API throws IOException
Then probably we are confusing FunctionalInterface with typical Interfaces. If you know this API will throw IOException, then most probably you also know some default/abstract behavior as well. I think you should define an interface and deploy your library (with default/abstract implementation) as follows
public interface MyAmazingAPI {
Integer myMethod(String s) throws IOException;
}
But, the try-catch problem still exists for the client. If I use your API in stream, I still need to handle IOException in hideous try-catch block.
Provide a default stream-friendly API as follows
public interface MyAmazingAPI {
Integer myMethod(String s) throws IOException;
default Optional<Integer> myMethod(String s, Consumer<? super Exception> exceptionConsumer) {
try {
return Optional.ofNullable(this.myMethod(s));
} catch (Exception e) {
if (exceptionConsumer != null) {
exceptionConsumer.accept(e);
} else {
e.printStackTrace();
}
}
return Optional.empty();
}
}
The default method takes the consumer object as argument, which will be responsible to handle the exception. Now, from client's point of view, the code will look like this
strStream.map(str -> amazingAPIs.myMethod(str, Exception::printStackTrace))
.filter(Optional::isPresent)
.map(Optional::get).collect(toList());
Nice right? Of course, logger or other handling logic could be used instead of Exception::printStackTrace.
You can also expose a method similar to https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html#exceptionally-java.util.function.Function- . Meaning that you can expose another method, which will contain the exception from previous method call. The disadvantage is that you are now making your APIs stateful, which means that you need to handle thread-safety and which will be eventually become a performance hit. Just an option to consider though.
By default, Java 8 Function does not allow to throw exception and as suggested in multiple answers there are many ways to achieve it, one way is:
#FunctionalInterface
public interface FunctionWithException<T, R, E extends Exception> {
R apply(T t) throws E;
}
Define as:
private FunctionWithException<String, Integer, IOException> myMethod = (str) -> {
if ("abc".equals(str)) {
throw new IOException();
}
return 1;
};
And add throws or try/catch the same exception in caller method.
I use an overloaded utility function called unchecked() which handles multiple use-cases.
SOME EAMPLE USAGES
unchecked(() -> new File("hello.txt").createNewFile());
boolean fileWasCreated = unchecked(() -> new File("hello.txt").createNewFile());
myFiles.forEach(unchecked(file -> new File(file.path).createNewFile()));
SUPPORTING UTILITIES
public class UncheckedUtils {
#FunctionalInterface
public interface ThrowingConsumer<T> {
void accept(T t) throws Exception;
}
#FunctionalInterface
public interface ThrowingSupplier<T> {
T get() throws Exception;
}
#FunctionalInterface
public interface ThrowingRunnable {
void run() throws Exception;
}
public static <T> Consumer<T> unchecked(
ThrowingConsumer<T> throwingConsumer
) {
return i -> {
try {
throwingConsumer.accept(i);
} catch (Exception ex) {
throw new RuntimeException(ex);
}
};
}
public static <T> T unchecked(
ThrowingSupplier<T> throwingSupplier
) {
try {
return throwingSupplier.get();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
public static void unchecked(
ThrowingRunnable throwing
) {
try {
throwing.run();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
}
You can use ET for this. ET is a small Java 8 library for exception conversion/translation.
With ET it looks like this:
// Do this once
ExceptionTranslator et = ET.newConfiguration().done();
...
// if your method returns something
Function<String, Integer> f = (t) -> et.withReturningTranslation(() -> myMethod(t));
// if your method returns nothing
Consumer<String> c = (t) -> et.withTranslation(() -> myMethod(t));
ExceptionTranslator instances are thread safe an can be shared by multiple components. You can configure more specific exception conversion rules (e.g. FooCheckedException -> BarRuntimeException) if you like.
If no other rules are available, checked exceptions are automatically converted to RuntimeException.
(Disclaimer: I am the author of ET)
If you don't mind using a third party library, with cyclops-react, a library I contribute to, you can use the FluentFunctions API to write
Function<String, Integer> standardFn = FluentFunctions.ofChecked(this::myMethod);
ofChecked takes a jOOλ CheckedFunction and returns the reference softened back to a standard (unchecked) JDK java.util.function.Function.
Alternatively you can keep working with the captured function via the FluentFunctions api!
For example to execute your method, retrying it up to 5 times and logging it's status you can write
FluentFunctions.ofChecked(this::myMethod)
.log(s->log.debug(s),e->log.error(e,e.getMessage())
.try(5,1000)
.apply("my param");
What I'm doing is to allow the user to give the value he actually want in case of exception .
So I've something looking like this
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;
}
And this can then be call like :
defaultIfThrows(child -> child.getID(), null)
Use Jool Library or say jOOλ library from JOOQ. It not only provides unchecked exception handled interfaces but also provides Seq class with lots of useful methods.
Also, it contains Functional Interfaces with up to 16 parameters. Also, it provides Tuple class which is used in different scenarios.
Jool Git Link
Specifically in library lookup for org.jooq.lambda.fi.util.function package. It contains all the Interfaces from Java-8 with Checked prepended. See below for reference:-
If you have lombok, you can annotate your method with #SneakyThrows
SneakyThrow does not silently swallow, wrap into RuntimeException, or otherwise modify any exceptions of the listed checked exception types. The JVM does not check for the consistency of the checked exception system; javac does, and this annotation lets you opt out of its mechanism.
https://projectlombok.org/features/SneakyThrows
Several of the offered solutions use a generic argument of E to pass in the type of the exception which gets thrown.
Take that one step further, and rather than passing in the type of the exception, pass in a Consumer of the type of exception, as in...
Consumer<E extends Exception>
You might create several re-usable variations of Consumer<Exception> which would cover the common exception handling needs of your application.
I will do something generic:
public interface Lambda {
#FunctionalInterface
public interface CheckedFunction<T> {
T get() throws Exception;
}
public static <T> T handle(CheckedFunction<T> supplier) {
try {
return supplier.get();
} catch (Exception exception) {
throw new RuntimeException(exception);
}
}
}
usage:
Lambda.handle(() -> method());
I'm the author of a tiny lib with some generic magic to throw any Java Exception anywhere without the need of catching them nor wrapping them into RuntimeException.
Usage:
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);
}
}
}
source: https://github.com/qoomon/unchecked-exceptions-java
For me the preferred solution is to use Lombok. It is a nice library anyway.
Instead of:
Integer myMethod(String s) throws IOException
you will have
import lombok.SneakyThrows;
#SneakyThrows
Integer myMethod(String s)
The exception is still thrown but you do not need to declare it with throws.
public void frankTest() {
int pageId= -1;
List<Book> users= null;
try {
//Does Not Compile: Object page=DatabaseConnection.getSpringConnection().queryForObject("SELECT * FROM bookmark_page", (rw, n) -> new Portal(rw.getInt("id"), "", users.parallelStream().filter(uu -> uu.getVbid() == rw.getString("user_id")).findFirst().get(), rw.getString("name")));
//Compiles:
Object page= DatabaseConnection.getSpringConnection().queryForObject("SELECT * FROM bookmark_page", (rw, n) -> {
try {
final Book bk= users.stream().filter(bp -> {
String name= null;
try {
name = rw.getString("name");
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return bp.getTitle().equals(name);
}).limit(1).collect(Collectors.toList()).get(0);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return new Portal(rw.getInt("id"), "", users.get(0), rw.getString("name"));
} );
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I'm trying to create a really simple callback using some Strings. The IDE's code sense is is moaning about an unchecked call to exceptionally. Can anyone give me a fix for this? The idea in the end is to wrap a network call so that the promised result is returned and I can tack on additional functions as needed.
import java.util.concurrent.*;
import java.util.function.BiConsumer;
import java.util.function.Function;
import java.util.function.Supplier;
public class FuturesTest {
public static void main(String[] args) throws Exception {
new FuturesTest().go();
}
private void go() throws ExecutionException, InterruptedException {
CompletableFuture.supplyAsync(new MakesANetworkCall())
.whenComplete(new BiConsumer<String, String>() {
#Override
public void accept(String result, String s) {
System.out.println(result.toString());
}
})
.exceptionally(new Function<Exception, Exception>() {
#Override
public Exception apply(Exception e) {
e.printStackTrace();
return e;
}
}
).thenApplyAsync(new Function<String, String>() {
#Override
public String apply(String o) {
System.out.println("Last action of all!");
return null;
}
});
System.out.println("Main thread will sleep");
Thread.sleep(2500);
System.out.println("Program over");
}
class MakesANetworkCall implements Supplier {
#Override
public String get() {
try {
System.out.println("Ground control to Major Tom");
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// int i = 2/0;
return new String("Major Tom reporting!");
}
}
}
First of all, your class MakesANetworkCall implements the raw type Supplier instead of Supplier<String>. This will effectively disable the type checking and hide all errors you made, so it’s not the single warning you should worry about, as that’s not the only thing wrong in your code:
The BiConsumer passed to whenComplete should be able to consume a Throwable as its second argument.
The Function passed to exceptionally should consume a Throwable and return an alternative result.
Further, you are invoking a static method using the expression new CompletableFuture<String>() as its target and you have an obsolete string creation expression as new String("Major Tom reporting!") where the simple constant "Major Tom reporting!" will do. Generally, you seem to try to always use an inappropriate method, i.e. one designed to consume things you don’t use or one for supplying a value where you don’t have one. Consider this:
CompletableFuture.supplyAsync(new MakesANetworkCall())
.thenAccept(result -> System.out.println(result))
.exceptionally(e -> { e.printStackTrace(); return null;})
.thenRun(()->System.out.println("Last action of all!"));
This does what seems to be your intention. If you ensure that your MakesANetworkCall correctly implements Supplier<String>, this should compile without any warnings.
Your core issue is with class MakesANetworkCall implements Supplier {. This is using raw types and therefore hides further problems. Fix that to class MakesANetworkCall implements Supplier<String> { and fix all ensuing issues and you get:
CompletableFuture.supplyAsync(new MakesANetworkCall())
// Not <String, String>
.whenComplete(new BiConsumer<String, Throwable>() {
#Override
public void accept(String result, Throwable t) {
System.out.println(result);
}
})
// Not <Exception,Exception>
.exceptionally(new Function<Throwable, String>() {
#Override
public String apply(Throwable t) {
t.printStackTrace();
// Must return a Streing
return t.getMessage();
}
}
).thenApplyAsync(new Function<String, String>() {
#Override
public String apply(String o) {
System.out.println("Last action of all!");
return null;
}
});
CompletableFuture.exceptionally is declared like so:
public CompletableFuture<T> exceptionally(Function<Throwable, ? extends T> fn);
You're passing it a Function<Exception, Exception>, whereas you should be passing it a Function<Throwable, String>.
My application have several execution modes, and in 1 mode it is normal that some of my tests will throw a concrete exception. I need to annotate this methods with something like #SkipOnFail that will set method as skipped if exception was thrown.
thanks in advance!
#Edit(for my question to be more clear)
#Test(expected=ConcreteException.class)
does not work for me because i need my tests to pass even if ConcreteException.class was not thrown(expected tag in junit will mark my test as failed if this exception won't be thrown), and to be skipped otherwise. In all other cases it should work as always.
#Solution that worked for me(junit v4.7) thx to #axtavt
#Rule
public MethodRule skipRule = new MethodRule() {
public Statement apply(final Statement base, FrameworkMethod method, Object target) {
if(method.getAnnotation(SkipOnFail.class) == null) return base;
return new Statement() {
#Override
public void evaluate() throws Throwable {
try{
base.evaluate();
} catch (ConcreteException e) {
Assume.assumeTrue(false);
}
}
};
}
};
#Thx
I don't think that such a feature is available out of the box, but it should be pretty easy to implement with custom TestRule and Assume, something like this:
#Rule
public TestRule skipRule = new TestRule() {
public Statement apply(final Statement base, Description desc) {
if (desc.getAnnotation(SkipOnFail.class) == null) return base;
return new Statement() {
public void evaluate() throws Throwable {
try {
base.evaluate();
} catch (MyExceptoion ex) {
Assume.assumeTrue(false);
}
}
};
}
};
What about using JUnit Extensions?
The following example is taken from their Tutorial.
It provides aditional annotations for Prerequisites (#Prerequisite): Ignore tests based on conditions.
The required approach would be to check this during running tests. So you can simply add a #Prerequisite(requires="") annotation.
public class TestFillDatabase {
#Prerequisite(requires = "databaseIsAvailable")
#Test public void fillData() {
// ...
}
public boolean databaseIsAvailable() {
boolean isAvailable = ...;
return isAvailable;
}
}
public class TestFillDatabase {
#Prerequisite(requires = "databaseIsAvailable")
#Test public void fillData() {
// ...
}
public boolean databaseIsAvailable() {
boolean isAvailable = ...;
return isAvailable ;
}
}
This specified methods with #Prerequisite(requires = "databaseIsAvailable") must be a public method, returning a boolean or Boolean value.
If these methods will be consolidated in helper classes, you can also specify static methods within a class to be called using #Prerequisite(requires = "databaseIsAvailable", callee="DBHelper").
public class TestFillDatabase {
#Prerequisite(requires = "databaseIsAvailable", callee="DBHelper")
#Test public void fillData() {
// ...
}
}
public class DBHelper {
public static boolean databaseIsAvailable() {
boolean isAvailable = ...;
return isAvailable ;
}
}
Also using the Assume class (since jUnit 4.4), you can use assumeNoException():
try{
base.evaluate();
} catch (ConcreteException e) {
Assume.assumeNoException("Concrete exception: skipping test", e);
}
I searched for the docs about JUnit and it appears that from version 4.9 they have introduced what they call test rules (see TestRule). You may start from this.
The ExpectedException class marked as #Rule could be of some help in order to check for exceptions thrown but not mandatory for the test to pass.
For more advanced usage I cannot say for the moment as I've just discovered it.