Consumer to enclose try catch logic does not work - java-8

I am refactoring some legacy code and I come across this function:
private static void parseOptionalValues(Product product, Input source) {
try {
product.setProductType(...some operation with source...);
} catch (IllegalArgumentException ignored) {}
try {
product.setMaterial(...some operation with source...);
} catch (IllegalArgumentException ignored) {}
try {
product.setUnitPricingBaseMeasure(...some operation with source...);
} catch (IllegalArgumentException ignored) {}
try {
product.setUnitPricingMeasure(...some operation with source...);
} catch(IllegalArgumentException ignored){}
}
My common sense says to me that in order to keep the Don't Repeat Yourself principle I should wrap this try-catch logic so I introduced this change:
private static void parseOptionalValues(Product product, Input source) {
setOptionalParameter(...some operation with source..., product::setProductType);
setOptionalParameter(...some operation with source..., product::setMaterial);
setOptionalParameter(...some operation with source..., product::setUnitPricingBaseMeasure);
setOptionalParameter(...some operation with source..., product::setUnitPricingMeasure);
}
private static <T> void setOptionalParameter(T value, Consumer<T> consumer) {
try {
consumer.accept(value);
} catch (IllegalArgumentException ignored) {}
}
I am running some unit tests and debugging but the code doesn't behave as previously as the IllegalArgumentException is not catched but raised so the program fails.
Any idea on how to solve this enclosing the try-catch logic in a single place?

I think the problem might be that the exception is thrown by the code that gets the arguments to be passed to the setters. So one possible approach would be to make that part of the code lazy by using a Supplier, then invoke .get() on the Supplier inside a the try/catch block (as well as invoking the Consumer):
private static <T> void setOptionalParameter(
Supplier<? extends T> supplier,
Consumer<? super T> consumer) {
try {
consumer.accept(supplier.get());
} catch (IllegalArgumentException ignored) {
}
}
You could invoke that method as follows:
setOptionalParameter(() -> ...some operation with source..., product::setProductType);
Note that I've improved the signature of your method so that it now accepts a wider range of generic subtypes and supertypes for the Supplier and Consumer, respectively.
EDIT: As per the comments, the approach above might be not flexible enough, i.e. if the method accepts more than one argument, etc. In this case, it would be better to use a Runnable instance:
private static void setOptionalParameter(Runnable action) {
try {
action.run();
} catch (IllegalArgumentException ignored) {
}
}
And invocation would now become:
setOptionalParameter(() -> {
ProductType productType = ...some operation with source...;
Material material = ...some operation with source...;
product.doSomethingWith2Args(productType, material);
});

Related

Throw actual exception from completeablefuture

I am making parallel call using completablefuture like below,
public Response getResponse() {
Response resultClass = new Response();
try {
CompletableFuture<Optional<ClassA>> classAFuture
= CompletableFuture.supplyAsync(() -> service.getClassA() );
CompletableFuture<ClassB> classBFuture
= CompletableFuture.supplyAsync(() -> {
try {
return service.getClassB();
}
catch (Exception e) {
throw new CompletionException(e);
}
});
CompletableFuture<Response> responseFuture =
CompletableFuture.allOf(classAFuture, classBFuture)
.thenApplyAsync(dummy -> {
if (classAFuture.join().isPresent() {
ClassA classA = classAFuture.join();
classA.setClassB(classBFuture.join());
response.setClassA(classA)
}
return response;
});
responseFuture.join();
} catch (CompletionExecution e) {
throw e;
}
return response;
}
I need to add try catch for return service.getClassB() as it throwing an exception inside the method getClassB.
Now problem I am facing is if service.getClassB() throws error it always comes wrapped inside java.util.concurrent.ExecutionException. There is a scenario where this method throws UserNameNotFoundException but this is wrapped inside ExecutionException and it is not getting caught in the right place #ControllerAdvice Exception handler class. I tried different option using throwable but it didn't help.
Is there a good way to handle the exception and unwrap and send it to #ControllerAdvice class?
Your code has several errors, like referring to a variable response that is not declared in this code and most probably supposed to be the resultClass declared at the beginning. The line
ClassA classA = classAFuture.join(); suddenly ignores that this future encapsulates an Optional and there are missing ) and ; separators.
Further, you should avoid accessing variables from the surrounding code when there’s a clean alternative. Also, using allOf to combine two futures is an unnecessary complication.
If I understood your intention correctly, you want to do something like
public Response getResponse() {
return CompletableFuture.supplyAsync(() -> service.getClassA())
.thenCombine(CompletableFuture.supplyAsync(() -> {
try {
return service.getClassB();
}
catch(ExecutionException e) {
throw new CompletionException(e.getCause());
}
}), (optA, b) -> {
Response response = new Response();
optA.ifPresent(a -> {
a.setClassB(b);
response.setClassA(a);
});
return response;
})
.join();
}
The key point to solve your described problem is to catch the most specific exception type. When you catch ExecutionException, you know that it will wrap the actual exception and can extract it unconditionally. When the getClassB() declares other checked exceptions which you have to catch, add another catch clause, but be specific instead of catching Exception, e.g.
try {
return service.getClassB();
}
catch(ExecutionException e) {
throw new CompletionException(e.getCause());
}
catch(IOException | SQLException e) { // all of getClassB()’s declared exceptions
throw new CompletionException(e); // except ExecutionException, of course
}

Java 8 - Streams - exception handling is mandatory in stream processing? [duplicate]

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();
}
}

CompletableFuture exceptionally breaks the work chain

The idea of using CompletableFuture is because it offers a chain, while the first several steps encapsulate beans before the last step uses it. Because any exception may happen in these steps and exceptionally is used to handle error. However, exceptionally only accepts Throwable argument and so far I haven't found a way to grab those encapsulated beans.
CompletableFuture.supplyAsync(this::msgSource)
.thenApply(this::sendMsg).exceptionally(this::errorHandler).thenAccept(this::saveResult)
public List<Msg> msgSource() // take message from somewhere.
public List<Msg> sendMsg(List<Msg>) // exceptions may happen like 403 or timeout
public List<Msg> errorHandler() // set a success flag to false in Msg.
public void saveResult(List<Msg>) // save send result like success or false in data center.
In the above example, comments are the working flow. However, since errorHandler neither accepts List<Msg> nor passes it on, so the chain is broken. How to get the return from msgSource?
EDIT
public class CompletableFutureTest {
private static Logger log = LoggerFactory.getLogger(CompletableFutureTest.class);
public static void main(String[] args) {
CompletableFutureTest test = new CompletableFutureTest();
CompletableFuture future = new CompletableFuture();
future.supplyAsync(test::msgSource)
.thenApply(test::sendMsg).exceptionally(throwable -> {
List<String> list = (List<String>) future.join(); // never complete
return list;
}).thenAccept(test::saveResult);
try {
future.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
private List<String> saveResult(List<String> list) {
return list;
}
private List<String> sendMsg(List<String> list) {
throw new RuntimeException();
}
public List<String> msgSource() {
List<String> result = new ArrayList<>();
result.add("1");
result.add("2");
return result;
}
}
A chain implies that each node, i.e. completion stage, uses the result of the previous one. But if the previous stage failed with an exception, there is no such result. It’s a special property of your sendMsg stage that its result is just the same value as it received from the previous stage, but that has no influence on the logic nor API design. If sendMsg fails with an exception, it has no result that the exception handler could use.
If you want to use the result of the msgSource stage in the exceptional case, you don’t have a linear chain any more. But CompletableFuture does allow to model arbitrary dependency graphs, not just linear chains, so you can express it like
CompletableFuture<List<Msg>> source = CompletableFuture.supplyAsync(this::msgSource);
source.thenApply(this::sendMsg)
.exceptionally(throwable -> {
List<Msg> list = source.join();
for(Msg m: list) m.success = false;
return list;
})
.thenAccept(this::saveResult);
However, there is no semantic difference nor advantage over
CompletableFuture.runAsync(() -> {
List<Msg> list = msgSource();
try {
list = sendMsg(list);
} catch(Throwable t) {
for(Msg m: list) m.success = false;
}
saveResult(list);
});
which expresses the same logic as an ordinary code flow.

Java 8 lambda catching exception

From the book Java 8 for the impatient by Cay Horstmann:
Didn’t you always hate it that you had to deal with checked
exceptions in a Runnable? Write a method uncheck that catches all
checked exceptions and turns them into unchecked exceptions. For
example,
new Thread(uncheck(
() -> { System.out.println("Zzz"); Thread.sleep(1000); })).start();
// Look, no catch (InterruptedException)!
Hint: Define an interface RunnableEx whose run method may throw any
exceptions. Then implement
public static Runnable uncheck(RunnableEx runner)
Use a lambda expression inside the uncheck function.
For which I code like this:
public interface RunnableEx {
void run() throws Exception;
}
public class TestUncheck {
public static Runnable uncheck(RunnableEx r) {
return new Runnable() {
#Override
public void run() {
try {
r.run();
} catch (Exception e) {
}
}
};
}
public static void main(String[] args) {
new Thread(uncheck(
() -> {
System.out.println("Zzz");
Thread.sleep(1000);
}
)).start();
}
}
Did I do according to what was hinted? Is there a better way of doing this?
Also there is another complementary question:
Why can’t you just use Callable<Void> instead of RunnableEx?
Your code fails to wrap the checked exception into an unchecked one. Further, it doesn’t following the hint to use a lambda expression. A corrected version would be:
public static Runnable uncheck(RunnableEx r) {
return () -> {
try {
r.run();
} catch (Exception e) {
throw new RuntimeException(e);
}
};
}
There are indeed possibilities to improve this further. Since the whole purpose of the RunnableEx interface is to wrap a Runnable, you could place the factory method inside the interface itself:
public interface RunnableEx {
void run() throws Exception;
public static Runnable uncheck(RunnableEx r) {
return () -> {
try {
r.run();
} catch (Exception e) {
throw new RuntimeException(e);
}
};
}
}
Of course, now your calling code has to be adapted to:
public static void main(String[] args) {
new Thread(RunnableEx.uncheck(
() -> {
System.out.println("Zzz");
Thread.sleep(1000);
}
)).start();
}
Now, the interface itself could implement the wrapping feature, becoming compatible with Runnable, which would eliminate the need to have a Runnable and a RunnableEx instance to represent a single action:
public interface RunnableEx extends Runnable {
void runWithException() throws Exception;
#Override default void run() {
try {
runWithException();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
public static Runnable uncheck(RunnableEx r) {
return r;
}
}
Note that while the calling code doesn’t change syntactically, it will implicitly create a Runnable instance in the first place, when creating the RunnableEx instance, that’s why uncheck becomes a no-op, merely serving as a marker that a RunnableEx should be created rather than a Runnable. With this interface definition, you could achieve the same via
public static void main(String[] args) {
new Thread( (RunnableEx) () -> {
System.out.println("Zzz");
Thread.sleep(1000);
}
).start();
}
The reason why you can’t “just use” a Callable<Void> here, is that Callable<Void> still is a Callable, requiring the implementation code to return a value. In other words, there is no implicit conversion from void to Void. So you can use it, but the lambda expression would require a return null; statement at its end then (null is the only value compatible with Void).
public class TestUncheck {
public static Runnable uncheck(Callable<Void> r) {
return () -> {
try { r.call(); }
catch (Exception e) { throw new RuntimeException(e); }
};
}
public static void main(String[] args) {
new Thread(uncheck(
() -> {
System.out.println("Zzz");
Thread.sleep(1000);
return null;
}
)).start();
}
}
This way of catching exceptions from lambdas works fine, and is (with a few additions) the one implemented in the Unchecked class from jOOλ, a popular Java library.
For comparison, see their static method Unchecked.runnable, which is identical to your solution, with the exception of their Exception handler and to the lambda abreviating the return value.
With regards to the assignment from Java 8 to the Impatients, your uncheck method does not use a lambda (for this, see the Unchecked.runnable method), and does not throw an unchecked exception. For this, your catchblock (currently empty) needs to wrap the exception into an unchecked exception. There are many ways to do it, and many questions on SO are relevant:
How to wrap checked exceptions but keep the original runtime exceptions in Java
Replace a checked exception with a runtime exception?
Handling Runtime exception in Java
But a simple way is:
throw (e instanceof RuntimeException) ? (RuntimeException) e : new RuntimeException(e);
Finally, to answer the Callable<Void>question, I am assuming you mean "instead of Runnable"? If so, it is because the constructors from Thread take a Runnableas an argument.

Addressing Scalability,Performance and Optimization issues in RMI Application?

my problem is: this design is working fine for one ball but i m unable to get it work for multiple balls, i have basically problem in replacing the "this" keyword in updateClients ().
i thought i need to do something like this but i m failed:
System.out.println("in ballimpl" + j.size());
for (ICallback aClient : j) {
aClient.updateClients(BallImpl[i]);
}
The current situation of code is :
The model remote object, which is iterating client list and calling update method of them,
public class BallImpl extends UnicastRemoteObject implements Ball,Runnable {
private List<ICallback> clients = new ArrayList<ICallback>();
protected static ServerServices chatServer;
static ServerServices si;
BallImpl() throws RemoteException {
super();
}
....
public synchronized void move() throws RemoteException {
loc.translate((int) changeInX, (int) changeInY);
}
public void start() throws RemoteException {
if (gameThread.isAlive()==false )
if (run==false){
gameThread.start();
}
}
/** Start the ball bouncing. */
// Run the game logic in its own thread.
public void run() {
while (true) {
run=true;
// Execute one game step
try {
updateClients();
} catch (RemoteException e) {
e.printStackTrace();
}
try {
Thread.sleep(50);
} catch (InterruptedException ex) {
}
}
}
public void updateClients() throws RemoteException {
si = new ServerServicesImpl();
List<ICallback> j = si.getClientNames();
System.out.println("in messimpl " + j.size());
if (j != null) {
System.out.println("in ballimpl" + j.size());
for (ICallback aClient : j) {
aClient.updateClients(this);
}
} else
System.err.println("Clientlist is empty");
}
}
The client which is implementing callback interface and has update method implementation :
public final class thenewBallWhatIwant implements Runnable, ICallback {
.....
#Override
public void updateClients(final Ball ball) throws RemoteException {
try {
ball.move();
try {
Thread.sleep(50);
} catch (Exception e) {
System.exit(0);
}
} catch (Exception e) {
System.out.println("Exception: " + e);
}
}
.....
}
thanks for any feedback.
jibbylala
Separate your RMI logic from your Ball logic.
You should be able to run your ball simulation without needing any RMI modules. Just to run it locally, to test it. Then you should find a way to wrap that process in RMI so that you can still run it locally to test it without any sort of RMI interface. This block of code is the engine, and it is very important to be able to test it in as atomic a form as possible. Having extra parts integrated with it just increases the complexity of what will undoubtedly be some of the most complex code.
Don't let any extra interfaces into your engine. It should be very specific and few the packages required to use your engine. Any new functionality your software needs, implement it appropriately in the engine to support generic design. Wrap that to provide specific functionality outside the core of the engine. This protects the engine design against changes to the environment. It also allows for more complete testing of the engine.
We make exceptions sometimes in cases where something will only ever be used in one way. But in this case, testing without RMI would seem to be critical to getting your engine working correctly. If your engine runs faster than the network can keep up due to large numbers of clients connecting, do you want the whole game to slow down, or do you want the clients to lag behind? I say, you want to be able to make that choice.

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