Throwable interfaces

In an attempt to reduce try/catch blocks inside lambda statements, this project extends all the major functional interfaces found in java.util.function.* with new functional interfaces that allow checked exceptions.

Basic usage

As an example for the new FunctionWithThrowable interface, consider we have a Stream<File> fileStream, which we wanted to map into its content.

Stream<String> content = fileStream.map(file -> {
   try {
      return IOUtils.readFile(file);
   } catch(IOException ioException) {
      throw new RuntimeException(ioException);
   }
});

With the FunctionWithThrowable interface, this can be cleaned up like this:

Stream<String> content = fileStream.map(FunctionWithThrowable.castFunctionWithThrowable(file -> {
      return IOUtils.readFile(file);
}));

Using a static import and method reference, we can even make this more streamline.

Stream<String> content = fileStream.map(castFunctionWithThrowable(IOUtils::readFile));

We can also force catching of the checked exception.

try {
    Stream<String> content = fileStream.map(asFunctionWithThrowableThatUnsafelyThrowsUnchecked(IOUtils::readFile));
} catch (IOException e) {
}

Interfaces

<E> Generic

Each new interface extends the original interface with the same generics, plus an additional <E extends Throwable> that denotes the exception type that this will throw.

The an implementation of the Function interface:

Function<File, String> readingFunction = (file) -> {
   try {
      return IOUtils.readFile(file);
   } catch(IOException ioException) {
      throw new RuntimeException(ioException);
   }
}

Can be expressed as:

FunctionWithThrowable<File, String, IOException> readingFunction = (file) -> {
      return IOUtils.readFile(file);
}

Default method

Each new 'WithThrowable' interface has two methods.

FunctionWithThrowable<File, String, IOException> readingFunction = (file) -> {
          return IOUtils.readFile(file);
}

// returns string, throws IOException.
readingFunction.applyWithThrowable(file); 

// returns string, internally calls .applyWithThrowable but does not 
// throw an IOException, instead throws SuppressedException.
readingFunction.apply(file); 

This means you can use the 'WithThrowable' interface interchangeably with the original interfaces without having the compiler complain about undeclared thrown exceptions.

You can still catch/rethrow the exceptions with

try {
  return fileStream.forEach(readingFunction);
} catch(SuppressedException e) {
  throw (IOException) e.getCause();
}

Cast method

Each new interface has a static method that casts a lamba. This is useful if you want to use the original interface as a type, but with the internal of the new "WithThrowable" interface.

Function<File, String> readingFunction = FunctionWithThrowable.castFunctionWithThrowable((file) -> {
   return IOUtils.readFile(file);
});

Convert Method

If you wanted to convert the original interface to the "WithThrowable" interface:

Function<File, String> someFunction = ...;
Function<File, String> readingFunction = FunctionWithThrowable.asFunctionWithThrowable(someFunction);

Exception Handling

The interfaces come with some handy methods:

withLogging(), withLogging(logger, message), withLogging(logger)

Returns an interface that will log messages when a exception has occurred. Uses slf4j loggers.

FunctionWithThrowable.castFunctionWithThrowable((file) -> {
   return IOUtils.readFile(file);
}).withLogging();

thatThrowsNothing()

Returns an interface that does nothing on exceptions. Only applicable on interfaces that specify no return type.

// no exception will be thrown
ConsumerWithThrowable.castConsumerWithThrowable((file) -> {
   if(!file.exists()) {
      throw new IOException("file does not exist");
   }
}).thatThrowsNothing();

thatIgnores(Class<? extends Throwable> ... throwableClasses)

Returns an interface that does nothing on exceptions. Only applicable on interfaces that specify no return type.

// no exception will be thrown
ConsumerWithThrowable.castConsumerWithThrowable((file) -> {
   if(!file.exists()) {
      throw new IOException("file does not exist");
   }
}).thatIgnores(IOException.class); 

thatReturnsOptional()

Returns an interface that will return Optional of the return type, which will be empty if there has been an error. Only applicable on interfaces that return non-primitive types.

thatReturnsOnCatch(defaultValue)

Returns an interface that will return some defaultValue if an exception occurs. Only applicable on interfaces that specify a return type.

thatUnsafelyThrowsUnchecked()

Rethrows the exception unsafely if one has occured.

About the library

Site

A site is generated at http://stefanliebenberg.github.io/throwable-interfaces/

Javadocs

Javadocs at http://stefanliebenberg.github.io/throwable-interfaces/apidocs

Maven ( and the rest )

This is published in central,

<dependency>
  <groupId>org.slieb</groupId>
  <artifactId>throwable-interfaces</artifactId>
  <version>...</version>
</dependency>

For latest version, see http://stefanliebenberg.github.io/throwable-interfaces/dependency-info.html

How it was built:

All the interfaces ( and their tests ) have actually been generated by reflecting the original interfaces. See src/tools/java.