Module dk.cloudcreate.essentials.shared

Package dk.cloudcreate.essentials.shared.functional

Interface CheckedFunction<T,R>

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface CheckedFunction<T,R>

Variant of Function that behaves like Function, but which allows checked Exception's to be thrown from its apply(Object) method
– the function argument type – the function result type

See Also:

• safe(CheckedFunction)
• safe(String, CheckedFunction)

Method Summary

Modifier and Type	Method	Description
R	apply(T argument)	This method performs the operation that may fail with a Checked Exception
static <T, R> Function<T,R>	safe(CheckedFunction<T,R> functionThatCanFailWithACheckedException)	Wraps a CheckedFunction (basically a lambda with one argument that returns a result and which throws a Checked Exception) by returning a new Function instance The returned Function.apply(Object) method delegates directly to the apply(Object) and catches any thrown checked Exception's and rethrows them as a CheckedExceptionRethrownException Unless you provide a context-message (using safe(String, CheckedFunction) then any caught checked Exception's message also becomes the CheckedExceptionRethrownException's message. Any RuntimeException's thrown aren't caught and the calling code will receive the original RuntimeException thrown. Usage example: Let's say we have a method called someOperation that cannot change, but which accepts a Function with the purpose of the calling the Function.apply(Object).
static <T, R> Function<T,R>	safe(String contextMessage, CheckedFunction<T,R> functionThatCanFailWithACheckedException)	Wraps a CheckedFunction (basically a lambda with one argument that returns a result and which throws a Checked Exception) by returning a new Function instance The returned Function.apply(Object) method delegates directly to the apply(Object) and catches any thrown checked Exception's and rethrows them as a CheckedExceptionRethrownException Any RuntimeException's thrown aren't caught and the calling code will receive the original RuntimeException thrown. Usage example: Let's say we have a method called someOperation that cannot change, but which accepts a Function with the purpose of the calling the Function.apply(Object).

Method Details

safe

static <T,
R> Function<T,R> safe(CheckedFunction<T,R> functionThatCanFailWithACheckedException)

Wraps a CheckedFunction (basically a lambda with one argument that returns a result and which throws a Checked Exception) by returning a new Function instance
The returned Function.apply(Object) method delegates directly to the apply(Object) and catches any thrown checked Exception's and rethrows them as a CheckedExceptionRethrownException
Unless you provide a context-message (using safe(String, CheckedFunction) then any caught checked Exception's message also becomes the CheckedExceptionRethrownException's message.
Any RuntimeException's thrown aren't caught and the calling code will receive the original RuntimeException thrown.

Usage example:
Let's say we have a method called someOperation that cannot change, but which accepts a Function with the purpose of the calling the Function.apply(Object).

 public void someOperation(Function<Integer, String> operation) {
      // ... Logic ...

      String value = operation.apply(10);

      // ... More logic ---
 }
 

The problem will Function.apply(Object) occurs when Function calls any API that throws a checked Exception, e.g. the File API.
Since Function.apply(Object) doesn't define that it throws any Exception's we're forced to add a try/catch to handle the IOException for the code to compile:

  someOperation(value -> {
                      try {
                          // Logic that uses the File API
                          return "some-value";
                      } catch (IOException e) {
                          throw new RuntimeException(e);
                      }
                }));
 

This is where the CheckedFunction comes to the aid as its apply(Object) methods defines that it throws a Checked Exception and its safe(CheckedFunction) will return a new Function instance with a Function.apply(Object) method that ensures that the apply(Object) method is called and any checked Exception's thrown will be caught and rethrown as a CheckedExceptionRethrownException:

  someOperation(CheckFunction.safe(value -> {
                      // Logic that uses the File API that throws IOException
                      return "some-value";
                }));
 
 

Type Parameters:

T - the argument type

R - the return type

Parameters:

functionThatCanFailWithACheckedException - the CheckedFunction instance that will be wrapped as a Function

Returns:

a Function with a Function.apply(Object) method that ensures that the apply(Object) method is called when Function.apply(Object) and any checked Exception's thrown will be caught and rethrown as a CheckedExceptionRethrownException.
Any RuntimeException's thrown aren't caught and the calling code will receive the original RuntimeException thrown.

Throws:

CheckedExceptionRethrownException - in case the apply(Object) method throws a checked Exception

safe

static <T,
R> Function<T,R> safe(String contextMessage,
 CheckedFunction<T,R> functionThatCanFailWithACheckedException)

Wraps a CheckedFunction (basically a lambda with one argument that returns a result and which throws a Checked Exception) by returning a new Function instance
The returned Function.apply(Object) method delegates directly to the apply(Object) and catches any thrown checked Exception's and rethrows them as a CheckedExceptionRethrownException
Any RuntimeException's thrown aren't caught and the calling code will receive the original RuntimeException thrown.

Usage example:
Let's say we have a method called someOperation that cannot change, but which accepts a Function with the purpose of the calling the Function.apply(Object).

 public void someOperation(Function<Integer, String> operation) {
      // ... Logic ...

      String value = operation.apply(10);

      // ... More logic ---
 }
 

The problem will Function.apply(Object) occurs when Function calls any API that throws a checked Exception, e.g. the File API.
Since Function.apply(Object) doesn't define that it throws any Exception's we're forced to add a try/catch to handle the IOException for the code to compile:

  someOperation(value -> {
                      try {
                          // Logic that uses the File API
                          return "some-value";
                      } catch (IOException e) {
                          throw new RuntimeException(e);
                      }
                }));
 

This is where the CheckedFunction comes to the aid as its apply(Object) methods defines that it throws a Checked Exception and its safe(CheckedFunction) will return a new Function instance with a Function.apply(Object) method that ensures that the apply(Object) method is called and any checked Exception's thrown will be caught and rethrown as a CheckedExceptionRethrownException:

  someOperation(CheckFunction.safe(msg("Processing file {}", fileName),
                value -> {
                      // Logic that uses the File API that throws IOException
                      return "some-value";
                }));
 
 

Type Parameters:

T - the argument type

R - the return type

Parameters:

contextMessage - a string that the described the content for the CheckedFunction and which will be used as message in any CheckedExceptionRethrownException thrown

functionThatCanFailWithACheckedException - the CheckedFunction instance that will be wrapped as a Function

Returns:

a Function with a Function.apply(Object) method that ensures that the apply(Object) method is called when Function.apply(Object) and any checked Exception's thrown will be caught and rethrown as a CheckedExceptionRethrownException.
Any RuntimeException's thrown aren't caught and the calling code will receive the original RuntimeException thrown.

Throws:

CheckedExceptionRethrownException - in case the apply(Object) method throws a checked Exception

apply

R apply(T argument)
 throws Exception

This method performs the operation that may fail with a Checked Exception

Parameters:

argument - the function argument

Returns:

the result of performing the function

Throws:

Exception - this method can throw both checked Exception's as well as RuntimeException's