layout	title	folder	permalink	categories	tags
pattern	Execute Around	execute-around	/patterns/execute-around/	Idiom	Extensibility

Intent

Execute Around idiom frees the user from certain actions that should always be executed before and after the business method. A good example of this is resource allocation and deallocation leaving the user to specify only what to do with the resource.

Explanation

Real world example

We need to provide a class that can be used to write text strings to files. To make it easy for the user we let our service class open and close the file automatically, the user only has to specify what is written into which file.

In plain words

Execute Around idiom handles boilerplate code before and after business method.

Stack Overflow says

Basically it's the pattern where you write a method to do things which are always required, e.g. resource allocation and clean-up, and make the caller pass in "what we want to do with the resource".

Programmatic Example

Let's introduce our file writer class.

@FunctionalInterface
public interface FileWriterAction {

  void writeFile(FileWriter writer) throws IOException;

}

public class SimpleFileWriter {

  public SimpleFileWriter(String filename, FileWriterAction action) throws IOException {
    try (var writer = new FileWriter(filename)) {
      action.writeFile(writer);
    }
  }
}

To utilize the file writer the following code is needed.

    FileWriterAction writeHello = writer -> {
      writer.write("Hello");
      writer.append(" ");
      writer.append("there!");
    };
    new SimpleFileWriter("testfile.txt", writeHello);

Class diagram

Applicability

Use the Execute Around idiom when

• You use an API that requires methods to be called in pairs such as open/close or allocate/deallocate.

Credits

• Functional Programming in Java: Harnessing the Power of Java 8 Lambda Expressions