I want to convert a list of nested objects into a flat list using Java streams. For this reason, a list of companies is first drawn up with employees:
// create Apple Employees
List<Employee> appleEmployees = List.of(
new Employee("John", "Doe"), new Employee("Joe", "Bloggs")
);
Company apple = new Company("Apple", appleEmployees);
// create Microsoft Employees
List<Employee> microsoftEmployees = List.of(
new Employee("John", "Public"), new Employee("Harry", "Fortune")
);
Company microsoft = new Company("Microsofr", microsoftEmployees);
// put apple and microsft in a list
List<Company> companies = List.of(apple, microsoft);
// data carrier
record CompanyData(String companyName,String employeeName, String employeeSurname) {}
What do I have to do now if I use Java Streams:
// How to stream this?
List<CompanyData> companyData = companies.stream().????
We should have a list of 4 CompanyData objects at the end of the stream, which contains the name of the company and the first and last name of the employee, something like this:
List<CompanyData> companyData = List.of(
new CompanyData("Apple", "John", "Doe"),
new CompanyData("Apple", "Joe", "Bloggs"),
new CompanyData("Microsoft", "John", "Public"),
new CompanyData("Microsoft", "Harry", "Fortune")
);
Is this even possible and should Java streams be used for the case?
You can use flatMap
:
List<CompanyData> companyData = companies.stream().flatMap(company ->
company.getEmployees().stream().map(employee ->
new CompanyData(company.getName(), employee.getName(), employee.getSurname())
)).toList();