In this post, we will see how to convert list of Users to employees in java8 way. In the following examples, we can use the below approaches:
- Using conversion function inside of map
- Java8 function : When conversion is complex and need to do lot of fields then custom function mapper is usefull
- Using Constructor method reference inside of map
In the below Example, We create list of users and want to transform to Employees with userId as employee Id and firstName+last name as employeeName:
Approach 1: Using conversion inside of map
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
/**
* @author Javasavvy
*
*/
public class JavaStreamExamples {
public static void main(String[] args) {
JavaStreamExamples eg = new JavaStreamExamples();
List<User> users = eg.prepareData();
List<Employee> employees = users.stream().
map((user) -> new Employee(user.getUserId(),
user.getFirstName() + " " + user.getLastName(),
user.getEmail())).
collect(Collectors.toList());
employees.stream().map(e -> e.getEmployeeId() + "," + e.getEmail() + ',' + e.getEmployeeName())
.forEach(System.out::println);
}
public List<User> prepareData() {
User u1 = new User(101L,"[email protected]", "Jayaram","p");
User u2 = new User(102L,"[email protected]", "vijay","r");
User u3 = new User(103L,"[email protected]", "Raghu","P");
User u4 = new User(104L,"[email protected]", "Raju","r");
User u5 = new User(105L,"[email protected]", "Ramu","j");
User u6 = new User(106L,"[email protected]", "Vinay","p");
User u7 = new User(107L,"[email protected]", "Krishna","L");
return Arrays.asList(u1,u2,u3,u4,u5,u6,u7);
}
}
Approach 2: Using java8 Function Mapper
In this example, userToEmployeeMapper is Function to map to User to Employee
/**
* @author Javasavvy
*
*/
public class FunctionIdentityMapper {
static Function<User, Employee> userToEmployeeMapper = user -> new Employee(user.getUserId(),
user.getFirstName() + " " + user.getLastName(), user.getEmail());
public static void main(String[] args) {
FunctionIdentityMapper eg = new FunctionIdentityMapper();
List<User> users = eg.prepareData();
List<Employee> employees = users.stream().
map(userToEmployeeMapper).
collect(Collectors.toList());
employees.stream().map(e -> e.getEmployeeId() + "," + e.getEmail() + ',' + e.getEmployeeName())
.forEach(System.out::println);
}
public List<User> prepareData() {
User u1 = new User(101L,"[email protected]", "Jayaram","p");
User u2 = new User(102L,"[email protected]", "vijay","r");
User u3 = new User(103L,"[email protected]", "Raghu","P");
User u4 = new User(104L,"[email protected]", "Raju","r");
User u5 = new User(105L,"[email protected]", "Ramu","j");
User u6 = new User(106L,"[email protected]", "Vinay","p");
User u7 = new User(107L,"[email protected]", "Krishna","L");
return Arrays.asList(u1,u2,u3,u4,u5,u6,u7);
}
}Approach 3: Using Constructor Method Reference:
In this we pass Constructor method reference to mapper function to convert and limitation is Employee should have constructor with User as parameter.
/**
* @author Javasavvy
*
*/
public class ConstructorMethodReference {
public static void main(String[] args) {
ConstructorMethodReference eg = new ConstructorMethodReference();
List<User> users = eg.prepareData();
List<Employee> employees = users.stream().
map(Employee::new).
collect(Collectors.toList());
employees.stream().map(e -> e.getEmployeeId() + "," + e.getEmail() + ',' + e.getEmployeeName())
.forEach(System.out::println);
}
public List<User> prepareData() {
User u1 = new User(101L,"[email protected]", "Jayaram","p");
User u2 = new User(102L,"[email protected]", "vijay","r");
User u3 = new User(103L,"[email protected]", "Raghu","P");
User u4 = new User(104L,"[email protected]", "Raju","r");
User u5 = new User(105L,"[email protected]", "Ramu","j");
User u6 = new User(106L,"[email protected]", "Vinay","p");
User u7 = new User(107L,"[email protected]", "Krishna","L");
return Arrays.asList(u1,u2,u3,u4,u5,u6,u7);
}
}User Object
/**
* @author Javasavvy
*/
public class User {
private long userId;
private String email;
private String firstName;
private String lastName;
public User(long userId, String email, String firstName, String lastName) {
super();
this.userId = userId;
this.email = email;
this.firstName = firstName;
this.lastName = lastName;
}
public long getUserId() {
return userId;
}
public void setUserId(long userId) {
this.userId = userId;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
Employee
/**
* @author Javasavvy
*/
public class Employee {
private long employeeId;
private String employeeName;
private String email;
public Employee(long employeeId, String employeeName, String email) {
super();
this.employeeId = employeeId;
this.employeeName = employeeName;
this.email = email;
}
public Employee(User user) {
super();
this.employeeId = user.getUserId();
this.employeeName = user.getFirstName()+" "+user.getLastName();
this.email = user.getEmail();
}
public long getEmployeeId() {
return employeeId;
}
public void setEmployeeId(long employeeId) {
this.employeeId = employeeId;
}
public String getEmployeeName() {
return employeeName;
}
public void setEmployeeName(String employeeName) {
this.employeeName = employeeName;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}
Thanks For Reading..
