动态修改列表，在列表的每个对象中添加新的字段

Question

我的学生班级如下:-

public class Student{
private long id;
private String name;
private String school;
}

现在我有来自DB的学生列表-

List<Student> students = apiService.getStudents();

我想动态地修改这个列表，这样它也将包含id和name的组合作为一个单独的字段。比如-

public class Student{
private long id;
private String name;
private String school;
private String idName;
}

我可以像这样映射-

students.stream().map(p -> p.getId() + ","+p.getName())).
collect(Collectors.toSet());

，但它不会保留原来的列表…

不知道怎么做

原始列表-

id= 576, name = "Kevin", school = "ABC"
id= 577, name = "Varon", school = "DEF"

New List -

id= 576, name = "Kevin", school = "ABC", idName= "576Kevin"
id= 577, name = "Varon", school = "DEF", idName= "577Varon"

Answer 1

如果使用相同的类

@Setter
@Getter
@ToString
static class Student{
private long id;
private String name;
private String school;
private String idName; //initially will be null
public Student(long id, String name, String school) {
this.id = id;
this.name = name;
this.school = school;
}
}

使用ForEach

list.forEach(student -> student.setIdName(student.id+student.name));

或流

list.stream().forEach(student -> student.setIdName(student.id+student.name));

如果你有两个独立的类，一个有idName字段，另一个没有，如问题所示。

List<Student> list = Stream
.of(new Student(1, "Sam", "School"),
new Student(2, "Ronald", "School2"))
.collect(Collectors.toList());
//Create a List with StudentPOJO object having another field as idName
List<StudentPOJO> newList = list
.stream()
.map(student -> new StudentPOJO(student.id, student.name, student.school, student.id + student.name))
.collect(Collectors.toList());

类

学生

@AllArgsConstructor
@Setter
@Getter
@ToString
static class Student{
private long id;
private String name;
private String school;
}

StudentPOJO

@AllArgsConstructor
@Setter
@Getter
@ToString
static class StudentPOJO{
private long id;
private String name;
private String school;
private String idName;
}

Answer 2

您可以创建一个新的修改学生列表，并将它们添加到原始列表中，如下所示:

List<Student> modifiedStudents = students.stream().map(s -> {
Student modifiedStudent = new Student();
modifiedStudent.setId(s.getId());
modifiedStudent.setName(s.getName());
modifiedStudent.setSchool(s.getSchool());
modifiedStudent.setIdName(s.getId() + "," + s.getName());
return modifiedStudent;
}).collect(Collectors.toList());
students.addAll(modifiedStudents);

这将保留原始列表，并将修改后的学生添加到其中。