举例:
在实际的业务处理中,我们经常会碰到需要合并同一个集合内相同属性对象的情况, 需要对一个List中的对象进行唯一值属性去重,属性求和。
// 统计每个学生的 总分 Student(name=张三, subject=数学, grade=92.5); Student(name=张三, subject=语文, grade=80.0); Student(name=李四, subject=数学, grade=88.5); Student(name=李四, subject=语文, grade=90.5); Student(name=王五, subject=数学, grade=100.0); Student(name=王五, subject=语文, grade=60.0);
期望结果:
Student(name=李四, subject=语文/数学, grade=179.0) Student(name=张三, subject=语文/数学, grade=172.5) Student(name=王五, subject=语文/数学, grade=160.0)
思路:
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list做循环求和,去重
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Java8的流进行处理
代码:
import lombok.AllArgsConstructor; import lombok.Data; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.stream.Collectors; public class Test { public static void main(String[] args) { List<Student> list1 = initData(); List<Student> list2 = initData(); List<Student> list3 = initData(); // 方法一: list做循环求和,去重 List<Student> students1 = method01(list1); students1.forEach(System.out::println); System.out.println("===================================="); // 方法二: Java8的流进行处理 List<Student> students2 = method02(list2); students2.forEach(System.out::println); System.out.println("===================================="); // 方法三 List<Student> students3 = method03(list3); students3.forEach(System.out::println); } // 方法一: list做循环求和,去重 private static List<Student> method01(List<Student> list) { Map<String, Student> map = new HashMap<>(); list.stream().forEach(a -> { Student last = map.get(a.getName()); if(null != last){ a.setGrade(a.getGrade() + last.getGrade()); a.setSubject(a.getSubject() + "/" + last.getSubject()); } map.put(a.getName(), a); }); return map.values().stream().collect(Collectors.toList()); } // 方法二: Java8的流进行处理 private static List<Student> method02(List<Student> list) { List<Student> result = list.stream().collect(Collectors.toMap(Student::getName, a -> a, (o1, o2) -> { o1.setGrade(o1.getGrade() + o2.getGrade()); o1.setSubject(o1.getSubject() + "/" + o2.getSubject()); return o1; })).values().stream().collect(Collectors.toList()); return result; } // 方法三 private static List<Student> method03(List<Student> list) { List<Student> students = new ArrayList<>(); list.stream().collect(Collectors.groupingBy(o -> o.getName(), Collectors.toList())).forEach( (id, transfer) -> { transfer.stream().reduce((a, b) -> new Student(a.getName(), a.getSubject() + "/" + b.getSubject(), a.getGrade() + b.getGrade())).ifPresent(students::add); } ); return students; } private static List<Student> initData(){ List<Student> students = new ArrayList<>(); students.add(new Student("张三", "数学", 92.5)); students.add(new Student("张三", "语文", 80)); students.add(new Student("李四", "数学", 88.5)); students.add(new Student("李四", "语文", 90.5)); students.add(new Student("王五", "数学", 100)); students.add(new Student("王五", "语文", 60)); return students; } } @Data @AllArgsConstructor class Student { private String name; // 学生名称 private String subject; // 学科 private double grade; // 成绩 }
执行结果:
Student(name=李四, subject=语文/数学, grade=179.0) Student(name=张三, subject=语文/数学, grade=172.5) Student(name=王五, subject=语文/数学, grade=160.0) ==================================== Student(name=李四, subject=数学/语文, grade=179.0) Student(name=张三, subject=数学/语文, grade=172.5) Student(name=王五, subject=数学/语文, grade=160.0) ==================================== Student(name=李四, subject=数学/语文, grade=179.0) Student(name=张三, subject=数学/语文, grade=172.5) Student(name=王五, subject=数学/语文, grade=160.0)