Java8 实现stream将对象集合list中抽取属性集合转化为map或list

@Data

public class Person {

  /** 编码 */

  private String code;

  /** 名字 */

  private String name;

  public Person(String code, String name) {

   this .code = code;

   this .name = name;

  }

}

public static void main(String[] args) {

  Person person1 = new Person( "001" , "张三" );

  Person person2 = new Person( "002" , "李四" );

  Person person3 = new Person( "002" , "王五" );

  List<Person> personList = new ArrayList<>();

  personList.add(person1);

  personList.add(person2);

  personList.add(person3);

  personList.forEach(t -> System.out.println(t.toString()));

}

private static HashMap<String, String> listToMap(List<Person> personList) {

  return (HashMap<String, String>)personList.stream()

    .filter(t -> t.getName()!= null )

    .collect(Collectors.toMap(Person::getCode,Person::getName,(k1,k2)->k2));

}

HashMap<String,String> personMap = listToMap(personList);

personMap.forEach((k,v)-> System.out.println(k.toString() + " - " + v.toString()));

private static List<String> getNameList(List<Person> personList) {

  return personList.stream().map(Person::getName).collect(Collectors.toList());

}

List<String> nameList = getNameList(personList);

nameList.forEach(t -> System.out.println(t.toString()));

import lombok.Data;

@Data

public class Student{

  private String stuId;

  private String name;

  private String age;

  private String sex;

}

public class Test {

  public static void main(String[] args) {

   // 创建学生List

   List<Student> list = createStudentList();

   // 1.获取value为Student对象，key为学生ID的Map

   getStudentObjectMap(list);

   // 2.获取value为学生姓名，key为学生ID的Map

   getStudentNameMap(list);

   // 3.获取学生姓名List

   getStudentNameList(list);

   //4.List中删除学生id = 1的对象

   list.removeIf(student -> student.getStuId().equals( 1 ));

   //5.如果StudentId为Long类型如何转？

   Map<String, String> mapStr = list.stream().collect(Collectors.toMap(student -> student.getStuId().toString(), student -> JSON.toJSONString(student)));

   //6.根据List中Student的学生姓名排序

   Collections.sort(list, (o1, o2) -> {

    if (o1.getName()测试数据pareTo(o2.getName()) > 0 ) {

     return 1 ;

    } else if (o1.getName()测试数据pareTo(o2.getName()) < 0 ) {

     return - 1 ;

    } else {

     return 0 ;

    }

   });

   //7.List遍历

   List<String> listStr = new ArrayList<>();

   List<Student> listStu = new ArrayList<>();

   listStr.forEach(studentStr -> {

    listStu.add(JSON.parseObject(studentStr, Student. class ));

   });

   //List根据某个字段过滤、排序

   listStu.stream()

     .filter(student -> student.getSex().equals( "女" ))

     .sorted(Comparator测试数据paring(Student::getName))

     .collect(Collectors.toList());

   //List根据某个字段分组

   Map<String,List<Student>> sexGroupMap = listStu.stream()

               .collect(Collectors.groupingBy(Student::getSex));

   //如果Map中多个名称相同，则studentId用逗号间隔

   Map<String,String> studentNameIdMap = listStu.stream()

               .collect(toMap(Student::getName,Student::getStuId,(s,a)->s+ "," +a));

  }

  public static List<Student> createStudentList() {

   List<Student> list = new ArrayList<Student>();

   Student lily = new Student();

   lily.setStuId( "1" );

   lily.setName( "lily" );

   lily.setAge( "14" );

   lily.setSex( "女" );

   Student xiaoming = new Student();

   xiaoming.setStuId( "2" );

   xiaoming.setName( "xiaoming" );

   xiaoming.setAge( "15" );

   xiaoming.setSex( "男" );

   list.add(lily);

   list.add(xiaoming);

   return list;

  }

  public static Map<Object, Object> getStudentObjectMap(List<Student> list) {

   Map<Object, Object> map = list.stream().collect(Collectors.toMap(Student::getStuId, student -> student));

   map.forEach((key, value) -> {

    System.out.println( "key:" + key + ",value:" + value);

   });

   return map;

  }

  public static Map<String, String> getStudentNameMap(List<Student> list) {

   Map<String, String> map = list.stream().collect(Collectors.toMap(Student::getStuId, Student::getName));

   map.forEach((key, value) -> {

    System.out.println( "key:" + key + ",value:" + value);

   });

   return map;

  }

  public static List<String> getStudentNameList(List<Student> list) {

   List<String> result = list.stream().map(student -> student.getName()).collect(Collectors.toList());

   for (String name : result) {

    System.out.println( "name:" + name);

   }

   return result;

  }

}