Java8 新特性 Stream流操作List集合 (一)

川长思鸟来 2022-11-22 10:25 230阅读 0赞

>     import com.alibaba.fastjson.JSON;
>     import com.alibaba.fastjson.JSONObject;
>     import java.util.ArrayList;
>     import java.util.List;
>     import java.util.stream.Collectors;
>     import java.util.stream.Stream;
>     
>     public class Test {
>         public static List<Employee> createEmployee() {
>             List<Employee> employeeList = new ArrayList<Employee>();
>             Employee employee1 = new Employee();
>             Employee employee2 = new Employee();
>             Employee employee3 = new Employee();
>     
>             employee1.setEmployeeId("1");
>             employee1.setEmployeeName("张三");
>             employee1.setEmployeeSex("男");
>     
>             employee2.setEmployeeId("2");
>             employee2.setEmployeeName("王五");
>             employee2.setEmployeeSex("男");
>     
>             employee3.setEmployeeId("3");
>             employee3.setEmployeeName("李四");
>             employee3.setEmployeeSex("男");
>     
>             employeeList.add(employee1);
>             employeeList.add(employee2);
>             employeeList.add(employee3);
>     
>             return employeeList;
>         }
>     
>         public static List<Object> createEmployeeByObject() {
>             List<Object> employeeList = new ArrayList<Object>();
>             Employee employee1 = new Employee();
>             Employee employee2 = new Employee();
>             Employee employee3 = new Employee();
>     
>             employee1.setEmployeeId("1");
>             employee1.setEmployeeName("张三");
>             employee1.setEmployeeSex("男");
>     
>             employee2.setEmployeeId("2");
>             employee2.setEmployeeName("王五");
>             employee2.setEmployeeSex("男");
>     
>             employee3.setEmployeeId("3");
>             employee3.setEmployeeName("李四");
>             employee3.setEmployeeSex("男");
>     
>             employeeList.add(employee1);
>             employeeList.add(employee2);
>             employeeList.add(employee3);
>     
>             return employeeList;
>         }
>     
>         public static void list() {
>             List<String> list = new ArrayList<String>();
>     
>             list.add("张无忌");
>             list.add("周芷若");
>             list.add("赵敏");
>             list.add("张强");
>             list.add("张三丰");
>     
>             /** stream 流 的终结方法 forEach 和 count **/
>             // Java8 遍历 stream 流 遍历  forEach
>             list.stream().forEach(item -> System.out.println(item));
>             System.out.println("******************************************************************");
>     
>             // stream 流 统计个数  count
>             System.out.println(list.stream().count());
>             System.out.println("******************************************************************");
>     
>             /** stream 流的 延迟方法 可以进行链式编程,可以一直点下去直到最后一步终结处理数据(forEach 或 count) **/
>             // 1、filter 过滤  stream 流 加上条件筛选过滤
>             list.stream().filter(item -> item.startsWith("张")).filter(item -> item.length() > 2).forEach(System.out::println);
>             System.out.println("******************************************************************");
>     
>             // 2、map() 方法  将流中的元素映射到另一个流中
>             Stream<String> stringStream = Stream.of("1", "2", "3", "4", "5");
>             // 将String转为Interger
>             stringStream.map(str -> Integer.parseInt(str)).forEach(System.out::println);
>             System.out.println("******************************************************************");
>             // 实体转字符串 流映射
>             List<Employee> employeeList = createEmployee();
>             // collect 是将数组转集合 ,这句话的意思是将员工集合遍历然后将名字取出来转为一个集合 结果是 [张三, 王五, 李四]
>             List<String> listString = employeeList.stream().map(employee -> employee.getEmployeeName()).collect(Collectors.toList());
>             System.out.println(listString);
>             System.out.println("******************************************************************");
>     
>             // 例子3 将List<Object> 转为 List<Employee>  Object 为 Employee 的JSON对象
>             List<Object> listObject = createEmployeeByObject();
>             List<Employee> listEmployee = listObject.stream().map(o -> JSONObject.parseObject(JSON.toJSONString(o), Employee.class)).collect(Collectors.toList());
>             System.out.println(listEmployee);
>             System.out.println("******************************************************************");
>     
>             // 3、contract 方法 将两个流合并成一个流
>             Stream<String> streamA = Stream.of("张无忌", "张翠山");
>             Stream<String> streamB = Stream.of("美羊羊", "喜羊羊");
>             Stream<String> streamC = Stream.of("张无忌", "张翠山");
>             Stream<String> streamD = Stream.of("美羊羊", "喜羊羊");
>     
>             // 写法方式 1
>             Stream.concat(streamA, streamB).forEach(System.out::println);
>             System.out.println("******************************************************************");
>     
>             // 写法方式 2
>             Stream<String> result = Stream.concat(streamC, streamD);
>             result.forEach(name -> System.out.println(name + "\t"));
>         }
>     
>         public static void main(String[] args) {
>             list();
>         }
>     }