public class Employee {    private Long id;    private String name;    private Integer age;    public Employee() {    }    public Employee(Long id, String name, Integer age) {        this.id = id;        this.name = name;        this.age = age;    }    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Integer getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }    @Override    public String toString() {        return new ToStringBuilder(this)                .append("id", id)                .append("name", name)                .append("age", age)                .toString();    }}

public class MyTest {    public static void main(String[] args) {        Employee employee1 = new Employee(11L, "hello1", 21);        Employee employee2 = new Employee(12L, "hello2", 22);        Employee employee3 = new Employee(13L, "hello3", 23);        Employee employee4 = new Employee(14L, "hello4", 24);        List
     
       employees = Lists.newArrayList();        employees.add(employee1);        employees.add(employee2);        employees.add(employee3);        employees.add(employee4);        List
      
        ems = employees.stream().filter(e -> e.getId() >= 12).collect(toList());        for (Employee e : ems) {            System.out.println(e);        }        List
       
         ems1 = employees.stream().filter(e -> e.getId() >= 12).map(Employee::getName).collect(toList());        for (String s : ems1) {            System.out.println(s);        }        /**         * @apiNote         * The following will accumulate strings into an ArrayList:         * 
        
{
    @code         *     List
         
           asList = stringStream.collect(Collectors.toList());         * }
         
         *         * 
        
The following will classify {
    @code Person} objects by city:         * 
        
{
    @code         *     Map
         
          > peopleByCity         *         = personStream.collect(Collectors.groupingBy(Person::getCity));         * }
         
         *         * 
        
The following will classify {
    @code Person} objects by state and city,         * cascading two {
    @code Collector}s together:         * 
        
{
    @code         *     Map
         
          >> peopleByStateAndCity         *         = personStream.collect(Collectors.groupingBy(Person::getState,         *                                                      Collectors.groupingBy(Person::getCity)));         * }
         
         */        Map
        
         > empById = ems.stream().collect(Collectors.groupingBy(Employee::getId));        List
         
           emps = empById.get(12L);        for (Employee e : emps) {            System.out.println(e);        }        List
          
            strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl"); String mergedString = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.joining(", ")); System.out.println("合并字符串: " + mergedString); }}
          
         
        
       
      
     

 参考文献

Introduction to Java 8 Streams

A Guide to Streams in Java 8: In-Depth Tutorial with Examples