通过解读源码，可以发现Supplier 在Java 8中，是一个功能接口，内置的一个函数式接口，可以用来创建新的对象，有别于关键字 new；它不带任何参数并返回结果。

Supplier.java

@FunctionalInterface

public interface Supplier {

T get();

}

Supplier

当前这个示例使用Supplier返回当前日期时间

Java8Supplier1.javaout

package com.willchu;

import java.time.LocalDateTime;

import java.time.format.DateTimeFormatter;

import java.util.function.Supplier;

public class Java8Supplier1 {

private static final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

public static void main(String[] args) {

Supplier s = () -> LocalDateTime.now();

LocalDateTime time = s.get();

System.out.println(time);

Supplier s1 = () -> dtf.format(LocalDateTime.now());

String time2 = s1.get();

System.out.println(time2);

}

}

控制台输出：

2020-03-02T16:10:49.281223

2020-03-02 16:10:49

2.返回一个Supplier

Java8Supplier2.java

package com.willchu;

import java.util.ArrayList;

import java.util.List;

import java.util.function.Supplier;

public class Java8Supplier2 {

public static void main(String[] args) {

Java8Example obj = new Java8Example();

List list = obj.supplier().get();

}

public Supplier> supplier() {

// lambda

// return () -> new ArrayList<>();

// constructor reference

return ArrayList::new;

}

}

3.工厂，Factory

返回Developer对象的简单工厂方法

Java8Supplier3.java

package com.willchu;

import java.math.BigDecimal;

import java.time.LocalDate;

import java.util.function.Supplier;

public class Java8Supplier3 {

public static void main(String[] args) {

Developer obj = factory(Developer::new);

System.out.println(obj);

Developer obj2 = factory(() -> new Developer("mkyong"));

System.out.println(obj2);

}

public static Developer factory(Supplier extends Developer> s) {

Developer developer = s.get();

if (developer.getName() == null || "".equals(developer.getName())) {

developer.setName("default");

}

developer.setSalary(BigDecimal.ONE);

developer.setStart(LocalDate.of(2017, 8, 8));

return developer;

}

}

Developer.java

package com.willchu;

import java.math.BigDecimal;

import java.time.LocalDate;

public class Developer {

String name;

BigDecimal salary;

LocalDate start;

public Developer(String name) {

this.name = name;

}

// get, set, constructor, toString

//...

}

控制台输出：

Developer{name='default', salary=1, start=2017-08-08}

Developer{name='mkyong', salary=1, start=2017-08-08}