Jdk8，Optional类：空值处理神器，简化代码

Jdk8，Optional类：空值处理神器，简化代码

前提

需要了解@FunctionalInterface：函数式接口，很多方法参数都是函数式接口，需要了解的可以看下这篇文章 数据初始化

1：empty2：of3：ofNullable 数据处理

1.非空判断2.过滤3.加工数据map方法4.加工数据flatMap方法 数据获取

1：直接获取2：空值直接获取3：空值执行方法获取4：空值抛出自定义异常

前提 需要了解@FunctionalInterface：函数式接口，很多方法参数都是函数式接口，需要了解的可以看下这篇文章

通俗易懂，Jdk8 @FunctionalInterface：函数式接口

比如获取值的orElseGet方法

比如过滤的filter方法

比如加工值的map方法

数据初始化 1：empty

	@Test
    public void empty() {
        System.out.println("Optional.empty() = " + Optional.empty());
    }

输出：

Optional.empty() = Optional.empty

2：of

	@Test
    public void of() {
        System.out.println("Optional.of(10) = " + Optional.of(10));

        System.out.println("Optional.of(null) = " + Optional.of(null));
    }

输出：如果值为空会抛出空指针异常

Optional.of(10) = Optional[10]
java.lang.NullPointerException

3：ofNullable

	@Test
    public void ofNullable() {
        System.out.println("Optional.ofNullable(10) = " + Optional.ofNullable(10));

        System.out.println("Optional.ofNullable(null) = " + Optional.ofNullable(null));
    }

输出：和of方法的区别，如果值为空不会抛出空指针异常

Optional.ofNullable(10) = Optional[10]
Optional.ofNullable(null) = Optional.empty

数据处理 1.非空判断

	@Test
    public void isPresent() {
        System.out.println("Optional.ofNullable(10).isPresent() = " + Optional.ofNullable(10).isPresent());

        System.out.println("Optional.ofNullable(null).isPresent() = " + Optional.ofNullable(null).isPresent());
    }

输出

Optional.ofNullable(10).isPresent() = true
Optional.ofNullable(null).isPresent() = false

2.过滤

	@Test
    public void filter() {
        System.out.println("Optional.ofNullable(data).filter(Objects::isNull) = "
                + Optional.ofNullable(10).filter(Objects::isNull));

        System.out.println("Optional.ofNullable(data).filter(Objects::nonNull) = "
                + Optional.ofNullable(10).filter(Objects::nonNull));
    }

输出：根据Objects::nonNull和Objects::isNull，也就是对象是否进行过滤

Optional.ofNullable(data).filter(Objects::isNull) = Optional.empty
Optional.ofNullable(data).filter(Objects::nonNull) = Optional[10]

3.加工数据map方法

	@Test
    public void map() {
        System.out.println("Optional.ofNullable("hello").map(t -> t + " world") = "
                + Optional.ofNullable("hello").map(t -> t + " world"));

        System.out.println("Optional.ofNullable(null).map(t -> t + " world") = "
                + Optional.ofNullable(null).map(t -> t + " world"));
    }

输出

Optional.ofNullable("hello").map(t -> t + " world") = Optional[hello world]
Optional.ofNullable(null).map(t -> t + " world") = Optional.empty

4.加工数据flatMap方法

	@Test
    public void flatMap() {
        System.out.println("Optional.ofNullable("hello").flatMap(t -> Optional.ofNullable(t + " world")) = "
                + Optional.ofNullable("hello").flatMap(t -> Optional.ofNullable(t + " world")));

        System.out.println("Optional.ofNullable(null).flatMap(t -> Optional.ofNullable(t + " world")) = "
                + Optional.ofNullable(null).flatMap(t -> Optional.ofNullable(t + " world")));
    }

跟map方法的不同是在返回值类型


输出

Optional.ofNullable("hello").flatMap(t -> Optional.ofNullable(t + " world")) = Optional[hello world]
Optional.ofNullable(null).flatMap(t -> Optional.ofNullable(t + " world")) = Optional.empty

数据获取 1：直接获取

	@Test
    public void get() {
        System.out.println("Optional.ofNullable(10).get() = " + Optional.ofNullable(10).get());

        System.out.println("Optional.ofNullable(null).get() = " + Optional.ofNullable(null).get());
    }

输出：如果数据为空会抛出异常

Optional.ofNullable(10).get() = 10
java.util.NoSuchElementException: No value present

2：空值直接获取

	@Test
    public void orElse() {
        System.out.println("Optional.ofNullable(10).orElse(100) = " + Optional.ofNullable(10).orElse(100));

        System.out.println("Optional.ofNullable(null).orElse(100) = " + Optional.ofNullable(null).orElse(100));
    }

三元表达式

	public T orElse(T other) {
        return value != null ? value : other;
    }

输出：这里写法等价于-> 10 != null ? 10 : 100，null != null ? 10 : 100

Optional.ofNullable(10).orElse(100) = 10
Optional.ofNullable(null).orElse(100) = 100

3：空值执行方法获取

	@Test
    public void orElseGet() {
        System.out.println("Optional.ofNullable(10).orElseGet(() -> 10 * 10) = "
                + Optional.ofNullable(10).orElseGet(() -> 10 * 10));

        System.out.println("Optional.ofNullable(null).orElseGet(() -> 10 * 10) = "
                + Optional.ofNullable(null).orElseGet(() -> 10 * 10));
    }

三元表达式

	public T orElseGet(Supplier other) {
        return value != null ? value : other.get();
    }

输出：如果为空执行() -> 10 * 10获取值

Optional.ofNullable(10).orElseGet(() -> 10 * 10) = 10
Optional.ofNullable(null).orElseGet(() -> 10 * 10) = 100

4：空值抛出自定义异常

	@Test
    public void orElseThrow() {
        System.out.println("Optional.ofNullable(10).orElseThrow(() -> new RuntimeException("自定义异常")) = "
                + Optional.ofNullable(10).orElseThrow(() -> new RuntimeException("自定义异常")));

        System.out.println("Optional.ofNullable(null).orElseThrow(() -> new RuntimeException("自定义异常")) = "
                + Optional.ofNullable(null).orElseThrow(() -> new RuntimeException("自定义异常")));
    }

输出：如果为空抛出new RuntimeException(“自定义异常”)

Optional.ofNullable(10).orElseThrow(() -> new RuntimeException("自定义异常")) = 10
java.lang.RuntimeException: 自定义异常