安全获取值

不推荐使用get方法

public static void main(String[] args) {
    Optional<Author> author = getAuthor();
    Author author1 = author.get();
}

private static Optional<Author> getAuthor() {
    //数据初始化
    Author author = new Author(1L, "蒙多", 33, "一个从菜刀中明悟哲理的祖安人", null);
    return Optional.ofNullable(null);
}

程序会发生异常：

Exception in thread "main" java.util.NoSuchElementException: No value present
	at java.util.Optional.get(Optional.java:135)
	at com.sanfen.StreamDemo01.main(StreamDemo01.java:23)

Process finished with exit code 1

orElseGet(默认值)方法：Optional封装的数据为null时，返回默认值。

public static void main(String[] args) {
    Optional<Author> author = getAuthor();
    Author author1 = author.orElseGet(() -> new Author());
    System.out.println(author1);
}

private static Optional<Author> getAuthor() {
    //数据初始化
    Author author = new Author(1L, "蒙多", 33, "一个从菜刀中明悟哲理的祖安人", null);
    return Optional.ofNullable(null);
}

Author(id=null, name=null, age=0, intro=null, books=null)

Process finished with exit code 0

orElseThrow方法：Optional封装的数据为null时，抛出异常。

public static void main(String[] args) throws Throwable {
    Optional<Author> author = getAuthor();
    author.orElseThrow(() -> new Exception("author异常"));
}

private static Optional<Author> getAuthor() {
    //数据初始化
    Author author = new Author(1L, "蒙多", 33, "一个从菜刀中明悟哲理的祖安人", null);
    return Optional.ofNullable(null);
}

结果：

Exception in thread "main" java.lang.Exception: author异常
	at com.sanfen.StreamDemo01.lambda$main$0(StreamDemo01.java:20)
	at java.util.Optional.orElseThrow(Optional.java:290)
	at com.sanfen.StreamDemo01.main(StreamDemo01.java:20)

Process finished with exit code 1