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介绍
Optional是java8引进的一个类，它能让开发者更好的规范代码。可以尽量避免空指针的出现。
创建
String str = "Optional"; Optional<String> empty = Optional.empty();
Optional<String> str1 = Optional.of(str); Optional<String> str2 =
Optional.ofNullable(str);
Optional创建有三种方法。
* Optional.empty() 直接创建一个空的Optional实例对象
* Optional.of(T t) 创建一个泛型Optional实例对象，当入参为null时会抛出异常
* Optional.offNullable(T t) 和2相同，支持传入null对象
取值
Optional使用get()方法取值，当Optional容器为空时，使用get()取值则会抛出异常
调用方法
* isEmpty() : 该方法可以判断Optional容器是否为空，为空返回true，否则返回false
* orElse(T t)：该方法可以获取Optional容器值，如果容器为空则取入参值。可以在不清楚容器是否存在值时使用当前方法获取值
* isPresent(): 该方法对Optional容器内值进行判断，如果存在则可以进行某些操作该方法里面放的是一个Consumer函数式接口
如下操作：
String str = "Optional"; Optional<String> str1 = Optional.of(str);
str1.ifPresent(new Consumer<String>() { @Override public void accept(String s)
{ System.out.println("不为空执行的方法"); } });
stream流操作
Optional可以进行stream流操作。演示如下
String str = "Optional"; Optional<String> str1 = Optional.of(str);
List<String> collect = str1.stream().filter(item -> item.equals("Optional"))
.collect(Collectors.toList()); System.out.println(JSON.toJSONString(collect));
输出结果如下
