虽然jdk1.8已经是很久以前更新的了，但是开发人员对于1.8的新特性使用可能不是很多，接下来文章会说一些1.8中用的比较多的功能，赶紧学起来
1，首先用的最多的是stream流的使用
以前我们对于集合的遍历是这样的(举个例子)
for (User user : list) {
//执行便利后的操作
user.setAge(user.getAge()+1);
}
stream在jdk1.8中使用
list.stream().forEach(r->{
r.setAge(r.getAge()+1);
});
在1.8中流对于集合还有很便利的操作
//获取集合中年龄大于10的用户
list.stream().filter(user -> user.getAge()>10).collect(Collectors.toList());
//根据用户的年纪排序
list.stream().sorted(Comparator.comparing(User::getAge)).collect(Collectors.toList());
//获取该集合中年龄最大的用户
list.stream().max(Comparator.comparing(User::getAge)).get();
//将用户集合中的用户年龄单独取出作为一个集合（常用与日常开发中根据主表id去查询子表数据的业务中）
list.stream().map(User::getAge).collect(Collectors.toList());
//将集合按照key是用户id，value是用户本省的map集合
list.stream().collect(Collectors.toMap(User::getId, Function.identity()));
这些是开发中常用的一些流的操作，我们在开发中可以组合起来操作
2，接下来是对于流的操作(输入流,输出流)
众所周知，我们在之前使用输入流，输出流的时候每次使用完之后都需要关闭流，但是在1.8以后我们还需要关闭吗？不需要了，1.8已经帮我们实现了自动关闭的功能了，那编码和以前有什么区别呢，1.8又是怎么样实现的呢？
那这其中最关键的一个接口
public interface AutoCloseable {
/**
* Closes this resource, relinquishing any underlying resources.
* This method is invoked automatically on objects managed by the
* {@code try}-with-resources statement.
*
* <p>While this interface method is declared to throw {@code
* Exception}, implementers are <em>strongly</em> encouraged to
* declare concrete implementations of the {@code close} method to
* throw more specific exceptions, or to throw no exception at all
* if the close operation cannot fail.
*
* <p> Cases where the close operation may fail require careful
* attention by implementers. It is strongly advised to relinquish
* the underlying resources and to internally <em>mark</em> the
* resource as closed, prior to throwing the exception. The {@code
* close} method is unlikely to be invoked more than once and so
* this ensures that the resources are released in a timely manner.
* Furthermore it reduces problems that could arise when the resource
* wraps, or is wrapped, by another resource.
*
* <p><em>Implementers of this interface are also strongly advised
* to not have the {@code close} method throw {@link
* InterruptedException}.</em>
*
* This exception interacts with a thread's interrupted status,
* and runtime misbehavior is likely to occur if an {@code
* InterruptedException} is {@linkplain Throwable#addSuppressed
* suppressed}.
*
* More generally, if it would cause problems for an
* exception to be suppressed, the {@code AutoCloseable.close}
* method should not throw it.
*
* <p>Note that unlike the {@link java.io.Closeable#close close}
* method of {@link java.io.Closeable}, this {@code close} method
* is <em>not</em> required to be idempotent. In other words,
* calling this {@code close} method more than once may have some
* visible side effect, unlike {@code Closeable.close} which is
* required to have no effect if called more than once.
*
* However, implementers of this interface are strongly encouraged
* to make their {@code close} methods idempotent.
*
* @throws Exception if this resource cannot be closed
*/
void close() throws Exception;
}
你去看看jdk中常用的流，你去看看他们的底层代码，没错都继承/实现了这个接口，这个接口的作用就是帮我们关闭流，那我们现在代码中应该怎么写呢?
try (FileOutputStream out = new FileOutputStream(new File("C://XXX"));
FileInputStream in = new FileInputStream(new File("C://XXX"));
) {
in.read();
out.write(12);
} catch (IOException e) {
e.printStackTrace();
}
这只是举个例子，具体的业务逻辑啥的根据自己功能来写，这两个流就会在执行完之后自动关闭，当然我们也可以模拟jdk对于流的操作，比如我们在使用redis来做分布式锁的时候我们可以给我们的分布式锁的工具类实现AutoCloseable 接口重写close方法，然后在close方法中完成对与锁的释放，根据自己业务需求可自由发挥使用
3，Optional的使用
Optional可以在很大程度上减少空指针的出现，话不多说直接上代码
ArrayList<User> list = new ArrayList<>();
//判断user是否为空如果为空就返回新创建的user
Optional.ofNullable(user).orElse(new User());
Optional<User> max = list.stream().max(Comparator.comparing(User::getAge));
//判断对象是否存在
boolean present = max.isPresent();
//获取返回的具体的对象实体
User user1 = max.get();
4，时间类LocalDateTime及其周边
在jdk1.8以后对于时间日历的操作更加方便了
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(System.currentTimeMillis() * 1000);
//获取年
calendar.get(Calendar.YEAR);
//获取月
calendar.get(Calendar.MONTH);
//获取日
calendar.get(Calendar.DAY_OF_MONTH);
//获取时
calendar.get(Calendar.HOUR_OF_DAY);
//获取分
calendar.get(Calendar.MINUTE);
//获取秒
calendar.get(Calendar.MILLISECOND);
现在的操作
LocalDateTime now = LocalDateTime.now();
int year = now.getYear();
int monthValue = now.getMonthValue();
int dayOfMonth = now.getDayOfMonth();
int dayOfMonth1 = now.getDayOfMonth();
int hour1 = now.getHour();
int minute1 = now.getMinute();
int second = now.getSecond();
更加方便的是对时间/日期的操作
LocalDateTime now = LocalDateTime.now();
int year = now.getYear();
int monthValue = now.getMonthValue();
int dayOfMonth = now.getDayOfMonth();
int dayOfMonth1 = now.getDayOfMonth();
int hour1 = now.getHour();
int minute1 = now.getMinute();
int second = now.getSecond();
//添加一天
LocalDateTime localDateTime = now.plusDays(1);
//添加一个小时
LocalDateTime localDateTime1 = now.plusHours(1);
//添加一分钟;
LocalDateTime localDateTime2 = now.plusMinutes(1);
//添加一周
LocalDateTime localDateTime3 = now.plusWeeks(1);
//比较两个时间的大小
int i = localDateTime.compareTo(localDateTime3);
localDateTime1.isAfter(localDateTime2);
localDateTime1.isBefore(localDateTime2);
localDateTime1.isEqual(localDateTime2);
//此外还提供了更加便捷的创建日历、时间的方式
LocalDateTime localDateTime4 = LocalDateTime.of(2020, 10, 21, 15, 30, 22);
LocalDate localDate = LocalDate.of(2020, 10, 21);
LocalTime localTime = LocalTime.of(12, 20, 12, 223);
//本月的第1天
localDate.with(TemporalAdjusters.firstDayOfMonth());
//下月的第1天
localDate.with(TemporalAdjusters.firstDayOfNextMonth());
localDate.with(TemporalAdjusters.firstDayOfNextYear());
//日期转时间戳ZoneOffset.of("+8")设置的是时区
Long second1 = localDateTime4.toEpochSecond(ZoneOffset.of("+8"));
//获取毫秒数
Long milliSecond = localDateTime4.toInstant(ZoneOffset.of("+8")).toEpochMilli();
//转字符串
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS");
String format = localDateTime4.format(formatter);
//还有一种创建的时候带时区的日历类（方法相似就不做阐述了）
ZoneId zoneId = ZoneId.of("UTC+1");
ZonedDateTime zonedDateTime = ZonedDateTime.now(zoneId);
在实际开发中灵活运用可以有效地提高开发的效率和代码质量。
