Stream + 并行流 +Optional +接口的方法 +日期组件+重复注解及类型注解

￡神魔★判官ぃ 2024-04-20 11:23 52阅读 0赞

## Stream + 并行流 +Optional +接口的方法 +日期组件+重复注解及类型注解 ##

### 一、Stream流 ###

#### 1.终止操作 - 归约 ####

> 归约：将流中的元素反复结合起来，得到一个值
> 
> map+reduce的连接通常称为map\_reduce模式，因Google用它进行网络搜索而出名

<table> 
 <thead> 
  <tr> 
   <th align="center">方法</th> 
   <th align="center">描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="center">reduce( T identity , BinaryOperator accumulator)</td> 
   <td align="center">参数：(初始值，结合逻辑)</td> 
  </tr> 
  <tr> 
   <td align="center">reduce(BinaryOperator accumulator)</td> 
   <td align="center">参数：(结合逻辑)</td> 
  </tr> 
 </tbody> 
</table>

public class Student implements Comparable<Student>{
        
    
    	private String name;
    	private int age;
    	private double salary;
    	private Course course;
    	
    	public Student() {
        
    	}
    	
    	public Student(String name, int age, double salary, Course course) {
        
    		this.name = name;
    		this.age = age;
    		this.salary = salary;
    		this.course = course;
    	}
    
    
    
    	public String getName() {
        
    		return name;
    	}
    
    	public void setName(String name) {
        
    		this.name = name;
    	}
    
    	public int getAge() {
        
    		return age;
    	}
    
    	public void setAge(int age) {
        
    		this.age = age;
    	}
    
    	public double getSalary() {
        
    		return salary;
    	}
    
    	public void setSalary(double salary) {
        
    		this.salary = salary;
    	}
    
    	public Course getCourse() {
        
    		return course;
    	}
    
    	public void setCourse(Course course) {
        
    		this.course = course;
    	}
    	
    	
    
    	@Override
    	public String toString() {
        
    		return "Student [name=" + name + ", age=" + age + ", salary=" + salary + ", course=" + course + "]";
    	}
    
    	@Override
    	public int hashCode(){
        
    		final int prime = 31;
    		int result = 1;
    		result = prime * result + age;
    		result = prime * result + ((course == null) ? 0 : course.hashCode());
    		result = prime * result + ((name == null) ? 0 : name.hashCode());
    		long temp;
    		temp = Double.doubleToLongBits(salary);
    		result = prime * result + (int)(temp ^ (temp >>> 32) );
    		return result;
    	}
    	
    	@Override
    	public boolean equals(Object obj) {
        
    		if(this == obj)
    			return true;
    		if(obj == null)
    			return false;
    		if(getClass() != obj.getClass())
    			return false;
    		Student other = (Student) obj;
    		if(age != other.age)
    			return false;
    		if(course != other.course)
    			return false;
    		if (name == null) {
        
    			if (other.name != null) 
    				return false;
    		} else if(!name.equals(other.name))
    			return false;
    		if(Double.doubleToLongBits(salary) != Double.doubleToLongBits(other.salary))
    			return false;
    		return true;
    	}
    	@Override
    	public int compareTo(Student o) {
        
    		if(this == o){
        
    			return 0;
    		}
    		if (this.age != o.age) {
        
    			return Integer.compare(this.age, o.age);
    		}
    		return 1;
    	}
    
    }

public enum Course {
        
    
    	JAVA,HTML,PYTHON;
    }

import java.util.Arrays;
    import java.util.List;
    import java.util.Optional;
    
    import org.junit.Test;
    
    public class Test01 {
        
    
    	List<Integer> numList = Arrays.asList(1,2,3,4,5,6,7,8,9,10);
    	List<Student> stuList = Arrays.asList(
    			new Student("张三", 28, 4800,Course.JAVA),
    			new Student("李四", 36, 7200,Course.JAVA),
    			new Student("王五", 19, 9600,Course.HTML),
    			new Student("赵六", 42, 6100,Course.HTML),
    			new Student("孙七", 23, 9600,Course.PYTHON),
    			new Student("吴八", 31, 3000,Course.PYTHON),
    			new Student("李四", 36, 7200,Course.JAVA));
    	
    	@Test
    	public void test01(){
        
    		//需求：获取numList集合中元素的总和
    		Integer reduce = numList.stream().reduce(0, (x,y)->x+y);
    		System.out.println(reduce);
    		
    	}
    	
    	@Test
    	public void test02(){
        
    		//需求：获取stuList集合中所有学生工资总和
    		Optional<Double> reduce = stuList.stream().map(Student::getSalary).reduce((salary1,salary2)->salary1+salary2);
    		Double sum = reduce.get();
    		System.out.println(sum);
    		
    	}
    }

#### 2.终止操作 - 收集 ####

> 收集：将流转换为其他形式。接收一个Collector接口的实现，用于给Stream中元素做汇总的方法

<table> 
 <thead> 
  <tr> 
   <th align="center">方法</th> 
   <th align="center">描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="center">collect(Collector&lt;? super T, A, R&gt; collector)</td> 
   <td align="center">把元素放入Collector集合中</td> 
  </tr> 
 </tbody> 
</table>

import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.DoubleSummaryStatistics;
    import java.util.List;
    import java.util.Map;
    import java.util.Map.Entry;
    import java.util.Optional;
    import java.util.Set;
    import java.util.stream.Collectors;
    
    import org.junit.Test;
    
    public class Test02 {
        
    	List<Student> stuList = Arrays.asList(
    			new Student("张三", 28, 4800,Course.JAVA),
    			new Student("李四", 36, 7200,Course.JAVA),
    			new Student("王五", 19, 9600,Course.HTML),
    			new Student("赵六", 42, 6100,Course.HTML),
    			new Student("孙七", 23, 9600,Course.PYTHON),
    			new Student("吴八", 31, 3000,Course.PYTHON),
    			new Student("李四", 36, 7200,Course.JAVA));
    	
    	@Test
    	public void test01(){
        
    		//需求1：把当前学生姓名提取出来，并把数据放入List集合中
    		List<String> list = stuList.stream().map((stu)->stu.getName()).collect(Collectors.toList());
    		for (String name : list) {
        
    			System.out.println(name);
    		}
    	}
    	
    	@Test
    	public void test02(){
        
    		//需求2：把当前学生姓名提取出来，并把数据放入Set集合中
    		Set<String> set = stuList.stream().map((stu)->stu.getName()).collect(Collectors.toSet());
    		for (String name : set) {
        
    			System.out.println(name);
    		}
    	}
    	
    	@Test
    	public void test03(){
        
    		//需求3：把当前学生姓名提取出来，并把数据放入指定集合中
    		ArrayList<String> arrayList = stuList.stream().map((stu)->stu.getName()).collect(Collectors.toCollection(ArrayList::new));
    		for (String name : arrayList) {
        
    			System.out.println(name);
    		}
    	}
    	
    	@Test
    	public void test04(){
        
    		//需求4：收集/获取学生个数
    		Long count = stuList.stream().collect(Collectors.counting());
    		System.out.println(count);
    	}
    	
    	@Test
    	public void test05(){
        
    		//需求5：收集/获取学生平均工资
    		Double avg = stuList.stream().collect(Collectors.averagingDouble(Student::getSalary));
    		System.out.println(avg);
    	}
    	
    	@Test
    	public void test06(){
        
    		//需求6：收集/获取学生总工资
    		 Double sum = stuList.stream().collect(Collectors.summingDouble(Student::getSalary));
    		 System.out.println(sum);
    	}
    	
    	@Test
    	public void test07(){
        
    		//需求7：收集/获取学生工资最大值
    		Optional<Double> maxOptional = stuList.stream().map((stu)->stu.getSalary()).collect(Collectors.maxBy(Double::compareTo));
    		Double max = maxOptional.get();
    		System.out.println(max);
    	}
    	
    	@Test
    	public void test08(){
        
    		//需求8：收集/获取学生工资最大值
    		Optional<Double> minOptional = stuList.stream().map((stu)->stu.getSalary()).collect(Collectors.minBy(Double::compareTo));
    		Double min = minOptional.get();
    		System.out.println(min);
    	}
    	
    	@Test
    	public void test09(){
        
    		//需求9：收集/获取工资最多的学生信息
    		Optional<Student> stuOptional = stuList.stream().collect(Collectors.maxBy(
    				(stu1,stu2)->Double.compare(stu1.getSalary(), stu2.getSalary())));
    		Student stu = stuOptional.get();
    		System.out.println(stu);
    	}
    	
    	@Test
    	public void test10(){
        
    		//需求10：收集/获取工资最少的学生信息
    		Optional<Student> stuOptional = stuList.stream().collect(Collectors.minBy(
    				(stu1,stu2)->Double.compare(stu1.getSalary(), stu2.getSalary())));
    		Student stu = stuOptional.get();
    		System.out.println(stu);
    	}
    	
    	@Test
    	public void test11(){
        
    		//需求11：按照学科分组
    		Map<Course, List<Student>> map = stuList.stream().collect(Collectors.groupingBy(Student::getCourse));
    		Set<Entry<Course,List<Student>>> entrySet = map.entrySet();
    		for (Entry<Course, List<Student>> entry : entrySet) {
        
    			System.out.println(entry);
    		}
    	}
    	
    	@Test
    	public void test12(){
        
    		//需求12：按照学科分组，在按照年龄分组
    		Map<Course, Map<String, List<Student>>> map = stuList.stream().collect(Collectors.groupingBy(Student::getCourse,Collectors.groupingBy((obj)->{
        
    			Student stu = (Student)obj;
    			int age = stu.getAge();
    			if(age<28){
        
    				return "青年";
    			}
    			if(age<40){
        
    				return "中年";
    			}
    			return "老年";
    		})));
    		Set<Entry<Course,Map<String,List<Student>>>> entrySet = map.entrySet();
    		for (Entry<Course, Map<String, List<Student>>> entry : entrySet) {
        
    			Course key = entry.getKey();
    			Map<String, List<Student>> value = entry.getValue();
    			System.out.println(key + " -- " + value);
    		}
    	}
    	
    	@Test
    	public void test13(){
        
    		//需求13：按照工资5000为标准分区
    		Map<Boolean, List<Student>> map = stuList.stream().collect(Collectors.partitioningBy((stu)->{
        
    			if(stu.getSalary() > 5000){
        
    				return true;
    			}
    			return false;
    		}));
    		Set<Entry<Boolean,List<Student>>> entrySet = map.entrySet();
    		for (Entry<Boolean, List<Student>> entry : entrySet) {
        
    			System.out.println(entry);
    		}
    		
    	}
    	
    	@Test
    	public void test14(){
        
    		//需求14：获取学生工资信息，再获取总值、平均值、最大值、最小值
    		
    		//DoubleSummaryStatistics对象 -- 学生工资信息
    		DoubleSummaryStatistics collect = stuList.stream().collect(Collectors.summarizingDouble(Student::getSalary));
    	
    		double sum = collect.getSum();
    		double avg = collect.getAverage();
    		double max = collect.getMax();
    		double min = collect.getMin();
    		System.out.println(sum);
    		System.out.println(avg);
    		System.out.println(sum);
    		System.out.println(max);
    		System.out.println(min);
    	}
    	
    	@Test
    	public void test15(){
        
    		//需求15：拼接学生姓名
    		
    		String str1 = stuList.stream().map(Student::getName).collect(Collectors.joining());
    		System.out.println(str1);
    		
    		String str2= stuList.stream().map(Student::getName).collect(Collectors.joining(","));
    		System.out.println(str2);
    		
    		String str3= stuList.stream().map(Student::getName).collect(Collectors.joining(",", "-", "-"));
    		System.out.println(str3);
    	}
    }

### 二、并行流与串行流 ###

> 并行流就是把一个内容拆分成多个数据块，并用不同的线程分别处理每个数据块的流。Java8中将并行进行了优化，我们可以很容易的对数据进行并行操作。Stream API可以声明性地通过 parallel() - 并行流 与sequential()-顺序流 之间进行切换。

#### 注意 ####

> 1.  默认为顺序流/串行流
> 2.  并行流一般在大数据搜索里使用到
> 3.  JDK1.8之前也有并行流，叫做Fork/Join并行计算框架

import java.util.stream.LongStream;
    
    public class Test03 {
        	
    	public static void main(String[] args) {
        
    		
    		//需求：计算1-10000000L之和
    		
    		long sum = LongStream.range(1, 10000000L).//获取Stream流对象，该对象中存储了1~10000000L的数字
    				parallel().//设置该流为并行流（底层会给我们拆分成多个线程去计算）
    				reduce(0, (x,y)->x+y);//归约
    		System.out.println(sum);
    	}
    }

### 三、Optional ###

> Optional类(java. util. Optional)是一个容器类，代表一个存在或不存在的值，原来用null表示一个值不存在，现在Optional可以更好的表达这个概念。并且可以避免空指针异常
> 
> 此类的设计就是更好的避免空指针异常

<table> 
 <thead> 
  <tr> 
   <th align="center">方法</th> 
   <th align="center">描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="center">Optional.of(T t)</td> 
   <td align="center">创建一个Optional实例</td> 
  </tr> 
  <tr> 
   <td align="center">Optional.empty()</td> 
   <td align="center">创建一 个空的 Optional实例</td> 
  </tr> 
  <tr> 
   <td align="center">Optional.ofNullable(T t)</td> 
   <td align="center">若t不为null,创建Optional实例,否则创建空实例</td> 
  </tr> 
  <tr> 
   <td align="center">get()</td> 
   <td align="center">获取Optional实例里的对象</td> 
  </tr> 
  <tr> 
   <td align="center">isPresent()</td> 
   <td align="center">判断是否包含值</td> 
  </tr> 
  <tr> 
   <td align="center">orElse(T t)</td> 
   <td align="center">如果调用对象包含值, 返回该值，否则返回t</td> 
  </tr> 
  <tr> 
   <td align="center">orElseGet(Supplier s)</td> 
   <td align="center">如果调用对象包含值，返回该值,否则返回s获取的值</td> 
  </tr> 
  <tr> 
   <td align="center">map(Function f)</td> 
   <td align="center">如果有值对其处理，并返回处理后的Optional,否则返回optional. empty()</td> 
  </tr> 
  <tr> 
   <td align="center">flatMap(Function mapper)</td> 
   <td align="center">与map 类似，要求返回值必须是Optional</td> 
  </tr> 
 </tbody> 
</table>

import java.util.Optional;
    
    import com.qf.stream.Student;
    
    public class Test01 {
        
    
    	public static void main(String[] args) {
        
    		//获取Optional的对象，该对象中存储了一个学生对象
    //		Optional<Student> optional = Optional.of(new Student());
    	
    		//获取Optional对象中的学生对象
    //		Student stu = optional.get();
    //		System.out.println(stu);
    		
    		//创建Optional的对象，该对象中没有存储了学生对象
    		Optional<Object> optional = Optional.empty();
    		
    		//获取Optional对象中的学生对象，但是Optional对象中没有学生对象，就创建个学生对象（最大化限度的减少了空指针异常）
    		Object stu = optional.orElse(new Student());
    		System.out.println(stu);
            
            //不同情况下可以返回不同对象，orElseGet()比orElse()可变性更强
    		boolean bool = true;
    		stu = op.orElseGet(()->{
        
    			if(bool){
        
    				return new Student("刘备", 26, 8888, Course.JAVA);
    			}else{
        
    				return new Student("甘夫人", 26, 8888, Course.JAVA);
    			}
    		});
    		
    		//获取原容器中的某个值并返回新容器中
    		//map(Function<? super T, ? extends U> mapper)
    		Optional<String> map = op.map(Student::getName);
    		System.out.println(map.get());
    		
    		//与map 类似，要求返回值必须是Optional
    		//flatMap(Function<? super T, Optional<U>> mapper)
    		Optional<String> flatMap = op.flatMap((e)->Optional.of(e.getName()));
    		System.out.println(flatMap.get());
    	}
    }

### 四、接口的默认方法与静态方法 ###

> 从JDK1.8开始，接口中可以有默认方法，既default修饰的方法，此方法可以让接口的实现类所调用，而接口中的静态方法直接用接口名调用即可

#### 接口默认方法的”类优先”原则： ####

> 如果一个接口中定义了一个默认方法，而接口实现类的父类定义了一个同名的方法时，选择父类中的方法

public class Test01 {
        
    
    	public static void main(String[] args) {
        
    		
    		B b = new B();
    		b.method();
    	}
    }
    
    class A{
        
    	public void method(){
        
    		System.out.println("父类中的method方法");
    	}
    }
    
    class B extends A implements I1{
        }
    interface I1{
        
    	default void method(){
        
    		System.out.println("接口中的默认方法");
    	}
    }

> 接口冲突：如果一个父接口提供一个默认方法，而另一个接口也提供了一个具有相同名称和参数列表的方法(不管方法是否是默认方法)，那么必须覆盖该方法来解决冲突

public class Test01 {
        
    
    	public static void main(String[] args) {
        
    		
    	}
    }
    
    interface I1{
        
    	default void method(){
        
    		System.out.println("I1接口中的默认方法");
    	}
    }
    
    interface I2 extends I1{
        
    	public void method();
    }
    
    class A implements I1,I2{
        
    	
    	@Override
    	public void method() {
        
    	}
    }

### 五、日期组件 ###

> JDK1.8提供的新日期类都是不可变的，既不管怎么样的改变，都会产生一个新的实例，他们都是线程安全的
> 
> 日期组件遵循与IOS-8601世界时间标准

#### 1.组件简介 ####

<table> 
 <thead> 
  <tr> 
   <th>包路径</th> 
   <th>类名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>java.time</td> 
   <td></td> 
   <td>针对日期和时间操作的包</td> 
  </tr> 
  <tr> 
   <td></td> 
   <td>LocalDate</td> 
   <td>用于表示日期的类</td> 
  </tr> 
  <tr> 
   <td></td> 
   <td>LocalTime</td> 
   <td>用于表示时间的类</td> 
  </tr> 
  <tr> 
   <td></td> 
   <td>LocalDateTime</td> 
   <td>用于表示日期时间的类</td> 
  </tr> 
  <tr> 
   <td></td> 
   <td>Instant</td> 
   <td>时间戳类（1970.1.1 0:0:0 到现在的毫秒数</td> 
  </tr> 
  <tr> 
   <td></td> 
   <td>Period</td> 
   <td>两个日期间隔类</td> 
  </tr> 
  <tr> 
   <td></td> 
   <td>Duration</td> 
   <td>两个时间间隔类</td> 
  </tr> 
  <tr> 
   <td>java.time.chrono</td> 
   <td></td> 
   <td>针对日期时间特殊格式操作的包</td> 
  </tr> 
  <tr> 
   <td>java.time.format</td> 
   <td></td> 
   <td>针对时间日期时间格式化操作的包</td> 
  </tr> 
  <tr> 
   <td></td> 
   <td>DateTimeFormatter</td> 
   <td>格式化日期时间类</td> 
  </tr> 
  <tr> 
   <td>java.time.temporal</td> 
   <td></td> 
   <td>针对时间矫正操作的包</td> 
  </tr> 
  <tr> 
   <td>java.time.zone</td> 
   <td></td> 
   <td>针对时区操作的包</td> 
  </tr> 
 </tbody> 
</table>

#### 2.日期时间类、时间戳、间隔类 ####

import java.time.Duration;
    import java.time.Instant;
    import java.time.LocalDate;
    import java.time.LocalDateTime;
    import java.time.LocalTime;
    import java.time.OffsetDateTime;
    import java.time.Period;
    import java.time.ZoneOffset;
    
    import org.junit.Test;
    
    public class Test01 {
        
    
    	@Test
    	public void test01(){
        
    		//LocalDate LocalTime LocalDateTime
    		//这三个日期类的使用大致一样
    
    		//获取当前日期时间对象
    		LocalDateTime ldt1 = LocalDateTime.now();
    		System.out.println(ldt1);//2022-10-31T11:23:18:102
    
    		//获取指定日期时间对象
    		LocalDateTime ldt2 = LocalDateTime.of(2020, 1, 23, 8, 30, 10, 10);
    		System.out.println(ldt2);//2020-1-23T8:30:10:10
    
    		//获取ldt1推后的时间日期对象
    		LocalDateTime ldt3 = ldt1.plusYears(2);//退后两年
    		System.out.println(ldt3);2024-10-31T11:23:18:102
    
    		//获取ldt1提前的时间日期对象
    		LocalDateTime ldt4 = ldt3.minusMonths(2);//提前两个月
    		System.out.println(ldt4);//2024-8-31T11:23:18:102
    
    		//获取日期中的单个信息
    		System.out.println(ldt4.getYear());
    		System.out.println(ldt4.getMonthValue());
    		System.out.println(ldt4.getDayOfMonth());
    		System.out.println(ldt4.getHour());
    		System.out.println(ldt4.getMinute());
    		System.out.println(ldt4.getSecond());
    	}
    
    	@Test
    	public void test02(){
        
    		//使用时间戳（从1970年1月1日0:0:0到现在的毫秒值）
    
    		//默认创建UTC(世界标准时间)时区的时间戳对象
    		Instant now1 = Instant.now();
    		System.out.println(now1);//2022-10-31T03:27:55.921Z
    
    		//获取偏移8小时的偏移日期时间对象
    		OffsetDateTime odt = now1.atOffset(ZoneOffset.ofHours(8));
    		System.out.println(odt);//2022-10-31T11:27:55.921+08:00
    
    		//获取时间戳的毫秒值形式
    		System.out.println(now1.toEpochMilli());
    
    		//获取一个1970年1月1日0:0:0 往后退1秒的时间戳对象
    		Instant now2 = Instant.ofEpochSecond(1);
    		System.out.println(now2);
    	}
    
    	@Test
    	public void test03() throws InterruptedException {
        
    		//Duration：时间间隔类
    
    		Instant now1 = Instant.now();
    		Thread.sleep(1000);
    		Instant now2 = Instant.now();
    
    		//获取时间间隔类对象
    		Duration duration1 = Duration.between(now1, now2);
    		System.out.println(duration1.toMillis());
    
    		System.out.println("-----------------------------");
    
    		LocalTime lt1 = LocalTime.now();
    		Thread.sleep(1000);
    		LocalTime lt2 = LocalTime.now();
    		//获取时间间隔类对象
    		Duration duration2 = Duration.between(lt1, lt2);
    		System.out.println(duration2.toMillis());
    	}	
    	@Test
    	public void test04() throws InterruptedException {
        
    		//Period：日期间隔类
    		LocalDate ld1 = LocalDate.of(2021, 12, 28);
    		Thread.sleep(1000);
    		LocalDate ld2 = LocalDate.of(2022, 10, 31);
    
    		//获取日期间隔类对象
    		Period period = Period.between(ld1, ld2);
    
    		System.out.println(period.getYears());//0
    		System.out.println(period.getMonths());//10
    		System.out.println(period.getDays());//3
    	}
    }

#### 3.日期时间格式化类-DateTimeFormatter ####

import java.time.LocalDateTime;
    import java.time.format.DateTimeFormatter;
    
    import org.junit.Test;
    
    public class Test02 {
        
    
    	@Test
    	public void test01() {
        
    		//格式化日期时间类
    		LocalDateTime ldt1 = LocalDateTime.now();//2022-10-31T11:35:18:122
    		
    		//获取本地标准的日期时间格式化对象
    		DateTimeFormatter dtf1 = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
    		String strDateTime1 = ldt1.format(dtf1);//格式化时间日期
    		System.out.println(strDateTime1);//2022-10-31T11:35:18:122
    		
    		//自定义日期时间格式化对象
    		DateTimeFormatter dtf2 = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss");
    		String strDateTime2 = ldt1.format(dtf2);//格式化时间日期
    		System.out.println(strDateTime2);
    		
    		//将指定格式的字符串解析成LocalDateTime对象
    		LocalDateTime parse = LocalDateTime.parse("2020年03月12日 11:04:14", dtf2);
    		System.out.println(parse);
    	}
    }

#### 4.时间矫正器类-TemporalAdjuster ####

import java.time.DayOfWeek;
    import java.time.LocalDateTime;
    import java.time.temporal.TemporalAdjusters;
    
    import org.junit.Test;
    
    public class Test04 {
        
    
    	@Test
    	public void test01() {
        
    		//时间矫正器
    		LocalDateTime ldt1 = LocalDateTime.now();//2022-10-31T14:03:18:122
    
    		//设置指定月份
    		LocalDateTime ldt2 = ldt1.withMonth(12);
    		System.out.println(ldt2);//2022-12-31T14:03:18:122
    
    		//设置下一个周末
    		LocalDateTime ldt3 = ldt1.with(TemporalAdjusters.next(DayOfWeek.SUNDAY));
    		System.out.println(ldt3);
    
    		//自定义时间矫正器：设置下一个工作日
    		LocalDateTime ldt4 = ldt1.with((temporal)->{
        
    			//获取到日期时间对象
    			LocalDateTime ldt = (LocalDateTime) temporal;
    			//获取周几？
    			DayOfWeek week = ldt.getDayOfWeek();
    			if(week.equals(DayOfWeek.FRIDAY)){
        //周五
    				return ldt.plusDays(3);//往后推3天
    			}else if(week.equals(DayOfWeek.SATURDAY)){
        //周六
    				return ldt.plusDays(2);//往后推2天
    			}else{
        
    				return ldt.plusDays(1);//往后推1天
    			}
    		});
    		System.out.println(ldt4);
    	}
    }

#### 5.时区类 ####

import java.time.LocalDateTime;
    import java.time.ZoneId;
    import java.time.ZonedDateTime;
    import java.util.Set;
    
    import org.junit.Test;
    
    public class Test03 {
        
    
    	@Test
    	public void test01() {
        
    		//时区类 
    
    		//获取所有时区字符串
    		Set<String> set = ZoneId.getAvailableZoneIds();
    		for (String str : set) {
        
    			System.out.println(str);
    		}
    		
    		System.out.println("-------------");
    		
    		//获取指定时区的日期时间对象
    		LocalDateTime ldt1 = LocalDateTime.now(ZoneId.of("Asia/Tokyo"));
    		System.out.println(ldt1);
    		
    		//获取指定时区的日期时间对象 + 偏移量
    		LocalDateTime ldt2 = LocalDateTime.now(ZoneId.of("Asia/Tokyo"));
    		ZonedDateTime zonedDateTime = ldt2.atZone(ZoneId.of("Asia/Tokyo"));
    		System.out.println(zonedDateTime);
    	}
    }

#### 6.传统日期格式化的线程问题 ####

需求：让多线程同时去解析日期

##### 1.使用JDK1.7时的日期时间类会出现问题 #####

> 错误示范

import java.text.SimpleDateFormat;
    import java.util.ArrayList;
    import java.util.Date;
    import java.util.concurrent.ArrayBlockingQueue;
    import java.util.concurrent.Callable;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    import java.util.concurrent.ThreadPoolExecutor;
    import java.util.concurrent.TimeUnit;
    
    public class Test01 {
        
    	public static void main(String[] args) throws Exception {
        
    		
    		//创建日期格式化类的对象	
    		SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
    		
    		//创建带有返回值的任务类的对象
    		Callable<Date> task = new Callable<Date>() {
        
    			@Override
    			public Date call() throws Exception {
        
    				Date date = sdf.parse("20200123");
    				return date;
    			}
    		};
    		
    		//创建线程池
    		ThreadPoolExecutor pool = new ThreadPoolExecutor(10, 10, 0L, TimeUnit.SECONDS, new ArrayBlockingQueue<>(1), Executors.defaultThreadFactory(), new ThreadPoolExecutor.AbortPolicy());
    		
    		//提交任务
    		ArrayList<Future<Date>> list = new ArrayList<>();
    		for (int i = 1; i <= 10; i++) {
        
    			Future<Date> future = pool.submit(task);
    			list.add(future);
    		}
    		
    		//遍历集合
    		for (Future<Date> future : list) {
        
    			Date date = future.get();
    			System.out.println(date);
    		}
    		
    		//关闭线程池
    		pool.shutdown();
    	}
    }

##### 2.使用JDK1.8的日期时间类 #####

> 正确示范

import java.time.LocalDate;
    import java.time.format.DateTimeFormatter;
    import java.util.ArrayList;
    import java.util.concurrent.ArrayBlockingQueue;
    import java.util.concurrent.Callable;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    import java.util.concurrent.ThreadPoolExecutor;
    import java.util.concurrent.TimeUnit;
    
    public class Test02 {
        
    	public static void main(String[] args) throws Exception {
        
    		
    		//创建日期格式化类的对象	
    		DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMdd");
    		
    		//创建带有返回值的任务类的对象
    		Callable<LocalDate> task = new Callable<LocalDate>() {
        
    			@Override
    			public LocalDate call() throws Exception {
        
    				
    				LocalDate localDate = LocalDate.parse("20200123", dtf);
    				return localDate;
    			}
    		};
    		
    		//创建线程池
    		ThreadPoolExecutor pool = new ThreadPoolExecutor(10, 10, 0L, TimeUnit.SECONDS, new ArrayBlockingQueue<>(1), Executors.defaultThreadFactory(), new ThreadPoolExecutor.AbortPolicy());
    		
    		//提交任务
    		ArrayList<Future<LocalDate>> list = new ArrayList<>();
    		for (int i = 1; i <= 10; i++) {
        
    			Future<LocalDate> future = pool.submit(task);
    			list.add(future);
    		}
    		
    		//遍历集合
    		for (Future<LocalDate> future : list) {
        
    			LocalDate date = future.get();
    			System.out.println(date);
    		}
    		
    		//关闭线程池
    		pool.shutdown();
    	}
    }

### 六、重复注解及类型注解 ###

> jdk1.8开始可以重复注解
> 
> ps：一个类可有多个同样的注解

import java.lang.reflect.Method;
    import java.lang.reflect.Parameter;
    
    @Author(name="G")
    @Author(name="Z")
    public class Test01 <@Author(name="L") T>{
        
    
    	public static void main(String[] args) throws Exception {
        
    		
    		Class<?> clazz = Test01.class;
    		
    		//利用反射获取类上的重复注解
    		Author[] typeAuthors = clazz.getAnnotationsByType(Author.class);
    		for (Author author : typeAuthors) {
        
    			String name = author.name();
    			System.out.println(name);
    		}
    		
    		//利用反射获取方法中参数上的注解
    		Method method = clazz.getDeclaredMethod("method", String.class);
    		Parameter[] parameters = method.getParameters();//获取方法上的参数对象
    		for (Parameter parameter : parameters) {
        
    			//获取参数上的重复注解
    			Author[] parameterAuthors = parameter.getAnnotationsByType(Author.class);
    			for (Author author : parameterAuthors) {
        
    				String name = author.name();
    				System.out.println(name);
    			}
    			
    			//获取参数类型
    			Class<?> type = parameter.getType();
    			System.out.println(type);
    			//获取参数名(参数名不会编译到class文件)
    			String name = parameter.getName();
    			System.out.println(name);
    			
    		}
    	}
    	public void method(@Author(name="GL") @Author(name="ZL")String xxx){
        }
    }

//作者注解
    import static java.lang.annotation.ElementType.*;
    import java.lang.annotation.Repeatable;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Repeatable(Authors.class)
    @Target({
        TYPE,PARAMETER,TYPE_PARAMETER})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Author {
        
    	
    	String name();
    }

//作者注解的容器
    import static java.lang.annotation.ElementType.*;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Target({
        TYPE,PARAMETER})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Authors {
        
    
    	Author[] value();
    }