Java 8 实战学习笔记

﹏ヽ暗。殇╰゛Y 2022-06-03 03:44 242阅读 0赞

# Java 8 实战学习笔记 #

@(JAVASE)\[java8, 实战, lambda\]

### 文章目录 ###

*  Java 8 实战学习笔记
 *   *  参考内容
     *   *  Lambda表达式
         *   *  Lambda环绕执行模式(抽离步骤)
             *   *  原始代码
                 *  第1步 行为参数化
                 *  第2步 使用函数式接口来传递行为
                 *  第3步 执行一个行为
                 *  第4步 传递Lambda
             *  函数接口及其原始类型特化
             *  方法引用
             *   *  Lambda及其等效方法引用的例子
                 *  方法引用主要有三类
                 *   *  指向静态方法的方法引用
                     *  指向任意类型实例方法的方法引用
                     *  指向现有对象的实例方法的方法引用
                 *  构造函数引用
         *  使用流
         *   *  归约
             *   *  中间操作和终端操作
             *  数值流
             *   *  原始类型流特化
                 *   *  映射到数值流
                     *  转换回对象流
                     *  默认值OptionalInt
                 *  数值范围
             *  构建流
             *   *  由值创建流
                 *  由数组创建流
                 *  由文件生成流
                 *  由函数生成流：创建无限流
                 *   *  迭代
                     *  生成
         *  用流收集数据
         *   *  Collectors类的静态工厂方法
             *  收集器接口
             *   *  顺序归约过程的逻辑步骤
                 *  使用combiner方法来并行化归约过程
                 *  案例
         *  用Optional取代null
         *   *  Optional类的方法
             *  实战示例
             *   *  用Optional封装可能为null的值
                 *  异常与Optional的对比
                 *  把所有内容整合起来
         *  CompletableFuture组合式异步编程
         *   *  实现异步API
             *  密集IO任务各种实现间的对比
             *   *  测试代码
                 *  JMH测试结果
                 *  调整线程池的大小
                 *  并行——使用流还是CompletableFutures？
             *  对多个异步任务进行流水线操作
             *   *  JMH测试结果
                 *  合并两个独立的CompletableFuture
             *  响应CompletableFuture的completion事件
         *  新的日期和时间API
         *   *  LocalDate、LocalTime、Instant、Duration 以及Period
             *   *  日期-时间类中表示时间间隔的通用方法
             *  操纵、解析和格式化日期
             *   *  表示时间点的日期-时间类的通用方法
                 *  TemporalAdjuster类中的工厂方法
                 *   *  TemporalAdjuster接口
                     *  定制的TemporalAdjuster
                 *  打印输出及解析日期-时间对象
                 *   *  构造一个DateTimeFormatter

## 参考内容 ##

### Lambda表达式 ###

#### Lambda环绕执行模式(抽离步骤) ####

##### 原始代码 #####

public static String processFile() throws IOException { 
    	try (BufferedReader br = new BufferedReader(new FileReader("data.txt"))) { 
    		// 行为
    		return br.readLine();
    	}
    }

##### 第1步 行为参数化 #####

// 打印一行
    String result = processFile((BufferedReader br) ->br.readLine());
    // 打印两行
    String result = processFile((BufferedReader br) ->br.readLine() + br.readLine());

##### 第2步 使用函数式接口来传递行为 #####

@FunctionalInterface
    public interface BufferedReaderProcessor { 
    	String process(BufferedReader b) throws IOException;
    }
    
    public static String processFile(BufferedReaderProcessor p) throws IOException { 
    	…
    }

##### 第3步 执行一个行为 #####

public static String processFile(BufferedReaderProcessor p) throws IOException { 
    	try (BufferedReader br = new BufferedReader(new FileReader("data.txt"))) { 
    		return p.process(br);
    	}
    }

##### 第4步 传递Lambda #####

// 打印一行
    String oneLine = processFile((BufferedReader br) ->br.readLine());
    // 打印两行
    String twoLines = processFile((BufferedReader br) ->br.readLine() + br.readLine());

#### 函数接口及其原始类型特化 ####

<table> 
 <thead> 
  <tr> 
   <th align="left">函数式接口</th> 
   <th align="center">函数描述符</th> 
   <th align="left">原始类型特化</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left"><code>Predicate&lt;T&gt;</code></td> 
   <td align="center"><code>T-&gt;boolean</code></td> 
   <td align="left"><code>IntPredicate</code>,<code>LongPredicate</code>, <code>DoublePredicate</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>Consumer&lt;T&gt;</code></td> 
   <td align="center"><code>T-&gt;void</code></td> 
   <td align="left"><code>IntConsumer</code>,<code>LongConsumer</code>, <code>DoubleConsumer</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>Function&lt;T,R&gt;</code></td> 
   <td align="center"><code>T-&gt;R</code></td> 
   <td align="left"><code>IntFunction&lt;R&gt;</code>,<code>IntToDoubleFunction</code>,<code>IntToLongFunction</code>,<br><code>LongFunction&lt;R&gt;</code>,<code>LongToDoubleFunction</code>,<code>LongToIntFunction</code>,<br><code>DoubleFunction&lt;R&gt;</code>,<code>ToIntFunction&lt;T&gt;</code>,<code>ToDoubleFunction&lt;T&gt;</code>,<br><code>ToLongFunction&lt;T&gt;</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>Supplier&lt;T&gt;</code></td> 
   <td align="center"><code>()-&gt;T</code></td> 
   <td align="left"><code>BooleanSupplier</code>,<code>IntSupplier</code>, <code>LongSupplier</code>, <code>DoubleSupplier</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>UnaryOperator&lt;T&gt;</code></td> 
   <td align="center"><code>T-&gt;T</code></td> 
   <td align="left"><code>IntUnaryOperator</code>,<code>LongUnaryOperator</code>, <code>DoubleUnaryOperator</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>BinaryOperator&lt;T&gt;</code></td> 
   <td align="center"><code>(T,T)-&gt;T</code></td> 
   <td align="left"><code>IntBinaryOperator</code>,<code>LongBinaryOperator</code>, <code>DoubleBinaryOperator</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>BiPredicate&lt;L,R&gt;</code></td> 
   <td align="center"><code>(L,R)-&gt;boolean</code></td> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><code>BiConsumer&lt;T,U&gt;</code></td> 
   <td align="center"><code>(T,U)-&gt;void</code></td> 
   <td align="left"><code>ObjIntConsumer&lt;T&gt;</code>,<code>ObjLongConsumer&lt;T&gt;</code>, <code>ObjDoubleConsumer&lt;T&gt;</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>BiFunction&lt;T,U,R&gt;</code></td> 
   <td align="center"><code>(T,U)-&gt;R</code></td> 
   <td align="left"><code>ToIntBiFunction&lt;T,U&gt;</code>,<code>ToLongBiFunction&lt;T,U&gt;</code>, <br><code>ToDoubleBiFunction&lt;T,U&gt;</code></td> 
  </tr> 
 </tbody> 
</table>

#### 方法引用 ####

##### Lambda及其等效方法引用的例子 #####

<table> 
 <thead> 
  <tr> 
   <th align="left">Lambda</th> 
   <th align="left">等效的方法引用</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left"><code>(Apple a) -&gt; a.getWeight()</code></td> 
   <td align="left"><code>Apple::getWeight</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>() -&gt; Thread.currentThread().dumpStack()</code></td> 
   <td align="left"><code>Thread.currentThread()::dumpStack</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>(str, i) -&gt; str.substring(i)</code></td> 
   <td align="left"><code>String::substring</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>(String s) -&gt; System.out.println(s)</code></td> 
   <td align="left"><code>System.out::println</code></td> 
  </tr> 
 </tbody> 
</table>

##### 方法引用主要有三类 #####

###### 指向静态方法的方法引用 ######

![指向静态方法的方法引用][format_png]

###### 指向任意类型实例方法的方法引用 ######

![指向任意类型实例方法的方法引用][format_png 1]

###### 指向现有对象的实例方法的方法引用 ######

![指向现有对象的实例方法的方法引用][format_png 2]

##### 构造函数引用 #####

Supplier<Apple> c1 = Apple::new;
    Apple a1 = c1.get();
    // 这就等价于
    Supplier<Apple> c1 = () -> new Apple();
    Apple a1 = c1.get();
    
    Function<Integer, Apple> c2 = Apple::new;
    Apple a2 = c2.apply(110);
    // 这就等价于
    Function<Integer, Apple> c2 = (weight) -> new Apple(weight);
    Apple a2 = c2.apply(110);
    
    BiFunction<String, Integer, Apple> c3 = Apple::new;
    Apple c3 = c3.apply("green", 110);
    // 这就等价于
    BiFunction<String, Integer, Apple> c3 = (color, weight) -> new Apple(color, weight);
    Apple c3 = c3.apply("green", 110);

### 使用流 ###

#### 归约 ####

##### 中间操作和终端操作 #####

<table> 
 <thead> 
  <tr> 
   <th align="left">操作</th> 
   <th align="left">类型</th> 
   <th align="left">返回类型</th> 
   <th align="left">使用的类型/函数式接口</th> 
   <th align="left">函数描述符</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left"><code>filter</code></td> 
   <td align="left">中间</td> 
   <td align="left"><code>Stream&lt;T&gt;</code></td> 
   <td align="left"><code>Predicate&lt;T&gt;</code></td> 
   <td align="left"><code>T -&gt; boolean</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>distinct</code></td> 
   <td align="left">中间(有状态-无界)</td> 
   <td align="left"><code>Stream&lt;T&gt;</code></td> 
   <td align="left"></td> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><code>skip</code></td> 
   <td align="left">中间(有状态-有界)</td> 
   <td align="left"><code>Stream&lt;T&gt;</code></td> 
   <td align="left"><code>long</code></td> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><code>limit</code></td> 
   <td align="left">中间(有状态-有界)</td> 
   <td align="left"><code>Stream&lt;T&gt;</code></td> 
   <td align="left"><code>long</code></td> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><code>map</code></td> 
   <td align="left">中间</td> 
   <td align="left"><code>Stream&lt;R&gt;</code></td> 
   <td align="left"><code>Function&lt;T,R&gt;</code></td> 
   <td align="left"><code>T -&gt; R</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>flatMap</code></td> 
   <td align="left">中间</td> 
   <td align="left"><code>Stream&lt;R&gt;</code></td> 
   <td align="left"><code>Function&lt;T,Stream&lt;R&gt;&gt;</code></td> 
   <td align="left"><code>T -&gt; Stream&lt;R&gt;</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>sorted</code></td> 
   <td align="left">中间(有状态-无界)</td> 
   <td align="left"><code>Stream&lt;T&gt;</code></td> 
   <td align="left"><code>Comparator&lt;T&gt;</code></td> 
   <td align="left"><code>(T, T) -&gt; int</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>anyMatch</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>boolean</code></td> 
   <td align="left"><code>Predicate&lt;T&gt;</code></td> 
   <td align="left"><code>T -&gt; boolean</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>noneMatch</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>boolean</code></td> 
   <td align="left"><code>Predicate&lt;T&gt;</code></td> 
   <td align="left"><code>T -&gt; boolean</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>allMatch</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>boolean</code></td> 
   <td align="left"><code>Predicate&lt;T&gt;</code></td> 
   <td align="left"><code>T -&gt; boolean</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>findAny</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>Optional&lt;T&gt;</code></td> 
   <td align="left"></td> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><code>findFirst</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>Optional&lt;T&gt;</code></td> 
   <td align="left"></td> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><code>forEach</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>void</code></td> 
   <td align="left"><code>Consumer&lt;T&gt;</code></td> 
   <td align="left"><code>T -&gt; void</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>collect</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>R</code></td> 
   <td align="left"><code>Collector&lt;T, A, R&gt;</code></td> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><code>reduce</code></td> 
   <td align="left">终端(有状态-有界)</td> 
   <td align="left"><code>Optional&lt;T&gt;</code></td> 
   <td align="left"><code>BinaryOperator&lt;T&gt;</code></td> 
   <td align="left"><code>(T, T) -&gt; T</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>count</code></td> 
   <td align="left">终端</td> 
   <td align="left"><code>long</code></td> 
   <td align="left"></td> 
   <td align="left"></td> 
  </tr> 
 </tbody> 
</table>

#### 数值流 ####

##### 原始类型流特化 #####

> `IntStream`、`DoubleStream`和`LongStream`。

###### 映射到数值流 ######

int calories = menu.stream()
    	.mapToInt(Dish::getCalories)
    	.sum();

###### 转换回对象流 ######

IntStream intStream = menu.stream().mapToInt(Dish::getCalories);
    Stream<Integer> stream = intStream.boxed();

###### 默认值OptionalInt ######

OptionalInt maxCalories = menu.stream()
    	.mapToInt(Dish::getCalories)
    	.max();
    int max = maxCalories.orElse(1);

##### 数值范围 #####

> `IntStream`和`LongStream`的静态方法`range`和`rangeClosed`

IntStream evenNumbers = IntStream.rangeClosed(1, 100).filter(n -> n % 2 == 0);
    System.out.println(evenNumbers.count());

#### 构建流 ####

##### 由值创建流 #####

Stream<String> stream = Stream.of("Java 8 ", "Lambdas ", "In ", "Action");
    stream.map(String::toUpperCase).forEach(System.out::println);
    // 空流
    Stream<String> emptyStream = Stream.empty();

##### 由数组创建流 #####

int[] numbers = { 2, 3, 5, 7, 11, 13};
    int sum = Arrays.stream(numbers).sum();

##### 由文件生成流 #####

long uniqueWords = 0;
    try(Stream<String> lines = Files.lines(Paths.get("data.txt"), Charset.defaultCharset())){ 
    	uniqueWords = lines.flatMap(line -> Arrays.stream(line.split(" ")))
    		.distinct()
    		.count();
    } catch(IOException e) { 
    	
    }

##### 由函数生成流：创建无限流 #####

> Stream API提供了两个静态方法来从函数生成流：`Stream.iterate`和`Stream.generate`。一般来说，应该使用limit(n)来对这种流加以限制，以避免打印无穷多个值。

###### 迭代 ######

> 流的第一个元素是初始值0。然后加上2来生成新的值2，再加上2来得到新的值4，以此类推。这种iterate操作基本上是顺序的，因为结果取决于前一次应用。

// (T,UnaryOperator<T>)
    Stream.iterate(0, n -> n + 2)
    	.limit(10)
    	.forEach(System.out::println);

###### 生成 ######

// Supplier<T>
    Stream.generate(Math::random)
    	.limit(5)
    	.forEach(System.out::println);

### 用流收集数据 ###

#### Collectors类的静态工厂方法 ####

<table> 
 <thead> 
  <tr> 
   <th align="left">工厂方法</th> 
   <th align="left">返回类型</th> 
   <th align="left">用于</th> 
   <th align="left">使用示例</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left"><code>toList</code></td> 
   <td align="left"><code>List&lt;T&gt;</code></td> 
   <td align="left">把流中所有项目收集到一个<code>List</code></td> 
   <td align="left"><code>List&lt;Dish&gt; dishes = menuStream.collect(toList());</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>toSet</code></td> 
   <td align="left"><code>Set&lt;T&gt;</code></td> 
   <td align="left">把流中所有项目收集到一个<code>Set</code>，删除重复项</td> 
   <td align="left"><code>Set&lt;Dish&gt; dishes = menuStream.collect(toSet());</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>toCollection</code></td> 
   <td align="left"><code>Collection&lt;T&gt;</code></td> 
   <td align="left">把流中所有项目收集到给定的供应源创建的集合</td> 
   <td align="left"><code>Collection&lt;Dish&gt; dishes = menuStream.collect( toCollection(),ArrayList::new);</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>counting</code></td> 
   <td align="left"><code>Long</code></td> 
   <td align="left">计算流中元素的个数</td> 
   <td align="left"><code>long howManyDishes = menuStream.collect(counting());</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>summingInt</code></td> 
   <td align="left"><code>Integer</code></td> 
   <td align="left">对流中项目的一个整数属性求和</td> 
   <td align="left"><code>int totalCalories = menuStream.collect( summingInt(Dish::getCalories));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>averagingInt</code></td> 
   <td align="left"><code>Double</code></td> 
   <td align="left">计算流中项目<code>Integer</code>属性的平均值</td> 
   <td align="left"><code>double avgCalories = menuStream.collect( averagingInt(Dish::getCalories));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>summarizingInt</code></td> 
   <td align="left"><code>IntSummaryStatistics</code></td> 
   <td align="left">收集关于流中项目<code>Integer</code>属性的统计值，例如最大、最小、总和与平均值</td> 
   <td align="left"><code>IntSummaryStatistics menuStatistics = menuStream.collect( summarizingInt(Dish::getCalories));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>joining</code></td> 
   <td align="left"><code>String</code></td> 
   <td align="left">连接对流中每个项目调用<code>toString</code>方法所生成的字符串</td> 
   <td align="left"><code>String shortMenu = menuStream.map(Dish::getName).collect( joining(", "));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>maxBy</code></td> 
   <td align="left"><code>Optional&lt;T&gt;</code></td> 
   <td align="left">一个包裹了流中按照给定比较器选出的最大元素的<code>Optional</code>，或如果流为空则为<code>Optional.empty()</code></td> 
   <td align="left"><code>Optional&lt;Dish&gt; fattest = menuStream.collect( maxBy(comparingInt(Dish::getCalories)));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>minBy</code></td> 
   <td align="left"><code>Optional&lt;T&gt;</code></td> 
   <td align="left">一个包裹了流中按照给定比较器选出的最小元素的<code>Optional</code>，或如果流为空则为<code>Optional.empty()</code></td> 
   <td align="left"><code>Optional&lt;Dish&gt; lightest = menuStream.collect( minBy(comparingInt(Dish::getCalories)));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>reducing</code></td> 
   <td align="left">归约操作产生的类型</td> 
   <td align="left">从一个作为累加器的初始值开始，利用<code>BinaryOperator</code>与流中的元素逐个结合，从而将流归约为单个值</td> 
   <td align="left"><code>int totalCalories = menuStream.collect(reducing(0, Dish::getCalories, Integer::sum));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>collectingAndThen</code></td> 
   <td align="left">转换函数返回的类型</td> 
   <td align="left">包裹另一个收集器，对其结果应用转换函数</td> 
   <td align="left"><code>int howManyDishes = menuStream.collect( collectingAndThen(toList(),List::size));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>groupingBy</code></td> 
   <td align="left"><code>Map&lt;K, List&lt;T&gt;&gt;</code></td> 
   <td align="left">根据项目的一个属性的值对流中的项目作问组，并将属性值作为结果<code>Map</code>的键</td> 
   <td align="left"><code>Map&lt;Dish.Type,List&lt;Dish&gt;&gt; dishesByType = menuStream.collect( groupingBy(Dish::getType));</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>partitioningBy</code></td> 
   <td align="left"><code>Map&lt;Boolean,List&lt;T&gt;&gt;</code></td> 
   <td align="left">根据对流中每个项目应用谓词的结果来对项目进行分区</td> 
   <td align="left"><code>Map&lt;Boolean,List&lt;Dish&gt;&gt; vegetarianDishes = menuStream.collect( partitioningBy(Dish::isVegetarian));</code></td> 
  </tr> 
 </tbody> 
</table>

#### 收集器接口 ####

>  *  T是流中要收集的项目的泛型。
>  *  A是累加器的类型，累加器是在收集过程中用于累积部分结果的对象。
>  *  R是收集操作得到的对象（通常但并不一定是集合）的类型。

public interface Collector<T, A, R> { 
    	// 建立新的结果容器
    	Supplier<A> supplier();
    	// 将元素添加到结果容器
    	BiConsumer<A, T> accumulator();
    	// 对结果容器应用最终转换
    	Function<A, R> finisher();
    	// 合并两个结果容器
    	BinaryOperator<A> combiner();
    	// UNORDERED——归约结果不受流中项目的遍历和累积顺序的影响。
    	// CONCURRENT——accumulator函数可以从多个线程同时调用，且该收集器可以并行归约流。如果收集器没有标为UNORDERED，那它仅在用于无序数据源时才可以并行归约。
    	// IDENTITY_FINISH——这表明完成器方法返回的函数是一个恒等函数，可以跳过。这种情况下，累加器对象将会直接用作归约过程的最终结果。这也意味着，将累加器A不加检查地转换为结果R是安全的。
    	Set<Characteristics> characteristics();
    }

##### 顺序归约过程的逻辑步骤 #####

![顺序归约过程的逻辑步骤][format_png 3]

##### 使用combiner方法来并行化归约过程 #####

![使用combiner方法来并行化归约过程][combiner]

##### 案例 #####

import java.util.*;
    import java.util.function.*;
    import java.util.stream.Collector;
    import static java.util.stream.Collector.Characteristics.*;
    public class ToListCollector<T> implements Collector<T, List<T>, List<T>> { 
    	@Override
    	public Supplier<List<T>> supplier() { 
    		return ArrayList::new;
    	}
    	
    	@Override
    	public BiConsumer<List<T>, T> accumulator() { 
    		return List::add;
    	}
    	
    	@Override
    	public Function<List<T>, List<T>> finisher() { 
    		return Function.indentity();
    	}
    	
    	@Override
    	public BinaryOperator<List<T>> combiner() { 
    		return (list1, list2) -> { 
    			list1.addAll(list2);
    			return list1;
    		};
    	}
    	
    	@Override
    	public Set<Characteristics> characteristics() { 
    		return Collections.unmodifiableSet(EnumSet.of(IDENTITY_FINISH, CONCURRENT));
    	}
    }

// 进行自定义收集而不去实现Collector
    // Supplier<R> supplier, BiConsumer<R, ? super T> accumulator, BiConsumer<R, R> combiner
    List<Dish> dishes = menuStream.collect(
    	ArrayList::new,
    	List::add,
    	List::addAll);

### 用Optional取代null ###

#### Optional类的方法 ####

<table> 
 <thead> 
  <tr> 
   <th align="left">方法</th> 
   <th align="left">描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left"><code>empty</code></td> 
   <td align="left">返回一个空的<code>Optional</code>实例</td> 
  </tr> 
  <tr> 
   <td align="left"><code>filter</code></td> 
   <td align="left">如果值存在并且满足提供的谓词，就返回包含该值的<code>Optional</code>对象；否则返回一个空的<code>Optional</code>对象</td> 
  </tr> 
  <tr> 
   <td align="left"><code>flatMap</code></td> 
   <td align="left">如果值存在，就对该值执行提供的<code>mapping</code>函数调用，返回一个<code>Optional</code>类型的值，否则就返回一个空的<code>Optional</code>对象</td> 
  </tr> 
  <tr> 
   <td align="left"><code>get</code></td> 
   <td align="left">如果该值存在，将该值用<code>Optional</code>封装返回，否则抛出一个<code>NoSuchElementException</code>异常</td> 
  </tr> 
  <tr> 
   <td align="left"><code>ifPresent</code></td> 
   <td align="left">如果值存在，就执行使用该值的方法调用，否则什么也不做</td> 
  </tr> 
  <tr> 
   <td align="left"><code>isPresent</code></td> 
   <td align="left">如果值存在就返回<code>true</code>，否则返回<code>false</code></td> 
  </tr> 
  <tr> 
   <td align="left"><code>map</code></td> 
   <td align="left">如果值存在，就对该值执行提供的<code>mapping</code>函数调用</td> 
  </tr> 
  <tr> 
   <td align="left"><code>of</code></td> 
   <td align="left">将指定值用<code>Optional</code>封装之后返回，如果该值为<code>null</code>，则抛出一个<code>NullPointerException</code>异常</td> 
  </tr> 
  <tr> 
   <td align="left"><code>ofNullable</code></td> 
   <td align="left">将指定值用<code>Optional</code>封装之后返回，如果该值为<code>null</code>，则返回一个空的<code>Optional</code>对象</td> 
  </tr> 
  <tr> 
   <td align="left"><code>orElse</code></td> 
   <td align="left">如果有值则将其返回，否则返回一个默认值</td> 
  </tr> 
  <tr> 
   <td align="left"><code>orElseGet</code></td> 
   <td align="left">如果有值则将其返回，否则返回一个由指定的<code>Supplier</code>接口生成的值</td> 
  </tr> 
  <tr> 
   <td align="left"><code>orElseThrow</code></td> 
   <td align="left">如果有值则将其返回，否则抛出一个由指定的<code>Supplier</code>接口生成的异常</td> 
  </tr> 
 </tbody> 
</table>

#### 实战示例 ####

##### 用Optional封装可能为null的值 #####

Optional<Object> value = Optional.ofNullable(map.get("key"));

##### 异常与Optional的对比 #####

public static Optional<Integer> stringToInt(String s) { 
    	try { 
    		return Optional.of(Integer.parseInt(s));
    	} catch (NumberFormatException e) { 
    		return Optional.empty();
    	}
    }

##### 把所有内容整合起来 #####

import org.junit.Test;
    
    import java.util.Optional;
    import java.util.Properties;
    
    import static org.junit.Assert.assertEquals;
    
    public class OptionalTest { 
        @Test
        public void testOptional() { 
            Properties props = new Properties();
            props.setProperty("a", "5");
            props.setProperty("b", "true");
            props.setProperty("c", "-3");
    
            assertEquals(5, readDuration(props, "a"));
            assertEquals(0, readDuration(props, "b"));
            assertEquals(0, readDuration(props, "c"));
            assertEquals(0, readDuration(props, "d"));
        }
    
        private int readDuration(Properties props, String name) { 
            return Optional.ofNullable(props.getProperty(name))
                    .flatMap(OptionalTest::stringToInt)
                    .filter(i -> i > 0)
                    .orElse(0);
        }
        
        private static Optional<Integer> stringToInt(String s) { 
            try { 
                return Optional.of(Integer.parseInt(s));
            } catch (NumberFormatException e) { 
                return Optional.empty();
            }
        }
    }

### CompletableFuture组合式异步编程 ###

#### 实现异步API ####

package com.switchvov.future;
    
    import java.util.concurrent.CompletableFuture;
    import java.util.concurrent.Future;
    import java.util.concurrent.ThreadLocalRandom;
    import java.util.concurrent.TimeUnit;
    
    /** * @Author Switch * @Date 2017/12/10 */
    public class Shop { 
        private String name;
    
        public Shop(String name) { 
            this.name = name;
        }
    
        public Future<Double> getPriceAsyncStatic(String product) { 
            return CompletableFuture.supplyAsync(() -> calculatePrice(product));
        }
    
        public Future<Double> getPriceAsync(String product) { 
            CompletableFuture<Double> futurePrice = new CompletableFuture<>();
            new Thread(() -> { 
                try { 
                    double price = calculatePrice(product);
                    futurePrice.complete(price);
                } catch (Exception e) { 
                    futurePrice.completeExceptionally(e);
                }
            }).start();
            return futurePrice;
        }
    
        public double getPrice(String product) { 
            return calculatePrice(product);
        }
    
        private double calculatePrice(String product) { 
            delay();
            return ThreadLocalRandom.current().nextDouble() 
    	        * product.charAt(0) + product.charAt(1);
        }
    
        private static void delay() { 
            try { 
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) { 
                throw new RuntimeException(e);
            }
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    }

package com.switchvov.future;
    
    import org.junit.Test;
    
    import java.util.concurrent.Future;
    
    /** * @Author Switch * @Date 2017/12/10 */
    public class ShopTest { 
        @Test
        public void testShop() { 
            Shop shop = new Shop("BestShop");
            long start = System.nanoTime();
            // Future<Double> futurePrice = shop.getPriceAsync("my favorite produce");
            Future<Double> futurePrice = shop.getPriceAsyncStatic("my favorite produce");
            long invocationTime = (System.nanoTime() - start) / 1_000_000;
            System.out.println("Invocation returned after " + invocationTime + " msecs");
    
            // doSomethingElse();
            try { 
                double price = futurePrice.get();
                System.out.printf("Price is %.2f%n", price);
            } catch (Exception e) { 
                throw new RuntimeException(e);
            }
            long retrievalTime = (System.nanoTime() - start) / 1_000_000;
            System.out.println("Price returned after " + retrievalTime + " msecs");
        }
    }

#### 密集IO任务各种实现间的对比 ####

##### 测试代码 #####

package com.switchvov.future;
    
    import java.util.concurrent.ThreadLocalRandom;
    import java.util.concurrent.TimeUnit;
    
    /** * @Author Switch * @Date 2017/12/10 */
    public class Shop { 
        private String name;
    
        public Shop(String name) { 
            this.name = name;
        }
    
        public double getPrice(String product) { 
            return calculatePrice(product);
        }
    	
        private double calculatePrice(String product) { 
            delay();
            return ThreadLocalRandom.current().nextDouble() 
    	        * product.charAt(0) + product.charAt(1);
        }
    
        private static void delay() { 
            try { 
                TimeUnit.MILLISECONDS.sleep(500);
            } catch (InterruptedException e) { 
                throw new RuntimeException(e);
            }
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    }

package com.switchvov.future;
    
    import org.openjdk.jmh.annotations.*;
    import org.openjdk.jmh.runner.Runner;
    import org.openjdk.jmh.runner.RunnerException;
    import org.openjdk.jmh.runner.options.Options;
    import org.openjdk.jmh.runner.options.OptionsBuilder;
    
    import java.util.List;
    import java.util.concurrent.CompletableFuture;
    import java.util.concurrent.Executor;
    import java.util.concurrent.Executors;
    import java.util.stream.Collectors;
    import java.util.stream.IntStream;
    
    /** * @Author Switch * @Date 2017/12/10 */
    @BenchmarkMode(Mode.AverageTime)
    @State(Scope.Benchmark)
    @Warmup(iterations = 1)
    @Measurement(iterations = 2)
    public class ShopMeasure { 
        private final String SHOP_PREFIX = "Shop ";
        private final int SHOP_NUMBER = Runtime.getRuntime().availableProcessors();
    // private final int SHOP_NUMBER = Runtime.getRuntime().availableProcessors() * 2 + 1;
        private final String PRODUCT_NAME = "Java 8实战";
    
        @Benchmark
        public void measureSequential() { 
            System.out.println(findPricesSequential(PRODUCT_NAME));
        }
    
        @Benchmark
        public void measureParallelStream() { 
            System.out.println(findPricesParallelStream(PRODUCT_NAME));
        }
    
        @Benchmark
        public void measureCompletableFuture() { 
            System.out.println(findPricesCompletableFuture(PRODUCT_NAME));
        }
    
        @Benchmark
        public void measureCustomCompletableFuture() { 
            System.out.println(findPricesCustomCompletableFuture(PRODUCT_NAME));
        }
    
        private List<String> findPricesSequential(String product) { 
            return getShops(SHOP_NUMBER).stream()
                    .map(shop -> String.format("%s price is %.2f", 
    	                shop.getName(), shop.getPrice(product)))
                    .collect(Collectors.toList());
        }
    
        private List<String> findPricesParallelStream(String product) { 
            return getShops(SHOP_NUMBER).parallelStream()
                    .map(shop -> String.format("%s price is %.2f", 
    	                shop.getName(), shop.getPrice(product)))
                    .collect(Collectors.toList());
        }
    
        private List<String> findPricesCompletableFuture(String product) { 
            List<CompletableFuture<String>> priceFutures = getShops(SHOP_NUMBER).stream()
                    .map(shop -> CompletableFuture.supplyAsync(
    	                () -> shop.getName() + " price is " + shop.getPrice(product)))
                    .collect(Collectors.toList());
            return priceFutures.stream()
                    .map(CompletableFuture::join)
                    .collect(Collectors.toList());
        }
    
        private final Executor executor = Executors.newFixedThreadPool(
    	    Math.min(getShops(SHOP_NUMBER).size(), 100), runnable -> { 
    	        Thread thread = new Thread(runnable);
    	        thread.setDaemon(true);
    	        return thread;
        });
    
        private List<String> findPricesCustomCompletableFuture(String product) { 
            List<CompletableFuture<String>> priceFutures = getShops(SHOP_NUMBER).stream()
                    .map(shop -> CompletableFuture.supplyAsync(
    	                () -> shop.getName() + " price is " + shop.getPrice(product), executor))
                    .collect(Collectors.toList());
            return priceFutures.stream()
                    .map(CompletableFuture::join)
                    .collect(Collectors.toList());
        }
    
        private List<Shop> getShops(int shopNumber) { 
            return IntStream.range(0, shopNumber)
                    .mapToObj(index -> new Shop(SHOP_PREFIX + index))
                    .collect(Collectors.toList());
        }
    
        public static void main(String[] args) throws RunnerException { 
            Options options = new OptionsBuilder()
                    .forks(1)
                    .include(ShopMeasure.class.getSimpleName())
                    .build();
            new Runner(options).run();
        }
    }

##### JMH测试结果 #####

*  商店数：`Runtime.getRuntime().availableProcessors()`

<table> 
 <thead> 
  <tr> 
   <th align="left">Benchmark</th> 
   <th align="center">Mode</th> 
   <th align="center">Cnt(次数)</th> 
   <th align="center">Score</th> 
   <th align="center">Error</th> 
   <th align="center">Units</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">ShopMeasure.measureCompletableFuture</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">1.001</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
  <tr> 
   <td align="left">ShopMeasure.measureCustomCompletableFuture</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">0.501</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
  <tr> 
   <td align="left">ShopMeasure.measureParallelStream</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">0.502</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
  <tr> 
   <td align="left">ShopMeasure.measureSequential</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">4.004</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
 </tbody> 
</table>

*  商店数：`Runtime.getRuntime().availableProcessors() * 2 + 1`

<table> 
 <thead> 
  <tr> 
   <th align="left">Benchmark</th> 
   <th align="center">Mode</th> 
   <th align="center">Cnt(次数)</th> 
   <th align="center">Score</th> 
   <th align="center">Error</th> 
   <th align="center">Units</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">ShopMeasure.measureCompletableFuture</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">1.502</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
  <tr> 
   <td align="left">ShopMeasure.measureCustomCompletableFuture</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">0.502</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
  <tr> 
   <td align="left">ShopMeasure.measureParallelStream</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">1.502</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
  <tr> 
   <td align="left">ShopMeasure.measureSequential</td> 
   <td align="center">avgt</td> 
   <td align="center">2</td> 
   <td align="center">8.506</td> 
   <td align="center"></td> 
   <td align="center">s/op</td> 
  </tr> 
 </tbody> 
</table>

> 由此可以看出在IO密集任务中，定制执行器的CompletableFuture效率是最高的。

##### 调整线程池的大小 #####

> [《Java并发编程实战》][Java]一书中，Brian Goetz和合著者们为线程池大小的优化提供了不少中肯的建议。这非常重要，如果线程池中线程的数量过多，最终它们会竞争稀缺的处理器和内存资源，浪费大量的时间在上下文切换上。反之，如果线程的数目过少，正如你的应用所面临的情况，处理器的一些核可能就无法充分利用。Brian Goetz建议，线程池大小与处理器的利用率之比可以使用下面的公式进行估算：  
>  N t h r e a d s = N C P U ∗ U C P U ∗ ( 1 + W C ) N\_\{threads\} = N\_\{CPU\} \* U\_\{CPU\} \* (1 + \\frac\{W\}\{C\}) Nthreads=NCPU∗UCPU∗(1\+CW)
> 
> 其中：
> 
>  *   N C P U N\_\{CPU\} NCPU是处理器的核的数目，可以通过`Runtime.getRuntime().availableProcessors()`得到
>  *   U C P U U\_\{CPU\} UCPU是期望的CPU利用率（该值应该介于0和1之间）
>  *   W C \\frac\{W\}\{C\} CW是等待时间与计算时间的比率，比如说IO操作即为等待时间，计算处理即为计算时间

##### 并行——使用流还是CompletableFutures？ #####

> 对集合进行并行计算有两种方式：要么将其转化为并行流，利用map这样的操作开展工作，要么枚举出集合中的每一个元素，创建新的线程，在CompletableFuture内对其进行操作。后者提供了更多的灵活性，可以调整线程池的大小，而这能帮助确保整体的计算不会因为线程都在等待I/O而发生阻塞。
> 
> 使用这些API的建议如下：
> 
>  *  如果进行的是计算密集型的操作，并且没有I/O，那么推荐使用Stream接口，因为实现简单，同时效率也可能是最高的（如果所有的线程都是计算密集型的，那就没有必要创建比处理器核数更多的线程）。
>  *  反之，如果并行的工作单元还涉及等待I/O的操作（包括网络连接等待），那么使用CompletableFuture灵活性更好，可以依据等待/计算，或者 W C \\frac\{W\}\{C\} CW的比率设定需要使用的线程数。这种情况不使用并行流的另一个原因是，处理流的流水线中如果发生I/O等待，流的延迟特性很难判断到底什么时候触发了等待。

#### 对多个异步任务进行流水线操作 ####

package com.switchvov.future;
    
    import java.util.concurrent.ThreadLocalRandom;
    import java.util.concurrent.TimeUnit;
    
    /** * @Author Switch * @Date 2017/12/10 */
    public class Shop { 
        private String name;
    
        public Shop(String name) { 
            this.name = name;
        }
    
        public String getPrice(String product) { 
            double price = calculatePrice(product);
            Discount.Code code = Discount.Code.values()
    	        [ThreadLocalRandom.current().nextInt(Discount.Code.values().length)];
            return String.format("%s:%.2f:%s", name, price, code);
        }
    
        private double calculatePrice(String product) { 
            delay();
            return ThreadLocalRandom.current().nextDouble() 
    	        * product.charAt(0) + product.charAt(1);
        }
    
        private static void delay() { 
            try { 
                TimeUnit.MILLISECONDS.sleep(1000);
            } catch (InterruptedException e) { 
                throw new RuntimeException(e);
            }
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    }

package com.switchvov.future;
    
    /** * @Author Switch * @Date 2017/12/10 */
    public class Quote { 
        private final String shopName;
        private final double price;
        private final Discount.Code discountCode;
    
        public Quote(String shopName, double price, Discount.Code discountCode) { 
            this.shopName = shopName;
            this.price = price;
            this.discountCode = discountCode;
        }
    
        public static Quote parse(String quoteString) { 
            String[] split = quoteString.split(":");
            String shopName = split[0];
            double price = Double.parseDouble(split[1]);
            Discount.Code discountCode = Discount.Code.valueOf(split[2]);
            return new Quote(shopName, price, discountCode);
        }
    
        public String getShopName() { 
            return shopName;
        }
    
        public double getPrice() { 
            return price;
        }
    
        public Discount.Code getDiscountCode() { 
            return discountCode;
        }
    }

package com.switchvov.future;
    
    import java.util.concurrent.TimeUnit;
    
    /** * @Author Switch * @Date 2017/12/10 */
    public class Discount { 
        public enum Code { 
            NONE(0), SILVER(5), GOLD(10), PLATINUM(15), DIAMOND(20);
    
            private final int percentage;
    
            Code(int percentage) { 
                this.percentage = percentage;
            }
        }
    
        public static String applyDiscount(Quote quote) { 
            return quote.getShopName() + " price is " + 
    	        Discount.applyDiscount(quote.getPrice(), quote.getDiscountCode());
        }
    
        private static double applyDiscount(double price, Code code) { 
            delay();
            return price * (100 - code.percentage) / 100;
        }
    
        private static void delay() { 
            try { 
                TimeUnit.MILLISECONDS.sleep(1000);
            } catch (InterruptedException e) { 
                throw new RuntimeException(e);
            }
        }
    }

package com.switchvov.future;
    
    import org.openjdk.jmh.annotations.*;
    import org.openjdk.jmh.runner.Runner;
    import org.openjdk.jmh.runner.RunnerException;
    import org.openjdk.jmh.runner.options.Options;
    import org.openjdk.jmh.runner.options.OptionsBuilder;
    
    import java.util.List;
    import java.util.concurrent.CompletableFuture;
    import java.util.concurrent.Executor;
    import java.util.concurrent.Executors;
    import java.util.stream.Collectors;
    import java.util.stream.IntStream;
    
    /** * @Author Switch * @Date 2017/12/10 */
    @BenchmarkMode(Mode.AverageTime)
    @State(Scope.Benchmark)
    @Warmup(iterations = 1)
    @Measurement(iterations = 2)
    public class ShopMeasure { 
        private final String SHOP_PREFIX = "Shop ";
        private final int SHOP_NUMBER = Runtime.getRuntime().availableProcessors();
        // private final int SHOP_NUMBER = Runtime.getRuntime().availableProcessors() * 2 + 1;
        private final String PRODUCT_NAME = "Java 8实战";
    
        @Benchmark
        public void measureSequential() { 
            System.out.println(findPricesSequential(PRODUCT_NAME));
        }
    
        @Benchmark
        public void measureCustomCompletableFuture() { 
            System.out.println(findPricesCustomCompletableFuture(PRODUCT_NAME));
        }
    
        private List<String> findPricesSequential(String product) { 
            return getShops(SHOP_NUMBER).stream()
                    .map(shop -> shop.getPrice(product))
                    .map(Quote::parse)
                    .map(Discount::applyDiscount)
                    .collect(Collectors.toList());
        }
    
        private final Executor executor = Executors.newFixedThreadPool(
    	    Math.min(getShops(SHOP_NUMBER).size(), 100), runnable -> { 
    	        Thread thread = new Thread(runnable);
    	        thread.setDaemon(true);
    	        return thread;
        });
    
        private List<String> findPricesCustomCompletableFuture(String product) { 
            List<CompletableFuture<String>> priceFutures = getShops(SHOP_NUMBER).stream()
                    .map(shop -> CompletableFuture.supplyAsync(
    	                () -> shop.getPrice(product), executor))
                    .map(future -> future.thenApply(Quote::parse))
                    .map(future -> future.thenCompose(
                            quote -> CompletableFuture.supplyAsync(
                                    () -> Discount.applyDiscount(quote), executor)))
                    .collect(Collectors.toList());
            return priceFutures.stream()
                    .map(CompletableFuture::join)
                    .collect(Collectors.toList());
        }
    
        private List<Shop> getShops(int shopNumber) { 
            return IntStream.range(0, shopNumber)
                    .mapToObj(index -> new Shop(SHOP_PREFIX + index))
                    .collect(Collectors.toList());
        }
    
        public static void main(String[] args) throws RunnerException { 
            Options options = new OptionsBuilder()
                    .forks(1)
                    .include(ShopMeasure.class.getSimpleName())
                    .build();
            new Runner(options).run();
        }
    }

##### JMH测试结果 #####

*  商店数：`Runtime.getRuntime().availableProcessors()`

##### 合并两个独立的CompletableFuture #####

private Future<Double> fromCNYToUSD(Shop shop, String product) { 
            return CompletableFuture.supplyAsync(() -> shop.getPrice(product))
                    .thenApply(productString -> Quote.parse(productString).getPrice())
                    .thenCombine(CompletableFuture.supplyAsync(
    	                () -> getRate(Money.CNY, Money.USD)), (price, rate) -> price * rate);
        }
        
        enum Money { 
            CNY(1), USD(0.15);
    
            private double rate;
    
            Money(double rate) { 
                this.rate = rate;
            }
        }
        
        private double getRate(Money from, Money to) { 
            delay();
            return to.rate / from.rate;
        }
    
        private static void delay() { 
            try { 
                TimeUnit.MILLISECONDS.sleep(1000);
            } catch (InterruptedException e) { 
                throw new RuntimeException(e);
            }
        }

#### 响应CompletableFuture的completion事件 ####

package com.switchvov.future;
    
    import java.util.concurrent.ThreadLocalRandom;
    import java.util.concurrent.TimeUnit;
    
    /** * @Author Switch * @Date 2017/12/10 */
    public class Shop { 
        private String name;
    
        public Shop(String name) { 
            this.name = name;
        }
    
        public String getPrice(String product) { 
            double price = calculatePrice(product);
            Discount.Code code = Discount.Code.values()
    	        [ThreadLocalRandom.current().nextInt(Discount.Code.values().length)];
            return String.format("%s:%.2f:%s", name, price, code);
        }
    
        private double calculatePrice(String product) { 
            randomDelay();
            return ThreadLocalRandom.current().nextDouble() * product.charAt(0) + product.charAt(1);
        }
    
        private static void randomDelay() { 
            int delay = 500 + ThreadLocalRandom.current().nextInt(2000);
            try { 
                TimeUnit.MILLISECONDS.sleep(delay);
            } catch (InterruptedException e) { 
                throw new RuntimeException(e);
            }
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    }

package com.switchvov.future;
    
    import org.openjdk.jmh.annotations.*;
    import org.openjdk.jmh.runner.Runner;
    import org.openjdk.jmh.runner.RunnerException;
    import org.openjdk.jmh.runner.options.Options;
    import org.openjdk.jmh.runner.options.OptionsBuilder;
    
    import java.util.List;
    import java.util.concurrent.*;
    import java.util.stream.Collectors;
    import java.util.stream.IntStream;
    import java.util.stream.Stream;
    
    /** * @Author Switch * @Date 2017/12/10 */
    @BenchmarkMode(Mode.AverageTime)
    @State(Scope.Benchmark)
    @Warmup(iterations = 1)
    @Measurement(iterations = 2)
    public class ShopMeasure { 
        private final String SHOP_PREFIX = "Shop ";
        private final int SHOP_NUMBER = Runtime.getRuntime().availableProcessors();
        // private final int SHOP_NUMBER = Runtime.getRuntime().availableProcessors() * 2 + 1;
        private final String PRODUCT_NAME = "Java 8实战";
    
        @Benchmark
        public void measureFindPricesCustomCompletableFutureStream() { 
            long start = System.currentTimeMillis();
            CompletableFuture[] futures = findPricesCustomCompletableFutureStream(PRODUCT_NAME)
                    .map(future -> future.thenAccept(string ->
                            System.out.println(string + " (done in " + (System.currentTimeMillis() - start) + " msecs)")))
                    .toArray(CompletableFuture[]::new);
            CompletableFuture.allOf(futures).join();
            System.out.println("All shops have now responded in " + (System.currentTimeMillis() - start) + " msecs");
        }
    
        private final Executor executor = Executors.newFixedThreadPool(Math.min(getShops(SHOP_NUMBER).size(), 100), runnable -> { 
            Thread thread = new Thread(runnable);
            thread.setDaemon(true);
            return thread;
        });
    
        private Stream<CompletableFuture<String>> findPricesCustomCompletableFutureStream(String product) { 
            return getShops(SHOP_NUMBER).stream()
                    .map(shop -> CompletableFuture.supplyAsync(() -> shop.getPrice(product), executor))
                    .map(future -> future.thenApply(Quote::parse))
                    .map(future -> future.thenCompose(
                            quote -> CompletableFuture.supplyAsync(
                                    () -> Discount.applyDiscount(quote), executor)));
        }
    
        private List<Shop> getShops(int shopNumber) { 
            return IntStream.range(0, shopNumber)
                    .mapToObj(index -> new Shop(SHOP_PREFIX + index))
                    .collect(Collectors.toList());
        }
    
        public static void main(String[] args) throws RunnerException { 
            Options options = new OptionsBuilder()
                    .forks(1)
                    .include(ShopMeasure.class.getSimpleName())
                    .build();
            new Runner(options).run();
        }
    }

> 其余类未更改，详见对多个异步任务进行流水线操作

### 新的日期和时间API ###

#### LocalDate、LocalTime、Instant、Duration 以及Period ####

LocalDate date = LocalDate.of(2017, 12, 11);
    System.out.println(date); // 2017-12-11
    System.out.println(date.getYear()); // 2017
    System.out.println(date.getMonth()); // DECEMBER
    System.out.println(date.getDayOfMonth()); // 11
    System.out.println(date.getDayOfWeek()); // MONDAY
    System.out.println(date.lengthOfMonth()); // 31
    System.out.println(date.isLeapYear()); // false
    
    LocalDate today = LocalDate.now(); // 获取今天Date
    
    int year = date.get(ChronoField.YEAR);
    int month = date.get(ChronoField.MONTH_OF_YEAR);
    int day = date.get(ChronoField.DAY_OF_MONTH);
    System.out.println(year + " " + month + " " + day); // 2017 12 11
    
    LocalTime time = LocalTime.of(20, 14, 30);
    System.out.println(time.getHour()); // 20
    System.out.println(time.getMinute()); // 14
    System.out.println(time.getSecond()); // 30
    
    date = LocalDate.parse("2017-12-11");
    System.out.println(date); // 2017-12-11
    time = LocalTime.parse("20:14:30");
    System.out.println(time); // 20:14:30
    
    LocalDateTime dt1 = LocalDateTime.of(2017, Month.DECEMBER, 11, 20, 14, 30);
    LocalDateTime dt2 = LocalDateTime.of(date, time);
    LocalDateTime dt3 = date.atTime(20, 14, 30);
    LocalDateTime dt4 = date.atTime(time);
    LocalDateTime dt5 = time.atDate(date);
    
    date = dt1.toLocalDate();
    time = dt1.toLocalTime();
    
    System.out.println(Instant.ofEpochSecond(3)); // 1970-01-01T00:00:03Z
    System.out.println(Instant.ofEpochSecond(3, 1)); // 1970-01-01T00:00:03.000000001Z
    System.out.println(Instant.ofEpochSecond(2, 1_000_000_000)); // 1970-01-01T00:00:03Z
    System.out.println(Instant.ofEpochSecond(4, -1_000_000_000)); // 1970-01-01T00:00:03Z
    
    Duration d1 = Duration.between(time, time.plus(1, ChronoUnit.MINUTES));
    System.out.println(d1); // PT1M
    Duration d2 = Duration.between(dt1, dt1.plus(1, ChronoUnit.DAYS));
    System.out.println(d2); // PT24H
    Duration d3 = Duration.between(dt1, dt1.minus(1, ChronoUnit.DAYS));
    System.out.println(d3); // PT-24H
    Duration d4 = Duration.between(Instant.ofEpochSecond(0), Instant.ofEpochSecond(2, 1));
    System.out.println(d4); // PT2.000000001S
    
    System.out.println(Duration.ofMinutes(3)); // PT3M
    System.out.println(Duration.of(3, ChronoUnit.MINUTES)); // PT3M
    System.out.println(Period.ofDays(10)); // P10D
    System.out.println(Period.ofWeeks(3)); // P21D
    System.out.println(Period.of(2, 6, 1)); // P2Y6M1D

##### 日期-时间类中表示时间间隔的通用方法 #####

<table> 
 <thead> 
  <tr> 
   <th align="left">方法名</th> 
   <th align="left">是否是静态方法</th> 
   <th align="left">方法描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">between</td> 
   <td align="left">是</td> 
   <td align="left">创建两个时间点之间的interval</td> 
  </tr> 
  <tr> 
   <td align="left">from</td> 
   <td align="left">是</td> 
   <td align="left">由一个临时时间点创建interval</td> 
  </tr> 
  <tr> 
   <td align="left">of</td> 
   <td align="left">是</td> 
   <td align="left">由它的组成部分创建interval的实例</td> 
  </tr> 
  <tr> 
   <td align="left">parse</td> 
   <td align="left">是</td> 
   <td align="left">由字符串创建interval的实例</td> 
  </tr> 
  <tr> 
   <td align="left">addTo</td> 
   <td align="left">否</td> 
   <td align="left">创建该interval的副本，并将其叠加到某个指定的temporal对象</td> 
  </tr> 
  <tr> 
   <td align="left">get</td> 
   <td align="left">否</td> 
   <td align="left">读取该interval的状态</td> 
  </tr> 
  <tr> 
   <td align="left">isNegative</td> 
   <td align="left">否</td> 
   <td align="left">检查该interval是否为负值，不包含零</td> 
  </tr> 
  <tr> 
   <td align="left">isZero</td> 
   <td align="left">否</td> 
   <td align="left">检查该interval的时长是否为零</td> 
  </tr> 
  <tr> 
   <td align="left">minus</td> 
   <td align="left">否</td> 
   <td align="left">通过减去一定的时间创建该interval的副本</td> 
  </tr> 
  <tr> 
   <td align="left">multipliedBy</td> 
   <td align="left">否</td> 
   <td align="left">将interval的值乘以某个标量创建该interval的副本</td> 
  </tr> 
  <tr> 
   <td align="left">negated</td> 
   <td align="left">否</td> 
   <td align="left">以忽略某个时长的方式创建该interval的副本</td> 
  </tr> 
  <tr> 
   <td align="left">plus</td> 
   <td align="left">否</td> 
   <td align="left">以增加某个指定的时长的方式创建该interval的副本</td> 
  </tr> 
  <tr> 
   <td align="left">subtractFrom</td> 
   <td align="left">否</td> 
   <td align="left">从指定的temporal对象中减去该interval</td> 
  </tr> 
 </tbody> 
</table>

#### 操纵、解析和格式化日期 ####

##### 表示时间点的日期-时间类的通用方法 #####

<table> 
 <thead> 
  <tr> 
   <th align="left">方法名</th> 
   <th align="left">是否是静态方法</th> 
   <th align="left">方法描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">from</td> 
   <td align="left">是</td> 
   <td align="left">依据传入的Temporal对象创建对象实例</td> 
  </tr> 
  <tr> 
   <td align="left">now</td> 
   <td align="left">是</td> 
   <td align="left">依据系统时钟创建Temporal对象</td> 
  </tr> 
  <tr> 
   <td align="left">of</td> 
   <td align="left">是</td> 
   <td align="left">由Temporal对象的某个部分创建该对象的实例</td> 
  </tr> 
  <tr> 
   <td align="left">parse</td> 
   <td align="left">是</td> 
   <td align="left">由字符串创建Temporal对象的实例</td> 
  </tr> 
  <tr> 
   <td align="left">atOffset</td> 
   <td align="left">否</td> 
   <td align="left">将Temporal对象和某个时区偏移相结合</td> 
  </tr> 
  <tr> 
   <td align="left">atZone</td> 
   <td align="left">否</td> 
   <td align="left">将Temporal对象和某个时区相结合</td> 
  </tr> 
  <tr> 
   <td align="left">format</td> 
   <td align="left">否</td> 
   <td align="left">使用某个指定的格式器将Temporal对象转换为字符串（Instant类不提供该方法）</td> 
  </tr> 
  <tr> 
   <td align="left">get</td> 
   <td align="left">否</td> 
   <td align="left">读取Temporal对象的某一部分的值</td> 
  </tr> 
  <tr> 
   <td align="left">minus</td> 
   <td align="left">否</td> 
   <td align="left">创建Temporal对象的一个副本，通过将当前Temporal对象的值减去一定的时长创建该副本</td> 
  </tr> 
  <tr> 
   <td align="left">plus</td> 
   <td align="left">否</td> 
   <td align="left">创建Temporal对象的一个副本，通过将当前Temporal对象的值加上一定的时长创建该副本</td> 
  </tr> 
  <tr> 
   <td align="left">with</td> 
   <td align="left">否</td> 
   <td align="left">以该Temporal对象为模板，对某些状态进行修改创建该对象的副本</td> 
  </tr> 
 </tbody> 
</table>

LocalDate date1 = LocalDate.of(2017, 12, 11);
    System.out.println(date1); // 2017-12-11
    LocalDate date2 = date1.withYear(2014);
    System.out.println(date2); // 2014-12-11
    LocalDate date3 = date2.withDayOfMonth(10);
    System.out.println(date3); // 2014-12-10
    LocalDate date4 = date3.with(ChronoField.MONTH_OF_YEAR, 5);
    System.out.println(date4); // 2014-05-10
    
    LocalDate date5 = date4.plusWeeks(1);
    System.out.println(date5); // 2014-05-17
    LocalDate date6 = date5.minusYears(3);
    System.out.println(date6); // 2011-05-17
    LocalDate date7 = date6.plus(6, ChronoUnit.MONTHS);
    System.out.println(date7); // 2011-11-17

##### TemporalAdjuster类中的工厂方法 #####

<table> 
 <thead> 
  <tr> 
   <th align="left">方法名</th> 
   <th align="left">描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">dayOfWeekInMonth</td> 
   <td align="left">创建一个新的日期，它的值为同一个月中每一周的第几天</td> 
  </tr> 
  <tr> 
   <td align="left">firstDayOfMonth</td> 
   <td align="left">创建一个新的日期，它的值为当月的第一天</td> 
  </tr> 
  <tr> 
   <td align="left">firstDayOfNextMonth</td> 
   <td align="left">创建一个新的日期，它的值为下月的第一天</td> 
  </tr> 
  <tr> 
   <td align="left">firstDayOfNextYear</td> 
   <td align="left">创建一个新的日期，它的值为明年的第一天</td> 
  </tr> 
  <tr> 
   <td align="left">firstDayOfYear</td> 
   <td align="left">创建一个新的日期，它的值为当年的第一天</td> 
  </tr> 
  <tr> 
   <td align="left">firstInMonth</td> 
   <td align="left">创建一个新的日期，它的值为同一个月中，第一个符合星期几要求的值</td> 
  </tr> 
  <tr> 
   <td align="left">lastDayOfMonth</td> 
   <td align="left">创建一个新的日期，它的值为当月的最后一天</td> 
  </tr> 
  <tr> 
   <td align="left">lastDayOfNextMonth</td> 
   <td align="left">创建一个新的日期，它的值为下月的最后一天</td> 
  </tr> 
  <tr> 
   <td align="left">lastDayOfNextYear</td> 
   <td align="left">创建一个新的日期，它的值为明年的最后一天</td> 
  </tr> 
  <tr> 
   <td align="left">lastDayOfYear</td> 
   <td align="left">创建一个新的日期，它的值为今年的最后一天</td> 
  </tr> 
  <tr> 
   <td align="left">lastInMonth</td> 
   <td align="left">创建一个新的日期，它的值为同一个月中，最后一个符合星期几要求的值</td> 
  </tr> 
  <tr> 
   <td align="left">next/previous</td> 
   <td align="left">创建一个新的日期，并将其值设定为日期调整后或者调整前，第一个符合指定星期几要求的日期</td> 
  </tr> 
  <tr> 
   <td align="left">nextOrSame/previousOrSame</td> 
   <td align="left">创建一个新的日期，并将其值设定为日期调整后或者调整前，第一个符合指定星期几要求的日期，如果该日期已经符合要求，直接返回该对象</td> 
  </tr> 
 </tbody> 
</table>

LocalDate date8 = date7.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));
    System.out.println(date8); // 2011-11-20
    LocalDate date9 = date8.with(TemporalAdjusters.lastDayOfMonth());
    System.out.println(date9); // 2011-11-30

###### TemporalAdjuster接口 ######

@FunctionalInterface
    public interface TemporalAdjuster { 
    	Temporal adjustInto(Temporal temporal);
    }

###### 定制的TemporalAdjuster ######

public class NextWorkingDay implements TemporalAdjuster { 
        @Override
        public Temporal adjustInto(Temporal temporal) { 
            DayOfWeek dow = DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
            int dayToAdd = 1;
            if (dow == DayOfWeek.FRIDAY) dayToAdd = 3;
            else if (dow == DayOfWeek.SATURDAY) dayToAdd = 2;
            return temporal.plus(dayToAdd, ChronoUnit.DAYS);
        }
    }

date = date.with(temporal -> { 
            DayOfWeek dow = DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
            int dayToAdd = 1;
            if (dow == DayOfWeek.FRIDAY) dayToAdd = 3;
            else if (dow == DayOfWeek.SATURDAY) dayToAdd = 2;
            return temporal.plus(dayToAdd, ChronoUnit.DAYS);
        });

TemporalAdjuster nextWorkingDay = TemporalAdjusters.ofDateAdjuster(temporal -> { 
            DayOfWeek dow = DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
            int dayToAdd = 1;
            if (dow == DayOfWeek.FRIDAY) dayToAdd = 3;
            if (dow == DayOfWeek.SATURDAY) dayToAdd = 2;
            return temporal.plus(dayToAdd, ChronoUnit.DAYS);
        });
        date =date.with(nextWorkingDay);

##### 打印输出及解析日期-时间对象 #####

LocalDate date = LocalDate.of(2017, 12, 11);
    String s1 = date.format(DateTimeFormatter.BASIC_ISO_DATE); // 20171211
    String s2 = date.format(DateTimeFormatter.ISO_LOCAL_DATE); // 2017-12-11
    LocalDate date1 = LocalDate.parse("20171211", DateTimeFormatter.BASIC_ISO_DATE);
    LocalDate date2 = LocalDate.parse("2017-12-11", DateTimeFormatter.ISO_LOCAL_DATE);
    
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
    LocalDate date1 = LocalDate.of(2017, 12, 11);
    String formattedDate = date1.format(formatter);
    LocalDate date2 = LocalDate.parse(formattedDate, formatter);

###### 构造一个DateTimeFormatter ######

DateTimeFormatter italianFormatter = new DateTimeFormatterBuilder()
    	.appendText(ChronoField.DAY_OF_MONTH)
    	.appendLiteral(". ")
    	.appendText(ChronoField.MONTH_OF_YEAR)
    	.appendLiteral(" ")
    	.appendText(ChronoField.YEAR)
    	.parseCaseInsensitive()
    	.toFormatter(Locale.ITALIAN);

\-----------参考[《Java 8 实战》][Java 8]

[format_png]: /images/20220603/ab425ba7cab344c88a9ca68e75d7570f.png
[format_png 1]: /images/20220603/a0ddfb0132e54433b233472937f6961d.png
[format_png 2]: /images/20220603/b5368f4927d2424fb31c9225a5d8a5c4.png
[format_png 3]: /images/20220603/5ac6de105d3949b993c9d35c4c599aa2.png
[combiner]: /images/20220603/70c982f6fd9443cc93618c66a84eec52.png
[Java]: http://jcip.net.s3-website-us-east-1.amazonaws.com/
[Java 8]: http://www.ituring.com.cn/book/1537