摘要：陳楊一流的定義流支持串行并行聚合操作元素序列二流的創建流的創建以方法生成流三

package com.java.design.java8.Stream.StreamDetail;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;
import java.util.List;
import java.util.UUID;
import java.util.stream.Stream;

/**
 * @author 陳楊
 */
@SpringBootTest
@RunWith(SpringRunner.class)
public class StreamDetail {

    private List integerList;

    @Before
    public void init() {
        integerList = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
    }

    @Test
    public void testStreamDetail() {

        //    Stream :  A sequence of elements supporting sequential and parallel aggregate operations.
        //    流: 支持 串行、并行 聚合操作 元素序列

        //    流的創建：
        //    Collection.stream()  Collection.parallelStream()

        //    Stream.generate
        System.out.println("-----------------------------------------
");
        System.out.println("以Stream.generate方法生成流");
        Stream generate = Stream.generate(UUID.randomUUID()::toString);
        generate.findFirst().ifPresent(System.out::println);
        System.out.println("-----------------------------------------
");

        //    對象引用流
        //    Stream , which is a stream of object references

        //    流的計算：    stream pipeline
        //    To perform a computation, stream operations are composed into a  stream pipeline.

        //    流管道組成：  源數據source-->數組、集合、生成器函數、IO通道等
        //                 [0,n) 中間操作（intermediate operations） 一個流轉換 為 另一個新流
        //                 終止操作（terminal operation）產生一個結果 或有副作用（修改流中元素 屬性或狀態）
        //    A stream pipeline consists of a source (which  might be an array,
        //    a collection, a generator function, an I/O channel,etc),
        //    zero or more intermediate operations (which transform a
        //    stream into another stream, such as {@link Stream#filter(Predicate)}), and a
        //    terminal operation (which produces a result or side-effect, such
        //    as {@link Stream#count()} or {@link Stream#forEach(Consumer)}).

        //    流的消費：  流中對于源數據的計算 有且僅有在終止操作觸發時才會被調用
        //               流中元素只有在被需要時才會被消費
        //               lazy（惰性）: 如果沒有終止操作 那么一系列的中間操作都不會被執行
        //               stream流操作只會執行一次： stream中有一個容器 將所有中間操作打包 放入容器中
        //               調用終止操作時 觸發容器的鏈式中間操作 將流中每一個元素 應用于中間業務邏輯
        //    Streams are lazy; computation on the source data is only performed when the
        //    terminal operation is initiated, and source elements are consumed only as needed.

        //    流創建后 只能被消費一次 否則拋異常
        //    除非流被設計成為顯示并發修改的流如ConcurrentHashMap 否則未期望或錯誤的行為就會在執行時產生
        //    Unless the source was explicitly designed for concurrent modification
        //    (such as a ConcurrentHashMap),unpredictable or erroneous behavior may result
        //    from modifying the stream source while it is being queried.
        //    java.lang.IllegalStateException: stream has already been operated upon or closed

        //    Lambda表達式的正確行為：
        //    To preserve correct behavior,these behavioral parameters:

        //    must be non-interfering
        //    (they do not modify the stream source);

        //    in most cases must be stateless
        //    (their result should not depend on any state that might change during execution
        //    of the stream pipeline).

//    流與集合：
//    集合關注的是對元素的管理與訪問
//    流不會直接提供直接訪問或操作其元素的方法
//    流提供聲明性描述： 源 與 建立于源之上的聚合計算執行操作
//    如果流沒有提供預期的功能 可執行受控遍歷（iterator、spliterator）
//    Collections and streams, while bearing some superficial similarities,
//    have different goals.  Collections are primarily concerned with the efficient
//    management of, and access to, their elements.  By contrast, streams do not
//    provide a means to directly access or manipulate their elements, and are
//    instead concerned with declaratively describing their source and the
//    computational operations which will be performed in aggregate on that source.
//    However, if the provided stream operations do not offer the desired
//    functionality, the {@link #iterator()} and {@link #spliterator()} operations
//    can be used to perform a controlled traversal.

//   流的MapReduce操作  求集合 每個元素的2倍 之和
//   此例中：Integer 每執行一次reduce操作 觸發 該元素的map操作一次
System.out.println(integerList.stream().map(i -> 2 * i).reduce(0, Integer::sum));
System.out.println("-----------------------------------------
");

package com.java.design.java8.Stream.StreamDetail;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

/**
 * @author 陳楊
 */
@SpringBootTest
@RunWith(SpringRunner.class)
public class AutoCloseableTest implements AutoCloseable {

    /*
     *      An object that may hold resources (such as file or socket handles)
     *      until it is closed. The {@link #close()} method of an {@code AutoCloseable}
     *      object is called automatically when exiting a {@code
     *      try}-with-resources block for which the object has been declared in
     *      the resource specification header. This construction ensures prompt
     *      release, avoiding resource exhaustion exceptions and errors that
     *      may otherwise occur.
     *
     *      實現AutoCloseable接口：
     *          使用try--with--resources 代碼塊 替代 try--catch--finally
     *          在代碼塊運行完畢后 自動實現 資源的關閉
     *      public interface AutoCloseable {
     *               void close() throws Exception;
     *                }
     */

    public void doSomeThing() {

        System.out.println("method doSomeThing invoked!");
    }


    @Override
    public void close() throws Exception {
        System.out.println("method close invoked!");
    }


    @Test
    public void testAutoCloseable() throws Exception {

        try (AutoCloseableTest autoCloseableTest = new AutoCloseableTest()) {
            autoCloseableTest.doSomeThing();
        }
    }


}

package com.java.design.java8.Stream.StreamDetail.BaseStreamDetail;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;

/**
 * @author 陳楊
 */
@SpringBootTest
@RunWith(SpringRunner.class)
public class BaseStreamDetail {

    private List list;
    private NullPointerException myException;

    @Before
    public void init() {
        list = Arrays.asList("Kirito", "Asuna", "Illyasviel", "Sakura");
        myException = new NullPointerException("my NullPointerException");
    }

    @Test
    public void testBaseStreamDetail() {

        // public interface Stream extends BaseStream>

      /*public interface BaseStream> extends AutoCloseable {

         Iterator iterator();

       * Returns a spliterator for the elements of this stream.

         Spliterator spliterator();


       *  當終止操作應用于流時 判斷其是否并行
       *  當執行終止操作之后 執行isParallel() 會得到不可預期的結果
       *    此方法需適用于終止操作之前
       *
       * Returns whether this stream, if a terminal operation were to be executed,
       * would execute in parallel.  Calling this method after invoking an
       * terminal stream operation method may yield unpredictable results.
       *
           boolean isParallel();


       * 返回一個等價的串行流
       *     流本身已經是串行 或 流的狀態已被修改為串行
       *
       * Returns an equivalent stream that is sequential.  May return
       * itself, either because the stream was already sequential, or because
       * the underlying stream state was modified to be sequential.
       *
        S sequential();


       * 返回一個等價的并行流
       *     流本身已經是并行 或 流的狀態已被修改為并行
       *
       * Returns an equivalent stream that is parallel.  May return
       * itself, either because the stream was already parallel, or because
       * the underlying stream state was modified to be parallel.
       *
          S parallel();


       * 返回一個等價的無序流
       *     流本身已經是無序 或 流的狀態已被修改為無序
       *
       * Returns an equivalent stream that is
       * unordered.  May return
       * itself, either because the stream was already unordered, or because
       * the underlying stream state was modified to be unordered.
       *
          S unordered();


       * 返回一個等價的流 有close handler
       *     close handler當流close()方法調用時觸發
       *     調用順序：close handlers被添加先后順序
       *
       *     所有的close handlers都會被調用 即使出現了異常
       *     如果任意close handler拋出異常
       *             那么第一個異常會傳遞給調用段
       *             其他異常（剩余或被抑制）會傳遞給調用段
       *                     除非其中有與第一個異常相同的異常（相同對象）  因為相同異常不能抑制自身
       *
       * Returns an equivalent stream with an additional close handler.  Close
       * handlers are run when the {@link #close()} method
       * is called on the stream, and are executed in the order they were
       * added.  All close handlers are run, even if earlier close handlers throw
       * exceptions.  If any close handler throws an exception, the first
       * exception thrown will be relayed to the caller of {@code close()}, with
       * any remaining exceptions added to that exception as suppressed exceptions
       * (unless one of the remaining exceptions is the same exception as the
       * first exception, since an exception cannot suppress itself.)  May
       * return itself.
       *
       * @param closeHandler A task to execute when the stream is closed
       * @return a stream with a handler that is run if the stream is closed

          S onClose(Runnable closeHandler);


       * 關閉流 調用流管道中的close handlers
       *
       * Closes this stream, causing all close handlers for this stream pipeline  to be called.

          @Override
          void close();
      }*/


        try (Stream stream = list.stream()) {
            stream.onClose(() -> {
                System.out.println("close handler first");
                // throw new NullPointerException("null pointer exception 1");
                throw myException;
            }).onClose(() -> {
                System.out.println("close handler second");
                // throw new NullPointerException("null pointer exception 2");
                throw myException;
            }).onClose(() -> {
                System.out.println("close handler third");
                // throw new NullPointerException("null pointer exception 3");
                throw myException;
            }).forEach(System.out::println);
        }


    }


}

testStreamDetail測試
  .   ____          _            __ _ _
 / / ___"_ __ _ _(_)_ __  __ _    
( ( )\___ | "_ | "_| | "_ / _` |    
 /  ___)| |_)| | | | | || (_| |  ) ) ) )
  "  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.2.RELEASE)

2019-02-20 17:40:31.060  INFO 15872 --- [           main] c.j.d.j.S.StreamDetail.StreamDetail      : Starting StreamDetail on DESKTOP-87RMBG4 with PID 15872 (started by 46250 in E:IdeaProjectsdesign)
2019-02-20 17:40:31.062  INFO 15872 --- [           main] c.j.d.j.S.StreamDetail.StreamDetail      : No active profile set, falling back to default profiles: default
2019-02-20 17:40:31.584  INFO 15872 --- [           main] c.j.d.j.S.StreamDetail.StreamDetail      : Started StreamDetail in 0.728 seconds (JVM running for 1.461)
-----------------------------------------

以Stream.generate方法生成流
2742c0e9-7bdb-4c7e-88c9-b5d94684215c
-----------------------------------------

90
-----------------------------------------

AutoCloseableTest測試
  .   ____          _            __ _ _
 / / ___"_ __ _ _(_)_ __  __ _    
( ( )\___ | "_ | "_| | "_ / _` |    
 /  ___)| |_)| | | | | || (_| |  ) ) ) )
  "  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.2.RELEASE)

2019-02-20 17:39:45.456  INFO 16320 --- [           main] c.j.d.j.S.S.AutoCloseableTest            : Starting AutoCloseableTest on DESKTOP-87RMBG4 with PID 16320 (started by 46250 in E:IdeaProjectsdesign)
2019-02-20 17:39:45.457  INFO 16320 --- [           main] c.j.d.j.S.S.AutoCloseableTest            : No active profile set, falling back to default profiles: default
2019-02-20 17:39:45.956  INFO 16320 --- [           main] c.j.d.j.S.S.AutoCloseableTest            : Started AutoCloseableTest in 0.716 seconds (JVM running for 1.433)
method doSomeThing invoked!
method close invoked!

testBaseStreamDetail測試
  .   ____          _            __ _ _
 / / ___"_ __ _ _(_)_ __  __ _    
( ( )\___ | "_ | "_| | "_ / _` |    
 /  ___)| |_)| | | | | || (_| |  ) ) ) )
  "  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.2.RELEASE)

2019-02-20 17:46:41.886  INFO 15216 --- [           main] c.j.d.j.S.S.B.BaseStreamDetail           : Starting BaseStreamDetail on DESKTOP-87RMBG4 with PID 15216 (started by 46250 in E:IdeaProjectsdesign)
2019-02-20 17:46:41.887  INFO 15216 --- [           main] c.j.d.j.S.S.B.BaseStreamDetail           : No active profile set, falling back to default profiles: default
2019-02-20 17:46:42.435  INFO 15216 --- [           main] c.j.d.j.S.S.B.BaseStreamDetail           : Started BaseStreamDetail in 0.762 seconds (JVM running for 1.48)
Kirito
Asuna
Illyasviel
Sakura
close handler first
close handler second
close handler third

java.lang.NullPointerException: my NullPointerException

Process finished with exit code -1