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(chuàng)建流的創(chuàng)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(chuàng)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(duì)象引用流
        //    Stream , which is a stream of object references

        //    流的計(jì)算：    stream pipeline
        //    To perform a computation, stream operations are composed into a  stream pipeline.

        //    流管道組成：  源數(shù)據(jù)source-->數(shù)組、集合、生成器函數(shù)、IO通道等
        //                 [0,n) 中間操作（intermediate operations） 一個(gè)流轉(zhuǎn)換 為 另一個(gè)新流
        //                 終止操作（terminal operation）產(chǎn)生一個(gè)結(jié)果 或有副作用（修改流中元素 屬性或狀態(tài)）
        //    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(fèi)：  流中對(duì)于源數(shù)據(jù)的計(jì)算 有且僅有在終止操作觸發(fā)時(shí)才會(huì)被調(diào)用
        //               流中元素只有在被需要時(shí)才會(huì)被消費(fèi)
        //               lazy（惰性）: 如果沒有終止操作 那么一系列的中間操作都不會(huì)被執(zhí)行
        //               stream流操作只會(huì)執(zhí)行一次： stream中有一個(gè)容器 將所有中間操作打包 放入容器中
        //               調(diào)用終止操作時(shí) 觸發(fā)容器的鏈?zhǔn)街虚g操作 將流中每一個(gè)元素 應(yīng)用于中間業(yè)務(wù)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(chuàng)建后 只能被消費(fèi)一次 否則拋異常
        //    除非流被設(shè)計(jì)成為顯示并發(fā)修改的流如ConcurrentHashMap 否則未期望或錯(cuò)誤的行為就會(huì)在執(zhí)行時(shí)產(chǎn)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(dá)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(guān)注的是對(duì)元素的管理與訪問
//    流不會(huì)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(jì)算執(zhí)行操作
//    如果流沒有提供預(yù)期的功能 可執(zhí)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(gè)元素的2倍 之和
//   此例中：Integer 每執(zhí)行一次reduce操作 觸發(fā) 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(shí)現(xiàn)AutoCloseable接口：
     *          使用try--with--resources 代碼塊 替代 try--catch--finally
     *          在代碼塊運(yùn)行完畢后 自動(dòng)實(shí)現(xiàn) 資源的關(guān)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(dāng)終止操作應(yīng)用于流時(shí) 判斷其是否并行
       *  當(dāng)執(zhí)行終止操作之后 執(zhí)行isParallel() 會(huì)得到不可預(yù)期的結(jié)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(gè)等價(jià)的串行流
       *     流本身已經(jīng)是串行 或 流的狀態(tài)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(gè)等價(jià)的并行流
       *     流本身已經(jīng)是并行 或 流的狀態(tài)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(gè)等價(jià)的無序流
       *     流本身已經(jīng)是無序 或 流的狀態(tài)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(gè)等價(jià)的流 有close handler
       *     close handler當(dāng)流close()方法調(diào)用時(shí)觸發(fā)
       *     調(diào)用順序：close handlers被添加先后順序
       *
       *     所有的close handlers都會(huì)被調(diào)用 即使出現(xiàn)了異常
       *     如果任意close handler拋出異常
       *             那么第一個(gè)異常會(huì)傳遞給調(diào)用段
       *             其他異常（剩余或被抑制）會(huì)傳遞給調(diào)用段
       *                     除非其中有與第一個(gè)異常相同的異常（相同對(duì)象）  因?yàn)橄嗤惓２荒芤种谱陨?       *
       * 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(guān)閉流 調(diào)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(cè)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(cè)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(cè)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