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 陈杨 */@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() {
    

一、流的定义

//    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

二、流的创建

//    流的创建：        //    Collection.stream()  Collection.parallelStream()

//    Stream.generate        System.out.println("-----------------------------------------\n");        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("-----------------------------------------\n");
    

三、对象引用流

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

四、流的计算

//    流的计算：    stream pipeline        //    To perform a computation, stream operations are composed into a  stream pipeline.

五、流管道组成

//    流管道组成：  源数据source-->数组、集合、生成器函数、IO通道等        //                 [0,n) 中间操作（intermediate operations） 一个流转换 为 另一个新流        //                 终止操作（terminal operation）产生一个结果 或有副作用（修改流中元素 属性或状态）        //    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)}).

六、流的消费

//    流的消费：  流中对于源数据的计算 有且仅有在终止操作触发时才会被调用        //               流中元素只有在被需要时才会被消费        //               lazy（惰性）: 如果没有终止操作 那么一系列的中间操作都不会被执行        //               stream流操作只会执行一次： stream中有一个容器 将所有中间操作打包 放入容器中        //               调用终止操作时 触发容器的链式中间操作 将流中每一个元素 应用于中间业务逻辑        //    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.

//    流创建后 只能被消费一次 否则抛异常        //    除非流被设计成为显示并发修改的流如ConcurrentHashMap 否则未期望或错误的行为就会在执行时产生        //    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

七、 Lambda表达式的正确行为

//    Lambda表达式的正确行为：        //    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).

八、流与集合

//    流与集合：//    集合关注的是对元素的管理与访问//    流不会直接提供直接访问或操作其元素的方法//    流提供声明性描述： 源 与 建立于源之上的聚合计算执行操作//    如果流没有提供预期的功能 可执行受控遍历（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.

九、 流的MapReduce操作

//   流的MapReduce操作  求集合 每个元素的2倍 之和//   此例中：Integer 每执行一次reduce操作 触发 该元素的map操作一次System.out.println(integerList.stream().map(i -> 2 * i).reduce(0, Integer::sum));System.out.println("-----------------------------------------\n");

十、流资源自动关闭 AutoCloseable接口实现

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 陈杨 */@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.     *     *      实现AutoCloseable接口：     *          使用try--with--resources 代码块 替代 try--catch--finally     *          在代码块运行完毕后 自动实现 资源的关闭     *      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();        }    }}

十一、认识BaseStream 与 closeHandler

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 陈杨 */@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(); * 当终止操作应用于流时 判断其是否并行 * 当执行终止操作之后 执行isParallel() 会得到不可预期的结果 * 此方法需适用于终止操作之前 * * 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(); * 返回一个等价的串行流 * 流本身已经是串行 或 流的状态已被修改为串行 * * 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(); * 返回一个等价的并行流 * 流本身已经是并行 或 流的状态已被修改为并行 * * 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(); * 返回一个等价的无序流 * 流本身已经是无序 或 流的状态已被修改为无序 * * 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(); * 返回一个等价的流 有close handler * close handler当流close()方法调用时触发 * 调用顺序：close handlers被添加先后顺序 * * 所有的close handlers都会被调用 即使出现了异常 * 如果任意close handler抛出异常 * 那么第一个异常会传递给调用段 * 其他异常（剩余或被抑制）会传递给调用段 * 除非其中有与第一个异常相同的异常（相同对象） 因为相同异常不能抑制自身 * * 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); * 关闭流 调用流管道中的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); } }}
          
         
        
       
      
     
    

十二、测试结果

testStreamDetail测试  .   ____          _            __ _ _ /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/  ___)| |_)| | | | | || (_| |  ) ) ) )  '  |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: 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:\IdeaProjects\design)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: default2019-02-20 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测试  .   ____          _            __ _ _ /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/  ___)| |_)| | | | | || (_| |  ) ) ) )  '  |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: 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:\IdeaProjects\design)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: default2019-02-20 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测试  .   ____          _            __ _ _ /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/  ___)| |_)| | | | | || (_| |  ) ) ) )  '  |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: 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:\IdeaProjects\design)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: default2019-02-20 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)KiritoAsunaIllyasvielSakuraclose handler firstclose handler secondclose handler thirdjava.lang.NullPointerException: my NullPointerExceptionProcess finished with exit code -1