Stream流與Lambda表達式（四）自定義收集器

一、自定義SetCustomCollector收集器

package com.java.design.Stream.CustomCollector;import java.util.*;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;/*** @author 陳楊*///  將List集合轉換為Set集合 存放相同元素
public class SetCustomCollector<T> implements Collector<T, Set<T>, Set<T>> {@Overridepublic Supplier<Set<T>> supplier() {System.out.println("supplier      invoked!");//  return TreeSet::new;return HashSet::new;}@Overridepublic BiConsumer<Set<T>, T> accumulator() {System.out.println("accumulator      invoked!");return Set<T>::add;}@Overridepublic BinaryOperator<Set<T>> combiner() {System.out.println("combiner      invoked!");return (first, last) -> {first.addAll(last);return first;};}@Overridepublic Function<Set<T>, Set<T>> finisher() {System.out.println("finisher      invoked!");return Function.identity();}@Overridepublic Set<Characteristics> characteristics() {System.out.println("characteristics      invoked!");return Collections.unmodifiableSet(EnumSet.of(Characteristics.IDENTITY_FINISH, Characteristics.UNORDERED));//  return Collections.unmodifiableSet(EnumSet.of(Characteristics.UNORDERED));}}

二、自定義StudentCustomCollector收集器

package com.java.design.Stream.CustomCollector;import com.java.design.java8.entity.Student;import java.util.*;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;/*** @author 陳楊*/// 將學生對象 按照HashMap<Integer,Student> 存放 sid student
public class StudentCustomCollector implements Collector<Student, List<Student>, Map<Integer, Student>> {@Overridepublic Supplier<List<Student>> supplier() {System.out.println("supplier      invoked!");return ArrayList::new;}@Overridepublic BiConsumer<List<Student>, Student> accumulator() {System.out.println("accumulator      invoked!");return (list, student) -> {System.out.println("accumulator：" + Thread.currentThread().getName());list.add(student);};}@Overridepublic BinaryOperator<List<Student>> combiner() {System.out.println("combiner      invoked!");return (first, last) -> {first.addAll(last);return first;};}@Overridepublic Function<List<Student>, Map<Integer, Student>> finisher() {System.out.println("finisher      invoked!");return list -> {Map<Integer, Student> map = new HashMap<>();list.forEach(student -> map.put(student.getId(), student));return map;};}@Overridepublic Set<Characteristics> characteristics() {System.out.println("Characteristics      invoked!");return Collections.unmodifiableSet(EnumSet.of(Characteristics.CONCURRENT));}//    Characteristics.IDENTITY_FINISH 從中間容器數據類型 轉換為 結果類型 數據類型一致//         若不一致 拋出類型轉換異常 finisher對中間容器數據-->結果類型 進行強制類型轉換//    Characteristics.CONCURRENT  多個線程同時操作同一個容器 --> 并行//          Indicates that this collector is <em>concurrent</em>, meaning that//          the result container can support the accumulator function being//          called concurrently with the same result container from multiple threads.//    parallelStream （多線程）并行流 操作 多個結果容器  -->  執行combiner//    Characteristics.CONCURRENT +  parallelStream  結果容器只有1個  ---> 不執行 combiner//    ConcurrentModificationException  并發修改異常//             注意：并行情況下 累加器對結果容器執行單一操作//                  不要在累加器返回的函數式接口實例中做額外的操作//                        不能打印集合類容 同時向集合里添加新元素//                          This exception may be thrown by methods that have detected concurrent//                          modification of an object when such modification is not permissible
}

三、SetCustomCollectorTest測試

package com.java.design.java8.Stream.CustomCollector;import com.java.design.Stream.CustomCollector.SetCustomCollector;
import com.java.design.java8.entity.Student;
import com.java.design.java8.entity.Students;
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.List;
import java.util.Set;/*** @author 陳楊*/@SpringBootTest
@RunWith(SpringRunner.class)
public class SetCustomCollectorTest {private List<Student> students;@Beforepublic void init() {students = new Students().init();}@Testpublic void testSetCustomCollector() {Set<Student> set = students.stream().collect(new SetCustomCollector<>());System.out.println(set);}/*public static <T, I> TerminalOp<T, I>makeRef(Collector<? super T, I, ?> collector) {Supplier<I> supplier = Objects.requireNonNull(collector).supplier();BiConsumer<I, ? super T> accumulator = collector.accumulator();BinaryOperator<I> combiner = collector.combiner();class ReducingSink extends Box<I>implements AccumulatingSink<T, I, ReducingSink> {@Overridepublic void begin(long size) {state = supplier.get();}@Overridepublic void accept(T t) {accumulator.accept(state, t);}@Overridepublic void combine(ReducingSink other) {state = combiner.apply(state, other.state);}}return new ReduceOp<T, I, ReducingSink>(StreamShape.REFERENCE) {@Overridepublic ReducingSink makeSink() {return new ReducingSink();}@Overridepublic int getOpFlags() {return collector.characteristics().contains(Collector.Characteristics.UNORDERED)? StreamOpFlag.NOT_ORDERED: 0;}};}*//*public final <R, A> R collect(Collector<? super P_OUT, A, R> collector) {A container;if (isParallel()&& (collector.characteristics().contains(Collector.Characteristics.CONCURRENT))&& (!isOrdered() || collector.characteristics().contains(Collector.Characteristics.UNORDERED))) {container = collector.supplier().get();BiConsumer<A, ? super P_OUT> accumulator = collector.accumulator();forEach(u -> accumulator.accept(container, u));}else {container = evaluate(ReduceOps.makeRef(collector));}return collector.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)? (R) container: collector.finisher().apply(container);}*///    執行流程   方法調用順序//    container = evaluate(ReduceOps.makeRef(collector));//    Supplier<I> supplier = Objects.requireNonNull(collector).supplier();//    BiConsumer<I, ? super T> accumulator = collector.accumulator();//    BinaryOperator<I> combiner = collector.combiner();//    return collector.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)是否有序//    return collector.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)是否包含IDENTITY_FINISH//     ? (R) container  注意強制類型轉換  （中間類型 與 返回結果類型）//    注意強制類型轉換/*CollectorImpl(Supplier<A> supplier,BiConsumer<A, T> accumulator,BinaryOperator<A> combiner,Set<Characteristics> characteristics) {this(supplier, accumulator, combiner, castingIdentity(), characteristics);}@SuppressWarnings("unchecked")private static <I, R> Function<I, R> castingIdentity() {return i -> (R) i;}*///    EnumSet.of(Characteristics.IDENTITY_FINISH, Characteristics.UNORDERED)//    包含 IDENTITY_FINISH 打印結果//    supplier      invoked!//    accumulator      invoked!//    combiner      invoked!//    characteristics      invoked!//    characteristics      invoked!//    Set<Student>集合對象//    EnumSet.of(Characteristics.UNORDERED)//    不包含 IDENTITY_FINISH 打印結果//    supplier      invoked!//    accumulator      invoked!//    combiner      invoked!//    characteristics      invoked!//    characteristics      invoked!//    finisher      invoked!//    Set<Student>集合對象}

四、StudentCustomCollectorTest測試

package com.java.design.java8.Stream.CustomCollector;import com.java.design.Stream.CustomCollector.StudentCustomCollector;
import com.java.design.java8.entity.Student;
import com.java.design.java8.entity.Students;
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.List;
import java.util.Map;/*** @author 陳楊*/@SpringBootTest
@RunWith(SpringRunner.class)
public class StudentCustomCollectorTest {private List<Student> students;@Beforepublic void init() {students = new Students().init();}@Testpublic void testStudentCustomCollectorTest() {System.out.println("單線程");Map<Integer, Student> sequentialMap = students.stream().collect(new StudentCustomCollector());System.out.println("串行流執行效果：\n---------------------------------------\n"+sequentialMap);System.out.println("---------------------------------------\n");System.out.println("多線程");Map<Integer, Student> parallelMap = students.parallelStream().collect(new StudentCustomCollector());System.out.println("并行流執行效果：\n---------------------------------------\n"+parallelMap);System.out.println("---------------------------------------\n");}}

五、測試結果

 SetCustomCollectorTest測試結果.   ____          _            __ _ _/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/  ___)| |_)| | | | | || (_| |  ) ) ) )'  |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot ::        (v2.1.2.RELEASE)2019-02-20 17:14:45.547  INFO 3260 --- [           main] c.j.d.j.S.C.SetCustomCollectorTest       : Starting SetCustomCollectorTest on DESKTOP-87RMBG4 with PID 3260 (started by 46250 in E:\IdeaProjects\design)
2019-02-20 17:14:45.548  INFO 3260 --- [           main] c.j.d.j.S.C.SetCustomCollectorTest       : No active profile set, falling back to default profiles: default
2019-02-20 17:14:46.055  INFO 3260 --- [           main] c.j.d.j.S.C.SetCustomCollectorTest       : Started SetCustomCollectorTest in 0.686 seconds (JVM running for 1.43)
supplier      invoked!
accumulator      invoked!
combiner      invoked!
characteristics      invoked!
characteristics      invoked!
[Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8), Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8), Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8), Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8), Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8)]

 StudentCustomCollectorTest測試.   ____          _            __ _ _/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/  ___)| |_)| | | | | || (_| |  ) ) ) )'  |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot ::        (v2.1.2.RELEASE)2019-02-20 17:15:52.817  INFO 3292 --- [           main] c.j.d.j.S.C.StudentCustomCollectorTest   : Starting StudentCustomCollectorTest on DESKTOP-87RMBG4 with PID 3292 (started by 46250 in E:\IdeaProjects\design)
2019-02-20 17:15:52.818  INFO 3292 --- [           main] c.j.d.j.S.C.StudentCustomCollectorTest   : No active profile set, falling back to default profiles: default
2019-02-20 17:15:53.354  INFO 3292 --- [           main] c.j.d.j.S.C.StudentCustomCollectorTest   : Started StudentCustomCollectorTest in 0.745 seconds (JVM running for 1.439)
單線程
supplier      invoked!
accumulator      invoked!
combiner      invoked!
Characteristics      invoked!
accumulator：main
accumulator：main
accumulator：main
accumulator：main
accumulator：main
Characteristics      invoked!
finisher      invoked!
串行流執行效果：
---------------------------------------
{1=Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8), 2=Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8), 3=Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8), 4=Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8), 5=Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)}
---------------------------------------多線程
Characteristics      invoked!
Characteristics      invoked!
supplier      invoked!
accumulator      invoked!
combiner      invoked!
Characteristics      invoked!
accumulator：main
accumulator：ForkJoinPool.commonPool-worker-5
accumulator：ForkJoinPool.commonPool-worker-5
accumulator：ForkJoinPool.commonPool-worker-3
accumulator：main
Characteristics      invoked!
finisher      invoked!
并行流執行效果：
---------------------------------------
{1=Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8), 2=Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8), 3=Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8), 4=Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8), 5=Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)}
---------------------------------------