Stream流与Lambda表达式（四）自定义收集器

一、自定义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 陈杨 /// 将List集合转换为Set集合存放相同元素public class SetCustomCollector<T> implements Collector<T, Set<T>, Set<T>> { @Override public Supplier<Set<T>> supplier() { System.out.println(“supplier invoked!”); // return TreeSet::new; return HashSet::new; } @Override public BiConsumer<Set<T>, T> accumulator() { System.out.println(“accumulator invoked!”); return Set<T>::add; } @Override public BinaryOperator<Set<T>> combiner() { System.out.println(“combiner invoked!”); return (first, last) -> { first.addAll(last); return first; }; } @Override public Function<Set<T>, Set<T>> finisher() { System.out.println(“finisher invoked!”); return Function.identity(); } @Override public 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、自定义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 陈杨 /// 将学生对象按照HashMap<Integer,Student> 存放 sid studentpublic class StudentCustomCollector implements Collector<Student, List<Student>, Map<Integer, Student>> { @Override public Supplier<List<Student>> supplier() { System.out.println(“supplier invoked!”); return ArrayList::new; } @Override public BiConsumer<List<Student>, Student> accumulator() { System.out.println(“accumulator invoked!”); return (list, student) -> { System.out.println(“accumulator：” + Thread.currentThread().getName()); list.add(student); }; } @Override public BinaryOperator<List<Student>> combiner() { System.out.println(“combiner invoked!”); return (first, last) -> { first.addAll(last); return first; }; } @Override public 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; }; } @Override public Set<Characteristics> characteristics() { System.out.println(“Characteristics invoked!”); return Collections.unmodifiableSet(EnumSet.of(Characteristics.CONCURRENT)); } // Characteristics.IDENTITY_FINISH 从中间容器数据类型转换为结果类型数据类型一致 // 若不一致抛出类型转换异常 finisher对中间容器数据–>结果类型进行强制类型转换 // Characteristics.CONCURRENT 多个线程同时操作同一个容器 –> 并行 // Indicates that this collector is concurrent, meaning that // the result container can support the accumulator function being // called concurrently with the same result container from multiple threads. // parallelStream （多线程）并行流操作多个结果容器 –> 执行combiner // Characteristics.CONCURRENT + parallelStream 结果容器只有1个 —> 不执行 combiner // ConcurrentModificationException 并发修改异常 // 注意：并行情况下累加器对结果容器执行单一操作 // 不要在累加器返回的函数式接口实例中做额外的操作 // 不能打印集合类容同时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测试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 陈杨 /@SpringBootTest@RunWith(SpringRunner.class)public class SetCustomCollectorTest { private List<Student> students; @Before public void init() { students = new Students().init(); } @Test public 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 supplier = Objects.requireNonNull(collector).supplier(); BiConsumer<I, ? super T> accumulator = collector.accumulator(); BinaryOperator combiner = collector.combiner(); class ReducingSink extends Box implements AccumulatingSink<T, I, ReducingSink> { @Override public void begin(long size) { state = supplier.get(); } @Override public void accept(T t) { accumulator.accept(state, t); } @Override public void combine(ReducingSink other) { state = combiner.apply(state, other.state); } } return new ReduceOp<T, I, ReducingSink>(StreamShape.REFERENCE) { @Override public ReducingSink makeSink() { return new ReducingSink(); } @Override public 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); }/ // 执行流程方法调用顺序 // container = evaluate(ReduceOps.makeRef(collector)); // Supplier supplier = Objects.requireNonNull(collector).supplier(); // BiConsumer<I, ? super T> accumulator = collector.accumulator(); // BinaryOperator 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 注意强制类型转换（中间类型与返回结果类型） // 注意强制类型转换 /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 打印结果 // supplier invoked! // accumulator invoked! // combiner invoked! // characteristics invoked! // characteristics invoked! // Set<Student>集合对象 // EnumSet.of(Characteristics.UNORDERED) // 不包含 IDENTITY_FINISH 打印结果 // supplier invoked! // accumulator invoked! // combiner invoked! // characteristics invoked! // characteristics invoked! // finisher invoked! // Set<Student>集合对象}四、StudentCustomCollectorTest测试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 陈杨 */@SpringBootTest@RunWith(SpringRunner.class)public class StudentCustomCollectorTest { private List<Student> students; @Before public void init() { students = new Students().init(); } @Test public void testStudentCustomCollectorTest() { System.out.println(“单线程”); Map<Integer, Student> sequentialMap = students.stream().collect(new StudentCustomCollector()); System.out.println(“串行流执行效果：\n—————————————\n”+sequentialMap); System.out.println("—————————————\n"); System.out.println(“多线程”); Map<Integer, Student> parallelMap = students.parallelStream().collect(new StudentCustomCollector()); System.out.println(“并行流执行效果：\n—————————————\n”+parallelMap); System.out.println("—————————————\n"); }}五、测试结果 SetCustomCollectorTest测试结果 . ____ _ __ _ _ /\ / ’ __ _ () __ __ _ \ \ \ ( ( )__ | ‘_ | ‘| | ‘ / | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: 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: default2019-02-20 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测试 . ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _ | \ \ \ \ \/ )| |)| | | | | || (| | ) ) ) ) ’ || .__|| ||| |_, | / / / / =========||==============|/=//// :: 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: default2019-02-20 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)单线程supplier invoked!accumulator invoked!combiner invoked!Characteristics invoked!accumulator：mainaccumulator：mainaccumulator：mainaccumulator：mainaccumulator：mainCharacteristics invoked!finisher invoked!串行流执行效果：—————————————{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)}—————————————多线程Characteristics invoked!Characteristics invoked!supplier invoked!accumulator invoked!combiner invoked!Characteristics invoked!accumulator：mainaccumulator：ForkJoinPool.commonPool-worker-5accumulator：ForkJoinPool.commonPool-worker-5accumulator：ForkJoinPool.commonPool-worker-3accumulator：mainCharacteristics invoked!finisher invoked!并行流执行效果：—————————————{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)}—————————————