摘要：一自定义收集器陈杨将集合转换为集合存放相同元素二自定义收集器陈杨将学生对象按照存放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对中间容器数据结果类型进行强制类型转换多个线程同时操作同一个容器并行多线
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 implements Collector, Set> {
@Override
public Supplier> supplier() {
System.out.println("supplier invoked!");
// return TreeSet::new;
return HashSet::new;
}
@Override
public BiConsumer, T> accumulator() {
System.out.println("accumulator invoked!");
return Set::add;
}
@Override
public BinaryOperator> combiner() {
System.out.println("combiner invoked!");
return (first, last) -> {
first.addAll(last);
return first;
};
}
@Override
public Function, Set> finisher() {
System.out.println("finisher invoked!");
return Function.identity();
}
@Override
public Set 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 存放 sid student
public class StudentCustomCollector implements Collector, Map> {
@Override
public Supplier> supplier() {
System.out.println("supplier invoked!");
return ArrayList::new;
}
@Override
public BiConsumer, Student> accumulator() {
System.out.println("accumulator invoked!");
return (list, student) -> {
System.out.println("accumulator：" + Thread.currentThread().getName());
list.add(student);
};
}
@Override
public BinaryOperator> combiner() {
System.out.println("combiner invoked!");
return (first, last) -> {
first.addAll(last);
return first;
};
}
@Override
public Function, Map> finisher() {
System.out.println("finisher invoked!");
return list -> {
Map map = new HashMap<>();
list.forEach(student -> map.put(student.getId(), student));
return map;
};
}
@Override
public Set 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 students;
@Before
public void init() {
students = new Students().init();
}
@Test
public void testSetCustomCollector() {
Set set = students.stream().collect(new SetCustomCollector<>());
System.out.println(set);
}
/*public static TerminalOp
makeRef(Collector collector) {
Supplier supplier = Objects.requireNonNull(collector).supplier();
BiConsumer accumulator = collector.accumulator();
BinaryOperator combiner = collector.combiner();
class ReducingSink extends Box
implements AccumulatingSink {
@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(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 collect(Collector collector) {
A container;
if (isParallel()
&& (collector.characteristics().contains(Collector.Characteristics.CONCURRENT))
&& (!isOrdered() || collector.characteristics().contains(Collector.Characteristics.UNORDERED))) {
container = collector.supplier().get();
BiConsumer 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 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 supplier,
BiConsumer accumulator,
BinaryOperator combiner,
Set characteristics) {
this(supplier, accumulator, combiner, castingIdentity(), characteristics);
}
@SuppressWarnings("unchecked")
private static Function 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 students;
@Before
public void init() {
students = new Students().init();
}
@Test
public void testStudentCustomCollectorTest() {
System.out.println("单线程");
Map sequentialMap = students.stream().collect(new StudentCustomCollector());
System.out.println("串行流执行效果：
---------------------------------------
"+sequentialMap);
System.out.println("---------------------------------------
");
System.out.println("多线程");
Map parallelMap = students.parallelStream().collect(new StudentCustomCollector());
System.out.println("并行流执行效果：
---------------------------------------
"+parallelMap);
System.out.println("---------------------------------------
");
}
}
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:IdeaProjectsdesign)
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:IdeaProjectsdesign)
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)
单线程
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：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)}
---------------------------------------
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