摘要：一自定義收集器陳楊將集合轉(zhuǎn)換為集合存放相同元素二自定義收集器陳楊將學(xué)生對(duì)象按照存放從中間容器數(shù)據(jù)類型轉(zhuǎn)換為結(jié)果類型數(shù)據(jù)類型一致若不一致拋出類型轉(zhuǎn)換異常對(duì)中間容器數(shù)據(jù)結(jié)果類型進(jìn)行強(qiáng)制類型轉(zhuǎn)換多個(gè)線程同時(shí)操作同一個(gè)容器并行多線
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(zhuǎn)換為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(xué)生對(duì)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 從中間容器數(shù)據(jù)類型 轉(zhuǎn)換為 結(jié)果類型 數(shù)據(jù)類型一致
// 若不一致 拋出類型轉(zhuǎn)換異常 finisher對(duì)中間容器數(shù)據(jù)-->結(jié)果類型 進(jìn)行強(qiáng)制類型轉(zhuǎn)換
// Characteristics.CONCURRENT 多個(gè)線程同時(shí)操作同一個(gè)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 （多線程）并行流 操作 多個(gè)結(jié)果容器 --> 執(zhí)行combiner
// Characteristics.CONCURRENT + parallelStream 結(jié)果容器只有1個(gè) ---> 不執(zhí)行 combiner
// ConcurrentModificationException 并發(fā)修改異常
// 注意：并行情況下 累加器對(duì)結(jié)果容器執(zhí)行單一操作
// 不要在累加器返回的函數(shù)式接口實(shí)例中做額外的操作
// 不能打印集合類容 同時(shí)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(cè)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 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);
}*/
// 執(zhí)行流程 方法調(diào)用順序
// 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 注意強(qiáng)制類型轉(zhuǎn)換 （中間類型 與 返回結(jié)果類型）
// 注意強(qiáng)制類型轉(zhuǎn)換
/*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 打印結(jié)果
// supplier invoked!
// accumulator invoked!
// combiner invoked!
// characteristics invoked!
// characteristics invoked!
// Set集合對(duì)象
// EnumSet.of(Characteristics.UNORDERED)
// 不包含 IDENTITY_FINISH 打印結(jié)果
// supplier invoked!
// accumulator invoked!
// combiner invoked!
// characteristics invoked!
// characteristics invoked!
// finisher invoked!
// Set集合對(duì)象
}
四、StudentCustomCollectorTest測(cè)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 students;
@Before
public void init() {
students = new Students().init();
}
@Test
public void testStudentCustomCollectorTest() {
System.out.println("單線程");
Map sequentialMap = students.stream().collect(new StudentCustomCollector());
System.out.println("串行流執(zhí)行效果：
---------------------------------------
"+sequentialMap);
System.out.println("---------------------------------------
");
System.out.println("多線程");
Map parallelMap = students.parallelStream().collect(new StudentCustomCollector());
System.out.println("并行流執(zhí)行效果：
---------------------------------------
"+parallelMap);
System.out.println("---------------------------------------
");
}
}
五、測(cè)試結(jié)果
SetCustomCollectorTest測(cè)試結(jié)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測(cè)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: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)
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(zhí)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(zhí)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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