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 studentpublic 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：\n---------------------------------------\n"+sequentialMap);        System.out.println("---------------------------------------\n");        System.out.println("多线程");        Map
      
        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)}---------------------------------------