并行for循环

系统管理员 2023-02-11 10:28 8阅读 0赞

## 流式for循环 ##

private static void test1() { 
            ArrayList<String> arrayList = new ArrayList<>();
            for (int i = 0; i < 100; i++) { 
                arrayList.add(i + "");
            }
            arrayList.stream().forEach(e -> System.out.println(Thread.currentThread().getName() + " " + e));
        }

## 并行流式for循环 ##

private static void test2() { 
            ArrayList<String> arrayList = new ArrayList<>();
            for (int i = 0; i < 100; i++) { 
                arrayList.add(i + "");
            }
            arrayList.parallelStream().forEach(e -> System.out.println(Thread.currentThread().getName() + " " + e));
        }

## forkjoin 并行流式for循环 ##

private static final ForkJoinPool pool = new ForkJoinPool(5);
    
        private static void test3() { 
            ArrayList<String> arrayList = new ArrayList<>();
            for (int i = 0; i < 100; i++) { 
                arrayList.add(i + "");
            }
            pool.submit(() -> arrayList.parallelStream().forEach(e -> { 
                System.out.println(Thread.currentThread().getName() + " " + e);
            })).join();
        }

## 并行MAP ##

private static void test4() { 
            ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(100, 100, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingDeque<>(1));
            List<String> arrayList  =new ArrayList<>();
            for(int i = 0; i < 100; ++i){ 
                arrayList .add(i + "");
            }
            //开始前
            Map<String, String> resultMap = arrayList .parallelStream().collect(Collectors.toMap(t -> t, t -> { 
                try { 
                    threadPoolExecutor.submit(() -> t).get();
                } catch (Exception e) { 
                    log.error("异常：{}" + e.getMessage());
                }
                return "";
            }));
        }

## 优化并行MAP ##

private static void test5() { 
            ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(100, 100, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingDeque<>(1));
            List<String> arrayList  =new ArrayList<>();
            for(int i = 0; i < 100; ++i){ 
                arrayList .add(i + "");
            }
            //优化后
            Map<String, Future<String>> futureMap = arrayList.stream().collect(Collectors.toMap(t -> t, t -> threadPoolExecutor.submit(() -> t),(oldValue, newValue)->newValue));
            futureMap.entrySet().stream().collect(Collectors.toMap(e->e.getKey(),e->{ 
                try { 
                    e.getValue().get();
                }catch (Exception t) { 
                    log.error("异常：{}" + t.getMessage());
                }
                return "";
            }));
        }

## 执行 ##

public static void main(String[] args) { 
            test1();
            test2();
            test3();
            test4();
            test5();
        }

## 空处理方式 ##

return Optional.ofNullable();
    
    return Lists.newArrayList();
    
    implements DependencyBase, Nullable{ }
    
    extends Nullable{ }
    
    return Collections.emptyList();
    
    return empty();
    
    return null;
    
    return Optional.empty();
    
    return new NullObject();
    
    return new Object();
    
    return BigDecimal.ZERO;
     
    return Collections.emptyMap();
    
    return Collections.emptySet();