引子
为了让程序更加高效,让CPU最大效率的工作,我们会采用异步编程。首先想到的是开启一个新的线程去做某项工作。再进一步,为了让新线程可以返回一个值,告诉主线程事情做完了,于是乎Future粉墨登场。然而Future提供的方式是主线程主动问询新线程,要是有个回调函数就爽了。所以,为了满足Future的某些遗憾,强大的CompletableFuture随着Java8一起来了。
Future
传统多线程的却让程序更加高效,毕竟是异步,可以让CPU充分工作,但这仅限于新开的线程无需你的主线程再费心了。比如你开启的新线程仅仅是为了计算1+...+n再打印结果。有时候你需要子线程返回计算结果,在主线程中进行进一步计算,就需要Future了。
看下面这个例子,主线程计算2+4+6+8+10;子线程计算1+3+5+7+9;最后需要在主线程中将两部分结果再相加。
public class OddNumber implements Callable<Integer> {
@Override
public Integer call() throws Exception {
Thread.sleep(3000);
int result = 1 + 3 + 5 + 7 + 9;
return result;
}
}
public class FutureTest {
public static void main(String[] args) {
ExecutorService executor = Executors.newCachedThreadPool();
OddNumber oddNumber = new OddNumber();
Future<Integer> future = executor.submit(oddNumber);
long startTime = System.currentTimeMillis();
int evenNumber = 2 + 4 + 6 + 8 + 10;
try {
Thread.sleep(1000);
System.out.println("0.开始了:"+ (System.currentTimeMillis()-startTime) +"秒");
int oddNumberResult = future.get();//这时间会被阻塞
System.out.println("1+2+...+9+10="+(evenNumber+oddNumberResult));
System.out.println("1.开始了:"+ (System.currentTimeMillis()-startTime) +"秒");
} catch (Exception e) {
System.out.println(e);
}
}
}
输出结果:
0.开始了:1001秒
1+2+...+9+10=55
1.开始了:3002秒
看一下Future接口,只有五个方法比较简单
//取消任务,如果已经完成或者已经取消,就返回失败
boolean cancel(boolean mayInterruptIfRunning);
//查看任务是否取消
boolean isCancelled();
//查看任务是否完成
boolean isDone();
//刚才用到了,查看结果,任务未完成就一直阻塞
V get() throws InterruptedException, ExecutionException;
//同上,但是加了一个过期时间,防止长时间阻塞,主线程也做不了事情
V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
CompletableFuture
上面的看到Future的五个方法,不是很丰富,既然我们的主线程叫做main,就应该以我为主,我更希望子线程做完了事情主动通知我。为此,Java8带来了CompletableFuture,一个Future的实现类。其实CompletableFuture最迷人的地方并不是极大丰富了Future的功能,而是完美结合了Java8流的新特性。
实现回调,自动后续操作
提前说一下CompletableFuture实现回调的方法(之一):thenAccept()
public CompletableFuture<Void> thenAccept(Consumer<? super T> action) {
return uniAcceptStage(null, action);
}
参数有个Consumer,用到了Java8新特性,行为参数化,就是参数不一定是基本类型或者类,也可以是函数(行为),或者说一个方法(接口)。
public class OddNumberPlus implements Supplier<Integer> {
@Override
public Integer get() {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return 1+3+5+7+9;
}
}
public class CompletableFutureTest {
public static void main(String[] args) {
long startTime = System.currentTimeMillis();
final int evenNumber = 2 + 4 + 6 + 8 + 10;
CompletableFuture<Integer> oddNumber = CompletableFuture.supplyAsync(new OddNumberPlus());
try {
Thread.sleep(1000);
System.out.println("0.开始了:"+ (System.currentTimeMillis()-startTime) +"秒");
//看这里,实现回调
oddNumber.thenAccept(oddNumberResult->
{
System.out.println("1.开始了:"+ (System.currentTimeMillis()-startTime) +"秒");
System.out.println("此时计算结果为:"+(evenNumber+oddNumberResult));
});
oddNumber.get();
} catch (Exception e) {
System.out.println(e);
}
}
}
输出结果:
0.开始了:1006秒
1.开始了:3006秒
此时计算结果为:55
值得一提的是,本例中并没有显示的创建任务连接池,程序会默认选择一个任务连接池ForkJoinPool.commonPool()
private static final Executor asyncPool = useCommonPool ?
ForkJoinPool.commonPool() : new ThreadPerTaskExecutor();
ForkJoinPool始自JDK7,叫做分支/合并框架。可以通过将一个任务递归分成很多分子任务,形成不同的流,进行并行执行,同时还伴随着强大的工作窃取算法。极大的提高效率。当然,你也可以自己指定连接池。
CompletableFuture合并
Java8的确丰富了Future实现,CompletableFuture有很多方法可供大家使用,但是但从上面的例子来看,其实CompletableFuture能做的功能,貌似Future。毕竟你CompletableFuture用get()这个方法的时候还不是阻塞了,我Future蛮可以自己拿到返回值,再手动执行一些操作嘛(虽说这样main方法一定很不爽)。那么接下来的事情,Future做起来就十分麻烦了。假设我们main方法只做奇数合集加上偶数合集这一个操作,提前算这两个合集的操作异步交给两个子线程,我们需要怎么做呢?没错,开启两个线程,等到两个线程都计算结束的时候,我们进行最后的相加,问题在于,你怎么知道那个子线程最后结束的呢?(貌似可以做个轮询,不定的调用isDone()这个方法...)丰富的CompletableFuture功能为我们提供了一个方法,用于等待两个子线程都结束了,再进行相加操作:
//asyncPool就是上面提到的默认线程池ForkJoinPool
public <U,V> CompletableFuture<V> thenCombineAsync(
CompletionStage<? extends U> other,
BiFunction<? super T,? super U,? extends V> fn) {
return biApplyStage(asyncPool, other, fn);
}
看个例子:
public class OddCombine implements Supplier<Integer> {
@Override
public Integer get() {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return 1+3+5+7+9;
}
}
public class EvenCombine implements Supplier<Integer> {
@Override
public Integer get() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return 2+4+6+8+10;
}
}
public class CompletableCombineTest {
public static void main(String[] args) throws Exception{
CompletableFuture<Integer> oddNumber = CompletableFuture.supplyAsync(new OddCombine());
CompletableFuture<Integer> evenNumber = CompletableFuture.supplyAsync(new EvenCombine());
long startTime = System.currentTimeMillis();
CompletableFuture<Integer> resultFuturn = oddNumber.thenCombine(evenNumber,(odd,even)->{
return odd + even;
});
System.out.println(resultFuturn.get());
System.out.println("0.开始了:"+ (System.currentTimeMillis()-startTime) +"秒");
}
}
输出结果:
55
0.开始了:3000秒
这边模拟一个睡1秒,一个睡3秒,但是真正的网络请求时间是不定的。是不是很爽,最爽的还不是现象,而是以上操作已经利用了Java8流的概念。
两个子线程还不够,那么还有**anyOff()**函数,可以承受多个CompletableFuture,会等待所有任务都完成。
public static CompletableFuture<Void> allOf(CompletableFuture<?>... cfs) {
return andTree(cfs, 0, cfs.length - 1);
}
与它长的很像的,有个方法,是当第一个执行结束的时候,就结束,后面任务不再等了,可以看作充分条件。
public static CompletableFuture<Object> anyOf(CompletableFuture<?>... cfs) {
return orTree(cfs, 0, cfs.length - 1);
}
在上面那个例子的基础上,把OddNumberPlus类时间调长一点:
public class OddNumberPlus implements Supplier<Integer> {
@Override
public Integer get() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return 1+3+5+7+9;
}
}
public class CompletableCombineTest {
public static void main(String[] args) throws Exception{
CompletableFuture<Integer> oddNumber = CompletableFuture.supplyAsync(new OddCombine());
CompletableFuture<Integer> evenNumber = CompletableFuture.supplyAsync(new EvenCombine());
CompletableFuture<Integer> testNumber = CompletableFuture.supplyAsync(new OddNumberPlus());
long startTime = System.currentTimeMillis();
CompletableFuture<Object> resultFuturn = CompletableFuture.anyOf(oddNumber,evenNumber,testNumber);
System.out.println(resultFuturn.get());
System.out.println("0.开始了:"+ (System.currentTimeMillis()-startTime) +"秒");
}
}
输出结果:
30
0.开始了:1000秒
实战:异步统计首页报表数据
/**
* 统计首页报表数据
* zfq
*/
@RequiresPermissions("udef:defWorksheet:view")
@ResponseBody
@RequestMapping(value = "homeReport")
public String findAjaxNum( HttpServletRequest request) {
Map<String,Object> resultMap=new HashMap<>();
User user = UserUtils.getUser();
List<Role> roleList = user.getRoleList();
Role role=new Role();
role.setId("");
roleList.contains(role);
String formRequest = request.getParameter("homeReportParameter");
String dsf = defWorksheetService.wkstDataScopeFilter(user.getCurrentUser(), "off", "u");
CompletableFuture<List<DefWorksheet>> todayAllNumFuture=null;//今日运维境况
CompletableFuture<Integer> yearAllNumFuture=null; //全年工单总量
CompletableFuture<Integer> yearFinishNumFuture=null;//全年工单完成量
CompletableFuture<List<DefWorksheet>> groupByMonthFuture=null;//月工单量统计
CompletableFuture<List<DefWorksheet>> groupByTypeFuture=null;//工单分类统计
CompletableFuture<List<DefWorksheet>> groupByMonthDayFuture=null;//工单分类统计
/*
Integer yearFinishNum=0;
Integer yearAllNum=0;
List<DefWorksheet> groupByTypeWorksheetList=new ArrayList<>();
List<DefWorksheet> groupByMonthDayWorksheetList=new ArrayList<>();
List<DefWorksheet> groupByMonthWorksheetList=new ArrayList<>();
List<DefWorksheet> todayAllNumWorksheetList=new ArrayList<>();
List<CompletableFuture> futureList=new ArrayList<>();*/
if(formRequest.contains("todayNum")) {
DefWorksheet defWorksheet=new DefWorksheet();
defWorksheet.getSqlMap().put("dsf",dsf);
defWorksheet.setBeginCreateDate(DateUtils.getDayStartTime(new Date()));
defWorksheet.setEndCreateDate(new Date());
defWorksheet.setWorksheetState(null);
todayAllNumFuture = CompletableFuture.supplyAsync(() -> defWorksheetService.findWorksheetStateCount(defWorksheet));
//futureList.add(todayAllNumFuture);
}
if(formRequest.contains("yearAllNum")){
DefWorksheet defWorksheet=new DefWorksheet();
defWorksheet.getSqlMap().put("dsf",dsf);
defWorksheet.setBeginCreateDate(DateUtils.getCurrYearFirst());
defWorksheet.setEndCreateDate(new Date());
defWorksheet.setWorksheetState(null);//全年运维工单总量
yearAllNumFuture = CompletableFuture.supplyAsync(() -> defWorksheetService.findYearCount(defWorksheet));
//futureList.add(yearAllNumFuture);
DefWorksheet defFinishWorksheet=new DefWorksheet();
defFinishWorksheet.getSqlMap().put("dsf",dsf);
defFinishWorksheet.setBeginCreateDate(DateUtils.getCurrYearFirst());
defFinishWorksheet.setEndCreateDate(new Date());
defFinishWorksheet.setWorksheetState(null);//全年运维工单总量
defFinishWorksheet.setWorksheetState(8);//全年工单完成总量
yearFinishNumFuture = CompletableFuture.supplyAsync(() -> defWorksheetService.findYearCount(defFinishWorksheet));
//futureList.add(yearFinishNumFuture);
}
if(formRequest.contains("groupByMonthNum")){
DefWorksheet defWorksheet=new DefWorksheet();
defWorksheet.getSqlMap().put("dsf",dsf);
defWorksheet.setBeginCreateDate(DateUtils.getBeforeMonthDate(new Date(),12));
defWorksheet.setEndCreateDate(new Date());
defWorksheet.setWorksheetState(null);//全年运维工单总量
groupByMonthFuture = CompletableFuture.supplyAsync(() -> defWorksheetService.groupByMonthNum(defWorksheet));
//futureList.add(groupByMonthFuture);
}
if(formRequest.contains("groupByWorksheetType")){
DefWorksheet defWorksheet=new DefWorksheet();
defWorksheet.getSqlMap().put("dsf",dsf);
defWorksheet.setBeginCreateDate(DateUtils.getmindate());
defWorksheet.setEndCreateDate(new Date());
defWorksheet.setWorksheetState(null);//本月工单分类统计
groupByTypeFuture = CompletableFuture.supplyAsync(() -> defWorksheetService.groupByWorksheetType(defWorksheet));
//futureList.add(groupByTypeFuture);
}
if(formRequest.contains("groupByMonthDayNum")){
DefWorksheet defWorksheet=new DefWorksheet();
defWorksheet.getSqlMap().put("dsf",dsf);
defWorksheet.setBeginCreateDate(DateUtils.getmindate());
defWorksheet.setEndCreateDate(new Date());
defWorksheet.setWorksheetState(null);//全年运维工单总量
groupByMonthDayFuture= CompletableFuture.supplyAsync(() -> defWorksheetService.groupByMonthDayNum(defWorksheet));
//futureList.add(groupByMonthDayFuture);
}
//CompletableFuture[] allFutureTask = new CompletableFuture[futureList.size()];
//futureList.toArray(allFutureTask);
/* if(todayAllNumFuture!=null&&yearAllNumFuture!=null &&yearFinishNumFuture!=null
&&groupByMonthFuture!=null&& groupByTypeFuture!=null&& groupByMonthDayFuture!=null){*/
//CompletableFuture.allOf(todayAllNumFuture,yearAllNumFuture,yearFinishNumFuture,groupByMonthFuture,groupByTypeFuture,groupByMonthDayFuture).join();
//}
//CompletableFuture.allOf(allFutureTask);
//CompletableFuture.allOf(yearAllNumFuture).join();
if(formRequest.contains("todayNum")){
List<DefWorksheet> todayAllNumWorksheetList = todayAllNumFuture.join();
AtomicReference<Integer> todayRegisterNum= new AtomicReference<>(0);
AtomicReference<Integer> todayHandleNum= new AtomicReference<>(0);
AtomicReference<Integer> todayFinishNum=new AtomicReference<>(0);
AtomicReference<Integer> todayTobeClaimedNum=new AtomicReference<>(0);
if(todayAllNumWorksheetList.size()>0){
resultMap.put("todayAllNum",todayAllNumWorksheetList.size());
todayAllNumWorksheetList.stream().forEach(defWorksheetD ->{
if(defWorksheetD.getWorksheetState()==-1){
todayRegisterNum.updateAndGet(v -> v + 1);
}else if(defWorksheetD.getWorksheetState()==3){
todayHandleNum.updateAndGet(v -> v + 1);
}else if(defWorksheetD.getWorksheetState()==8){
todayFinishNum.updateAndGet(v -> v + 1);
}else if(defWorksheetD.getWorksheetState()==2){
todayTobeClaimedNum.updateAndGet(v -> v + 1);
}
});
}
resultMap.put("todayRegisterNum",todayRegisterNum);
resultMap.put("todayHandleNum",todayHandleNum);
resultMap.put("todayFinishNum",todayFinishNum);
resultMap.put("todayTobeClaimedNum",todayTobeClaimedNum);
}
if(formRequest.contains("yearAllNum")){
Integer yearAllNum=yearAllNumFuture.join();
resultMap.put("yearAllNum",yearAllNum);
Integer yearFinishNum =yearFinishNumFuture.join();
resultMap.put("yearFinishNum",yearFinishNum);
}
if(formRequest.contains("groupByMonthNum")){
List<DefWorksheet> groupByMonthWorksheetList=groupByMonthFuture.join();
List<Object> resultList=new ArrayList<>();
List<String> months=new ArrayList<>();
List<Integer> integers=new ArrayList<>();
groupByMonthWorksheetList.stream().forEach(defWorksheetD ->{
months.add(defWorksheetD.getGroupDate());
integers.add(defWorksheetD.getCountValue());
});
resultList.add(months);
resultList.add(integers);
resultMap.put("groupByMonthNum",resultList);
}
if(formRequest.contains("groupByWorksheetType")){
List<Object> resultList=new ArrayList<>();
List<DefWorksheet> groupByTypeWorksheetList= groupByTypeFuture.join();
groupByTypeWorksheetList.stream().forEach(defWorksheetD ->{
Map<String,Object> mapData=new HashMap<>();
String name="";
if(StringUtils.isBlank(defWorksheetD.getQsType1())){
name="未选择";
}else{
name=BasicTreeUtils.getBasicTreeLabel(defWorksheetD.getQsType1(),"sys_basicTree_gong_dan_fen_lei","");
}
mapData.put("name",name);
mapData.put("value",defWorksheetD.getCountValue());
resultList.add(mapData);
});
resultMap.put("groupByWorksheetType",resultList);
}
if(formRequest.contains("groupByMonthDayNum")){
List<DefWorksheet> groupByMonthDayWorksheetList=groupByMonthDayFuture.join();
List<Object> resultList=new ArrayList<>();
List<String> months=new ArrayList<>();
List<Integer> integers=new ArrayList<>();
groupByMonthDayWorksheetList.stream().forEach(defWorksheetD ->{
String substringDate = defWorksheetD.getGroupDate().substring(defWorksheetD.getGroupDate().length() - 2);
System.out.println(substringDate);
months.add(substringDate);
integers.add(defWorksheetD.getCountValue());
});
resultList.add(months);
resultList.add(integers);
resultMap.put("groupByMonthDayNum",resultList);
}
return JsonMapper.toJsonString(resultMap);
}
本此实战完全是为了用而用,场景并不太好
其实前台ajax异步请求就是并行的,增加这个 异步并行的 CompletableFuture无非就就是把多个ajax请求放到一起再返回,
一定要说快到哪了,就是节省了请求和响应时间
CompletableFuture常用的方法总结
//比较特殊,他入参就是返回值,也就是说他可以用来执行需要其他返回值的异步任务。
public static <U> CompletableFuture<U> completedFuture(U value)
//无返回值,使用默认线程池
public static CompletableFuture<Void> runAsync(Runnable runnable)
//无返回值,使用自定义线程池
public static CompletableFuture<Void> runAsync(Runnable runnable, Executor executor)
//有返回值,使用默认线程池
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)
//有返回值,使用自定义线程池
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier, Executor executor)
//等待全部任务都结束,线程任务才全部结束
public static CompletableFuture<Void> allOf(CompletableFuture<?>... cfs
//任何一个任务结束,线程任务全部结束
public static CompletableFuture<Object> anyOf(CompletableFuture<?>... cfs)
join()和get() 和getNow(T valueIfAbsent) 都是获取返回结果调用
1.join()方法抛出的是uncheck异常(即未经检查的异常),不会强制开发者抛出,
会将异常包装成CompletionException异常 /CancellationException异常,但是本质原因还是代码内存在的真正的异常,
2.get()方法抛出的是经过检查的异常,ExecutionException, InterruptedException 需要用户手动处理(抛出或者 try catch,
3.join() 和get()阻塞获取结果 都会一定拿到返回结果,除非异常
getNow() 是非阻塞的,尝试获取结果,不一定能拿得到
其它方法参考 java8 CompletableFuture入门 使用教程 详解所有方法 附实例
小结
CompletableFuture的方法其实还有很多,常用的比如说runAsync(),类似于supplyAsync(),只是没有返回值;除了thenApply()可以加回调函数以外,还有thenApply();还有注入runAfterBoth()、runAfterEither(),这些见名知意。还有很多,可以点开CompletableFuture这个类的源码仔细看一看。见微知著,透过CompletableFuture,更加感觉到Java8的强大,强大的流概念、行为参数化、高效的并行理念等等,不仅让Java写起来更爽,还不断丰富Java整个生态。Java一直在进步,所以没有被时代淘汰,我们Javaer也可以继续职业生涯,感谢Java,一起进步。