stream | 易学教程

JAVA8新特性之：Stream 详解

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【推荐阅读】微服务还能火多久？>>> Java 8 中的 Stream 是对集合（Collection）对象功能的增强，它专注于对集合对象进行各种非常便利、高效的聚合操作（aggregate operation），或者大批量数据操作 (bulk data operation)。 Stream代表数据流，流中的数据元素的数量可能是有限的，也可能是无限的。 Stream和其它集合类的区别在于：其它集合类主要关注与有限数量的数据的访问和有效管理(增删改)，而Stream并没有提供访问和管理元素的方式，而是通过声明数据源的方式，利用可计算的操作在数据源上执行，当然 BaseStream.iterator() 和 BaseStream.spliterator() 操作提供了遍历元素的方法。 Java Stream提供了提供了串行和并行两种类型的流，保持一致的接口，提供函数式编程方式，以管道方式提供中间操作和最终执行操作，为Java语言的集合提供了现代语言提供的类似的高阶函数操作，简化和提高了Java集合的功能。 Stream接口还包含几个基本类型的子接口如IntStream, LongStream 和 DoubleStream。关于流和其它集合具体的区别，可以参照下面的列表：不存储数据。流是基于数据源的对象，它本身不存储数据元素，而是通过管道将数据源的元素传递给操作。函数式编程

How do I handle character encoding for stdout stream of (cli) output in/from node.js?

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问题 I am confused about how to safely store and read the process.stdout output in Node.js: Is the CLI output of console.log() (and such) done in a specific character encoding? Or is it raw binary of unspecified form? Can there be binary data? (I have no idea) Node.js is very utf8 oriented, but then JS is UCS2 and I have no idea what the stream does with it. And related: is it safe to apply a string-diff to the stream if I convert the Buffer to String in utf8 (the default)? Note my diff renderer

Read HttpContent stream until a character limit using StreamReader

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问题 I am trying to convert the following code that reads the complete string response of a HttpContent into a string, to read only a certain maximum number of characters. Existing code: private static async Task<string> GetContentStringAsync(HttpContent content) { string responseContent = await content.ReadAsStringAsync().ConfigureAwait(false); return responseContent; } Code that I have now: private static async Task<string> GetContentStringAsync(HttpContent content, int ResponseContentMaxLength)

Given a recursive function, how do I change it to tail recursive and streams?

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问题 Given a recursive function in scheme how do I change that function to tail recursive, and then how would I implement it using streams? Are there patterns and rules that you follow when changing any function in this way? Take this function as an example which creates a list of numbers from 2-m (this is not tail recursive?) Code: (define listupto (lambda (m) (if (= m 2) '(2) (append (listupto (- m 1)) (list m))))) 回答1: I'll start off by explaining your example. It is definitely not tail

Dart yield stream events from another stream listener

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问题 I have a function that generates stream of specific events. Now I have a stream coming from storage service which has its own events. Looking for a way to yield my events when something changes in the storage stream . This code snippet doesn't do the trick. Stream<BlocState> mapEventToState( BlocEvent event, ) async* { if (event is UploadData) { yield UploadDataProgress(progress: 0.0); final Storage storage = Storage(); final Stream<StorageEvent> upload = storage.upload(event.data); upload

How to subscribe to changes in DynamoDB

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问题 I don't know how to subscribe to changes in DynamoDB database. Let me show an example: User A sends a message (which is saved in the database) to User B and in the User B's app the message automatically appears. I know this is possible with recently released AWS AppSync, but I couldn't integrate it with Ionic (which I am using). However, there must be an alternative since AWS AppSync was released only at the end of 2017/beginning of 2018. I've also seen something called Streams in DynamoDB

How to subscribe to changes in DynamoDB

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The component cannot be found. (Exception from HRESULT: 0x88982F50)

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问题 The above exception occurs at line await bitmapImage.SetSourceAsync(fileStream); whenever I tried to retrieve image from local file. This is the method I'm using for storing and retrieving the image file. public async Task<BitmapImage> RetrieveImageFromFile(String fileName) { try { StorageFile localFile = await _storageFolder.GetFileAsync(fileName + "Img"); BitmapImage bitmapImage = new BitmapImage(); using (IRandomAccessStream fileStream = await localFile.OpenAsync(FileAccessMode.Read)) {

Java class loader bug: Caused by: java.io.IOException: Stream closed

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问题 I'm getting a strange bug regarding I believe class loader issues when I deploy my webapp to Tomcat. The bug doesn't appear when I run my webapp locally using Jetty. It seems like my input streams for my .yml resource files are being closed for some reason when they shouldn't be. This bug first appeared when I tried to convert my single module project into a multi module project. Before that, it was working fine on Tomcat using the exact same code: Caused by: org.yaml.snakeyaml.error

gulp中如何保证任务执行顺序。

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某厂面试归来，发现自己落伍了！>>> 举一个简单了例子： gulp.task('task2',function(){ setTimeout(function(){ console.log("task2 has been completed") },3000) }) gulp.task('task1',['task2'],function(){ console.log("task1 has been completed") }) 在命令行中执行gulp task1 通过命令行的任务流程，我们可以看出，任务并没有像我们想象的那样运行。这是因为在gulp中，所有task都是异步执行的，那么此时我们需要引入q模块来帮助我们解决这个问题。通过命令行输入gulp install q --save-dev来安装q模块 var Q = require('q'); var Q = require('q'); gulp.task('task2',function(){ var deferred = Q.defer(); setTimeout(function(){ console.log("task2 has been completed") deferred.resolve(); },3000) return deferred.promise; }) gulp.task('task1',[