bytebuffer | 易学教程

网络编程之NIO

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概述：网络编程IO主要分为：同步、异步、阻塞、非阻塞。在Java1.4之前的I/O系统中，提供的都是面向流的I/O系统，系统一次一个字节地处理数据，一个输入流产生一个字节的数据，一个输出流消费一个字节的数据，面向流的I/O速度非常慢，而在Java 1.4中推出了NIO，这是一个面向块的I/O系统，系统以块的方式处理处理，每一个操作在一步中产生或者消费一个数据库，按块处理要比按字节处理数据快的多。在NIO中有几个核心对象需要掌握：缓冲区（Buffer）、通道（Channel）、选择器（Selector）。 Channel channel是个双向通道和BIO的Stream不同，Stream是单向通道。但他们都用于数据的读写。 Channel的实现 FileChannel (从文件中) DatagramChannel (从UDP中) SocketChannel (通过TCP读写) ServerSocketChannel (监听新进来的TCP连接) 打开 SocketChannel： SocketChannel socketChannel = SocketChannel.open(); socketChannel.connect(new InetSocketAddress("http://jenkov.com", 80)); 从 SocketChannel 读取数据：

Java: Converting String to and from ByteBuffer and associated problems

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问题 I am using Java NIO for my socket connections, and my protocol is text based, so I need to be able to convert Strings to ByteBuffers before writing them to the SocketChannel, and convert the incoming ByteBuffers back to Strings. Currently, I am using this code: public static Charset charset = Charset.forName("UTF-8"); public static CharsetEncoder encoder = charset.newEncoder(); public static CharsetDecoder decoder = charset.newDecoder(); public static ByteBuffer str_to_bb(String msg){ try{

ByteBuffer.allocate() vs. ByteBuffer.allocateDirect()

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To allocate() or to allocateDirect() , that is the question. For some years now I've just stuck to the thought that since DirectByteBuffer s are a direct memory mapping at OS level, that it would perform quicker with get/put calls than HeapByteBuffer s. I never was really interested in finding out the exact details regarding the situation until now. I want to know which of the two types of ByteBuffer s are faster and on what conditions. Ron Hitches in his excellent book Java NIO seems to offer what I thought could be a good answer to your question: Operating systems perform I/O operations on

How to convert a double into a byte array in swift?

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问题 I know how to do it in java (see here), but I couldn\'t find a swift equivalent for java\'s ByteBuffer, and consequently its .putDouble(double value) method. Basically, I\'m looking for a function like this: func doubleToByteArray(value: Double) -> [UInt8]? { . . . } doubleToByteArray(1729.1729) // should return [64, 155, 4, 177, 12, 178, 149, 234] 回答1: typealias Byte = UInt8 func toByteArray<T>(var value: T) -> [Byte] { return withUnsafePointer(&value) { Array(UnsafeBufferPointer(start:

ByteBuffer.allocate() vs. ByteBuffer.allocateDirect()

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问题 To allocate() or to allocateDirect() , that is the question. For some years now I\'ve just stuck to the thought that since DirectByteBuffer s are a direct memory mapping at OS level, that it would perform quicker with get/put calls than HeapByteBuffer s. I never was really interested in finding out the exact details regarding the situation until now. I want to know which of the two types of ByteBuffer s are faster and on what conditions. 回答1: Ron Hitches in his excellent book Java NIO seems

Byte array to image conversion

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问题 I want to convert a byte array to an image. This is my database code from where I get the byte array: public void Get_Finger_print() { try { using (SqlConnection thisConnection = new SqlConnection(@\"Data Source=\" + System.Environment.MachineName + \"\\\\SQLEXPRESS;Initial Catalog=Image_Scanning;Integrated Security=SSPI \")) { thisConnection.Open(); string query = \"select pic from Image_tbl\";// where Name=\'\" + name + \"\'\"; SqlCommand cmd = new SqlCommand(query, thisConnection); byte[]

converting Java bitmap to byte array

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问题 Bitmap bmp = intent.getExtras().get(\"data\"); int size = bmp.getRowBytes() * bmp.getHeight(); ByteBuffer b = ByteBuffer.allocate(size); bmp.copyPixelsToBuffer(b); byte[] bytes = new byte[size]; try { b.get(bytes, 0, bytes.length); } catch (BufferUnderflowException e) { // always happens } // do something with byte[] When I look at the buffer after the call to copyPixelsToBuffer the bytes are all 0... The bitmap returned from the camera is immutable... but that shouldn\'t matter since it\'s

Netty学习笔记

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Netty简单认识：　　1) Netty 是由JBOSS 提供的一个Java 开源框架。　　2) Netty 是一个异步的、基于事件驱动的网络应用框架，用以快速开发高性能、高可靠性的网络I0 程序。　　3) Netty 主要针对在TCP协议下的使用　　4)Netty本质是- 个NIO框架，适用于服务器通讯相关的多种应用场景 Netty应用：　　 https://netty.io/wiki/related-projects.html 这里面是和netty有关的框架　　Netty应用于网络间的通信，如阿里的dubbo框架，应用于服务之间的调用；谷歌的grpc框架； I/O模型：　　 netty是基于nio开发，所以我们需要了解java中的I/O模型： Bio:同步阻塞io，服务器实现模式为一一个连接-一个线程，即客户端有连接请求时服务器端就需要启动一个线程进行处理　　如果这个连接不做任何事情会造成不必要的线程开销，适用于连接数小的和固定的，编程简单。 Nio:同步非阻塞，JavaNIO :同步非阻塞，服务器实现模式为- -个线程处理多个请求(连接)，即客户端发送的连接请求　　都会注册到多路复用器上，多路复用器轮询到连接有I/O请求就进行处理，适用于连接数多的连接时间短的，编程复杂。（1.4以后版本） Aio:异步非阻塞，有效的请求才启动线程

converting Java bitmap to byte array

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Bitmap bmp = intent.getExtras().get("data"); int size = bmp.getRowBytes() * bmp.getHeight(); ByteBuffer b = ByteBuffer.allocate(size); bmp.copyPixelsToBuffer(b); byte[] bytes = new byte[size]; try { b.get(bytes, 0, bytes.length); } catch (BufferUnderflowException e) { // always happens } // do something with byte[] When I look at the buffer after the call to copyPixelsToBuffer the bytes are all 0... The bitmap returned from the camera is immutable... but that shouldn't matter since it's doing a copy. What could be wrong with this code? Mezm Try something like this: Bitmap bmp = intent