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第一个stream的例子：
const fs = require('fs')
const stream = fs.createWriteStream('./big_file.txt')
for(let i=0;i{
fs.readFile('./big_file.txt',(error,data)=>{
if(error) throw error
response.end(data)
console.log('done')
})
})
server.listen(8888)
console.log('started-----8888')
此时我们创建一个http服务，当我们试图读取刚刚创建的文件时，发现node.js的服务内存瞬间增加了100MB,此时如果存在多个请求，将会对机器造成很大的压力. 2. 通过createReadStream读取文件; const fs = require('fs') const http = require('http') const server = http.createServer() server.on('request',(request,response)=>{ const stream = fs.createReadStream('./big_file.txt') stream.pipe(response) }) server.listen(8888) console.log('started at 8888')此时我们可以看到node.js服务的内存只增加了20多MB,虽然读取的速度不如比之前fs.readFile慢一些。 管道pipe两个流可以用一个管道相连，stream1的末尾连上stream2开头 stream1.pipe(stream2) //链式操作 a.pipe(b).pipe(c) Stream对象的原型链 const s = fs.createReadStream(path)s的对象层级为： 自身属性(由fs.ReadStream构造) 原型：stream.Readable.prototype 二级原型:stream.Stream.prototype 三级原型:events.EventEmitter.prototype 四级原型:Object.prototype  image.png
 image.png
Stream 分类
Readable 可读
Writable 可写
Duplex 可读可写（双向，默认读写分离，互相不干扰）
Transform 可读可写（变化，相当于一个转换器，比如babel写入es6，然后读取的是es5）
Readable stream
默认处于paused态
添加data事件，变成flowing态
删掉data事件，变为paused态
调用pause()可以变为paused态
调用resume()可以变为flowing态
const fs = require('fs')
const http = require('http')
const server = http.createServer()
server.on('request',(request,response)=>{
const stream = fs.createReadStream('./big_file.txt')
stream.pipe(response)
stream.pause()
})
server.listen(8888)
console.log('started-----8888')
此时我们发送请求，无法获得任何的响应，因为调用了pause() stream.pipe(response) stream.pause() setTimeout(()=>{ console.log('3s 后恢复') stream.resume() },3000)我们在3秒后调用resume(),此时响应恢复 创建一个readable stream const {Readable} = require('stream') const inStream = new Readable() inStream.push('ABCDEFG') inStream.push('EFGHI') inStream.push(null) inStream.pipe(process.stdout)目前的方法不是按需供给的 const { Readable } = require("stream"); const inStream = new Readable({ read(size) { const char = String.fromCharCode(this.currentCharCode++) this.push(char); console.log(`push ${char}`) if (this.currentCharCode > 90) { this.push(null); } } }) inStream.currentCharCode = 65 inStream.pipe(process.stdout)用户调用read才会调用 Writable stream 1.drain事件我们在调用stream.write(chunk)的时候可能会得到false，表示写的太快，数据积压，要监听到drain事件后才能继续write 2. finish事件调用stream.end()后，且缓冲区数据都传递给底层系统后，触发finish事件 创建一个writable stream const {Writable} = require('stream') const outStream = new Writable({ write(chunk, encoding, callback) { console.log('get user input:') console.log(chunk.toString()) callback() } }) process.stdin.pipe(outStream)这时我们输入一个值，终端会出现你输入的值 Duplex stream const { Duplex } = require("stream"); const inoutStream = new Duplex({ write(chunk, encoding, callback) { console.log(chunk.toString()); callback(); }, read(size) { this.push(String.fromCharCode(this.currentCharCode++)); if (this.currentCharCode > 90) { this.push(null); } } }); inoutStream.currentCharCode = 65; process.stdin.pipe(inoutStream).pipe(process.stdout); Transform stream const { Transform } = require("stream"); const upperCaseTr = new Transform({ transform(chunk, encoding, callback) { this.push(chunk.toString().toUpperCase()); callback(); } }); process.stdin.pipe(upperCaseTr).pipe(process.stdout); 创建一个gzip流 const fs = require("fs"); const zlib = require("zlib"); const file = process.argv[2]; fs.createReadStream(file) .pipe(zlib.createGzip()) .pipe(fs.createWriteStream(file + ".gz")); |
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