Nodejs學習筆記（二）--流的操作

1、讀取流

var readStream = fs.createReadStream(“57b51ea9Nb862ca5e.png”);

readStream.on(“data”,function(chunk){

console.log(chunk);

});

readStream.on(“end”,function(){

console.log(“end”);

});

readStream.on(“error”,function(){

console.log(“error”);

});

2、寫入流

var writeStream = fs.createWriteStream(“1.txt”);

writeStream.write(“加的老師\ndasd”);

writeStream.on(“end”,function () {

console.log(“end”);

});

所有可以讀取資料的流都繼承自stream.Readable，所有可以寫入的流都繼承自stream.Writable。

3、使用pipe

Readable中有一個pipe（），該方法可以将一個Readable流傳送到一個Writeable流，其實複制檔案也是這個思路，一邊讀取檔案，一邊寫入檔案：

var readStream = fs.createReadStream(“1.txt”);

var writeStream = fs.createWriteStream(“3.txt”);//3.txt不存在會自動建立

readStream.pipe(writeStream);

預設情況下，當Readable流的資料讀取完畢，end事件觸發後，将自動關閉Writable流。如果我們不希望自動關閉Writable流，需要傳入參數，傳入end傳輸為false，則觸發end事件時write流不會關閉：

readStream.pipe(writeStream , {end : false});

4、複制大檔案（視訊等）的例子

“use strict”;

var fs = require(“fs”);

var writeStream = fs.createWriteStream(“copy.avi”);//建立寫入流

var readStream = fs.createReadStream(“7-Activiti完成自動發送郵件功能.avi”);//建立讀取流

var totalSize = fs.statSync(“7-Activiti完成自動發送郵件功能.avi”).size;//總大小

var start = Date.now();//開始時間

var hasWriteStream = 0;//已經複制的内容

var timer = setInterval(compute,10);//定時器，每10豪秒執行一次compute函數

readStream.on(“data”,function (chunk) {

hasWriteStream += chunk.length;//累加已讀取内容

if(writeStream.write(chunk) === false){ // 若資料沒有完全寫入，則暫停隻讀流讀取資料

readStream.pause();

}

});

readStream.on(“end”,function () {

writeStream.end();//寫入全部結束觸發end事件

clearInterval(timer);//清除定時器

});

writeStream.on(“drain”,function(){

//若寫入流的資料已寫入完畢，則喚醒隻讀流繼續讀取資料

readStream.resume();

});

function compute(){

var domain = Date.now() - start;

console.log(“用時：” + domain +“ms----------”+ “已讀取：” + hasWriteStream / 1000000 + “M” )

}