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Node.js數(shù)據(jù)流Stream之Duplex流和Transform流用法

更新時間：2022年07月06日 10:19:37 作者：社會主義接班人

這篇文章介紹了Node.js數(shù)據(jù)流Stream之Duplex流和Transform流的用法，文中通過示例代碼介紹的非常詳細(xì)。對大家的學(xué)習(xí)或工作具有一定的參考借鑒價值，需要的朋友可以參考下

Duplex流一個很好的例子是TCP套接字連接.需要實現(xiàn)_read(size)和_Write(data,encoding,callback)方法.

var stream = require('stream');
var util = require('util');
util.inherits(Duplexer, stream.Duplex);
function Duplexer(opt) {
  stream.Duplex.call(this, opt);
  this.data = [];
}
Duplexer.prototype._read = function readItem(size) {
  var chunk = this.data.shift();
  if (chunk == "stop"){
    this.push(null);
  } else{
    if(chunk){
      this.push(chunk);
    }
  }
};
Duplexer.prototype._write = function(data, encoding, callback) {
  this.data.push(data);
  callback();
};
var d = new Duplexer({allowHalfOpen:true});
d.on('data', function(chunk){
  console.log('read: ', chunk.toString());
});
d.on('readable',function(){
  console.log("readable");
})
d.on('end', function(){
  console.log('Message Complete');
});
d.write("I think, ");
d.write("therefore ");
d.write("I am.");
d.write("Rene Descartes");
d.write("stop");

輸出結(jié)果：

"C:\Program Files (x86)\JetBrains\WebStorm 11.0.3\bin\runnerw.exe" F:\nodejs\node.exe stream_duplex.js
read: I think,
read: therefore
read: I am.
read: Rene Descartes
readable
readable
readable
Message Complete

Process finished with exit code 0

Transform變換流擴展了Duplex流，不需要實現(xiàn)而是直接提供。但要實現(xiàn)_transform(chunk,encoding,callback)._flush()這個方法不知道用來做什么的目前

var stream = require("stream");
var util = require("util");
util.inherits(JSONObjectStream, stream.Transform);
function JSONObjectStream (opt) {
  stream.Transform.call(this, opt);
};
JSONObjectStream.prototype._transform = function (data, encoding, callback) {
  object = data ? JSON.parse(data.toString()) : "";
  this.emit("object", object);
  object.handled = true;
  this.push(JSON.stringify(object));
  callback();
};
var tc = new JSONObjectStream();
tc.on("object", function(object){
  console.log("Name: %s", object.name);
  console.log("Color: %s", object.color);
});
tc.on("data", function(data){
  console.log("Data: %s", data.toString());
});
tc.write('{"name":"Carolinus", "color": "Green"}');
tc.write('{"name":"Solarius", "color": "Blue"}');
tc.write('{"name":"Lo Tae Zhao", "color": "Gold"}');
tc.write('{"name":"Ommadon", "color": "Red"}');

輸出結(jié)果：

"C:\Program Files (x86)\JetBrains\WebStorm 11.0.3\bin\runnerw.exe" F:\nodejs\node.exe stream_transform.js
Name: Carolinus
Color: Green
Data: {"name":"Carolinus","color":"Green","handled":true}
Name: Solarius
Color: Blue
Data: {"name":"Solarius","color":"Blue","handled":true}
Name: Lo Tae Zhao
Color: Gold
Data: {"name":"Lo Tae Zhao","color":"Gold","handled":true}
Name: Ommadon
Color: Red
Data: {"name":"Ommadon","color":"Red","handled":true}

Process finished with exit code 0

到此這篇關(guān)于Node.js數(shù)據(jù)流Stream之Duplex流和Transform流的文章就介紹到這了。希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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