Node.js数据流Stream之Duplex流和Transform流用法

Node.js数据流Stream之Duplex流和Transform流用法

Duplex流一个很好的例子是TCP套接字连接.需要实现_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");

输出结果:

"C:Program Files (x86)JetBrainsWebStorm 11.0.3in unnerw.exe" F: odejs ode.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变换流扩展了Duplex流,不需要实现而是直接提供。但要实现_transform(chunk,encoding,callback)._flush()这个方法不知道用来做什么的目前

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"}");

输出结果:

"C:Program Files (x86)JetBrainsWebStorm 11.0.3in unnerw.exe" F: odejs ode.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

到此这篇关于Node.js数据流Stream之Duplex流和Transform流的文章就介绍到这了。希望对大家的学习有所帮助,也希望大家多多支持云海天教程。

原文地址:https://www.cnblogs.com/5ishare/p/5303376.html