Node.js流stream

流是一种等对文件读写、网络通信等过程中有大量数据处理和管理的高效处理方式。与其他数据处理方式相比，有2大优势：

1）内存消耗低，无需全部加载进内存，才可以处理；

2）时间快，获得部分数据就开始处理；

流的类型有4种：

1）可写流（writable）：只能读取数据

2）可读流（readable）：只可写入数据

3）双工流（duplex）：既能读也可以写

4）转换流（transform）：既能读也可以写。类似于双工流、但其输出是其输入的转换。

Node.js内置了stream模块，专门负责处理所有流操作。

/**
 * 流：大量数据管理的高效处理方式
 */

const fs = require("fs");

//可写流
var writeStream = fs.createWriteStream("song.txt");
var writeStr = "天籁之音";
writeStream.write(writeStr,"UTF8");
writeStream.end();
writeStream.on("finish",function(){
    console.log("文件写入完成！");
});
writeStream.on("error",function(err){
    console.log("文件写入错误：",err);
});


//可读流
var readStream = fs.createReadStream("song.txt");
var resStr = "";
    readStream.on("data",function(chunk){
       resStr += chunk;
    });

    readStream.on("end",function(chunk){
        console.log("song1.txt文件内容读取完成：",resStr);
    });

    readStream.on("error",function(err){
       console.log("文件读取错误：",err);
    });


//可读可写双流
var readStream2 = fs.createReadStream("song.txt");
var writeStream2 = fs.createWriteStream("song2.txt");
readStream2.pipe(writeStream2);
readStream2.on("end",()=>{
   writeStream2.end();

   var readStream3 = fs.createReadStream("song2.txt");
   var str = "";
   readStream3.on("data",function(chunk){
      str += chunk;
   });
   readStream3.on("end",function(chunk){
     console.log("song2.txt文件内容读取完成：",str);
   });
   readStream3.on("error",function(err){
    console.log("文件读取错误：",err);
   });
});
readStream2.on("error",function(err){
   readStream2.unpipe(); 
});

运行结果如下：

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