05.流Stream

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1. 所有Stream对象同时也是EventEmitter的实例,Stream对象常用的事件有
   

   事件名	触发条件
   data	当有数据可读时触发
   end	没有数据可读时触发
   error	在读取或写入过程中发生错误时触发
   finish	所有数据已被写入到底层系统时触发

2. 从流读取数据
   读取数据readData.js代码如下

   var fs = require('fs');
   
   var readerStream = fs.createReadStream('input.txt');
   readerStream.setEncoding('UTF-8');
   
   var data = '';
   
   readerStream.on('data',function(chunk){
       data += chunk;
   });
   
   readerStream.on('end',function(){
   	console.log(data);
   });
   
   readerStream.on('error',function(err){
   	console.log('自定义错误日志:',err.stack);
   });
   
   console.log('程序执行完毕');

    运行结果
   

   >node readData.js
   程序执行完毕
   这里是被测试的文件;
      hello,this is a test file.
   
   

    
3. 向流写数据
   写数据writeData.js代码如下
   

   var fs = require('fs');
   
   var writerStream = fs.createWriteStream('output.txt');
   
   writerStream.write('真是的,这么好的天气没出门sss','utf-8');
   writerStream.end();
   
   writerStream.on('finish',function(){
     console.log('写入完成');
   });
   
   writerStream.on('error',function(err){
   	console.log('自定义错误日志:',err.stack);
   });
   
   console.log('程序执行完毕');

    运行结果如下
   

   >node Stream.js
   程序执行完毕
   写入完成
   

    
4. 管道与链式流
     pipeStream.js代码如下
   

   var fs = require('fs');
   var zlib = require('zlib');
   
   var readerStream = fs.createReadStream('input.txt');
   var writeCompressGz = fs.createWriteStream('compress.txt.gz');
   
   writeCompressGz.on('finish',function(){
   	fs.createReadStream('compress.txt.gz')
            .pipe(zlib.createGunzip())
            .pipe(fs.createWriteStream('compress.txt'));
   });
   
   readerStream.pipe(zlib.createGzip()).pipe(writeCompressGz);
   
   console.log('程序执行完毕');