Summary of Node.js file operation methods_node.js

Node.js, like other languages, also has file operations. Let’s not talk about the file operations in node.js. File operations in other languages ​​generally include opening, closing, reading, writing, file information, creating and deleting directories, deleting files, detecting file paths, etc. The same is true in node.js. They also have these functions. Maybe the API is different from other languages.

1. Synchronous and asynchronous opening and closing

/**
 * Created by Administrator on 2016/3/21.
 */
var fs=require("fs");
//同步读 fs.openSync = function(path, flags, mode)
//模块fs.js文件中如上面定义的openSync 函数3个参数
//.1.path 文件路径
//2.flags 打开文件的模式
//3.model 设置文件访问模式
//fd文件描述
var fd=fs.openSync("data/openClose.txt",'w');
//fs.closeSync = function(fd)
fs.closeSync(fd);

//异步读写
//fs.open = function(path, flags, mode, callback_)
//fs.close = function(fd, callback)
fs.open("data/openColse1.txt",'w',function(err,fd) {
  if (!err)
  {
    fs.close(fd,function(){
      console.log("closed");
    });
  }
});

The flags are also found in other languages. In fact, they are mainly divided into three parts: r, w, and a. They are similar to those in C.

1.r - Open the file in read-only mode, the initial position of the data stream is at the beginning of the file
2.r+ - Open the file in read-write mode, the initial position of the data stream is at the beginning of the file
3.w - If the file exists, the file length will be cleared to 0, that is, the file content will be lost. If it doesn't exist, try to create it. The initial position of the data stream is at the beginning of the file
4.w+ - Open the file in read-write mode. If the file does not exist, try to create it. If the file exists, set the file length to 0, that is, the file content will be lost. The initial position of the data stream is at the beginning of the file
5.a - Open the file in write-only mode. If the file does not exist, try to create it. The initial position of the data stream is at the end of the file. Each subsequent write operation will append the data to the end of the file.
6.a+ - Open the file for reading and writing. If the file does not exist, try to create it. The initial position of the data stream is at the end of the file. Each subsequent write operation will append data to the end of the file.

2. Reading and Writing

1. Simple file reading and writing

/**
 * Created by Administrator on 2016/3/21.
 */
var fs = require('fs');
var config = {
  maxFiles: 20,
  maxConnections: 15,
  rootPath: "/webroot"
};
var configTxt = JSON.stringify(config);

var options = {encoding:'utf8', flag:'w'};
//options 定义字符串编码 打开文件使用的模式 标志的encoding、mode、flag属性 可选
//异步
//fs.writeFile = function(path, data, options, callback_)
//同步
//fs.writeFileSync = function(path, data, options)

fs.writeFile('data/config.txt', configTxt, options, function(err){
  if (err){
    console.log("Config Write Failed.");
  } else {
    console.log("Config Saved.");
    readFile();
  }
});
function readFile()
{
  var fs = require('fs');
  var options = {encoding:'utf8', flag:'r'};
  //异步
  //fs.readFile = function(path, options, callback_)
  //同步
  //fs.readFileSync = function(path, options)
  fs.readFile('data/config.txt', options, function(err, data){
    if (err){
      console.log("Failed to open Config File.");
    } else {
      console.log("Config Loaded.");
      var config = JSON.parse(data);
      console.log("Max Files: " + config.maxFiles);
      console.log("Max Connections: " + config.maxConnections);
      console.log("Root Path: " + config.rootPath);
    }
  });
}

"C:\Program Files (x86)\JetBrains\WebStorm 11.0.3\bin\runnerw.exe" F:\nodejs\node.exe SimpleReadWrite.js
Config Saved.
Config Loaded.
Max Files: 20
Max Connections: 15
Root Path: /webroot

Process finished with exit code 0

2. Synchronous reading and writing

/**
 * Created by Administrator on 2016/3/21.
 */
var fs = require('fs');
var veggieTray = ['carrots', 'celery', 'olives'];

fd = fs.openSync('data/veggie.txt', 'w');
while (veggieTray.length){
  veggie = veggieTray.pop() + " ";
  //系统api 
  //fd 文件描述 第二个参数是被写入的String或Buffer
  // offset是第二个参数开始读的索引 null是表示当前索引
  //length 写入的字节数 null一直写到数据缓冲区末尾
  //position 指定在文件中开始写入的位置 null 文件当前位置
  // fs.writeSync(fd, buffer, offset, length[, position]);
  // fs.writeSync(fd, string[, position[, encoding]]);
  //fs.writeSync = function(fd, buffer, offset, length, position)
  var bytes = fs.writeSync(fd, veggie, null, null);
  console.log("Wrote %s %dbytes", veggie, bytes);
}
fs.closeSync(fd);

var fs = require('fs');
fd = fs.openSync('data/veggie.txt', 'r');
var veggies = "";
do {
  var buf = new Buffer(5);
  buf.fill();
  //fs.readSync = function(fd, buffer, offset, length, position)
  var bytes = fs.readSync(fd, buf, null, 5);
  console.log("read %dbytes", bytes);
  veggies += buf.toString();
} while (bytes > 0);
fs.closeSync(fd);
console.log("Veggies: " + veggies);

"C:\Program Files (x86)\JetBrains\WebStorm 11.0.3\bin\runnerw.exe" F:\nodejs\node.exe syncReadWrite.js
Wrote olives 7bytes
Wrote celery 7bytes
Wrote carrots 8bytes
read 5bytes
read 5bytes
read 5bytes
read 5bytes
read 2bytes
read 0bytes
Veggies: olives celery carrots     

Process finished with exit code 0

3. Asynchronous reading and writing and synchronous reading and writing almost have more parameters callback

/**
 * Created by Administrator on 2016/3/21.
 */
var fs = require('fs');
var fruitBowl = ['apple', 'orange', 'banana', 'grapes'];
function writeFruit(fd){
  if (fruitBowl.length){
    var fruit = fruitBowl.pop() + " ";
   // fs.write(fd, buffer, offset, length[, position], callback);
   // fs.write(fd, string[, position[, encoding]], callback);
   // fs.write = function(fd, buffer, offset, length, position, callback)
    fs.write(fd, fruit, null, null, function(err, bytes){
      if (err){
        console.log("File Write Failed.");
      } else {
        console.log("Wrote: %s %dbytes", fruit, bytes);
        writeFruit(fd);
      }
    });
  } else {
    fs.close(fd);
    ayncRead();
  }
}
fs.open('data/fruit.txt', 'w', function(err, fd){
  writeFruit(fd);
});

function ayncRead()
{
  var fs = require('fs');
  function readFruit(fd, fruits){
    var buf = new Buffer(5);
    buf.fill();
    //fs.read = function(fd, buffer, offset, length, position, callback)
    fs.read(fd, buf, 0, 5, null, function(err, bytes, data){
      if ( bytes > 0) {
        console.log("read %dbytes", bytes);
        fruits += data;
        readFruit(fd, fruits);
      } else {
        fs.close(fd);
        console.log ("Fruits: %s", fruits);
      }
    });
  }
  fs.open('data/fruit.txt', 'r', function(err, fd){
    readFruit(fd, "");
  });
}

"C:\Program Files (x86)\JetBrains\WebStorm 11.0.3\bin\runnerw.exe" F:\nodejs\node.exe asyncReadWrite.js
Wrote: grapes 7bytes
Wrote: banana 7bytes
Wrote: orange 7bytes
Wrote: apple 6bytes
read 5bytes
read 5bytes
read 5bytes
read 5bytes
read 5bytes
read 2bytes
Fruits: grapes banana orange apple  

Process finished with exit code 0

4. Streaming reading and writing

/**
 * Created by Administrator on 2016/3/21.
 */
var fs = require('fs');
var grains = ['wheat', 'rice', 'oats'];
var options = { encoding: 'utf8', flag: 'w' };
//从下面的系统api可以看到 createWriteStream 就是创建了一个writable流
//fs.createWriteStream = function(path, options) {
//  return new WriteStream(path, options);
//};
//
//util.inherits(WriteStream, Writable);
//fs.WriteStream = WriteStream;
//function WriteStream(path, options)
var fileWriteStream = fs.createWriteStream("data/grains.txt", options);
fileWriteStream.on("close", function(){
  console.log("File Closed.");
  //流式读
  streamRead();
});
while (grains.length){
  var data = grains.pop() + " ";
  fileWriteStream.write(data);
  console.log("Wrote: %s", data);
}
fileWriteStream.end();

//流式读
function streamRead()
{
  var fs = require('fs');
  var options = { encoding: 'utf8', flag: 'r' };
  //fs.createReadStream = function(path, options) {
  //  return new ReadStream(path, options);
  //};
  //
  //util.inherits(ReadStream, Readable);
  //fs.ReadStream = ReadStream;
  //
  //function ReadStream(path, options)
  //createReadStream 就是创建了一个readable流
  var fileReadStream = fs.createReadStream("data/grains.txt", options);
  fileReadStream.on('data', function(chunk) {
    console.log('Grains: %s', chunk);
    console.log('Read %d bytes of data.', chunk.length);
  });
  fileReadStream.on("close", function(){
    console.log("File Closed.");
  });
}

"C:\Program Files (x86)\JetBrains\WebStorm 11.0.3\bin\runnerw.exe" F:\nodejs\node.exe StreamReadWrite.js
Wrote: oats 
Wrote: rice 
Wrote: wheat 
File Closed.
Grains: oats rice wheat 
Read 16 bytes of data.
File Closed.

Process finished with exit code 0

Personally, I think these APIs will be ok once you use them and get a feel for them, and you just need to be able to use them when you encounter them.