Accessing Application Files

This topic describes how to enable an application to view, create, read, write, delete, move, or copy an application file and obtain file information.

Available APIs

You can use ohos.file.fs to implement access to application files. The following table describes the common APIs.

Table 1 APIs for basic application file operations

Development Example

Before performing any file operation, obtain the application file path. The following example shows how to obtain a HAP file path using UIAbilityContext. For details about how to obtain UIAbilityContext, see Obtaining the Context of UIAbility.

The following walks you through on how to perform common file operations.

Creating, Reading, and Writing a File

The following example demonstrates how to create a file, read data from it, and write data to it.

// pages/xxx.ets
import fs from '@ohos.file.fs';
import common from '@ohos.app.ability.common';
import buffer from '@ohos.buffer';

// Obtain the application file path.
let context = getContext(this) as common.UIAbilityContext;
let filesDir = context.filesDir;

function createFile(): void {
  // Create a file and open it.
  let file = fs.openSync(filesDir + '/test.txt', fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
  // Write data to the file.
  let writeLen = fs.writeSync(file.fd, "Try to write str.");
  console.info("The length of str is: " + writeLen);
  // Read data from the file.
  let arrayBuffer = new ArrayBuffer(1024);
  class Option {
    public offset: number = 0;
    public length: number = 0;
  }
  let option = new Option();
  option.length = arrayBuffer.byteLength;
  let readLen = fs.readSync(file.fd, arrayBuffer, option);
  let buf = buffer.from(arrayBuffer, 0, readLen);
  console.info("the content of file: " + buf.toString());
  // Close the file.
  fs.closeSync(file);
}

Copying Data to Another File

The following example demonstrates how to read data from a file and copy it to another file.

// pages/xxx.ets
import fs from '@ohos.file.fs';
import common from '@ohos.app.ability.common';

// Obtain the application file path.
let context = getContext(this) as common.UIAbilityContext;
let filesDir = context.filesDir;

function readWriteFile(): void {
  // Open the source and destination files.
  let srcFile = fs.openSync(filesDir + '/test.txt', fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
  let destFile = fs.openSync(filesDir + '/destFile.txt', fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
  // Read data from the source file and copy it to the destination file.
  let bufSize = 4096;
  let readSize = 0;
  let buf = new ArrayBuffer(bufSize);
  class Option {
    public offset: number = 0;
    public length: number = bufSize;
  }
  let option = new Option();
  option.offset = readSize;
  let readLen = fs.readSync(srcFile.fd, buf, option);
  while (readLen > 0) {
    readSize += readLen;
    fs.writeSync(destFile.fd, buf);
    option.offset = readSize;
    readLen = fs.readSync(srcFile.fd, buf, option);
  }
  // Close the files.
  fs.closeSync(srcFile);
  fs.closeSync(destFile);
}

NOTE

When using read() or write(), pay attention to the optional parameter offset. For a file that has been read or written, offset points to the end position of the last read or write operation by default.

Reading and Writing Files in a Stream

The following example demonstrates how to read and write file data using a stream.

// pages/xxx.ets
import fs from '@ohos.file.fs';
import common from '@ohos.app.ability.common';

// Obtain the application file path.
let context = getContext(this) as common.UIAbilityContext;
let filesDir = context.filesDir;

async function readWriteFileWithStream(): Promise<void> {
  // Open the file streams.
  let inputStream = fs.createStreamSync(filesDir + '/test.txt', 'r+');
  let outputStream = fs.createStreamSync(filesDir + '/destFile.txt', "w+");
  // Read data from the source file and write the data to the destination file using a stream.
  let bufSize = 4096;
  let readSize = 0;
  let buf = new ArrayBuffer(bufSize);
  class Option {
    public offset: number = 0;
    public length: number = bufSize;
  }
  let option = new Option();
  option.offset = readSize;
  let readLen = await inputStream.read(buf, option);
  readSize += readLen;
  while (readLen > 0) {
    await outputStream.write(buf);
    option.offset = readSize;
    readLen = await inputStream.read(buf, option);
    readSize += readLen;
  }
  // Close the streams.
  inputStream.closeSync();
  outputStream.closeSync();
}

NOTE

• Close the stream once it is not required.
• Comply with the programming specifications for Stream APIs in asynchronous mode and avoid mixed use of the APIs in synchronous mode and asynchronous mode.
• The Stream APIs do not support concurrent read and write operations.

Listing Files

The following example demonstrates how to list files that meet the specified conditions.

import fs, { Filter } from '@ohos.file.fs';
import common from '@ohos.app.ability.common';

// Obtain the application file path.
let context = getContext(this) as common.UIAbilityContext;
let filesDir = context.filesDir;

// List files that meet the specified conditions.
function getListFile(): void {
  class ListFileOption {
    public recursion: boolean = false;
    public listNum: number = 0;
    public filter: Filter = {};
  }
  let option = new ListFileOption();
  option.filter.suffix = ['.png', '.jpg', '.txt'];          // The file name extension can be '.png', '.jpg', or '.txt'.
  option.filter.displayName = ['test%'];                    // The file name starts with 'test'.
  option.filter.fileSizeOver = 0;                           // The file size is greater than or equal to 0.
  option.filter.lastModifiedAfter = new Date(0).getTime();  // The latest modification time of the file is later than January 1, 1970.
  let files = fs.listFileSync(filesDir, option);
  for (let i = 0; i < files.length; i++) {
    console.info(`The name of file: ${files[i]}`);
  }
}