Accessing Application Files

This topic describes how to view, create, read, write, delete, move, or copy a file in the application file directory and obtain the file information.

Available APIs

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

Table 1 APIs for basic application file operations

API	Description	Type	Synchronous Programming	Asynchronous Programming
access	Checks whether a file exists.	Method	√	√
close	Closes a file.	Method	√	√
copyFile	Copies a file.	Method	√	√
createStream	Creates a stream based on the specified file path.	Method	√	√
listFile	Lists all files in a directory.	Method	√	√
mkdir	Creates a directory.	Method	√	√
moveFile	Moves a file.	Method	√	√
open	Opens a file.	Method	√	√
read	Reads data from a file.	Method	√	√
rename	Renames a file or folder.	Method	√	√
rmdir	Deletes a directory.	Method	√	√
stat	Obtains detailed file information.	Method	√	√
unlink	Deletes a single file.	Method	√	√
write	Writes data to a file.	Method	√	√
Stream.close	Closes a stream.	Method	√	√
Stream.flush	Flushes all data from this stream.	Method	√	√
Stream.write	Writes data to a stream.	Method	√	√
Stream.read	Reads data from a stream.	Method	√	√
File.fd	Defines a file descriptor.	Attribute	√	×
OpenMode	Defines the mode for opening a file.	Attribute	√	×
Filter	Defines the options for setting the file filter.	Type	×	×

Development Example

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 describes 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';

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

  // 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 buf = new ArrayBuffer(1024);
  let readLen = fs.readSync(file.fd, buf, { offset: 0 });
  console.info("the content of file: " + String.fromCharCode.apply(null, new Uint8Array(buf.slice(0, readLen))));
  // Close the file.
  fs.closeSync(file);
}

Copying Data to Another File

The following example demonstrates how to write the data read from a file to another file.

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

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

  // Open the source and destination files.
  let srcFile = fs.openSync(filesDir + '/test.txt', fs.OpenMode.READ_WRITE);
  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);
  let readLen = fs.readSync(srcFile.fd, buf, { offset: readSize });
  while (readLen > 0) {
    readSize += readLen;
    fs.writeSync(destFile.fd, buf);
    readLen = fs.readSync(srcFile.fd, buf, { offset: readSize });
  }
  // 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, the offset pointer is at 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';

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

  // 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);
  let readLen = await inputStream.read(buf, { offset: readSize });
  readSize += readLen;
  while (readLen > 0) {
    await outputStream.write(buf);
    readLen = await inputStream.read(buf, { offset: readSize });
    readSize += readLen;
  }
  // Close the streams.
  inputStream.closeSync();
  outputStream.closeSync();
}

NOTE

Close the stream that is no longer used in a timely manner.
Comply with the related 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.

// List files.
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;

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