Java - 文件到读取器（File to Reader）

In this quick tutorial we’re going to illustrate how to convert a File to a Reader using plain Java, Guava or Apache Commons IO. Let’s get started.

This article is part of the “Java – Back to Basic” series here on Baeldung.

1. With Plain Java

Let’s first look at the simple Java solution:

@Test
public void givenUsingPlainJava_whenConvertingFileIntoReader_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/test/resources/initialFile.txt");
    initialFile.createNewFile();
    Reader targetReader = new FileReader(initialFile);
    targetReader.close();
}

2. With Guava

Now – let’s see the same conversion, this time using the Guava library:

@Test
public void givenUsingGuava_whenConvertingFileIntoReader_thenCorrect() throws 
  IOException {
    File initialFile = new File("src/test/resources/initialFile.txt");
    com.google.common.io.Files.touch(initialFile);
    Reader targetReader = Files.newReader(initialFile, Charset.defaultCharset());
    targetReader.close();
}

3. With Commons IO

And finally, let’s end with the Commons IO code sample, doing the conversion via an intermediary byte array:

@Test
public void givenUsingCommonsIO_whenConvertingFileIntoReader_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/test/resources/initialFile.txt");
    FileUtils.touch(initialFile);
    FileUtils.write(initialFile, "With Commons IO");
    byte[] buffer = FileUtils.readFileToByteArray(initialFile);
    Reader targetReader = new CharSequenceReader(new String(buffer));
    targetReader.close();
}

And there we have it – 3 ways to convert a File into a Reader – first with plain Java, then with Guava and finally with the Apache Commons IO library. Make sure to check out the sample over on GitHub.