让我添加另一个不使用第三方库的解决方案。它重用了Scott提出的异常处理模式(链接)。我把丑陋的部分移动到一个单独的消息(我会隐藏在一些FileUtils类;))

public void someMethod() {
    final byte[] buffer = read(new File("test.txt"));
}

private byte[] read(final File file) {
    if (file.isDirectory())
        throw new RuntimeException("Unsupported operation, file "
                + file.getAbsolutePath() + " is a directory");
    if (file.length() > Integer.MAX_VALUE)
        throw new RuntimeException("Unsupported operation, file "
                + file.getAbsolutePath() + " is too big");

    Throwable pending = null;
    FileInputStream in = null;
    final byte buffer[] = new byte[(int) file.length()];
    try {
        in = new FileInputStream(file);
        in.read(buffer);
    } catch (Exception e) {
        pending = new RuntimeException("Exception occured on reading file "
                + file.getAbsolutePath(), e);
    } finally {
        if (in != null) {
            try {
                in.close();
            } catch (Exception e) {
                if (pending == null) {
                    pending = new RuntimeException(
                        "Exception occured on closing file" 
                             + file.getAbsolutePath(), e);
                }
            }
        }
        if (pending != null) {
            throw new RuntimeException(pending);
        }
    }
    return buffer;
}

我相信这是最简单的方法:

org.apache.commons.io.FileUtils.readFileToByteArray(file);

import java.io.RandomAccessFile;
RandomAccessFile f = new RandomAccessFile(fileName, "r");
byte[] b = new byte[(int)f.length()];
f.readFully(b);

Java 8文档:http://docs.oracle.com/javase/8/docs/api/java/io/RandomAccessFile.html

以下方法不仅将Java .io. file转换为byte[]，我还发现它是读取文件的最快方法，当测试许多不同的Java文件读取方法时:

java.nio.file.Files.readAllBytes ()

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;

public class ReadFile_Files_ReadAllBytes {
  public static void main(String [] pArgs) throws IOException {
    String fileName = "c:\\temp\\sample-10KB.txt";
    File file = new File(fileName);

    byte [] fileBytes = Files.readAllBytes(file.toPath());
    char singleChar;
    for(byte b : fileBytes) {
      singleChar = (char) b;
      System.out.print(singleChar);
    }
  }
}

Guava有Files.toByteArray()可以提供给您。它有几个优点:

它涵盖了文件报告长度为0但仍然有内容的极端情况 它是高度优化的，如果在加载文件之前试图读入一个大文件，你会得到一个OutOfMemoryException。(通过巧妙地使用file.length()) 你没必要白费力气。

使用与社区wiki答案相同的方法，但更干净，并编译开箱即用(如果你不想导入Apache Commons库，例如在Android上，首选的方法):

public static byte[] getFileBytes(File file) throws IOException {
    ByteArrayOutputStream ous = null;
    InputStream ios = null;
    try {
        byte[] buffer = new byte[4096];
        ous = new ByteArrayOutputStream();
        ios = new FileInputStream(file);
        int read = 0;
        while ((read = ios.read(buffer)) != -1)
            ous.write(buffer, 0, read);
    } finally {
        try {
            if (ous != null)
                ous.close();
        } catch (IOException e) {
            // swallow, since not that important
        }
        try {
            if (ios != null)
                ios.close();
        } catch (IOException e) {
            // swallow, since not that important
        }
    }
    return ous.toByteArray();
}