//The file that you wanna convert into byte[]
File file=new File("/storage/0CE2-EA3D/DCIM/Camera/VID_20190822_205931.mp4"); 

FileInputStream fileInputStream=new FileInputStream(file);
byte[] data=new byte[(int) file.length()];
BufferedInputStream bufferedInputStream=new BufferedInputStream(fileInputStream);
bufferedInputStream.read(data,0,data.length);

//Now the bytes of the file are contain in the "byte[] data"

从JDK 7开始，您可以使用Files.readAllBytes(Path)。

例子:

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

File file;
// ...(file is initialised)...
byte[] fileContent = Files.readAllBytes(file.toPath());

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);
    }
  }
}

public static byte[] readBytes(InputStream inputStream) throws IOException {
    byte[] buffer = new byte[32 * 1024];
    int bufferSize = 0;
    for (;;) {
        int read = inputStream.read(buffer, bufferSize, buffer.length - bufferSize);
        if (read == -1) {
            return Arrays.copyOf(buffer, bufferSize);
        }
        bufferSize += read;
        if (bufferSize == buffer.length) {
            buffer = Arrays.copyOf(buffer, bufferSize * 2);
        }
    }
}

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

从文件中读取字节的最简单方法

import java.io.*;

class ReadBytesFromFile {
    public static void main(String args[]) throws Exception {
        // getBytes from anyWhere
        // I'm getting byte array from File
        File file = null;
        FileInputStream fileStream = new FileInputStream(file = new File("ByteArrayInputStreamClass.java"));

        // Instantiate array
        byte[] arr = new byte[(int) file.length()];

        // read All bytes of File stream
        fileStream.read(arr, 0, arr.length);

        for (int X : arr) {
            System.out.print((char) X);
        }
    }
}