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());

//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"

正如有人所说，Apache Commons File Utils可能有您正在寻找的东西

public static byte[] readFileToByteArray(File file) throws IOException

示例使用(Program.java):

import org.apache.commons.io.FileUtils;
public class Program {
    public static void main(String[] args) throws IOException {
        File file = new File(args[0]);  // assume args[0] is the path to file
        byte[] data = FileUtils.readFileToByteArray(file);
        ...
    }
}

基本上你必须在记忆中读它。打开文件，分配数组，并将文件中的内容读入数组。

最简单的方法是这样的:

public byte[] read(File file) throws IOException, FileTooBigException {
    if (file.length() > MAX_FILE_SIZE) {
        throw new FileTooBigException(file);
    }
    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) {
        }

        try {
            if (ios != null)
                ios.close();
        } catch (IOException e) {
        }
    }
    return ous.toByteArray();
}

这对文件内容有一些不必要的复制(实际上数据复制了三次:从文件到缓冲区，从缓冲区到ByteArrayOutputStream，从ByteArrayOutputStream到实际的结果数组)。

你还需要确保你只在内存中读取一定大小的文件(这通常取决于应用程序):-)。

您还需要在函数外部处理IOException。

另一种方式是:

public byte[] read(File file) throws IOException, FileTooBigException {
    if (file.length() > MAX_FILE_SIZE) {
        throw new FileTooBigException(file);
    }

    byte[] buffer = new byte[(int) file.length()];
    InputStream ios = null;
    try {
        ios = new FileInputStream(file);
        if (ios.read(buffer) == -1) {
            throw new IOException(
                    "EOF reached while trying to read the whole file");
        }
    } finally {
        try {
            if (ios != null)
                ios.close();
        } catch (IOException e) {
        }
    }
    return buffer;
}

这没有不必要的复制。

FileTooBigException是自定义应用程序异常。 MAX_FILE_SIZE常量是一个应用程序参数。

对于大文件，您可能应该考虑流处理算法或使用内存映射(参见java.nio)。

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

File file = getYourFile();
Path path = file.toPath();
byte[] data = Files.readAllBytes(path);

// Returns the contents of the file in a byte array.
    public static byte[] getBytesFromFile(File file) throws IOException {        
        // Get the size of the file
        long length = file.length();

        // You cannot create an array using a long type.
        // It needs to be an int type.
        // Before converting to an int type, check
        // to ensure that file is not larger than Integer.MAX_VALUE.
        if (length > Integer.MAX_VALUE) {
            // File is too large
            throw new IOException("File is too large!");
        }

        // Create the byte array to hold the data
        byte[] bytes = new byte[(int)length];

        // Read in the bytes
        int offset = 0;
        int numRead = 0;

        InputStream is = new FileInputStream(file);
        try {
            while (offset < bytes.length
                   && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
                offset += numRead;
            }
        } finally {
            is.close();
        }

        // Ensure all the bytes have been read in
        if (offset < bytes.length) {
            throw new IOException("Could not completely read file "+file.getName());
        }
        return bytes;
    }