// 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;
    }

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);
    }
  }
}

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());

试试这个:

import sun.misc.IOUtils;
import java.io.IOException;

try {
    String path="";
    InputStream inputStream=new FileInputStream(path);
    byte[] data=IOUtils.readFully(inputStream,-1,false);
}
catch (IOException e) {
    System.out.println(e);
}

在JDK8

Stream<String> lines = Files.lines(path);
String data = lines.collect(Collectors.joining("\n"));
lines.close();

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。