如果你碰巧使用谷歌Guava，它将像使用ByteStreams一样简单:

byte[] bytes = ByteStreams.toByteArray(inputStream);

下面的代码

public static byte[] serializeObj(Object obj) throws IOException {
  ByteArrayOutputStream baOStream = new ByteArrayOutputStream();
  ObjectOutputStream objOStream = new ObjectOutputStream(baOStream);

  objOStream.writeObject(obj); 
  objOStream.flush();
  objOStream.close();
  return baOStream.toByteArray(); 
} 

OR

BufferedImage img = ...
ByteArrayOutputStream baos = new ByteArrayOutputStream(1000);
ImageIO.write(img, "jpeg", baos);
baos.flush();
byte[] result = baos.toByteArray();
baos.close();

你可以试试仙人掌:

byte[] array = new BytesOf(stream).bytes();

你可以完全避免缓冲。

从http://www.exampledepot.com/egs/java.io/File2ByteArray.html复制的代码(是的，它非常冗长，但需要的内存大小是其他解决方案的一半)。

// Returns the contents of the file in a byte array.
public static byte[] getBytesFromFile(File file) throws IOException {
    InputStream is = new FileInputStream(file);

    // 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
    }

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

    // Read in the bytes
    int offset = 0;
    int numRead = 0;
    while (offset < bytes.length
           && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
        offset += numRead;
    }

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

    // Close the input stream and return bytes
    is.close();
    return bytes;
}

Java 7及以上版本:

import sun.misc.IOUtils;
...
InputStream in = ...;
byte[] buf = IOUtils.readFully(in, -1, false);

Java 9最终会给你一个很好的方法:

InputStream in = ...;
ByteArrayOutputStream bos = new ByteArrayOutputStream();
in.transferTo( bos );
byte[] bytes = bos.toByteArray();