ReadFully从当前文件指针开始，将b.length字节从这个文件读入字节数组。该方法从文件中重复读取，直到读取所请求的字节数。该方法将阻塞，直到读取请求的字节数、检测到流的末尾或抛出异常。

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

你也可以使用NIO api来实现。只要总文件大小(以字节为单位)适合int类型，我就可以用这段代码做到这一点。

File f = new File("c:\\wscp.script");
FileInputStream fin = null;
FileChannel ch = null;
try {
    fin = new FileInputStream(f);
    ch = fin.getChannel();
    int size = (int) ch.size();
    MappedByteBuffer buf = ch.map(MapMode.READ_ONLY, 0, size);
    byte[] bytes = new byte[size];
    buf.get(bytes);

} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} finally {
    try {
        if (fin != null) {
            fin.close();
        }
        if (ch != null) {
            ch.close();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

我认为它非常快，因为它使用MappedByteBuffer。

从文件中读取字节的另一种方法

Reader reader = null;
    try {
        reader = new FileReader(file);
        char buf[] = new char[8192];
        int len;
        StringBuilder s = new StringBuilder();
        while ((len = reader.read(buf)) >= 0) {
            s.append(buf, 0, len);
            byte[] byteArray = s.toString().getBytes();
        }
    } catch(FileNotFoundException ex) {
    } catch(IOException e) {
    }
    finally {
        if (reader != null) {
            reader.close();
        }
    }

如果你的目标版本少于26个API，试试这个

 private static byte[] readFileToBytes(String filePath) {

    File file = new File(filePath);
    byte[] bytes = new byte[(int) file.length()];

    // funny, if can use Java 7, please uses Files.readAllBytes(path)
    try(FileInputStream fis = new FileInputStream(file)){
        fis.read(bytes);
        return bytes;
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;

}

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;
}

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);
}