Java类库中字节流由InputStream类和OutputStream类派生。由于InputStream,OutputStream是针对字节流的,所以读取文件前先要定义byte[]，然后把文件流读取到byte[]里面.-Derived　the InputStream class and OutputStream class byte stream in the Java class library. Thanks to InputStream, OutputStream is aimed at the byte stream, so must be defined before reading byte[] file, then the file stream to read into byte[].