//useReadAheadInput属性默认是true
//this.mysqlInput默认情况下就是ReadAheadInputStream了
if (this.connection.getUseReadAheadInput()) {
//默认16384字节(16k)缓冲空间
this.mysqlInput = new ReadAheadInputStream(this.mysqlConnection.getInputStream(), 16384,
this.connection.getTraceProtocol(), this.connection.getLog());
} else if (this.connection.useUnbufferedInput()) {
//useUnbufferedInput属性默认是true
this.mysqlInput = this.mysqlConnection.getInputStream();
} else {