java – 如何找出ByteBuffer中存储的总字节数？

下面是我们如何将data_record_value表示为一个字节数组,然后从Java代码写入我们的数据库.

Offset   Length (in bytes)          Purpose

0           2                       - clientId byte array
2           8                       - value of lastModifiedDate
2+8         4                       - length of avroBinaryValue array
2+8+4       Y                       - avroBinaryValue array

这就是我从数据库中提取它的方式 –

ByteBuffer data_record_value = r.getBytes("data_record_value");

// now how do I extract total number of bytes I have stored in data_record_value?

在做了一些研究之后,我发现了多种方法来提取我的ByteBuffer data_record_value中存储的字节总数,我不确定哪一个是对的？

第一种方式是：

byte[] b = new byte[data_record_value.remaining()];
record_value.get(b);

// this will be in bytes right?
System.out.println("Byte Array Length: " + b.length);

第二种方式是：

int numberOfBytesInRecord = data_record_value.limit();

第三种方式是：

int numberOfBytesInRecord = data_record_value.remaining();

但是上述所有方式的数字完全不相符？我不确定应该使用哪一个？我需要提取data_record_value中存储的总字节数.

要进行交叉检查,我们可以从data_record_value ByteBuffer中提取单个字段,并计算我们存储的总字节数,并与上述任何方法进行比较.

// clientId (of two bytes by using short)
short extractClientId = data_record_value.getShort();

// lastModifiedDate ( of 8 bytes which can be long )
long extractLastModifiedDate = data_record_value.getLong();

int extractAvroBinaryValueLength = data_record_value.getInt();

byte[] extractAvroBinaryValue = new byte[extractAvroBinaryValueLength];

data_record_value.get(extractAvroBinaryValue); // read attributeValue from the remaining buffer

System.out.println(extractClientId);
System.out.println(extractLastModifiedDate);
System.out.println(new String(extractAvroBinaryValue));

更新： –

在其中一个ByteBuffer data_record_value上,这是我打印出来的 –

System.out.println("Record Value Capacity: " + data_record_value.capacity());
System.out.println("Record Value Position: " + data_record_value.position());
System.out.println("Record Value Limit: " + data_record_value.limit());
System.out.println("Record Value Remaining: " + data_record_value.remaining());
System.out.println("Record Value: " + data_record_value);

这就是打印出来的 –

Record Value Capacity: 387
Record Value Position: 185
Record Value Limit: 250
Record Value Remaining: 65
Record Value: java.nio.HeapByteBuffer[pos=185 lim=250 cap=387]