如何将字节数组转换为其数值（Java）？
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How to convert a byte array to its numeric value (Java)?
提问by pirate
I have an 8 byte array and I want to convert it to its corresponding numeric value.
我有一个 8 字节的数组，我想将其转换为相应的数值。
e.g.
例如
byte[] by = new byte[8]; // the byte array is stored in 'by'
// CONVERSION OPERATION
// return the numeric value
I want a method that will perform the above conversion operation.
我想要一种执行上述转换操作的方法。
采纳答案by Mnementh
Assuming the first byte is the least significant byte:
假设第一个字节是最低有效字节：
long value = 0;
for (int i = 0; i < by.length; i++)
{
value += ((long) by[i] & 0xffL) << (8 * i);
}
Is the first byte the most significant, then it is a little bit different:
第一个字节是最重要的，那么它有点不同：
long value = 0;
for (int i = 0; i < by.length; i++)
{
value = (value << 8) + (by[i] & 0xff);
}
Replace long with BigInteger, if you have more than 8 bytes.
如果您有超过 8 个字节，请用BigInteger替换 long 。
Thanks to Aaron Digulla for the correction of my errors.
感谢 Aaron Digulla 纠正我的错误。
回答by coobird
One could use the Buffers that are provided as part of the java.niopackage to perform the conversion.
可以使用Buffer作为java.nio包的一部分提供的s来执行转换。
Here, the source byte[]array has a of length 8, which is the size that corresponds with a longvalue.
这里，源byte[]数组的长度为 8，这是与long值对应的大小。
First, the byte[]array is wrapped in a ByteBuffer, and then the ByteBuffer.getLongmethod is called to obtain the longvalue:
首先将byte[]数组包裹在 a 中ByteBuffer，然后ByteBuffer.getLong调用该方法获取long值：
ByteBuffer bb = ByteBuffer.wrap(new byte[] {0, 0, 0, 0, 0, 0, 0, 4});
long l = bb.getLong();
System.out.println(l);
Result
结果
4
I'd like to thank dfa for pointing out the ByteBuffer.getLongmethod in the comments.
我要感谢 dfaByteBuffer.getLong在评论中指出了方法。
Although it may not be applicable in this situation, the beauty of the Buffers come with looking at an array with multiple values.
尽管在这种情况下它可能不适用，但Buffers的美妙之处在于查看具有多个值的数组。
For example, if we had a 8 byte array, and we wanted to view it as two intvalues, we could wrap the byte[]array in an ByteBuffer, which is viewed as a IntBufferand obtain the values by IntBuffer.get:
例如，如果我们有一个 8 字节的数组，并且希望将其视为两个int值，则可以将byte[]数组包装在 an 中ByteBuffer，将其视为 aIntBuffer并通过IntBuffer.get以下方式获取值：
ByteBuffer bb = ByteBuffer.wrap(new byte[] {0, 0, 0, 1, 0, 0, 0, 4});
IntBuffer ib = bb.asIntBuffer();
int i0 = ib.get(0);
int i1 = ib.get(1);
System.out.println(i0);
System.out.println(i1);
Result:
结果：
1
4
回答by Vincent Robert
If this is an 8-bytes numeric value, you can try:
如果这是一个 8 字节的数值，您可以尝试：
BigInteger n = new BigInteger(byteArray);
If this is an UTF-8 character buffer, then you can try:
如果这是一个 UTF-8 字符缓冲区，那么您可以尝试：
BigInteger n = new BigInteger(new String(byteArray, "UTF-8"));
回答by iBog
Complete java converter code for all primitive types to/from arrays http://www.daniweb.com/code/snippet216874.html
所有原始类型到/从数组的完整 java 转换器代码 http://www.daniweb.com/code/snippet216874.html
回答by Chen Yi
Simply, you could use or refer to guavalib provided by google, which offers utiliy methods for conversion between long and byte array. My client code:
简单来说，你可以使用或参考谷歌提供的guavalib，它提供了用于长数组和字节数组之间转换的实用方法。我的客户代码：
long content = 212000607777l;
byte[] numberByte = Longs.toByteArray(content);
logger.info(Longs.fromByteArray(numberByte));
回答by Jamel Toms
You can also use BigInteger for variable length bytes. You can convert it to Long, Integer or Short, whichever suits your needs.
您还可以将 BigInteger 用于可变长度字节。您可以根据需要将其转换为 Long、Integer 或 Short。
new BigInteger(bytes).intValue();
or to denote polarity:
或表示极性：
new BigInteger(1, bytes).intValue();
回答by Asaf Pinhassi
Each cell in the array is treated as unsigned int:
数组中的每个单元格都被视为无符号整数：
private int unsignedIntFromByteArray(byte[] bytes) {
int res = 0;
if (bytes == null)
return res;
for (int i=0;i<bytes.length;i++){
res = res | ((bytes[i] & 0xff) << i*8);
}
return res;
}
