从127.0.0.1到2130706433,然后再回来

Question

使用标准Java库,从IPV4-address("127.0.0.1")的虚线字符串表示到等效整数表示(2130706433)的最快方法是什么.

相应地,反转所述操作的最快方法是什么 - 从整数2130706433到字符串表示"127.0.0.1"？

Answer 1

字符串到int:

int pack(byte[] bytes) {
  int val = 0;
  for (int i = 0; i < bytes.length; i++) {
    val <<= 8;
    val |= bytes[i] & 0xff;
  }
  return val;
}

pack(InetAddress.getByName(dottedString).getAddress());

Int到字符串:

byte[] unpack(int bytes) {
  return new byte[] {
    (byte)((bytes >>> 24) & 0xff),
    (byte)((bytes >>> 16) & 0xff),
    (byte)((bytes >>>  8) & 0xff),
    (byte)((bytes       ) & 0xff)
  };
}


InetAddress.getByAddress(unpack(packedBytes)).getHostAddress()

Answer 2

您还可以使用Google Guava InetAddress类

String ip = "192.168.0.1";
InetAddress addr = InetAddresses.forString(ip);
// Convert to int
int address = InetAddresses.coerceToInteger(addr);
// Back to str 
String addressStr = InetAddresses.fromInteger(address));

Answer 3

我修改了原来的答案.在Sun的实现中InetAddress,该hashCode方法生成IPv4地址的整数表示,但正如评论者正确指出的那样,JavaDoc无法保证这一点.因此,我决定使用ByteBuffer该类来计算IPv4地址的值.

import java.net.InetAddress;
import java.nio.ByteBuffer;

// ...

try {
    // Convert from integer to an IPv4 address
    InetAddress foo = InetAddress.getByName("2130706433");
    String address = foo.getHostAddress();
    System.out.println(address);

    // Convert from an IPv4 address to an integer
    InetAddress bar = InetAddress.getByName("127.0.0.1");
    int value = ByteBuffer.wrap(bar.getAddress()).getInt();
    System.out.println(value);

} catch (Exception e) {
    e.printStackTrace();
}

输出将是:

127.0.0.1
2130706433

Answer 4

如果您需要学习长手数学，您可以使用 Substr 来删除八位字节。将表示类别的第一个八位字节乘以 (256*256*256) 或 (2^24) 第二个乘以 (256*256) (2^16) 第三个乘以 (256) (2^8) 第四个乘以 1 或(2^0)

127 * (2^24) + 0 *(2^16) + 0 * (2^8) + 1 * (2^0) 2130706432 + 0 + 0 + 1 = 2130706433