java将IP地址转换为数字以及逆向转换（位运算和0xFF的使用）第二季

原文：

http://www.mkyong.com/java/java-convert-ip-address-to-decimal-number/

来自同一个博客。

IP转为数字（第二种算法。用左移、按位或实现。效率比上一篇的更高。）：

public long ipToLong(String ipAddress) {

long result = 0;

String[] ipAddressInArray = ipAddress.split("\\.");

for (int i = 3; i >= 0; i--) {

long ip = Long.parseLong(ipAddressInArray[3 - i]);

//left shifting 24,16,8,0 and bitwise OR

//1. 192 << 24
//1. 168 << 16
//1. 1   << 8
//1. 2   << 0
result |= ip << (i * 8);

}
return result;
}

数字转为IP，两种算法都差不多：

//ip = 3232235778
public String longToIp(long ip) {
StringBuilder result = new StringBuilder(15);

for (int i = 0; i < 4; i++) {

result.insert(0,Long.toString(ip & 0xff));

if (i < 3) {
result.insert(0,'.');
}

ip = ip >> 8;
}
return result.toString();
}

//ip = 3232235778
public String longToIp2(long ip) {

return ((ip >> 24) & 0xFF) + "."
+ ((ip >> 16) & 0xFF) + "."
+ ((ip >> 8) & 0xFF) + "."
+ (ip & 0xFF);
}

完整代码：
public class JavaBitwiseExample {

public static void main(String[] args) {

JavaBitwiseExample obj = new JavaBitwiseExample();

System.out.println("iptoLong : " + obj.ipToLong("192.168.1.2"));
System.out.println("iptoLong2 : " + obj.ipToLong2("192.168.1.2"));

System.out.println("longToIp : " + obj.longToIp(3232235778L));
System.out.println("longToIp2 : " + obj.longToIp2(3232235778L));

}

// example : 192.168.1.2
public long ipToLong(String ipAddress) {

// ipAddressInArray[0] = 192
String[] ipAddressInArray = ipAddress.split("\\.");

long result = 0;
for (int i = 0; i < ipAddressInArray.length; i++) {

int power = 3 - i;
int ip = Integer.parseInt(ipAddressInArray[i]);

// 1. 192 * 256^3
// 2. 168 * 256^2
// 3. 1 * 256^1
// 4. 2 * 256^0
result += ip * Math.pow(256, power);

}

return result;

}

public long ipToLong2(String ipAddress) {

long result = 0;

String[] ipAddressInArray = ipAddress.split("\\.");

for (int i = 3; i >= 0; i--) {

long ip = Long.parseLong(ipAddressInArray[3 - i]);

// left shifting 24,16,8,0 and bitwise OR

// 1. 192 << 24
// 1. 168 << 16
// 1. 1 << 8
// 1. 2 << 0
result |= ip << (i * 8);

}

return result;
}

public String longToIp(long i) {

return ((i >> 24) & 0xFF) +
"." + ((i >> 16) & 0xFF) +
"." + ((i >> 8) & 0xFF) +
"." + (i & 0xFF);

}

public String longToIp2(long ip) {
StringBuilder sb = new StringBuilder(15);

for (int i = 0; i < 4; i++) {

// 1. 2
// 2. 1
// 3. 168
// 4. 192
sb.insert(0, Long.toString(ip & 0xff));

if (i < 3) {
sb.insert(0, '.');
}

// 1. 192.168.1.2
// 2. 192.168.1
// 3. 192.168
// 4. 192
ip = ip >> 8;

}

return sb.toString();
}
}

Output:

iptoLong  : 3232235778
iptoLong2 : 3232235778
longToIp  : 192.168.1.2
longToIp2 : 192.168.1.2