Java根据网段计算子网掩码，起始IP，结束IP

/**
 * IP的相关计算
 * @author zengchaowang
 * @version 1.0
 *
 */
public class IpCaculate {

	/**
	 * 根据掩码位数计算掩码
	 * @param maskIndex 掩码位
	 * @return 子网掩码
	 */
	public static String getNetMask(String maskIndex) {
		StringBuilder mask = new StringBuilder();
		Integer inetMask = 0;
		try {
			inetMask = Integer.parseInt(maskIndex);
		} catch (NumberFormatException e) {
			System.out.println(e.getMessage());
			return null;
		}
		if (inetMask > 32) {
			return null;
		}
		// 子网掩码为1占了几个字节
		int num1 = inetMask / 8;
		// 子网掩码的补位位数
		int num2 = inetMask % 8;
		int array[] = new int[4];
		for (int i = 0; i < num1; i++) {
			array[i] = 255;
		}
		for (int i = num1; i < 4; i++) {
			array[i] = 0;
		}
		for (int i = 0; i < num2; num2--) {
			array[num1] += 1 << 8 - num2;
		}
		for (int i = 0; i < 4; i++) {
			if (i == 3) {
				mask.append(array[i]);
			} else {
				mask.append(array[i] + ".");
			}
		}
		return mask.toString();
	}

	/**
	 * 根据网段计算起始IP 网段格式:x.x.x.x/x
	 * 一个网段0一般为网络地址,255一般为广播地址.
	 * 起始IP计算:网段与掩码相与之后加一的IP地址
	 * @param segment  网段
	 * @return 起始IP
	 */
	public static String getStartIp(String segment) {
		StringBuffer startIp = new StringBuffer();
		if (segment == null) {
			return null;
		}
		String arr[] = segment.split("/");
		String ip = arr[0];
		String maskIndex = arr[1];
		String mask = IpCaculate.getNetMask(maskIndex);
		if (4 != ip.split("\\.").length || mask == null) {
			return null;
		}
		int ipArray[] = new int[4];
		int netMaskArray[] = new int[4];
		for (int i = 0; i < 4; i++) {
			try {
				ipArray[i] = Integer.parseInt(ip.split("\\.")[i]);
				netMaskArray[i] = Integer.parseInt(mask.split("\\.")[i]);
				if (ipArray[i] > 255 || ipArray[i] < 0 || netMaskArray[i] > 255 || netMaskArray[i] < 0) {
					return null;
				}
				ipArray[i] = ipArray[i] & netMaskArray[i];
				if(i==3){
					startIp.append(ipArray[i]+1);
				}else{
					startIp.append(ipArray[i]+".");
				}
			} catch (NumberFormatException e) {
				System.out.println(e.getMessage());
			}
		}
		 return startIp.toString();
	}
	
	/**
	 * 根据网段计算结束IP
	 * @param segment
	 * @return 结束IP
	 */
	public static String getEndIp(String segment) {    
		StringBuffer endIp=new StringBuffer();
		String startIp = getStartIp(segment);    
		if (segment == null) {
			return null;
		}
		String arr[] = segment.split("/");
		String maskIndex = arr[1];
		//实际需要的IP个数
	    int hostNumber = 0;
	    int startIpArray[] = new int[4];
		try {
			hostNumber=1<<32-(Integer.parseInt(maskIndex));
			for (int i = 0; i <4; i++) {    
				startIpArray[i] = Integer.parseInt(startIp.split("\\.")[i]);    
		        if(i == 3){    
		        	startIpArray[i] = startIpArray[i] - 1;    
		            break;
		        }    
		    }    
			startIpArray[3] = startIpArray[3] + (hostNumber - 1); 
		} catch (NumberFormatException e) {
			System.out.println(e.getMessage());
		}
	   
		if(startIpArray[3] >255){    
	        int k = startIpArray[3] / 256;    
	        startIpArray[3] = startIpArray[3] % 256;    
	        startIpArray[2] = startIpArray[2] + k;    
	    }    
	    if(startIpArray[2] > 255){    
	        int  j = startIpArray[2] / 256;    
	        startIpArray[2] = startIpArray[2] % 256;    
	        startIpArray[1] = startIpArray[1] + j;    
	           if(startIpArray[1] > 255){    
	               int  k = startIpArray[1] / 256;    
	               startIpArray[1] = startIpArray[1] % 256;    
	               startIpArray[0] = startIpArray[0] + k;    
	           }    
	       }    
	    for(int i = 0; i < 4; i++){    
	        if(i == 3){    
	        	startIpArray[i] = startIpArray[i] - 1;    
	        }    
	        if("" == endIp.toString()||endIp.length()==0){    
	        	endIp.append(startIpArray[i]);    
	        }else{    
	        	endIp.append("." + startIpArray[i]);    
	        }    
	    }    
		return endIp.toString();
	}  
}

根据网段计算起始IP 网段格式:x.x.x.x/x

网段内需要的IP数量为：2的（32-掩码位）次方个。

因为一个网段0一般为网络地址,255一般为广播地址， 所以第一个可用IP起始IP计算:网段与掩码相与之后加一的IP地址，结束IP为通过计算需要的所有IP数然后做累加运算，超过256则进位进行运算。