Java Code Snippets

Byte array to hex string

public static String toHexString(byte[] array) {
    return javax.xml.bind.DatatypeConverter.printHexBinary(array);
}

Code in comments

/**
 * <PRE>
 * insert code as you would anywhere else
 * </PRE>
 */

An Example from a java.awt.Event method javadoc:

/**
 * <PRE>
 *    int onmask = SHIFT_DOWN_MASK | BUTTON1_DOWN_MASK;
 *    int offmask = CTRL_DOWN_MASK;
 *    if ((event.getModifiersEx() & (onmask | offmask)) == onmask) {
 *        ...
 *    }
 * </PRE>
 */

Get field descriptions (names)

public static <T, K> Map<K, String> getFieldDescriptions(Class<T> clazz) {
	Map<K, String> map = new HashMap<K,String>();
	for (Field f : clazz.getDeclaredFields()) {
		int mod = f.getModifiers();
		if (Modifier.isPublic(mod) && Modifier.isFinal(mod) && Modifier.isStatic(mod)) {
			try {
				@SuppressWarnings("unchecked")
				K fld = (K) f.get(null);
				
				Integer st = null;
				if (fld instanceof Integer) {
					st = (Integer) fld;
				} else if (fld instanceof Short) {
					st = (int) (short) (Short) fld;
				}
				map.put(fld, String.format("0x%04X, %s", st&0xFFFFFFFF, f.getName()));
			} catch (Exception ex) {
				/* ignore */
			}
		}
	}
	
	return map;
}

Check if AJAX request

public static boolean isAjax(HttpServletRequest request) {
	return "XMLHttpRequest".equalsIgnoreCase(request.getHeader("X-Requested-With"));
}

Check if POST request

public static boolean isPost(HttpServletRequest request) {
	return "POST".equals(request.getMethod());
}

Get web root

public static String getWebRootPath() {
	return HttpUtils.class.getProtectionDomain().getCodeSource().getLocation().getPath().split("WEB-INF/")[0];
}

Get client ip, event if the server is behind a proxy server (e.g. nginx)

public static String getIpAddr(HttpServletRequest request) {     
	String ip = request.getHeader("x-forwarded-for");     
	if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)){
		ip = request.getHeader("Proxy-Client-IP");     
	} else if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
		ip = request.getHeader("WL-Proxy-Client-IP");
	} else if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
		ip = request.getRemoteAddr();     
	}    
	return ip; 
}

Get all net interfaces’ IP

public static List<String> getAllLocalIPs() {
	List<String> ipLst = new ArrayList<>();
	try {
		Enumeration<NetworkInterface> e = NetworkInterface.getNetworkInterfaces();
		while (e.hasMoreElements()) {
			NetworkInterface n = (NetworkInterface) e.nextElement();
			Enumeration<InetAddress> ee = n.getInetAddresses();
			while (ee.hasMoreElements()) {
				InetAddress i = (InetAddress) ee.nextElement();
				ipLst.add(i.getHostAddress());
			}
		}
	} catch (Exception e) {
		e.printStackTrace();
		if (ipLst.size() == 0) {
			ipLst.add(LOCALHOST);
		}
	}
	return ipLst;
}

Set bits of a long variable

public static long setBits(long num, long val, int offset, int len) {
	int shift = Long.SIZE-offset-len;
	if (len > 1 || val == 0) {
		long ones = ((1L << len) - 1) << shift; //[] 1L
		return ((num & ~ones) | (val << shift));
	} else {
		return (long) (num | (1 << shift));
	}
}