[#42] Move precondition checks into common package/class.

src/main/java/org/irods/irods4j/input_validation/PreconditionViolationException.java

@@ -0,0 +1,11 @@
+package org.irods.irods4j.input_validation;
+
+public class PreconditionViolationException extends RuntimeException {
+
+	private static final long serialVersionUID = 1L;
+
+	public PreconditionViolationException(String message) {
+		super(message);
+	}
+
+}

src/main/java/org/irods/irods4j/input_validation/Preconditions.java

@@ -0,0 +1,54 @@
+package org.irods.irods4j.input_validation;
+
+public class Preconditions {
+
+	/**
+	 * Checks if the object is null.
+	 * 
+	 * @param o       The object to check for null.
+	 * @param message The precondition violation message.
+	 * 
+	 * @throws PreconditionViolationException If the object is null.
+	 * 
+	 * @since 0.1.0
+	 */
+	public static void notNull(Object o, String message) {
+		if (null == o) {
+			throw new PreconditionViolationException(message);
+		}
+	}
+
+	/**
+	 * Checks if a string is null or empty.
+	 * 
+	 * @param s       The string to check.
+	 * @param message The precondition violation message.
+	 * 
+	 * @throws PreconditionViolationException If the object is null.
+	 * 
+	 * @since 0.1.0
+	 */
+	public static void notNullOrEmpty(String s, String message) {
+		if (null == s || s.isEmpty()) {
+			throw new PreconditionViolationException(message);
+		}
+	}
+
+	/**
+	 * Checks if an integer is greater than or equal to a threshold.
+	 * 
+	 * @param value     The integer to test.
+	 * @param threshold The integer to test against.
+	 * @param message   The precondition violation message.
+	 * 
+	 * @throws PreconditionViolationException If the object is null.
+	 * 
+	 * @since 0.1.0
+	 */
+	public static void greaterThanOrEqualToValue(long value, long threshold, String message) {
+		if (value < threshold) {
+			throw new PreconditionViolationException(message);
+		}
+	}
+
+}