VersionUtils: add a method to compare versions

This compares two version strings by splitting them by dot, then
comparing each split token numerically and/or lexicographically as
appropriate. SemVer version strings will compare as expected, although
the algorithm used is not limited to SemVer-compliant strings.

This commit is dedicated to Stefan Helfrich.

Author: ctrueden

src/main/java/org/scijava/util/VersionUtils.java

@@ -114,4 +114,57 @@ public static String getBuildNumber(final Class<?> c) {
 		return m == null ? null : m.getImplementationBuild();
 	}
 
+	/**
+	 * Compares two version strings.
+	 * @param v1 The first version string.
+	 * @param v2 The second version string.
+	 * @return a negative integer, zero, or a positive integer as the
+	 *         first argument is less than, equal to, or greater than the
+	 *         second.
+	 */
+	public static int compare(final String v1, final String v2) {
+		final String[] t1 = splitDots(v1), t2 = splitDots(v2);
+		final int count = Math.min(t1.length, t2.length);
+		for (int t=0; t<count; t++) {
+			final int c = compareToken(t1[t], t2[t]);
+			if (c != 0) return c;
+		}
+		if (t1.length == t2.length) return 0;
+		// NB: Token count differs. More tokens means newer -- e.g. 1.5 < 1.5.1.
+		return t1.length < t2.length ? -1 : 1;
+	}
+
+	// -- Helper methods --
+
+	/** Splits the given version string by dots. */
+	private static String[] splitDots(final String s) {
+		// NB: -1 split limit causes split not to remove empty values.
+		// See: https://stackoverflow.com/a/14602089/1207769
+		return s.isEmpty() ? new String[0] : s.split("\\.", -1);
+	}
+
+	/** Compares one token of a multi-token version string. */
+	private static int compareToken(final String t1, final String t2) {
+		final int i1 = digitIndex(t1), i2 = digitIndex(t2);
+		if (i1 > 0 && i2 > 0) {
+			// Versions start with digits; compare them numerically.
+			final long d1 = Long.parseLong(t1.substring(0, i1));
+			final long d2 = Long.parseLong(t2.substring(0, i2));
+			if (d1 < d2) return -1;
+			if (d1 > d2) return 1;
+		}
+		// Compare remaining characters lexicographically.
+		return t1.substring(i1).compareTo(t2.substring(i2));
+	}
+
+	/** Gets the subsequent index to all the given string's leading digits. */
+	private static int digitIndex(final String s) {
+		int index = 0;
+		for (int i=0; i<s.length(); i++) {
+			final char ch = s.charAt(index);
+			if (ch < '0' || ch > '9') break;
+			index++;
+		}
+		return index;
+	}
 }

src/test/java/org/scijava/util/VersionUtilsTest.java

@@ -0,0 +1,97 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
+ * Institute of Molecular Cell Biology and Genetics, University of
+ * Konstanz, and KNIME GmbH.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/**
+ * Tests {@link VersionUtils}.
+ * 
+ * @author Curtis Rueden
+ */
+public class VersionUtilsTest {
+
+	/** Tests {@link VersionUtils#compare(String, String)}. */
+	@Test
+	public void testCompare() {
+		// SemVer PATCH version.
+		assertTrue(VersionUtils.compare("1.5.1", "1.5.2") < 0);
+		assertTrue(VersionUtils.compare("1.5.2", "1.5.1") > 0);
+
+		// SemVer MINOR version.
+		assertTrue(VersionUtils.compare("1.5.2", "1.6.2") < 0);
+		assertTrue(VersionUtils.compare("1.6.2", "1.5.2") > 0);
+
+		// SemVer MAJOR version.
+		assertTrue(VersionUtils.compare("1.7.3", "2.7.3") < 0);
+		assertTrue(VersionUtils.compare("2.7.3", "1.7.3") > 0);
+
+		// Suffix indicates version is older than final release.
+		assertTrue(VersionUtils.compare("1.5.2", "1.5.2-beta-1") < 0);
+
+		// Check when number of version tokens does not match.
+		assertTrue(VersionUtils.compare("1.5", "1.5.1") < 0);
+		assertTrue(VersionUtils.compare("1.5.1", "1.5") > 0);
+
+		// Check equality.
+		assertEquals(VersionUtils.compare("1.5", "1.5"), 0);
+
+		// Check ImageJ 1.x style versions.
+		assertTrue(VersionUtils.compare("1.50a", "1.50b") < 0);
+
+		// Check four version tokens.
+		assertTrue(VersionUtils.compare("1.5.1.3", "1.5.1.4") < 0);
+		assertTrue(VersionUtils.compare("1.5.1.6", "1.5.1.5") > 0);
+		assertEquals(VersionUtils.compare("10.4.9.8", "10.4.9.8"), 0);
+
+		// Check non-numeric tokens.
+		assertTrue(VersionUtils.compare("a.b.c", "a.b.d") < 0);
+		
+		// Check for numerical (not lexicographic) comparison.
+		assertTrue(VersionUtils.compare("2.0", "23.0") < 0);
+		assertTrue(VersionUtils.compare("23.0", "2.0") > 0);
+		assertTrue(VersionUtils.compare("3.0", "23.0") < 0);
+		assertTrue(VersionUtils.compare("23.0", "3.0") > 0);
+
+		// Check weird stuff.
+		assertTrue(VersionUtils.compare("1", "a") < 0);
+		assertTrue(VersionUtils.compare("", "1") < 0);
+		assertTrue(VersionUtils.compare("1", "1.") < 0);
+		assertTrue(VersionUtils.compare("", ".") < 0);
+		assertTrue(VersionUtils.compare("", "..") < 0);
+		assertTrue(VersionUtils.compare(".", "..") < 0);
+	}
+}