Fixes #36 new property "os.detected.bitness". (#41)

Caveats:
  - might result in '31' for zOS legacy systems.
  - will report '32' for a 32-bit JVM running on a 64bit system.

src/main/java/kr/motd/maven/os/DetectExtension.java

@@ -47,6 +47,8 @@
  * <ul>
  * <li>{@code os.detected.name} - normalized {@code os.name} (e.g. {@code linux}, {@code osx})</li>
  * <li>{@code os.detected.arch} - normalized {@code os.arch} (e.g. {@code x86_64}, {@code x86_32})</li>
+ * <li>{@code os.detected.bitness} - bitness from wither {@code sun.arch.data.model} or {@code com.ibm.vm.bitmode} or {@code os.arch}
+ *     (e.g. {@code 64}, {@code 32})</li>
  * <li>{@code os.detected.version} - {@code os.detected.version.major}.{@code os.detected.version.minor}</li>
  * <li>{@code os.detected.version.major} - major part of {@code os.version} (integer value)</li>
  * <li>{@code os.detected.version.minor} - minor part of {@code os.version} (integer value)</li>
@@ -104,6 +106,7 @@ public void afterProjectsRead(MavenSession session) throws MavenExecutionExcepti
         final Map<String, String> dict = new LinkedHashMap<String, String>();
         dict.put(Detector.DETECTED_NAME, sessionProps.getProperty(Detector.DETECTED_NAME));
         dict.put(Detector.DETECTED_ARCH, sessionProps.getProperty(Detector.DETECTED_ARCH));
+        dict.put(Detector.DETECTED_BITNESS, sessionProps.getProperty(Detector.DETECTED_BITNESS));
         dict.put(Detector.DETECTED_CLASSIFIER, sessionProps.getProperty(Detector.DETECTED_CLASSIFIER));
         for (Map.Entry<Object, Object> entry : sessionProps.entrySet()) {
             if (entry.getKey().toString().startsWith(Detector.DETECTED_RELEASE)) {

src/main/java/kr/motd/maven/os/DetectMojo.java

@@ -35,6 +35,8 @@
  * <ul>
  * <li>{@code os.detected.name} - normalized {@code os.name} (e.g. {@code linux}, {@code osx})</li>
  * <li>{@code os.detected.arch} - normalized {@code os.arch} (e.g. {@code x86_64}, {@code x86_32})</li>
+ * <li>{@code os.detected.bitness} - bitness from wither {@code sun.arch.data.model} or {@code com.ibm.vm.bitmode} or {@code os.arch}
+ *     (e.g. {@code 64}, {@code 32})</li>
  * <li>{@code os.detected.classifier} - a shortcut for {@code 'os.detectedName'.'os.detectedArch'}
  *     (e.g. {@code linux-x86_64}). If the property {@code ${os.detection.classifierWithLikes}} is set,
  *     the first value for which a corresponding {@code os.detected.release.like.{variant}} property

src/main/java/kr/motd/maven/os/Detector.java

@@ -36,6 +36,7 @@ public abstract class Detector {
 
     public static final String DETECTED_NAME = "os.detected.name";
     public static final String DETECTED_ARCH = "os.detected.arch";
+    public static final String DETECTED_BITNESS = "os.detected.bitness";
     public static final String DETECTED_VERSION = "os.detected.version";
     public static final String DETECTED_VERSION_MAJOR = DETECTED_VERSION + ".major";
     public static final String DETECTED_VERSION_MINOR = DETECTED_VERSION + ".minor";
@@ -69,9 +70,11 @@ protected void detect(Properties props, List<String> classifierWithLikes) {
 
         final String detectedName = normalizeOs(osName);
         final String detectedArch = normalizeArch(osArch);
+        final int detectedBitness = determineBitness(detectedArch);
 
         setProperty(props, DETECTED_NAME, detectedName);
         setProperty(props, DETECTED_ARCH, detectedArch);
+        setProperty(props, DETECTED_BITNESS,"" + detectedBitness);
 
         final Matcher versionMatcher = VERSION_REGEX.matcher(osVersion);
         if (versionMatcher.matches()) {
@@ -364,6 +367,34 @@ private static String normalizeOsReleaseValue(String value) {
         return value.trim().replace("\"", "");
     }
 
+    public static int determineBitness(String architecture) {
+        // try the widely adopted sun specification first.
+        String bitness = System.getProperty("sun.arch.data.model", "");
+
+        if (!bitness.isEmpty() && bitness.matches("[0-9]+")) {
+            return Integer.parseInt(bitness, 10);
+        }
+
+        // bitness from sun.arch.data.model cannot be used. Try the IBM specification.
+        bitness = System.getProperty("com.ibm.vm.bitmode", "");
+
+        if (!bitness.isEmpty() && bitness.matches("[0-9]+")) {
+            return Integer.parseInt(bitness, 10);
+        }
+
+        // as a last resort, try to determine the bitness from the architecture.
+      return guessBitnessFromArchitecture(architecture);
+    }
+
+    public static int guessBitnessFromArchitecture(final String arch) {
+        if (arch.contains("64")) {
+            return 64;
+        }
+
+        return 32;
+    }
+
+
     private static void closeQuietly(Closeable obj) {
         try {
             if (obj != null) {