Add checkstyle support

Fixes #481

Execute checkstyle validation at build time.
Add minimal set of rules.
Ensure that existing code conforms to the rules.

spring-cloud-stream-binders/spring-cloud-stream-binder-test/src/main/java/org/springframework/cloud/stream/binder/TestUtils.java

@@ -24,38 +24,41 @@ import org.springframework.util.Assert;
  */
 public class TestUtils {
 
-    /**
-     * Uses nested {@link DirectFieldAccessor}s to obtain a property using dotted notation to traverse fields; e.g.
-     * "foo.bar.baz" will obtain a reference to the baz field of the bar field of foo. Adopted from Spring Integration.
-     * @param root The object.
-     * @param propertyPath The path.
-     * @return The field.
-     */
-    public static Object getPropertyValue(Object root, String propertyPath) {
-        Object value = null;
-        DirectFieldAccessor accessor = new DirectFieldAccessor(root);
-        String[] tokens = propertyPath.split("\\.");
-        for (int i = 0; i < tokens.length; i++) {
-            value = accessor.getPropertyValue(tokens[i]);
-            if (value != null) {
-                accessor = new DirectFieldAccessor(value);
-            }
-            else if (i == tokens.length - 1) {
-                return null;
-            }
-            else {
-                throw new IllegalArgumentException("intermediate property '" + tokens[i] + "' is null");
-            }
-        }
-        return value;
-    }
+	/**
+	 * Uses nested {@link DirectFieldAccessor}s to obtain a property using dotted notation
+	 * to traverse fields; e.g. "foo.bar.baz" will obtain a reference to the baz field of
+	 * the bar field of foo. Adopted from Spring Integration.
+	 * @param root The object.
+	 * @param propertyPath The path.
+	 * @return The field.
+	 */
+	public static Object getPropertyValue(Object root, String propertyPath) {
+		Object value = null;
+		DirectFieldAccessor accessor = new DirectFieldAccessor(root);
+		String[] tokens = propertyPath.split("\\.");
+		for (int i = 0; i < tokens.length; i++) {
+			value = accessor.getPropertyValue(tokens[i]);
+			if (value != null) {
+				accessor = new DirectFieldAccessor(value);
+			}
+			else if (i == tokens.length - 1) {
+				return null;
+			}
+			else {
+				throw new IllegalArgumentException(
+						"intermediate property '" + tokens[i] + "' is null");
+			}
+		}
+		return value;
+	}
 
-    @SuppressWarnings("unchecked")
-    public static <T> T getPropertyValue(Object root, String propertyPath, Class<T> type) {
-        Object value = getPropertyValue(root, propertyPath);
-        if (value != null) {
-            Assert.isAssignable(type, value.getClass());
-        }
-        return (T) value;
-    }
+	@SuppressWarnings("unchecked")
+	public static <T> T getPropertyValue(Object root, String propertyPath,
+			Class<T> type) {
+		Object value = getPropertyValue(root, propertyPath);
+		if (value != null) {
+			Assert.isAssignable(type, value.getClass());
+		}
+		return (T) value;
+	}
 }