implement ConfigObject.hasPath()

src/main/java/com/typesafe/config/ConfigObject.java

@@ -18,10 +18,13 @@ import java.util.Map;
  * files, sometimes double quotes are needed around special characters.)
  *
  * ConfigObject implements the standard Java Map interface, but the mutator
- * methods all throw UnsupportedOperationException.
+ * methods all throw UnsupportedOperationException. This Map is immutable.
  *
- * TODO add OrNull variants of all these getters? Or better to avoid convenience
- * API for that?
+ * The Map may contain null values, which will have ConfigValue.valueType() ==
+ * ConfigValueType.NULL. When using methods from the Map interface, such as
+ * get() or containsKey(), these null ConfigValue will be visible. But hasPath()
+ * returns false for null values, and getInt() etc. throw ConfigException.Null
+ * for null values.
  */
 public interface ConfigObject extends ConfigValue, Map<String, ConfigValue> {
 
@@ -38,6 +41,25 @@ public interface ConfigObject extends ConfigValue, Map<String, ConfigValue> {
     @Override
     ConfigObject withFallbacks(ConfigValue... others);
 
+    /**
+     * Checks whether a value is present and non-null at the given path. This
+     * differs in two ways from containsKey(): it looks for a path expression,
+     * not a key; and it returns false for null values, while containsKey()
+     * returns true indicating that the object contains a null value for the
+     * key.
+     * 
+     * If a path exists according to hasPath(), then getValue() will never throw
+     * an exception. However, the typed getters, such as getInt(), will still
+     * throw if the value is not convertible to the requested type.
+     *
+     * @param path
+     *            the path expression
+     * @return true if a non-null value is present at the path
+     * @throws ConfigException.BadPath
+     *             if the path expression is invalid
+     */
+    boolean hasPath(String path);
+
     boolean getBoolean(String path);
 
     Number getNumber(String path);

src/main/java/com/typesafe/config/impl/AbstractConfigObject.java

@@ -121,6 +121,13 @@ abstract class AbstractConfigObject extends AbstractConfigValue implements
         return ConfigValueType.OBJECT;
     }
 
+    @Override
+    public boolean hasPath(String pathExpression) {
+        Path path = Path.newPath(pathExpression);
+        ConfigValue peeked = peekPath(path, null, 0, null);
+        return peeked != null && peeked.valueType() != ConfigValueType.NULL;
+    }
+
     @Override
     AbstractConfigObject transformed(ConfigTransformer newTransformer) {
         if (newTransformer != transformer)

src/test/scala/com/typesafe/config/impl/ConfigValueTest.scala

@@ -371,4 +371,38 @@ class ConfigValueTest extends TestUtils {
         // merge three
         assertEquals("merge of a,b,c", m(o("a", false), o("b", false), o("c", false)))
     }
+
+    @Test
+    def hasPathWorks() {
+        val empty = parseObject("{}")
+
+        assertFalse(empty.hasPath("foo"))
+
+        val obj = parseObject("a=null, b.c.d=11, foo=bar")
+
+        // returns true for the non-null values
+        assertTrue(obj.hasPath("foo"))
+        assertTrue(obj.hasPath("b.c.d"))
+        assertTrue(obj.hasPath("b.c"))
+        assertTrue(obj.hasPath("b"))
+
+        // hasPath() is false for null values but containsKey is true
+        assertEquals(nullValue(), obj.get("a"))
+        assertTrue(obj.containsKey("a"))
+        assertFalse(obj.hasPath("a"))
+
+        // false for totally absent values
+        assertFalse(obj.containsKey("notinhere"))
+        assertFalse(obj.hasPath("notinhere"))
+
+        // throws proper exceptions
+        intercept[ConfigException.BadPath] {
+            empty.hasPath("a.")
+        }
+
+        intercept[ConfigException.BadPath] {
+            empty.hasPath("..")
+        }
+
+    }
 }