#12 - EmptyJson and MissingJson.

src/main/java/com/vzurauskas/nereides/javax/EmptyJson.java

@@ -0,0 +1,14 @@
+package com.vzurauskas.nereides.javax;
+
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+
+/**
+ * Empty {@link Json}. It is equivalent to {@code new Json.Of("{}")}.
+ */
+public final class EmptyJson implements Json {
+    @Override
+    public InputStream bytes() {
+        return new ByteArrayInputStream("{}".getBytes());
+    }
+}

src/main/java/com/vzurauskas/nereides/javax/MissingJson.java

@@ -0,0 +1,18 @@
+package com.vzurauskas.nereides.javax;
+
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+
+/**
+ * {@link Json}, which is missing. It is equivalent to
+ * {@code new Json.Of(new byte[0])}.
+ */
+public final class MissingJson implements Json {
+
+    private static final byte[] MISSING = new byte[0];
+
+    @Override
+    public InputStream bytes() {
+        return new ByteArrayInputStream(MISSING);
+    }
+}

src/main/java/com/vzurauskas/nereides/javax/SmartJson.java

@@ -5,6 +5,7 @@
 import java.io.Writer;
 import java.util.Collections;
 import java.util.Optional;
+import javax.json.JsonException;
 import javax.json.JsonObject;
 import javax.json.JsonStructure;
 import javax.json.JsonValue;
@@ -176,10 +177,21 @@ public JsonStructure jsonStructure() {
      * @return The nested JSON, which could be missing.
      */
     public SmartJson at(String path) {
-        return new SmartJson(
-            new Of(
-                structure.value().asJsonObject().getValue(path).asJsonObject()
-            )
-        );
+        JsonObject whole = structure.value().asJsonObject();
+        JsonValue target;
+        try {
+            target = whole.getValue(path);
+        } catch (JsonException e) {
+            return new SmartJson(new MissingJson());
+        }
+        return new SmartJson(new Json.Of(target.asJsonObject()));
+    }
+
+    /**
+     * Method which tells if this JSON is missing.
+     * @return true if this JSON is missing; otherwise false.
+     */
+    public boolean isMissing() {
+        return byteArray().length == 0;
     }
 }

src/test/java/com/vzurauskas/nereides/javax/EmptyJsonTest.java

@@ -0,0 +1,13 @@
+package com.vzurauskas.nereides.javax;
+
+import org.junit.jupiter.api.Test;
+
+final class EmptyJsonTest {
+    @Test
+    void creates() {
+        new EqualityAssertion(
+            new Json.Of("{}"),
+            new EmptyJson()
+        ).affirm();
+    }
+}

src/test/java/com/vzurauskas/nereides/javax/EqualityAssertion.java

@@ -0,0 +1,20 @@
+package com.vzurauskas.nereides.javax;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public final class EqualityAssertion {
+    private final Json first;
+    private final Json second;
+
+    public EqualityAssertion(Json first, Json second) {
+        this.first = first;
+        this.second = second;
+    }
+
+    public void affirm() {
+        assertEquals(
+            new SmartJson(first).pretty(),
+            new SmartJson(second).pretty()
+        );
+    }
+}

src/test/java/com/vzurauskas/nereides/javax/MissingJsonTest.java

@@ -0,0 +1,15 @@
+package com.vzurauskas.nereides.javax;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import java.io.IOException;
+import org.junit.jupiter.api.Test;
+
+final class MissingJsonTest {
+    @Test
+    void creates() throws IOException {
+        assertEquals(
+            0,
+            new MissingJson().bytes().available()
+        );
+    }
+}

src/test/java/com/vzurauskas/nereides/javax/SmartJsonTest.java

@@ -311,6 +311,15 @@ void findsPathInArray() {
         );
     }
 
+    @Test
+    void handlesNonExistentPaths() {
+        assertTrue(
+            new SmartJson(
+                new Json.Of(deep)
+            ).at("/ocean/nothing").isMissing()
+        );
+    }
+
     @Disabled("https://github.com/vzurauskas/nereides-javax/issues/26")
     @Test
     void understandsArrays() {
@@ -335,4 +344,14 @@ void reallyUnderstandsArrays() {
             ).at("/ocean/rock1/nereid1/associates").at("/0").leaf("name").get()
         );
     }
+
+    @Test
+    void knowsIfMissing() {
+        assertTrue(new SmartJson(new MissingJson()).isMissing());
+    }
+
+    @Test
+    void knowsIfNotMissing() {
+        assertFalse(new SmartJson(new Json.Of("{}")).isMissing());
+    }
 }