From e4d8d30fca3bc621e0f5ec6eba6117b510621c6f Mon Sep 17 00:00:00 2001
From: Peter Wu <peter@lekensteyn.nl>
Date: Sat, 10 May 2014 01:06:28 +0200
Subject: Add validator debugger where the wrong type is returned

---
 src/data/DebuggingJsonDeserializer.java       | 41 +++++++++++++++++++++++++++
 src/data/ValidatingJsonDeserializer.java      |  2 +-
 src/io/TweetReader.java                       | 14 ++++++++-
 test/data/ValidatingJsonDeserializerTest.java | 10 +++++++
 4 files changed, 65 insertions(+), 2 deletions(-)
 create mode 100644 src/data/DebuggingJsonDeserializer.java

diff --git a/src/data/DebuggingJsonDeserializer.java b/src/data/DebuggingJsonDeserializer.java
new file mode 100644
index 0000000..1b00d4d
--- /dev/null
+++ b/src/data/DebuggingJsonDeserializer.java
@@ -0,0 +1,41 @@
+package data;
+
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParseException;
+import java.lang.reflect.Type;
+
+/**
+ * Validates the deserialization of a JSON string. The main motivation of this
+ * class is to print the property name of an object that throws an
+ * IllegalStateException because a string was expected, but a different type got
+ * returned.
+ *
+ * @author Peter Wu
+ */
+public class DebuggingJsonDeserializer extends ValidatingJsonDeserializer {
+
+    private final Class overriddenClass;
+
+    private DebuggingJsonDeserializer(Class overriddenClass) {
+        this.overriddenClass = overriddenClass;
+    }
+
+    @Override
+    public Object deserialize(JsonElement je, Type type,
+            JsonDeserializationContext jdc) throws JsonParseException {
+        checkObject("", je, overriddenClass);
+        return null;
+    }
+
+    public static void tryValidate(String json, Class cls) {
+        new GsonBuilder()
+                .registerTypeAdapter(Dummy.class, new DebuggingJsonDeserializer(cls))
+                .create()
+                .fromJson(json, Dummy.class);
+    }
+
+    private class Dummy {
+    }
+}
diff --git a/src/data/ValidatingJsonDeserializer.java b/src/data/ValidatingJsonDeserializer.java
index c168821..f44b681 100644
--- a/src/data/ValidatingJsonDeserializer.java
+++ b/src/data/ValidatingJsonDeserializer.java
@@ -30,7 +30,7 @@ public class ValidatingJsonDeserializer<T> implements JsonDeserializer<T> {
         return obj;
     }
 
-    private void checkObject(String path, JsonElement je, Class type) {
+    void checkObject(String path, JsonElement je, Class type) {
         JsonObject jsonObj = je.getAsJsonObject();
         for (Field f : type.getDeclaredFields()) {
             JsonElement val = jsonObj.get(f.getName());
diff --git a/src/io/TweetReader.java b/src/io/TweetReader.java
index bf89a2c..f67daf8 100644
--- a/src/io/TweetReader.java
+++ b/src/io/TweetReader.java
@@ -2,7 +2,9 @@ package io;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonParseException;
 import com.google.gson.JsonSyntaxException;
+import data.DebuggingJsonDeserializer;
 import data.Tweet;
 import data.ValidatingJsonDeserializer;
 import java.io.BufferedReader;
@@ -40,7 +42,7 @@ public class TweetReader implements ITweetReader {
             try {
                 tweet = gson.fromJson(line, Tweet.class);
             } catch (JsonSyntaxException ex) {
-                // TODO: handle something?
+                debugTweet(line, ex);
                 throw ex;
             }
         }
@@ -54,4 +56,14 @@ public class TweetReader implements ITweetReader {
         } catch (IOException ex) {
         }
     }
+
+    private void debugTweet(String line, JsonSyntaxException ex) {
+        try {
+            System.err.println("Faulty line: " + line);
+            DebuggingJsonDeserializer.tryValidate(line, Tweet.class);
+            System.err.println("No error occured, how strange?");
+        } catch (JsonParseException jse) {
+            System.err.println("The error was: " + jse);
+        }
+    }
 }
diff --git a/test/data/ValidatingJsonDeserializerTest.java b/test/data/ValidatingJsonDeserializerTest.java
index 2d3ffd1..a1f9884 100644
--- a/test/data/ValidatingJsonDeserializerTest.java
+++ b/test/data/ValidatingJsonDeserializerTest.java
@@ -534,4 +534,14 @@ public class ValidatingJsonDeserializerTest {
         tweet.add("place", null);
         checkTweetPass(tweet);
     }
+
+    @Test
+    public void testNotATweetObject() {
+        try {
+            DebuggingJsonDeserializer.tryValidate("{}", Tweet.class);
+            fail("DebuggingJsonDeserializer must also check for type.");
+        } catch (JsonParseException ex) {
+            assertEquals("Missing field: id", ex.getMessage());
+        }
+    }
 }
-- 
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