Add json containers for Tweet and User objects

1 files changed, 72 insertions, 0 deletions

diff --git a/src/data/ValidatingJsonDeserializer.java b/src/data/ValidatingJsonDeserializer.java
new file mode 100644
index 0000000..91c1709
--- /dev/null
+++ b/src/data/ValidatingJsonDeserializer.java
@@ -0,0 +1,72 @@
+package data;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import java.lang.reflect.Field;
+import java.lang.reflect.Type;
+
+/**
+ * JSON deserializer which validates that all fields are present.
+ *
+ * @author Peter Wu.
+ */
+public class ValidatingJsonDeserializer<T> implements JsonDeserializer<T> {
+
+    @Override
+    public T deserialize(JsonElement je, Type type,
+            JsonDeserializationContext jdc) throws JsonParseException {
+        T obj = new Gson().fromJson(je, type);
+        JsonObject jsonObj = je.getAsJsonObject();
+        for (Field f : obj.getClass().getDeclaredFields()) {
+            if (!jsonObj.has(f.getName())) {
+                if (f.getAnnotation(Nullable.class) != null) {
+                    // null allowed, skip
+                    continue;
+                }
+                throw new JsonParseException("Missing field: " + f.getName());
+            }
+            // TODO: validate type?
+        }
+        return obj;
+    }
+
+    public static GsonBuilder addValidation(GsonBuilder gson, Type type) {
+        GsonBuilder gb = new GsonBuilder();
+        gson.registerTypeAdapter(type, new ValidatingJsonDeserializer());
+        for (Field f : type.getClass().getDeclaredFields()) {
+            Validator v = f.getAnnotation(Validator.class);
+            if (v != null) {
+                addValidation(gson, v.deserializer());
+            }
+        }
+        return gb;
+    }
+
+    /**
+     * Marks a member as object that should be validated too.
+     */
+    @Retention(RetentionPolicy.RUNTIME)
+    @Target(ElementType.FIELD)
+    public @interface Validator {
+
+        Class deserializer() default ValidatingJsonDeserializer.class;
+    }
+
+    /**
+     * Marks a member as nullable, that is, it can be missing from the JSON
+     * object.
+     */
+    @Retention(RetentionPolicy.RUNTIME)
+    @Target(ElementType.FIELD)
+    public @interface Nullable {
+    }
+}