A type adapter for Class that throws an UnsupportedOperationException.

gson/src/main/java/com/google/gson/Gson.java

@@ -241,6 +241,7 @@ public final class Gson {
     factories.add(new MapTypeAdapterFactory(constructorConstructor, complexMapKeySerialization));
     factories.add(ArrayTypeAdapter.FACTORY);
     factories.add(TypeAdapters.ENUM_FACTORY);
+    factories.add(TypeAdapters.CLASS_FACTORY);
     factories.add(reflectiveTypeAdapterFactory);
 
     this.factories = Collections.unmodifiableList(factories);

gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java

@@ -53,6 +53,24 @@ import java.util.UUID;
 public final class TypeAdapters {
   private TypeAdapters() {}
 
+  @SuppressWarnings("rawtypes")
+  public static final TypeAdapter<Class> CLASS = new TypeAdapter<Class>() {
+	@Override
+	public void write(JsonWriter out, Class value) throws IOException {
+	  if (value == null) {
+	    return;
+	  }
+	  throw new UnsupportedOperationException("Attempted to serialize java.lang.Class: "
+	      + value.getName() + ". Forgot to register a type adapter?");
+	}
+	@Override
+	public Class read(JsonReader in) throws IOException {
+      throw new UnsupportedOperationException(
+          "Attempted to deserialize a java.lang.Class. Forgot to register a type adapter?");
+	}
+  };
+  public static final TypeAdapter.Factory CLASS_FACTORY = newFactory(Class.class, CLASS);
+
   public static final TypeAdapter<BitSet> BIT_SET = new TypeAdapter<BitSet>() {
     public BitSet read(JsonReader in) throws IOException {
       if (in.peek() == JsonToken.NULL) {

gson/src/test/java/com/google/gson/functional/DefaultTypeAdaptersTest.java

@@ -15,17 +15,7 @@
  */
 package com.google.gson.functional;
 
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-import com.google.gson.JsonArray;
-import com.google.gson.JsonDeserializationContext;
-import com.google.gson.JsonDeserializer;
-import com.google.gson.JsonElement;
-import com.google.gson.JsonNull;
-import com.google.gson.JsonObject;
-import com.google.gson.JsonParseException;
-import com.google.gson.JsonPrimitive;
-import com.google.gson.reflect.TypeToken;
+import java.io.IOException;
 import java.lang.reflect.Type;
 import java.math.BigDecimal;
 import java.math.BigInteger;
@@ -49,8 +39,24 @@ import java.util.Set;
 import java.util.TimeZone;
 import java.util.TreeSet;
 import java.util.UUID;
+
 import junit.framework.TestCase;
 
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonNull;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.TypeAdapter;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+
 /**
  * Functional test for Json serialization and deserialization for common classes for which default
  * support is provided in Gson. The tests for Map types are available in {@link MapTest}.
@@ -77,6 +83,24 @@ public class DefaultTypeAdaptersTest extends TestCase {
     super.tearDown();
   }
 
+  public void testClassSerialization() {
+    try {
+      gson.toJson(String.class);  
+    } catch (UnsupportedOperationException expected) {}
+    // Override with a custom type adapter for class.
+    gson = new GsonBuilder().registerTypeAdapter(Class.class, new MyClassTypeAdapter()).create();
+    assertEquals("\"java.lang.String\"", gson.toJson(String.class));  
+  }
+
+  public void testClassDeserialization() {
+    try {
+      gson.fromJson("String.class", String.class.getClass());  
+    } catch (UnsupportedOperationException expected) {}
+    // Override with a custom type adapter for class.
+    gson = new GsonBuilder().registerTypeAdapter(Class.class, new MyClassTypeAdapter()).create();
+    assertEquals(String.class, gson.fromJson("java.lang.String", Class.class));  
+  }
+
   public void testUrlSerialization() throws Exception {
     String urlValue = "http://google.com/";
     URL url = new URL(urlValue);
@@ -633,4 +657,21 @@ public class DefaultTypeAdaptersTest extends TestCase {
     StringBuffer sb = gson.fromJson("'abc'", StringBuffer.class);
     assertEquals("abc", sb.toString());
   }
+
+  @SuppressWarnings("rawtypes")
+  private static class MyClassTypeAdapter extends TypeAdapter<Class> {
+    @Override
+    public void write(JsonWriter out, Class value) throws IOException {
+      out.value(value.getName());
+    }
+    @Override
+    public Class read(JsonReader in) throws IOException {
+      String className = in.nextString();
+      try {
+        return Class.forName(className);
+      } catch (ClassNotFoundException e) {
+        throw new IOException(e);
+      }
+    }
+  }
 }