diff --git a/README.md b/README.md
index 374f78c..e298eee 100644
--- a/README.md
+++ b/README.md
@@ -36,7 +36,7 @@ You define the api meta data in classes' static code blocks, then it was collect
 static Mapping<?> petStatus = $(text(oneOf(Arrays.asList("available", "pending", "sold"))))
     .desc("pet status in the store").example("available").$$;
 static Mapping<?> pet = $(mapping(
-    field("id", $(vLong()).desc("pet id").example(gen("petId").or(gen(() -> new Faker().number().randomNumber()))).$$),
+    field("id", $(vLong()).desc("pet id").example(gen("petId").or(gen(() -> faker.number().randomNumber()))).$$),
     field("name", $(text(required())).desc("pet name").$$),
     field("category", attach(required()).to($(mapping(
           field("id", vLong(required())),
diff --git a/example/java-jaxrs/src/main/java/com/example/resource/PetResource.java b/example/java-jaxrs/src/main/java/com/example/resource/PetResource.java
index d92444c..fbb73e2 100644
--- a/example/java-jaxrs/src/main/java/com/example/resource/PetResource.java
+++ b/example/java-jaxrs/src/main/java/com/example/resource/PetResource.java
@@ -43,14 +43,16 @@
 @Path("/pet")
 @Produces({"application/json", "application/xml"})
 public class PetResource {
-    static PetData petData = new PetData();
+    private static PetData petData = new PetData();
+    private static Faker faker = new Faker();
+
     private ResourceBundle bundle = ResourceBundle.getBundle("bind-messages");
     private Messages messages = (key) -> bundle.getString(key);
 
     static Mapping<?> petStatus = $(text(oneOf(Arrays.asList("available", "pending", "sold"))))
             .desc("pet status in the store").example("available").$$;
     static Mapping<?> pet = $(mapping(
-            field("id", $(longv()).desc("pet id").example(gen("petId").or(gen(() -> new Faker().number().randomNumber()))).$$),
+            field("id", $(longv()).desc("pet id").example(gen("petId").or(gen(() -> faker.number().randomNumber()))).$$),
             field("name", $(text(required())).desc("pet name").$$),
             field("category", $(mapping(
                     field("id", longv(required())),
diff --git a/src/main/java/com/github/tminglei/swagger/fake/DataWriterImpl.java b/src/main/java/com/github/tminglei/swagger/fake/DataWriterImpl.java
index 2b7eb61..a6735be 100644
--- a/src/main/java/com/github/tminglei/swagger/fake/DataWriterImpl.java
+++ b/src/main/java/com/github/tminglei/swagger/fake/DataWriterImpl.java
@@ -2,6 +2,7 @@
 
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
 
 import java.io.IOException;
 import java.io.Writer;
@@ -17,14 +18,15 @@ public class DataWriterImpl implements DataWriter {
     private static final String FORMAT_JSON = "application/json";
     private static final String FORMAT_XML  = "application/xml";
 
+    private static final ObjectMapper objectMapper = new ObjectMapper()
+        .setSerializationInclusion(JsonInclude.Include.NON_NULL)
+        .configure(SerializationFeature.INDENT_OUTPUT, true);
+
     @Override
     public void write(Writer writer, String format, DataProvider provider) throws IOException {
         switch (format.toLowerCase()) {
             case FORMAT_JSON:
-                String dataJson = new ObjectMapper()
-                    .setSerializationInclusion(JsonInclude.Include.NON_NULL)
-                    .writer().withDefaultPrettyPrinter()
-                    .writeValueAsString(provider.get());
+                String dataJson = objectMapper.writeValueAsString(provider.get());
                 writer.write(dataJson);
                 break;
             case FORMAT_XML: