diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/Request.java b/webmagic-core/src/main/java/us/codecraft/webmagic/Request.java
index 9fc2861..a59b206 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/Request.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/Request.java
@@ -1,13 +1,14 @@
 package us.codecraft.webmagic;
 
+import java.io.Serializable;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
 import us.codecraft.webmagic.downloader.Downloader;
 import us.codecraft.webmagic.model.HttpRequestBody;
 import us.codecraft.webmagic.utils.Experimental;
 
-import java.io.Serializable;
-import java.util.HashMap;
-import java.util.Map;
-
 /**
  * Object contains url to crawl.<br>
  * It contains some additional information.<br>
@@ -35,7 +36,7 @@ public class Request implements Serializable {
     /**
      * Store additional information in extras.
      */
-    private Map<String, Object> extras;
+    private Map<String, Object> extras = new HashMap<>();
 
     /**
      * cookies for current url, if not set use Site's cookies
@@ -93,9 +94,6 @@ public class Request implements Serializable {
     }
 
     public <T> Request putExtra(String key, T value) {
-        if (extras == null) {
-            extras = new HashMap<String, Object>();
-        }
         extras.put(key, value);
         return this;
     }
@@ -105,11 +103,11 @@ public class Request implements Serializable {
     }
 
     public Map<String, Object> getExtras() {
-        return extras;
+        return Collections.unmodifiableMap(extras);
     }
 
     public Request setExtras(Map<String, Object> extras) {
-        this.extras = extras;
+        this.extras.putAll(extras);
         return this;
     }
 
diff --git a/webmagic-core/src/test/java/us/codecraft/webmagic/RequestTest.java b/webmagic-core/src/test/java/us/codecraft/webmagic/RequestTest.java
index c7e4943..b8f699a 100644
--- a/webmagic-core/src/test/java/us/codecraft/webmagic/RequestTest.java
+++ b/webmagic-core/src/test/java/us/codecraft/webmagic/RequestTest.java
@@ -1,10 +1,14 @@
 package us.codecraft.webmagic;
 
-import org.junit.Test;
-import us.codecraft.webmagic.utils.HttpConstant;
-
 import static org.assertj.core.api.Assertions.assertThat;
 
+import java.util.Collections;
+import java.util.Map;
+
+import org.junit.Test;
+
+import us.codecraft.webmagic.utils.HttpConstant;
+
 /**
  * @author code4crafter@gmail.com
  *         Date: 17/3/11
@@ -22,4 +26,28 @@ public class RequestTest {
         assertThat(requestA).isNotEqualTo(requestB);
         assertThat(requestA.hashCode()).isNotEqualTo(requestB.hashCode());
     }
+
+    @Test
+    public void testSetExtras() {
+        Request request = new Request();
+        Map<String, Object> extras = Collections.singletonMap("a", "1");
+        request.setExtras(extras);
+        request.putExtra("b", "2");
+        assertThat(request.<String>getExtra("a")).isEqualTo("1");
+        assertThat(request.<String>getExtra("b")).isEqualTo("2");
+    }
+
+    @Test
+    public void testGetExtras() {
+        Request request = new Request();
+        request.putExtra("a", "1");
+        assertThat(request.getExtras()).containsEntry("a", "1");
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void testGetExtrasShouldBeUnmodifiable() {
+        Request request = new Request();
+        request.getExtras().put("a", "1");
+    }
+
 }