diff --git a/src/main/java/xyz/zhouxy/plusone/commons/util/AbstractMapWrapper.java b/src/main/java/xyz/zhouxy/plusone/commons/collection/AbstractMapWrapper.java
similarity index 97%
rename from src/main/java/xyz/zhouxy/plusone/commons/util/AbstractMapWrapper.java
rename to src/main/java/xyz/zhouxy/plusone/commons/collection/AbstractMapWrapper.java
index 31623e5..ca6f2f5 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/util/AbstractMapWrapper.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/collection/AbstractMapWrapper.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package xyz.zhouxy.plusone.commons.util;
+package xyz.zhouxy.plusone.commons.collection;
 
 import java.util.Collection;
 import java.util.Collections;
@@ -164,7 +164,7 @@ public abstract class AbstractMapWrapper<K, V, T extends AbstractMapWrapper<K, V
         return this.map.toString();
     }
 
-    protected abstract static class Builder<K, V, T extends AbstractMapWrapper<K, V, T>> {
+    public abstract static class Builder<K, V, T extends AbstractMapWrapper<K, V, T>> {
         protected final Map<K, V> map;
         protected Consumer<K> keyChecker;
         protected Consumer<V> valueChecker;
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/util/MapWrapper.java b/src/main/java/xyz/zhouxy/plusone/commons/collection/MapWrapper.java
similarity index 98%
rename from src/main/java/xyz/zhouxy/plusone/commons/util/MapWrapper.java
rename to src/main/java/xyz/zhouxy/plusone/commons/collection/MapWrapper.java
index 151b0a9..6330673 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/util/MapWrapper.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/collection/MapWrapper.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package xyz.zhouxy.plusone.commons.util;
+package xyz.zhouxy.plusone.commons.collection;
 
 import java.util.Collections;
 import java.util.Comparator;
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/jdbc/DbRecord.java b/src/main/java/xyz/zhouxy/plusone/commons/jdbc/DbRecord.java
index a57327c..e8c1892 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/jdbc/DbRecord.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/jdbc/DbRecord.java
@@ -31,7 +31,7 @@ import java.util.Set;
 
 import com.google.common.annotations.Beta;
 
-import xyz.zhouxy.plusone.commons.util.AbstractMapWrapper;
+import xyz.zhouxy.plusone.commons.collection.AbstractMapWrapper;
 import xyz.zhouxy.plusone.commons.util.Assert;
 import xyz.zhouxy.plusone.commons.util.OptionalUtil;
 
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/util/DateTimeUtil.java b/src/main/java/xyz/zhouxy/plusone/commons/util/DateTimeUtil.java
index ffebe8a..51099c0 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/util/DateTimeUtil.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/util/DateTimeUtil.java
@@ -14,6 +14,8 @@ import java.util.TimeZone;
 
 import org.apache.commons.lang3.StringUtils;
 
+import xyz.zhouxy.plusone.commons.collection.MapWrapper;
+
 public class DateTimeUtil {
 
     private static final MapWrapper<String, DateTimeFormatter> DATE_TIME_FORMATTER_CHCHE = MapWrapper