diff --git a/CHANGELOG.md b/CHANGELOG.md
index 469046fb5..89a86ac37 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,7 +6,9 @@
 ## 5.0.4
 
 ### 新特性
+* 【core】       XmlUtil中mapToStr支持namespace（pr#599@Github）
 ### Bug修复
+* 【core】       解决ConcurrentHashSet不能序列化的问题（issue#600@Github）
 
 -------------------------------------------------------------------------------------------------------------
 
diff --git a/hutool-core/src/main/java/cn/hutool/core/collection/ConcurrentHashSet.java b/hutool-core/src/main/java/cn/hutool/core/collection/ConcurrentHashSet.java
index 8787f47b9..c3fb02ddd 100644
--- a/hutool-core/src/main/java/cn/hutool/core/collection/ConcurrentHashSet.java
+++ b/hutool-core/src/main/java/cn/hutool/core/collection/ConcurrentHashSet.java
@@ -17,8 +17,8 @@ public class ConcurrentHashSet<E> extends AbstractSet<E> implements java.io.Seri
 	private static final long serialVersionUID = 7997886765361607470L;
 
 	/** 持有对象。如果值为此对象表示有数据，否则无数据 */
-	private static final Object PRESENT = new Object();
-	private final ConcurrentHashMap<E, Object> map;
+	private static final Boolean PRESENT = true;
+	private final ConcurrentHashMap<E, Boolean> map;
 
 	// ----------------------------------------------------------------------------------- Constructor start
 	/**
diff --git a/hutool-core/src/main/java/cn/hutool/core/util/XmlUtil.java b/hutool-core/src/main/java/cn/hutool/core/util/XmlUtil.java
index e79361ccd..8ae26e4f1 100644
--- a/hutool-core/src/main/java/cn/hutool/core/util/XmlUtil.java
+++ b/hutool-core/src/main/java/cn/hutool/core/util/XmlUtil.java
@@ -387,8 +387,7 @@ public class XmlUtil {
 	 * @since 4.1.2
 	 */
 	public static DocumentBuilder createDocumentBuilder() {
-		final DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
-		disableXXE(dbf);
+		final DocumentBuilderFactory dbf = disableXXE(DocumentBuilderFactory.newInstance());
 		DocumentBuilder builder;
 		try {
 			builder = dbf.newDocumentBuilder();
@@ -406,9 +405,21 @@ public class XmlUtil {
 	 * @return XML文档
 	 */
 	public static Document createXml(String rootElementName) {
-		final Document doc = createXml();
-		doc.appendChild(doc.createElement(rootElementName));
+		return createXml(rootElementName, null);
+	}
 
+	/**
+	 * 创建XML文档<br>
+	 * 创建的XML默认是utf8编码，修改编码的过程是在toStr和toFile方法里，即XML在转为文本的时候才定义编码
+	 *
+	 * @param rootElementName 根节点名称
+	 * @param namespace 命名空间，无则传null
+	 * @return XML文档
+	 * @since 5.0.4
+	 */
+	public static Document createXml(String rootElementName, String namespace) {
+		final Document doc = createXml();
+		doc.appendChild(null == namespace ? doc.createElement(rootElementName) : doc.createElementNS(rootElementName, namespace));
 		return doc;
 	}
 
@@ -674,7 +685,7 @@ public class XmlUtil {
 	 * @since 4.0.8
 	 */
 	public static Map<String, Object> xmlToMap(String xmlStr) {
-		return xmlToMap(xmlStr, new HashMap<String, Object>());
+		return xmlToMap(xmlStr, new HashMap<>());
 	}
 
 	/**
@@ -685,7 +696,7 @@ public class XmlUtil {
 	 * @since 4.0.8
 	 */
 	public static Map<String, Object> xmlToMap(Node node) {
-		return xmlToMap(node, new HashMap<String, Object>());
+		return xmlToMap(node, new HashMap<>());
 	}
 
 	/**
@@ -804,9 +815,22 @@ public class XmlUtil {
 	 * @return 子节点
 	 * @since 4.0.9
 	 */
+	public static Element appendChild(Node node, String tagName) {
+		return appendChild(node, tagName, null);
+	}
+
+	/**
+	 * 在已有节点上创建子节点
+	 *
+	 * @param node    节点
+	 * @param tagName 标签名
+	 * @param namespace 命名空间，无传null
+	 * @return 子节点
+	 * @since 5.0.4
+	 */
 	public static Element appendChild(Node node, String tagName, String namespace) {
 		Document doc = (node instanceof Document) ? (Document) node : node.getOwnerDocument();
-		Element child = doc.createElementNS(namespace, tagName);
+		Element child = (null == namespace) ? doc.createElement(tagName) : doc.createElementNS(namespace, tagName);
 		node.appendChild(child);
 		return child;
 	}
diff --git a/hutool-db/src/main/java/cn/hutool/db/Page.java b/hutool-db/src/main/java/cn/hutool/db/Page.java
index 3f51ee4a3..32df9e155 100644
--- a/hutool-db/src/main/java/cn/hutool/db/Page.java
+++ b/hutool-db/src/main/java/cn/hutool/db/Page.java
@@ -42,7 +42,7 @@ public class Page implements Serializable {
 	 * @param pageSize 每页结果数
 	 */
 	public Page(int pageNumber, int pageSize) {
-		this.pageNumber = pageNumber < 0 ? 0 : pageNumber;
+		this.pageNumber = Math.max(pageNumber, 0);
 		this.pageSize = pageSize <= 0 ? DEFAULT_PAGE_SIZE : pageSize;
 	}
 
@@ -73,7 +73,7 @@ public class Page implements Serializable {
 	 * @param pageNumber 页码
 	 */
 	public void setPageNumber(int pageNumber) {
-		this.pageNumber = pageNumber < 0 ? 0 : pageNumber;
+		this.pageNumber = Math.max(pageNumber, 0);
 	}
 
 	/**