MyCATApache/Mycat-Server · error · ConfigException

elements length over one!

Error message

${tagName} elements length  over one!

What it means

ConfigUtil.loadElement expects at most one XML element with the given tagName under the parent. If getElementsByTagName returns more than one match, it throws ConfigException because the result would be ambiguous. This enforces single-element semantics for config sections.

Solutions

1. Open the XML file and remove or merge the duplicate '<tagName>' elements so only one remains
2. Identify the file/section by the tagName reported in the message
3. If duplicates are legitimate, change the loader code to iterate the NodeList instead of using loadElement

Example fix

<!-- before -->
<user name="a"/><user name="b"/>
<!-- after -->
<user name="a"/>  <!-- keep only one -->

NodeList nl = parent.getElementsByTagName(tagName);
if (nl.getLength() > 1) throw new ConfigException("duplicate <" + tagName + "> found; keep exactly one");

try { Element e = ConfigUtil.loadElement(parent, tag); } catch (ConfigException e) { log.error("config has duplicates for <{}>", tag); throw e; }

When it happens

Trigger: Calling loadElement(parent, tagName) where the parsed XML document contains two or more sibling (or descendant) elements with that tag name.

Common situations: Duplicated XML stanzas in server.xml/schema.xml from a bad merge or accidental copy-paste (e.g. two <user> or two <system> blocks); generating config with a template loop that emitted a section twice.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• elements length over one!
• ConfigException wrapping cause (no message)
• dataHost name duplicated!
• dataNode reference dataHost: not exists!
• dataNode define error ,attribute can't be empty

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/a22dee6292a26006. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/config/util/ConfigUtil.java:134

    }

    public static Map<String, Object> loadAttributes(Element e) {
        Map<String, Object> map = new HashMap<String, Object>();
        NamedNodeMap nm = e.getAttributes();
        for (int j = 0; j < nm.getLength(); j++) {
            Node n = nm.item(j);
            if (n instanceof Attr) {
                Attr attr = (Attr) n;
                map.put(attr.getName(), attr.getNodeValue());
            }
        }
        return map;
    }

    public static Element loadElement(Element parent, String tagName) {
        NodeList nodeList = parent.getElementsByTagName(tagName);
        if (nodeList.getLength() > 1) {
            throw new ConfigException(tagName + " elements length  over one!");
        }
        if (nodeList.getLength() == 1) {
            return (Element) nodeList.item(0);
        } else {
            return null;
        }
    }

    /**
     * 获取节点下所有property
     * @param parent
     * @return key-value property键值对
     */
    public static Map<String, Object> loadElements(Element parent) {
        Map<String, Object> map = new HashMap<String, Object>();
        NodeList children = parent.getChildNodes();
        for (int i = 0; i < children.getLength(); i++) {
            Node node = children.item(i);

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