如何在 JAVA 中的 XML 字符串中添加新属性？ 条件：基于父密钥，如果我们需要进行解析或 SAX，我只能使用 JAVA 内部 api

Question

I have a following xml string .

<aa>
    <bb>
        <cc>
            <cmd>
                <efg sid="C1D7B70D7AF705731B0" mid="C1D7D7AF705731B0" stid="-1" dopt="3">
                    <pqr>
                        <dru fo="1" fps="1" nku="WBECDD6CC37656E6C9" tt="1"/>
                        <dpo drpr="67" dpi="16"/>
                        <dres >
                            <dre dreid="BB:8D679D3511D3E4981000E787EC6DE8A4:1:1:0:2:1" fa="1" dpt= "1" o="0"/>
                        </dres>
                    </pqr>
                </efg>
            </cmd>
        </cc>
    </bb>
</aa>

I need to add "login" attribute inside <efg> tag. So new XML would be

<aa>
    <bb>
        <cc>
            <cmd>
                <efg sid="C1D7B70D7AF705731B0" login="sdf34234dfs" mid="C1D7D7AF705731B0" stid="-1" dopt="3">
                    <pqr>
                        <dru fo="1" fps="1" nku="WBECDD6CC37656E6C9" tt="1"/>
                        <dpo drpr="67" dpi="16"/>
                        <dres >
                            <dre dreid="BB:8D679D3511D3E4981000E787EC6DE8A4:1:1:0:2:1" fa="1" dpt= "1" o="0"/>
                        </dres>
                    </pqr>
                </efg>
            </cmd>
        </cc>
    </bb>
</aa>

Condition is:

1. I can only use inbuilt Java API (java 8) or SAX parser or xmlbuilder
2. Add condition is based on Parent tag ie need to check <cmd> then in child need to add <login> because it is not sure always that <efg> tag would always be there with the same name, it could be with any name.

I have tried with DOM parser with following code.

String xml = "xmlString";
        //Use method to convert XML string content to XML Document object
        Document doc = convertStringToXML( xml );
        doc.getDocumentElement().normalize();

        Node m = doc.getElementsByTagName("cmd").item(0).getFirstChild();
        Attr login = doc.createAttribute("login");
        login.setValue("123567");
        m.appendChild(login);

However, I am getting following error in my last line of code.

Exception in thread "main" org.w3c.dom.DOMException: HIERARCHY_REQUEST_ERR: An attempt was made to insert a node where it is not permitted.

Please anyone suggest me, how to add new attribute login into based on my condition no 2.

Answer 1

NodeList nodeList = doc.getElementsByTagName("cmd");
                    //Check <cmd> tag is present and then check <cmd> tag has child nodes
                    if (nodeList != null && nodeList.item(0).hasChildNodes()) {
                        //Get first child node of <cmd> xml tag
                        String nodeName = doc.getElementsByTagName("cmd").item(0).getFirstChild().getNodeName();

                        NodeList childNodeList = doc.getElementsByTagName(nodeName);
                        Element el = (Element) childNodeList.item(0);
                        //set pgd_login attribute with respective value
                        el.setAttribute("login", "xyz");

                        //Convert back into xml string from Document
                        xml = XMLHelpers.TransformDOMDocumentToString(doc);
                    }