How to find and replace an attribute value in a XML

Question

I am building a "XML scanner" in Java that finds attribute values starting with "!Here:". The attribute value contains instructions to replace later. for example I have this xml file filled with records like

<bean value="!Here:Sring:HashKey"></bean>

How can I find and replace the attribute values only knowing it starts with "!Here:"?

Answer 1

In order to modify some element or attribute values in the XML file, while still being respectful of XML structure, you will need to use a XML parser. It's a bit more involved than just String$replace()...

Given an example XML like:

<?xml version="1.0" encoding="UTF-8"?>
<beans> 
    <bean id="exampleBean" class="examples.ExampleBean">
        <!-- setter injection using -->
        <property name="beanTwo" ref="anotherBean"/>
        <property name="integerProperty" value="!Here:Integer:Foo"/>
    </bean>
    <bean id="anotherBean" class="examples.AnotherBean">
        <property name="stringProperty" value="!Here:String:Bar"/>
    </bean>
</beans>

In order to change the 2 markers !Here, you need

1. to load the file into a dom Document,
2. select with xpath the wanted nodes. Here I search for all nodes in the document with an attribute value that contains the string !Here. The xpath expression is //*[contains(@value, '!Here')].

3. do the transformation you want on each selected nodes. Here I just change !Here by What?.

4. save the modified dom Document into a new file.

---

static String inputFile = "./beans.xml";
static String outputFile = "./beans_new.xml";

// 1- Build the doc from the XML file
Document doc = DocumentBuilderFactory.newInstance()
            .newDocumentBuilder().parse(new InputSource(inputFile));

// 2- Locate the node(s) with xpath
XPath xpath = XPathFactory.newInstance().newXPath();
NodeList nodes = (NodeList)xpath.evaluate("//*[contains(@value, '!Here')]",
                                          doc, XPathConstants.NODESET);

// 3- Make the change on the selected nodes
for (int idx = 0; idx < nodes.getLength(); idx++) {
    Node value = nodes.item(idx).getAttributes().getNamedItem("value");
    String val = value.getNodeValue();
    value.setNodeValue(val.replaceAll("!Here", "What?"));
}

// 4- Save the result to a new XML doc
Transformer xformer = TransformerFactory.newInstance().newTransformer();
xformer.transform(new DOMSource(doc), new StreamResult(new File(outputFile)));

The resulting XML file is:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<beans> 
    <bean class="examples.ExampleBean" id="exampleBean">
        <!-- setter injection using -->
        <property name="beanTwo" ref="anotherBean"/>
        <property name="integerProperty" value="What?:Integer:Foo"/>
    </bean>
    <bean class="examples.AnotherBean" id="anotherBean">
        <property name="stringProperty" value="What?:String:Bar"/>
    </bean>
</beans>