PersistenceDescriptorModifier.java

package some;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.xpath.*;
import java.io.IOException;
import java.io.StringWriter;

public class PersistenceDescriptorModifier {

    private final Document doc;
    private final XPath xPath;
    private final XPathExpression persistenceUnitExpression;
    private final XPathExpression propertiesExpression;

    public PersistenceDescriptorModifier(InputSource inputSource) throws ParserConfigurationException, IOException, SAXException, XPathExpressionException {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        final DocumentBuilder builder = factory.newDocumentBuilder();
        this.doc = builder.parse(inputSource);
        final XPathFactory xPathFactory = XPathFactory.newInstance();
        this.xPath = xPathFactory.newXPath();
        this.persistenceUnitExpression = xPath.compile("/persistence/persistence-unit");
        this.propertiesExpression = xPath.compile("properties");
    }

    public void setProperty(String name, String value) throws XPathExpressionException {
        final Node persistenceUnit = (Node) persistenceUnitExpression.evaluate(doc, XPathConstants.NODE);
        if (persistenceUnit == null) {
            // no persistence unit
            throw new IllegalStateException("no persistence unit");
        }

        final Node properties = (Node) propertiesExpression.evaluate(persistenceUnit, XPathConstants.NODE);
        if (properties == null) {
            // construct a properties element which contains a property element
            persistenceUnit.appendChild(createPropertiesElement(doc, name, value));
            return;
        }

        final Node property = (Node) xPath.evaluate("property[@name='" + name + "']", persistenceUnit, XPathConstants.NODE);
        if (property != null) {
            // delete the existing property element
            properties.removeChild(property);
        }

        // add a property element
        properties.appendChild(createPropertyElement(doc, name, value));
    }

    @Override
    public String toString() {
        try {
            return toString(doc);
        } catch (TransformerException | IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static Element createPropertiesElement(Document doc, String name, String value) {
        final Element properties = doc.createElement("properties");
        properties.appendChild(createPropertyElement(doc, name, value));
        return properties;
    }

    private static Element createPropertyElement(Document doc, String name, String value) {
        final Element property = doc.createElement("property");
        property.setAttribute("name", name);
        property.setAttribute("value", value);
        return property;
    }

    private static String toString(Document doc) throws TransformerException, IOException {
        final TransformerFactory factory = TransformerFactory.newInstance();
        factory.setAttribute("indent-number", 4);
        final Transformer transformer = factory.newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
        try (final StringWriter sw = new StringWriter()) {
            transformer.transform(new DOMSource(doc), new StreamResult(sw));
            return sw.toString();
        }
    }
}

PersistenceDescriptorModifierTest.java

package some;

import org.junit.Assert;
import org.junit.Test;
import org.xml.sax.InputSource;

import java.io.StringReader;

public class PersistenceDescriptorModifierTest {
    private static final String expected = "<property name=\"javax.persistence.schema-generation.database.action\" value=\"drop-and-create\"/>";

    @Test
    public void modify() throws Exception {
        String s = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<persistence xmlns=\"http://xmlns.jcp.org/xml/ns/persistence\" version=\"2.1\">\n" +
                "    <persistence-unit name=\"Model2PU\">\n" +
                "        <jta-data-source>java:jboss/datasources/Model2DS</jta-data-source>\n" +
                "        <properties>\n" +
                "            <property name=\"javax.persistence.schema-generation.database.action\" value=\"none\"/>\n" +
                "            <property name=\"someProp\" value=\"someValue\"/>\n" +
                "        </properties>\n" +
                "    </persistence-unit>\n" +
                "</persistence>";
        try (StringReader r = new StringReader(s)) {
            PersistenceDescriptorModifier m = new PersistenceDescriptorModifier(new InputSource(r));
            m.setProperty("javax.persistence.schema-generation.database.action", "drop-and-create");
            Assert.assertTrue(m.toString().contains(expected));
        }
    }

    @Test
    public void add1() throws Exception {
        String s = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<persistence xmlns=\"http://xmlns.jcp.org/xml/ns/persistence\" version=\"2.1\">\n" +
                "    <persistence-unit name=\"Model2PU\">\n" +
                "        <jta-data-source>java:jboss/datasources/Model2DS</jta-data-source>\n" +
                "        <properties>\n" +
                "            <property name=\"someProp\" value=\"someValue\"/>\n" +
                "        </properties>\n" +
                "    </persistence-unit>\n" +
                "</persistence>";
        try (StringReader r = new StringReader(s)) {
            PersistenceDescriptorModifier m = new PersistenceDescriptorModifier(new InputSource(r));
            m.setProperty("javax.persistence.schema-generation.database.action", "drop-and-create");
            Assert.assertTrue(m.toString().contains(expected));
        }
    }

    @Test
    public void add2() throws Exception {
        String s = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<persistence xmlns=\"http://xmlns.jcp.org/xml/ns/persistence\" version=\"2.1\">\n" +
                "    <persistence-unit name=\"Model2PU\">\n" +
                "        <jta-data-source>java:jboss/datasources/Model2DS</jta-data-source>\n" +
                "    </persistence-unit>\n" +
                "</persistence>";
        try (StringReader r = new StringReader(s)) {
            PersistenceDescriptorModifier m = new PersistenceDescriptorModifier(new InputSource(r));
            m.setProperty("javax.persistence.schema-generation.database.action", "drop-and-create");
            Assert.assertTrue(m.toString().contains(expected));
        }
    }
}

Hello Sir,

How can i invoke the class "PersistenceDescriptorModifier.java" ? Is there any Listener or Xml file or dependency injection to instantiate the class?

Do you have any example ?

Thanks,
Breno