XPath waluty v3 sum / count

ObslugaXML/src/main/java/przyklady_xpath/WalutyXPath3.java

+package przyklady_xpath;
+
+import org.w3c.dom.Document;
+import org.w3c.dom.Node;
+import org.w3c.dom.NodeList;
+import org.xml.sax.SAXException;
+
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.parsers.ParserConfigurationException;
+import javax.xml.xpath.XPath;
+import javax.xml.xpath.XPathConstants;
+import javax.xml.xpath.XPathExpressionException;
+import javax.xml.xpath.XPathFactory;
+import java.io.IOException;
+
+public class WalutyXPath3 {
+
+    public static void main(String[] args) {
+        String szukanyKod = "USD";
+        // chcemy obliczyć średni kurs podanej waluty z całego pliku
+
+        System.out.println("Konfiguracja");
+        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
+        XPathFactory xpf = XPathFactory.newInstance();
+        try {
+            XPath xpath = xpf.newXPath();
+            DocumentBuilder builder = factory.newDocumentBuilder();
+            System.out.println("Czytanie pliku");
+            Document doc = builder.parse("waluty_2022.xml");
+
+            String ratesPath = "//Rate[Code = '" + szukanyKod + "']";
+            String path = "sum(" + ratesPath + "/Mid) div count(" + ratesPath + ")";
+            System.out.println("Ewaluacja wyrażenia " + path);
+            double srednia = (double)xpath.evaluate(path, doc, XPathConstants.NUMBER);
+
+            System.out.println("Średni kurs waluty " + szukanyKod + " = " + srednia);
+        } catch (ParserConfigurationException | SAXException | IOException | XPathExpressionException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}