Dodatkowe klasy do obsługi kursów walut

Projekt4/app/src/main/java/com/example/waluty/ExchangeRatesTable.java

+package com.example.waluty;
+
+import java.time.LocalDate;
+import java.util.Collection;
+import java.util.Map;
+import java.util.TreeMap;
+
+public class ExchangeRatesTable {
+    private final String table;
+    private final String no;
+    private final LocalDate effectiveDate;
+    private final Map<String, Rate> rates = new TreeMap<>();
+    
+    public ExchangeRatesTable() {
+        table = null;
+        no = null;
+        effectiveDate = null;
+    }
+
+    public ExchangeRatesTable(String table, String no, LocalDate effectiveDate) {
+        this.table = table;
+        this.no = no;
+        this.effectiveDate = effectiveDate;
+    }
+
+    public String getTable() {
+        return table;
+    }
+
+    public String getNo() {
+        return no;
+    }
+
+    public LocalDate getEffectiveDate() {
+        return effectiveDate;
+    }
+
+    @Override
+    public String toString() {
+        return "Tabela " + table + " nr " + no
+                + " z dnia " + effectiveDate + " (" + rates.size() + " walut)";
+    }
+    
+    public void add(Rate waluta) {
+        rates.put(waluta.getCode(), waluta);
+    }
+    
+    public Rate find(String kod) {
+        return rates.get(kod);
+    }
+    
+    public Collection<Rate> getRates() {
+        return rates.values();
+    }
+    
+    private static final String[] PUSTA_TABLICA = new String[0];
+    
+    public String[] getCodes() {
+        return rates.keySet().toArray(PUSTA_TABLICA);
+    }
+
+}
+

Projekt4/app/src/main/java/com/example/waluty/ObslugaNBP.java

+package com.example.waluty;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.math.BigDecimal;
+import java.net.URL;
+import java.time.LocalDate;
+
+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 org.w3c.dom.Document;
+import org.w3c.dom.Node;
+import org.w3c.dom.NodeList;
+import org.xml.sax.SAXException;
+
+public class ObslugaNBP {
+    private static final String ADRES = "http://api.nbp.pl/api/exchangerates/tables";
+
+    /** Pobiera tabelę z bieżącymi kursami walut.
+     * Zwraca null w przypadku błędów.
+     */
+    public static ExchangeRatesTable pobierzBiezaceKursy() {
+        Document doc = wczytajXmlZAdresu(ADRES + "/A?format=xml");
+        return tabelaZXml(doc);
+    }
+    
+    /** Pobiera tabelę z archiwalnymi kursami walut z określonej daty.
+     * Zwraca null w przypadku błędów, np. wtedy, gdy dla danej daty nie istnieje tabela.
+     */
+    public static ExchangeRatesTable pobierzKursyHistoryczne(String data) {
+        Document doc = wczytajXmlZAdresu(ADRES + "/A/" + data + "?format=xml");
+        return tabelaZXml(doc);
+    }
+
+    private static Document wczytajXmlZAdresu(String adres) {
+        // Document Object Model
+        
+        try {
+            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
+            DocumentBuilder db = dbf.newDocumentBuilder();
+
+            URL url = new URL(adres);
+            try (InputStream in = url.openStream()) {
+                return db.parse(in);
+            }
+        } catch (ParserConfigurationException | SAXException | IOException e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
+
+    private static ExchangeRatesTable tabelaZXml(Document doc) {
+        if (doc == null)
+            return null;
+        try {
+            XPathFactory xpf = XPathFactory.newInstance();
+            XPath xpath = xpf.newXPath();
+
+            // String numer = xpath.evaluate(
+            // "/ArrayOfExchangeRatesTable/ExchangeRatesTable/No", doc);
+
+            String nazwaTabeli = xpath.evaluate("//Table", doc);
+            String numerTabeli = xpath.evaluate("//No", doc);
+            LocalDate data = LocalDate.parse(xpath.evaluate("//EffectiveDate", doc));
+
+            ExchangeRatesTable tabela = new ExchangeRatesTable(nazwaTabeli, numerTabeli, data);
+
+            NodeList rates = (NodeList) xpath.evaluate("//Rate", doc, XPathConstants.NODESET);
+            final int n = rates.getLength();
+            for (int i = 0; i < n; i++) {
+                Node node = rates.item(i);
+                String kod = xpath.evaluate("Code", node);
+                String nazwa = xpath.evaluate("Currency", node);
+                String kurs = xpath.evaluate("Mid", node);
+                BigDecimal kursBD = new BigDecimal(kurs);
+                Rate rate = new Rate(kod, nazwa, kursBD);
+                tabela.add(rate);
+            }
+
+            return tabela;
+        } catch (XPathExpressionException e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
+}
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