BAEL-1570 (#3762)

* Create pom.xml

* Update pom.xml

* Create pom.xml

* Update pom.xml

* add impl

* add app

java-spi/exchange-rate-api/pom.xml

@@ -0,0 +1,14 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>exchange-rate-api</artifactId>
+    <packaging>jar</packaging>
+    
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>java-spi</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+</project>

java-spi/exchange-rate-api/src/main/java/com/baeldung/rate/ExchangeRate.java

@@ -0,0 +1,42 @@
+package com.baeldung.rate;
+
+import com.baeldung.rate.exception.ProviderNotFoundException;
+import com.baeldung.rate.spi.ExchangeRateProvider;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ServiceLoader;
+
+public final class ExchangeRate {
+
+    private static final String DEFAULT_PROVIDER = "com.baeldung.rate.spi.YahooFinanceExchangeRateProvider";
+
+    //All providers
+    public static List<ExchangeRateProvider> providers() {
+        List<ExchangeRateProvider> services = new ArrayList<>();
+        ServiceLoader<ExchangeRateProvider> loader = ServiceLoader.load(ExchangeRateProvider.class);
+        loader.forEach(exchangeRateProvider -> {
+            services.add(exchangeRateProvider);
+        });
+        return services;
+    }
+
+    //Default provider
+    public static ExchangeRateProvider provider() {
+        return provider(DEFAULT_PROVIDER);
+    }
+
+    //provider by name
+    public static ExchangeRateProvider provider(String providerName) {
+        ServiceLoader<ExchangeRateProvider> loader = ServiceLoader.load(ExchangeRateProvider.class);
+        Iterator<ExchangeRateProvider> it = loader.iterator();
+        while (it.hasNext()) {
+            ExchangeRateProvider provider = it.next();
+            if (providerName.equals(provider.getClass().getName())) {
+                return provider;
+            }
+        }
+        throw new ProviderNotFoundException("Exchange Rate provider " + providerName + " not found");
+    }
+}

java-spi/exchange-rate-api/src/main/java/com/baeldung/rate/api/Quote.java

@@ -0,0 +1,44 @@
+package com.baeldung.rate.api;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+
+public class Quote {
+    private String currency;
+    private BigDecimal ask;
+    private BigDecimal bid;
+    private LocalDate date;
+    //...
+
+    public String getCurrency() {
+        return currency;
+    }
+
+    public void setCurrency(String currency) {
+        this.currency = currency;
+    }
+
+    public BigDecimal getAsk() {
+        return ask;
+    }
+
+    public void setAsk(BigDecimal ask) {
+        this.ask = ask;
+    }
+
+    public BigDecimal getBid() {
+        return bid;
+    }
+
+    public void setBid(BigDecimal bid) {
+        this.bid = bid;
+    }
+
+    public LocalDate getDate() {
+        return date;
+    }
+
+    public void setDate(LocalDate date) {
+        this.date = date;
+    }
+}

java-spi/exchange-rate-api/src/main/java/com/baeldung/rate/api/QuoteManager.java

@@ -0,0 +1,8 @@
+package com.baeldung.rate.api;
+
+import java.time.LocalDate;
+import java.util.List;
+
+public interface QuoteManager {
+    List<Quote> getQuotes(String baseCurrency, LocalDate date);
+}

java-spi/exchange-rate-api/src/main/java/com/baeldung/rate/exception/ProviderNotFoundException.java

@@ -0,0 +1,13 @@
+package com.baeldung.rate.exception;
+
+public class ProviderNotFoundException extends RuntimeException {
+
+    public ProviderNotFoundException() {
+        super();
+    }
+
+    public ProviderNotFoundException(String message) {
+        super(message);
+    }
+
+}

java-spi/exchange-rate-api/src/main/java/com/baeldung/rate/spi/ExchangeRateProvider.java

@@ -0,0 +1,7 @@
+package com.baeldung.rate.spi;
+
+import com.baeldung.rate.api.QuoteManager;
+
+public interface ExchangeRateProvider {
+    QuoteManager create();
+}