added code example using HikariCP in Boot 1.x and 2.x (#5007)

* added code example using HikariCP in Boot 1.x and 2.x

* code formatting

spring-4/src/test/java/com/baeldung/connectionpool/ApplicationWithHikariConnectionPool.java

@@ -0,0 +1,12 @@
+package com.baeldung.connectionpool;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class ApplicationWithHikariConnectionPool {
+
+    public static void main(String[] args) {
+        SpringApplication.run(ApplicationWithHikariConnectionPool.class, args);
+    }
+}

spring-4/src/test/java/com/baeldung/connectionpool/HikariIntegrationTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.connectionpool;
+
+import static org.junit.Assert.*;
+
+import javax.sql.DataSource;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringRunner;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest(
+    // instead of setting this property, we can exclude the dependency to org.apache.tomcat:tomcat-jdbc in pom.xml
+    properties = "spring.datasource.type=com.zaxxer.hikari.HikariDataSource")
+public class HikariIntegrationTest {
+
+    @Autowired
+    private DataSource dataSource;
+
+    @Test
+    public void hikariConnectionPoolIsConfigured() {
+        assertEquals("com.zaxxer.hikari.HikariDataSource", dataSource.getClass()
+            .getName());
+    }
+
+}