BAEL-1818 A Simple Guide to Connection Pooling in Java (#4823)

* Initial Commit

* Update parent pom.xml

* Update BasicConnectionPool class

* Update BasicConnectionPool class

* BAEL-1818 removed code from core-java module, cleaned up a little pom files

* BAEL-1818 moved the code from connectionpool.connectionpools package to connectionpool

core-java-persistence/pom.xml

@@ -0,0 +1,59 @@
+<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>
+    <groupId>com.baeldung.core-java-persistence</groupId>
+    <artifactId>core-java-persistence</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>core-java-persistence</name>
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <version>${h2database.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-dbcp2</artifactId>
+            <version>${commons-dbcp2.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.zaxxer</groupId>
+            <artifactId>HikariCP</artifactId>
+            <version>${HikariCP.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.mchange</groupId>
+            <artifactId>c3p0</artifactId>
+            <version>${c3p0.version}</version>
+        </dependency>
+    </dependencies>
+    <build>
+        <finalName>core-java-persistence</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>    
+    <properties>
+        <assertj-core.version>3.10.0</assertj-core.version>
+        <h2database.version>1.4.197</h2database.version>
+        <commons-dbcp2.version>2.4.0</commons-dbcp2.version>
+        <HikariCP.version>3.2.0</HikariCP.version>
+        <c3p0.version>0.9.5.2</c3p0.version>
+    </properties>
+</project>

core-java-persistence/src/main/java/com/baeldung/connectionpool/BasicConnectionPool.java

@@ -1,4 +1,4 @@
-package com.baeldung.connectionpool.connectionpools;
+package com.baeldung.connectionpool;
 
 import java.sql.Connection;
 import java.sql.DriverManager;
@@ -56,10 +56,16 @@ public class BasicConnectionPool implements ConnectionPool {
         return DriverManager.getConnection(url, user, password);
     }
 
+    @Override
     public int getSize() {
         return connectionPool.size() + usedConnections.size();
     }
 
+    @Override
+    public List<Connection> getConnectionPool() {
+        return connectionPool;
+    }
+    
     @Override
     public String getUrl() {
         return url;
@@ -75,6 +81,7 @@ public class BasicConnectionPool implements ConnectionPool {
         return password;
     }
     
+    @Override
     public void shutdown() throws SQLException {
         usedConnections.forEach(this::releaseConnection);
         for (Connection c : connectionPool) {

core-java-persistence/src/main/java/com/baeldung/connectionpool/C3poDataSource.java

@@ -1,4 +1,4 @@
-package com.baeldung.connectionpool.connectionpools;
+package com.baeldung.connectionpool;
 
 import com.mchange.v2.c3p0.ComboPooledDataSource;
 import java.beans.PropertyVetoException;

core-java-persistence/src/main/java/com/baeldung/connectionpool/ConnectionPool.java

@@ -1,4 +1,4 @@
-package com.baeldung.connectionpool.connectionpools;
+package com.baeldung.connectionpool;
 
 import java.sql.Connection;
 import java.sql.SQLException;
@@ -10,9 +10,15 @@ public interface ConnectionPool {
     
     boolean releaseConnection(Connection connection);
     
+    List<Connection> getConnectionPool();
+    
+    int getSize();
+    
     String getUrl();
     
     String getUser();
 
     String getPassword();
+    
+    void shutdown() throws SQLException;;
 }   

core-java-persistence/src/main/java/com/baeldung/connectionpool/DBCPDataSource.java

@@ -1,4 +1,4 @@
-package com.baeldung.connectionpool.connectionpools;
+package com.baeldung.connectionpool;
 
 import java.sql.Connection;
 import java.sql.SQLException;

core-java-persistence/src/main/java/com/baeldung/connectionpool/HikariCPDataSource.java

@@ -1,4 +1,4 @@
-package com.baeldung.connectionpool.connectionpools;
+package com.baeldung.connectionpool;
 
 import com.zaxxer.hikari.HikariConfig;
 import com.zaxxer.hikari.HikariDataSource;

core-java-persistence/src/test/java/com/baeldung/connectionpool/BasicConnectionPoolUnitTest.java

@@ -1,10 +1,8 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.BasicConnectionPool;
-import com.baeldung.connectionpool.connectionpools.ConnectionPool;
 import java.sql.Connection;
 import java.sql.SQLException;
-import java.util.List;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;

core-java-persistence/src/test/java/com/baeldung/connectionpool/C3poDataSourceUnitTest.java

@@ -1,6 +1,5 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.C3poDataSource;
 import java.sql.SQLException;
 import static org.junit.Assert.assertTrue;
 import org.junit.Test;

core-java-persistence/src/test/java/com/baeldung/connectionpool/DBCPDataSourceUnitTest.java

@@ -1,6 +1,5 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.DBCPDataSource;
 import java.sql.SQLException;
 import static org.junit.Assert.assertTrue;
 import org.junit.Test;

core-java-persistence/src/test/java/com/baeldung/connectionpool/HikariCPDataSourceUnitTest.java

@@ -1,6 +1,5 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.HikariCPDataSource;
 import java.sql.SQLException;
 import static org.junit.Assert.assertTrue;
 import org.junit.Test;

core-java/pom.xml

@@ -158,21 +158,6 @@
             <artifactId>jmimemagic</artifactId>
             <version>${jmime-magic.version}</version>
         </dependency>
-        <dependency>
-            <groupId>org.apache.commons</groupId>
-            <artifactId>commons-dbcp2</artifactId>
-            <version>${commons-dbcp2.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>com.zaxxer</groupId>
-            <artifactId>HikariCP</artifactId>
-            <version>${HikariCP.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>com.mchange</groupId>
-            <artifactId>c3p0</artifactId>
-            <version>${c3p0.version}</version>
-        </dependency>
         <!-- instrumentation -->
         <dependency>
             <groupId>org.javassist</groupId>
@@ -544,11 +529,6 @@
         <!-- testing -->
         <assertj-core.version>3.10.0</assertj-core.version>
 
-        <!-- JDBC pooling frameworks -->
-        <commons-dbcp2.version>2.4.0</commons-dbcp2.version>
-        <HikariCP.version>3.2.0</HikariCP.version>
-        <c3p0.version>0.9.5.2</c3p0.version>
-        
         <!-- maven plugins -->
         <maven-surefire-plugin.version>2.19.1</maven-surefire-plugin.version>
         <springframework.spring-web.version>4.3.4.RELEASE</springframework.spring-web.version>

pom.xml

@@ -312,6 +312,7 @@
 				<module>core-java-collections</module>
 				<module>core-java-io</module>
 				<module>core-java-8</module>
+                <module>core-java-persistence</module>
 				<module>core-kotlin</module>
 				<module>core-groovy</module>
 				<module>core-java-concurrency</module>
@@ -1233,6 +1234,4 @@
 		<!-- <maven-pmd-plugin.version>3.9.0</maven-pmd-plugin.version> -->
 		<maven-pmd-plugin.version>3.8</maven-pmd-plugin.version>
 	</properties>
-
 </project>
-