A Guide to Connection Pools in Java

patterns/design-patterns/pom.xml

@@ -1,60 +1,85 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<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</groupId>
-    <artifactId>design-patterns</artifactId>
-    <version>1.0</version>
-    <packaging>jar</packaging>
-    <parent>
-        <groupId>com.baeldung</groupId>
-        <artifactId>patterns-parent</artifactId>
-        <version>1.0.0-SNAPSHOT</version>
-        <relativePath>..</relativePath>
-    </parent>
-
-    <dependencies>
-        <dependency>
-            <groupId>org.assertj</groupId>
-            <artifactId>assertj-core</artifactId>
-            <version>${assertj-core.version}</version>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>javax</groupId>
-            <artifactId>javaee-api</artifactId>
-            <version>${javaee.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>org.hibernate</groupId>
-            <artifactId>hibernate-core</artifactId>
-            <version>${hibernate-core.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>mysql</groupId>
-            <artifactId>mysql-connector-java</artifactId>
-            <version>${mysql-connector.version}</version>
-            <type>jar</type>
-        </dependency>
-        <dependency>
-            <groupId>log4j</groupId>
-            <artifactId>log4j</artifactId>
-            <version>${log4j.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>com.googlecode.grep4j</groupId>
-            <artifactId>grep4j</artifactId>
-            <version>${grep4j.version}</version>
-        </dependency>
-    </dependencies>
-    <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>1.8</maven.compiler.target>
-        <grep4j.version>1.8.7</grep4j.version>
-        <assertj-core.version>3.9.1</assertj-core.version>
-        <javaee.version>8.0</javaee.version>
-        <hibernate-core.version>5.2.16.Final</hibernate-core.version>
-        <mysql-connector.version>6.0.6</mysql-connector.version>
-    </properties>
-</project>
+<?xml version="1.0" encoding="UTF-8"?>
+<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.design-patterns</groupId>
+    <artifactId>design-patterns</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+     <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>patterns-parent</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>..</relativePath>
+    </parent>
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.9.1</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-core</artifactId>
+            <version>1.3</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>javax</groupId>
+            <artifactId>javaee-api</artifactId>
+            <version>8.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.hibernate</groupId>
+            <artifactId>hibernate-core</artifactId>
+            <version>5.2.16.Final</version>
+        </dependency>
+        <dependency>
+            <groupId>mysql</groupId>
+            <artifactId>mysql-connector-java</artifactId>
+            <version>8.0.11</version>
+        </dependency>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <version>1.4.197</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-dbcp2</artifactId>
+            <version>2.4.0</version>
+        </dependency>
+        <dependency>
+            <groupId>com.zaxxer</groupId>
+            <artifactId>HikariCP</artifactId>
+            <version>3.1.0</version>
+        </dependency>
+        <dependency>
+            <groupId>c3p0</groupId>
+            <artifactId>c3p0</artifactId>
+            <version>0.9.1.2</version>
+        </dependency>
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>1.2.17</version>
+        </dependency>
+        <dependency>
+            <groupId>com.googlecode.grep4j</groupId>
+            <artifactId>grep4j</artifactId>
+            <version>1.8.7</version>
+        </dependency>
+    </dependencies>
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+</project>

patterns/design-patterns/src/main/java/com/baeldung/connectionpool/application/Application.java

@@ -0,0 +1,28 @@
+package com.baeldung.connectionpool.application;
+
+import com.baeldung.connectionpool.connectionpools.BasicConnectionPool;
+import com.baeldung.connectionpool.connectionpools.C3poDataSource;
+import com.baeldung.connectionpool.connectionpools.ConnectionPool;
+import com.baeldung.connectionpool.connectionpools.DBCPDataSource;
+import com.baeldung.connectionpool.connectionpools.HirakiDataSource;
+import java.sql.Connection;
+import java.sql.SQLException;
+
+public class Application {
+
+    public static void main(String[] args) throws SQLException {
+        ConnectionPool cp1 = BasicConnectionPool.createFromDriverManager("jdbc:mysql://localhost:3306/mydb", "user", "password");
+        Connection con1 = cp1.getConnection(0);
+        System.out.println(con1);
+        cp1.releaseConnection(con1);
+
+        Connection con3 = DBCPDataSource.getConnection();
+        System.out.println(con3);
+
+        Connection con4 = C3poDataSource.getConnection();
+        System.out.println(con4);
+
+        Connection con5 = HirakiDataSource.getConnection();
+        System.out.println(con5);
+    }
+}

patterns/design-patterns/src/main/java/com/baeldung/connectionpool/connectionpools/BasicConnectionPool.java

@@ -0,0 +1,65 @@
+package com.baeldung.connectionpool.connectionpools;
+
+import com.mysql.cj.jdbc.MysqlDataSource;
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.List;
+
+public class BasicConnectionPool implements ConnectionPool {
+
+    private final String url;
+    private final String user;
+    private final String password;
+    private final List<Connection> connectionPool;
+    private static final int MAX_CONNECTIONS = 10;
+
+    public static BasicConnectionPool createFromDriverManager(String url, String user, String password) throws SQLException {
+        List<Connection> pool = new ArrayList<>(MAX_CONNECTIONS);
+        for (int i = 0; i < MAX_CONNECTIONS; i++) {
+            pool.add(DriverManager.getConnection(url, user, password));
+        }
+        return new BasicConnectionPool(url, user, password, pool);
+    }
+
+    private BasicConnectionPool(String url, String user, String password, List<Connection> connectionPool) {
+        this.url = url;
+        this.user = user;
+        this.password = password;
+        this.connectionPool = connectionPool;
+    }
+
+    @Override
+    public Connection getConnection(int id) {
+        if (id < 0 || id > MAX_CONNECTIONS) {
+            throw new RuntimeException();
+        }
+        return connectionPool.get(id);
+    }
+
+    @Override
+    public void releaseConnection(Connection connection) {
+        connectionPool.add(connection);
+    }
+
+    @Override
+    public List<Connection> getConnectionPool() {
+        return connectionPool;
+    }
+
+    @Override
+    public String getUrl() {
+        return url;
+    }
+
+    @Override
+    public String getUser() {
+        return user;
+    }
+
+    @Override
+    public String getPassword() {
+        return password;
+    }
+}

patterns/design-patterns/src/main/java/com/baeldung/connectionpool/connectionpools/C3poDataSource.java

@@ -0,0 +1,28 @@
+package com.baeldung.connectionpool.connectionpools;
+
+import com.mchange.v2.c3p0.ComboPooledDataSource;
+import java.beans.PropertyVetoException;
+import java.sql.Connection;
+import java.sql.SQLException;
+
+public class C3poDataSource {
+
+    private static final ComboPooledDataSource cpds = new ComboPooledDataSource();
+
+    static {
+        try {
+            cpds.setDriverClass("com.mysql.jdbc.Driver");
+            cpds.setJdbcUrl("jdbc:mysql://localhost:3306/mydb");
+            cpds.setUser("user");
+            cpds.setPassword("password");
+        } catch (PropertyVetoException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public static Connection getConnection() throws SQLException {
+        return cpds.getConnection();
+    }
+
+    private C3poDataSource(){}
+}

patterns/design-patterns/src/main/java/com/baeldung/connectionpool/connectionpools/ConnectionPool.java

@@ -0,0 +1,19 @@
+package com.baeldung.connectionpool.connectionpools;
+
+import java.sql.Connection;
+import java.util.List;
+
+public interface ConnectionPool {
+
+    Connection getConnection(int id);
+
+    void releaseConnection(Connection connection);
+
+    List<Connection> getConnectionPool();
+
+    String getUrl();
+
+    String getUser();
+
+    String getPassword();
+}   

patterns/design-patterns/src/main/java/com/baeldung/connectionpool/connectionpools/DBCPDataSource.java

@@ -0,0 +1,25 @@
+package com.baeldung.connectionpool.connectionpools;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import org.apache.commons.dbcp2.BasicDataSource;
+
+public class DBCPDataSource {
+
+    private static final BasicDataSource ds = new BasicDataSource();
+
+    static {
+        ds.setUrl("jdbc:mysql://localhost:3306/mydb");
+	ds.setUsername("user");
+	ds.setPassword("password");
+        ds.setMinIdle(5);
+	ds.setMaxIdle(10);
+	ds.setMaxOpenPreparedStatements(100);
+    }
+
+    public static Connection getConnection() throws SQLException {
+        return ds.getConnection();
+    }
+
+    private DBCPDataSource(){}
+}

patterns/design-patterns/src/main/java/com/baeldung/connectionpool/connectionpools/HirakiDataSource.java

@@ -0,0 +1,28 @@
+package com.baeldung.connectionpool.connectionpools;
+
+import com.zaxxer.hikari.HikariConfig;
+import com.zaxxer.hikari.HikariDataSource;
+import java.sql.Connection;
+import java.sql.SQLException;
+
+public class HirakiDataSource {
+
+    private static final HikariConfig config = new HikariConfig();
+    private static final HikariDataSource ds;
+
+    static {
+        config.setJdbcUrl("jdbc:mysql://localhost:3306/mydb");
+        config.setUsername("user");
+        config.setPassword("password");
+        config.addDataSourceProperty("cachePrepStmts", "true");
+        config.addDataSourceProperty("prepStmtCacheSize", "250");
+        config.addDataSourceProperty("prepStmtCacheSqlLimit", "2048");
+        ds = new HikariDataSource(config);
+    }
+
+    public static Connection getConnection() throws SQLException {
+        return ds.getConnection();
+    }
+
+    private HirakiDataSource(){}
+}

patterns/design-patterns/src/test/java/com/baeldung/connectionpool/test/BasicConnectionPoolIntegrationtTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.connectionpool.test;
+
+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 org.junit.BeforeClass;
+import org.junit.Test;
+
+public class BasicConnectionPoolIntegrationtTest {
+
+    private static ConnectionPool connectionPool;
+
+
+    @BeforeClass
+    public static void setUpBasicConnectionPoolInstance() throws SQLException {
+        connectionPool = BasicConnectionPool.createFromDriverManager("jdbc:mysql://localhost:3306/mydb", "user", "password");
+    }
+
+    @Test
+    public void givenBasicConnectionPoolInstance_whenCalledgetConnection_thenCorrect() {
+        assertThat(connectionPool.getConnection(1)).isInstanceOf(Connection.class);
+    }
+
+    @Test
+    public void givenBasicConnectionPoolInstance_whenCalledgetConnectionPool_thenCorrect() {
+        assertThat(connectionPool.getConnectionPool()).isInstanceOf(List.class);
+    }
+}

patterns/design-patterns/src/test/java/com/baeldung/connectionpool/test/C3poDataSourceUnitTest.java

@@ -0,0 +1,15 @@
+package com.baeldung.connectionpool.test;
+
+import com.baeldung.connectionpool.connectionpools.C3poDataSource;
+import java.sql.Connection;
+import java.sql.SQLException;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class C3poDataSourceUnitTest {
+
+    @Test
+    public void givenC3poDataSourceClass_whenCalledgetConnection_thenCorrect() throws SQLException {
+        assertThat(C3poDataSource.getConnection()).isInstanceOf(Connection.class);
+    }   
+}