如果每次操作数据库都需要重新连接数据库，那么会很浪费资源。因此建议使用数据库的连接池来满足多线程的数据库操作。
Java中数据库连接池有多种实现方法，推荐使用DBCP，这是Apache 提供的数据库连接池的实现。
在Maven中添加如下依赖：
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-dbcp2</artifactId>
<version>2.6.0</version>
</dependency>
注意：2.6.0版本是最新的版本，不支持低于Java8的版本，更多内容参考官方文档:DBCP – Overview
官方样例：
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;
//
// Here are the dbcp-specific classes.
// Note that they are only used in the setupDataSource
// method. In normal use, your classes interact
// only with the standard JDBC API
//
import org.apache.commons.pool2.ObjectPool;
import org.apache.commons.pool2.impl.GenericObjectPool;
import org.apache.commons.dbcp2.ConnectionFactory;
import org.apache.commons.dbcp2.PoolableConnection;
import org.apache.commons.dbcp2.PoolingDataSource;
import org.apache.commons.dbcp2.PoolableConnectionFactory;
import org.apache.commons.dbcp2.DriverManagerConnectionFactory;
//
// Here's a simple example of how to use the PoolingDataSource.
//
//
// Note that this example is very similar to the PoolingDriver
// example. In fact, you could use the same pool in both a
// PoolingDriver and a PoolingDataSource
//
//
// To compile this example, you'll want:
// * commons-pool2-2.3.jar
// * commons-dbcp2-2.1.jar
// in your classpath.
//
// To run this example, you'll want:
// * commons-pool2-2.3.jar
// * commons-dbcp2-2.1.jar
// * commons-logging-1.2.jar
// * the classes for your (underlying) JDBC driver
// in your classpath.
//
// Invoke the class using two arguments:
// * the connect string for your underlying JDBC driver
// * the query you'd like to execute
// You'll also want to ensure your underlying JDBC driver
// is registered. You can use the "jdbc.drivers"
// property to do this.
//
// For example:
// java -Djdbc.drivers=org.h2.Driver \
// -classpath commons-pool2-2.3.jar:commons-dbcp2-2.1.jar:commons-logging-1.2.jar:h2-1.3.152.jar:. \
// PoolingDataSourceExample \
// "jdbc:h2:~/test" \
// "SELECT 1"
//
public class PoolingDataSourceExample {
public static void main(String[] args) {
//
// First we load the underlying JDBC driver.
// You need this if you don't use the jdbc.drivers
// system property.
//
System.out.println("Loading underlying JDBC driver.");
try {
Class.forName("org.h2.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
System.out.println("Done.");
//
// Then, we set up the PoolingDataSource.
// Normally this would be handled auto-magically by
// an external configuration, but in this example we'll
// do it manually.
//
System.out.println("Setting up data source.");
DataSource dataSource = setupDataSource(args[0]);
System.out.println("Done.");
//
// Now, we can use JDBC DataSource as we normally would.
//
Connection conn = null;
Statement stmt = null;
ResultSet rset = null;
try {
System.out.println("Creating connection.");
conn = dataSource.getConnection();
System.out.println("Creating statement.");
stmt = conn.createStatement();
System.out.println("Executing statement.");
rset = stmt.executeQuery(args[1]);
System.out.println("Results:");
int numcols = rset.getMetaData().getColumnCount();
while(rset.next()) {
for(int i=1;i<=numcols;i++) {
System.out.print("\t" + rset.getString(i));
}
System.out.println("");
}
} catch(SQLException e) {
e.printStackTrace();
} finally {
try { if (rset != null) rset.close(); } catch(Exception e) { }
try { if (stmt != null) stmt.close(); } catch(Exception e) { }
try { if (conn != null) conn.close(); } catch(Exception e) { }
}
}
public static DataSource setupDataSource(String connectURI) {
//
// First, we'll create a ConnectionFactory that the
// pool will use to create Connections.
// We'll use the DriverManagerConnectionFactory,
// using the connect string passed in the command line
// arguments.
//
ConnectionFactory connectionFactory =
new DriverManagerConnectionFactory(connectURI,null);
//
// Next we'll create the PoolableConnectionFactory, which wraps
// the "real" Connections created by the ConnectionFactory with
// the classes that implement the pooling functionality.
//
PoolableConnectionFactory poolableConnectionFactory =
new PoolableConnectionFactory(connectionFactory, null);
//
// Now we'll need a ObjectPool that serves as the
// actual pool of connections.
//
// We'll use a GenericObjectPool instance, although
// any ObjectPool implementation will suffice.
//
ObjectPool<PoolableConnection> connectionPool =
new GenericObjectPool<>(poolableConnectionFactory);
// Set the factory's pool property to the owning pool
poolableConnectionFactory.setPool(connectionPool);
//
// Finally, we create the PoolingDriver itself,
// passing in the object pool we created.
//
PoolingDataSource<PoolableConnection> dataSource =
new PoolingDataSource<>(connectionPool);
return dataSource;
}
}