最简单的数据源，数据库连接池。

数据库连接池需要满足

• javax.sql.DataSource
• 对象池，对象池实际上是java.sql.Connection的缓存池。

实现

• maven依赖
  我使用的是org.apache.commons>commons-pool2做的对象池。

      <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-pool2</artifactId>
            <version>2.4.2</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.34</version>
        </dependency>

• Java代码

package org.march.dbp.pool;

import org.apache.commons.pool2.impl.GenericObjectPoolConfig;

public class ConnectionConfig extends GenericObjectPoolConfig {
    public ConnectionConfig() {
    }
}

package org.march.dbp.pool;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.DriverManager;

import org.apache.commons.pool2.BasePooledObjectFactory;
import org.apache.commons.pool2.PooledObject;
import org.apache.commons.pool2.impl.DefaultPooledObject;
import org.march.dbp.conn.JdbcConfig;

public class ConnectionFactory extends BasePooledObjectFactory<Connection> {

    private static final Class<?>[] IFACES = new Class<?>[] { Connection.class };

    private JdbcConfig jdbcConfig;

    private ConnectionPool connectionPool;

    public ConnectionFactory(JdbcConfig jdbcConfig, ConnectionPool connectionPool) {
        this.jdbcConfig = jdbcConfig;
        this.connectionPool = connectionPool;
    }

    @Override
    public Connection create() throws Exception {
        Connection connection = DriverManager.getConnection(jdbcConfig.getUrl(), jdbcConfig.getPassword(),
                jdbcConfig.getPassword());
        Connection con = (Connection) Proxy.newProxyInstance(Connection.class.getClassLoader(), IFACES,
                new InvocationHandler() {
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        if (method.getName().equals("close")) {
                            connectionPool.returnConn((Connection) proxy);
                            return null;
                        } else {
                            return method.invoke(connection, args);
                        }
                    }
                });
        return con;
    }

    @Override
    public PooledObject<Connection> wrap(Connection obj) {
        return new DefaultPooledObject<Connection>(obj);
    }

}

package org.march.dbp.pool;

import java.sql.Connection;

import org.apache.commons.pool2.impl.GenericObjectPool;
import org.march.dbp.conn.JdbcConfig;

public class ConnectionPool {
    private GenericObjectPool<Connection> pool = null;

    public static ConnectionPool build(JdbcConfig jdbcConfig) {
        return new ConnectionPool(jdbcConfig);
    }

    private ConnectionPool(JdbcConfig jdbcConfig) {
        ConnectionConfig myPoolConfig = new ConnectionConfig();
        myPoolConfig.setMaxTotal(5);
        pool = new GenericObjectPool<>(new ConnectionFactory(jdbcConfig, this), myPoolConfig);
    }

    public Connection getConn() {
        try {
            Connection conn = pool.borrowObject();
            return conn;
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    public void returnConn(Connection conn) {
        pool.returnObject(conn);
    }
}

package org.march.dbp.conn;

public class JdbcConfig {
    private String url;
    private String username;
    private String password;

    public JdbcConfig(String url, String username, String password) {
        this.url = url;
        this.username = username;
        this.password = password;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return url + " " + username + " " + password;
    }
}


package org.march.dbp.ds;

import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.logging.Logger;

import javax.sql.DataSource;

import org.march.dbp.conn.JdbcConfig;
import org.march.dbp.pool.ConnectionPool;

public class MarchDataSource implements DataSource {

    private PrintWriter out;

    private int loginTimeout;

    private ConnectionPool connectionPool;

    public MarchDataSource(String url, String username, String password) {
        connectionPool = ConnectionPool.build(new JdbcConfig(url, username, password));
    }

    @Override
    public PrintWriter getLogWriter() throws SQLException {
        return out;
    }

    @Override
    public void setLogWriter(PrintWriter out) throws SQLException {
        this.out = out;
    }

    @Override
    public void setLoginTimeout(int seconds) throws SQLException {
        this.loginTimeout = seconds;
    }

    @Override
    public int getLoginTimeout() throws SQLException {
        return loginTimeout;
    }

    @Override
    public Logger getParentLogger() throws SQLFeatureNotSupportedException {
        return null;
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return null;
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return false;
    }

    @Override
    public Connection getConnection() throws SQLException {
        return connectionPool.getConn();
    }

    @Override
    public Connection getConnection(String username, String password) throws SQLException {
        return null;
    }

}

• 测试

public class MarchDataSourceTest extends TestCase {
    public MarchDataSourceTest(String testName) {
        super(testName);
    }

    public void testApp() throws SQLException {
        MarchDataSource m = new MarchDataSource("jdbc:mysql://127.0.0.1:3306/wang", "root", "root");
        Connection con = m.getConnection();
        System.out.println(con);
        con.close();
    }
}

代码在 https://github.com/faicm/march/tree/master/march-dbp。我还会持续修改。