一、引言
池化技术在Java中应用的很广泛，简而论之，使用对象池存储某个实例数受限制的实例，开发者从对象池中获取实例，使用完之后再换回对象池，从而在一定程度上减少了系统频繁创建对象销毁对象的开销。Java线程池和数据库连接池就是典型的应用，但并非所有的对象都适合拿来池化，对于创建开销比较小的对象拿来池化反而会影响性能，因为维护对象池也需要一定的资源开销，对于创建开销较大，又频繁创建使用的对象，采用池化技术会极大提高性能。
业界有很多成熟的数据库连接池，比如C3P0，DBCP，Proxool以及阿里的Druid。很多以及开源，在GitHub可以找到源码，开发者可以根据自己的需求结合各种连接池的特点和性能进行选择。本文仅是为了了解学习池化技术，实现的一个简单的数据库连接池，如有错误，还望批评指正。
二、设计
主要类和接口
.ConnectionParam - 数据库连接池参数类，负责配置数据库连接以及连接池相关参数。使用Builder实现。
driver url user password - 连接数据库所需
minConnection - 最小连接数
maxConnection - 最大连接数
minIdle - 最小空闲连接数
maxWait - 最长等待时间
private final String driver; private final String url; private final String user; private final String password; private final int minConnection; private final int maxConnection; private final int minIdle; private final long maxWait;
.ConnectionPool - 数据库连接池
ConnectionPool构造方法声明为保护，禁止外部创建，交由ConnectionPoolFactory统一管理。
ConnectionPool实现DataSource接口，重新getConnection()方法。
ConnectionPool持有两个容器 - 一个Queue存储空闲的Connection，另一个Vector（考虑到同步）存储正在使用的Connection。
当开发者使用数据库连接时，从Queue中获取，没有则返回空；使用完成close连接时，则放回Vector。
ConnectionPool提供了一个简单的基于minIdle和maxConnection的动态扩容机制。
private static final int INITIAL_SIZE = 5; private static final String CLOSE_METHOD = "close"; private static Logger logger; private int size; private ConnectionParam connectionParam; private ArrayBlockingQueue<Connection> idleConnectionQueue; private Vector<Connection> busyConnectionVector;
.ConnectionPoolFactory -连接池管理类
ConnectionPoolFactory持有一个静态ConcurrentHashMap用来存储连接池对象。
ConnectionPoolFactory允许创建多个不同配置不同数据库的连接池。
开发者首次需要使用特定的名称注册（绑定）连接池，以后每次从指定的连接池获取Connection。
如果连接池不再使用，开发者可以注销（解绑）连接池。
private static Map<String, ConnectionPool> poolMap = new ConcurrentHashMap<>(); public static Connection getConnection(String poolName) throws SQLException { nameCheck(poolName); ConnectionPool connectionPool = poolMap.get(poolName); return connectionPool.getConnection(); } public static void registerConnectionPool(String name, ConnectionParam connectionParam) { registerCheck(name); poolMap.put(name, new ConnectionPool(connectionParam)); } // Let GC public static void unRegisterConnectionPool(String name) { nameCheck(name); final ConnectionPool connectionPool = poolMap.get(name); poolMap.remove(name); new Thread(new Runnable() { @Override public void run() { connectionPool.clear(); } }).start(); }核心代码
数据库连接池核心代码在于getConnection()方法，通常，开发者处理完数据库操作后，都会调用close()方法，Connection此时应该被关闭并释放资源。而在数据库连接池中，用户调用close()方法，不应直接关闭Connection，而是要放回池中，重复使用，这里就用到Java动态代理机制，getConnection返回的并不是“真正”的Connection，而是自定义的代理类(此处使用匿名类)，当用户调用close()方法时，进行拦截，放回池中。有关动态代理，可以参看另一篇博客《Java动态代理简单应用》
@Override public Connection getConnection() throws SQLException { try { final Connection connection = idleConnectionQueue.poll(connectionParam.getMaxWait(), TimeUnit.MILLISECONDS); if (connection == null) { logger.info(emptyMsg()); ensureCapacity(); return null; } busyConnectionVector.add(connection); return (Connection) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{Connection.class}, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (!method.getName().equals(CLOSE_METHOD)) { return method.invoke(connection, args); } else { idleConnectionQueue.offer(connection); busyConnectionVector.remove(connection); return null; } } }); } catch (InterruptedException e) { e.printStackTrace(); } return null; }二、使用
首先用户构建数据库连接池参数（ConnectionParam），包括driver、url、user、password必须项，可以自定义minConnection、maxConnection等可选项，如果不设置，则使用系统默认值，这是使用Builder构建含有大量属性的好处，其中包括必须属性和可选属性。然后向ConnectionPoolFactory使用特定的名称注册连接池，最后通过调用ConnectionPoolFactory静态工厂方法获取Connection。
String driver = "com.mysql.jdbc.Driver"; String url = "jdbc:mysql://localhost:3306/test"; String user = "root"; String password = "root"; ConnectionParam connectionParam = new ConnectionParam.ConnectionParamBuilder(driver, url, user, password).build(); ConnectionPoolFactory.registerConnectionPool("test", connectionParam); Connection connection = ConnectionPoolFactory.getConnection("test");三、代码
.ParamConfiguration
package database.config;import java.io.Serializable;/** * DataBase Connection Parameters * Created by Michael Wong on 2016/1/18. */public class ParamConfiguration implements Serializable { public static final int MIN_CONNECTION = 5; public static final int MAX_CONNECTION = 50; public static final int MIN_IDLE = 5; public static final long MAX_WAIT = 30000; private ParamConfiguration() {}}.Builder
package database;/** * Builder * Created by Michael Wong on 2016/1/18. */public interface Builder<T> { T build();}.ConnectionParam
package database;import database.config.ParamConfiguration;/** * DataBase Connection Parameters * Created by Michael Wong on 2016/1/18. */public class ConnectionParam { private final String driver; private final String url; private final String user; private final String password; private final int minConnection; private final int maxConnection; private final int minIdle; private final long maxWait; private ConnectionParam(ConnectionParamBuilder builder) { this.driver = builder.driver; this.url = builder.url; this.user = builder.user; this.password = builder.password; this.minConnection = builder.minConnection; this.maxConnection = builder.maxConnection; this.minIdle = builder.minIdle; this.maxWait = builder.maxWait; } public String getDriver() { return this.driver; } public String getUrl() { return this.url; } public String getUser() { return this.user; } public String getPassword() { return this.password; } public int getMinConnection() { return this.minConnection; } public int getMaxConnection() { return this.maxConnection; } public int getMinIdle() { return this.minIdle; } public long getMaxWait() { return this.maxWait; } public static class ConnectionParamBuilder implements Builder<ConnectionParam> { // Required parameters private final String driver; private final String url; private final String user; private final String password; // Optional parameters - initialized to default value private int minConnection = ParamConfiguration.MIN_CONNECTION; private int maxConnection = ParamConfiguration.MAX_CONNECTION; private int minIdle = ParamConfiguration.MIN_IDLE; // Getting Connection wait time private long maxWait = ParamConfiguration.MAX_WAIT; public ConnectionParamBuilder(String driver, String url, String user, String password) { this.driver = driver; this.url = url; this.user = user; this.password = password; } public ConnectionParamBuilder minConnection(int minConnection) { this.minConnection = minConnection; return this; } public ConnectionParamBuilder maxConnection(int maxConnection) { this.maxConnection = maxConnection; return this; } public ConnectionParamBuilder minIdle(int minIdle) { this.minIdle = minIdle; return this; } public ConnectionParamBuilder maxWait(int maxWait) { this.maxWait = maxWait; return this; } @Override public ConnectionParam build() { return new ConnectionParam(this); } }}.ConnectionPool
package database.factory;import database.ConnectionParam;import javax.sql.DataSource;import java.io.PrintWriter;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import java.sql.SQLFeatureNotSupportedException;import java.util.Vector;import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.TimeUnit;import java.util.logging.Logger;/** * Connection Pool * Created by Michael Wong on 2016/1/18. */public class ConnectionPool implements DataSource { private static final int INITIAL_SIZE = 5; private static final String CLOSE_METHOD = "close"; private static Logger logger; private int size; private ConnectionParam connectionParam; private ArrayBlockingQueue<Connection> idleConnectionQueue; private Vector<Connection> busyConnectionVector; protected ConnectionPool(ConnectionParam connectionParam) { this.connectionParam = connectionParam; int maxConnection = connectionParam.getMaxConnection(); idleConnectionQueue = new ArrayBlockingQueue<>(maxConnection); busyConnectionVector = new Vector<>(); logger = Logger.getLogger(this.getClass().getName()); initConnection(); } private void initConnection() { int minConnection = connectionParam.getMinConnection(); int initialSize = INITIAL_SIZE < minConnection ? minConnection : INITIAL_SIZE; try { Class.forName(connectionParam.getDriver()); for (int i = 0; i < initialSize + connectionParam.getMinConnection(); i++) { idleConnectionQueue.put(newConnection()); size++; } } catch (Exception e) { throw new ExceptionInInitializerError(e); } } @Override public Connection getConnection() throws SQLException { try { final Connection connection = idleConnectionQueue.poll(connectionParam.getMaxWait(), TimeUnit.MILLISECONDS); if (connection == null) { logger.info(emptyMsg()); ensureCapacity(); return null; } busyConnectionVector.add(connection); return (Connection) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{Connection.class}, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (!method.getName().equals(CLOSE_METHOD)) { return method.invoke(connection, args); } else { idleConnectionQueue.offer(connection); busyConnectionVector.remove(connection); return null; } } }); } catch (InterruptedException e) { e.printStackTrace(); } return null; } private Connection newConnection() throws SQLException { String url = connectionParam.getUrl(); String user = connectionParam.getUser(); String password = connectionParam.getPassword(); return DriverManager.getConnection(url, user, password); } protected int size() { return size; } protected int idleConnectionQuantity() { return idleConnectionQueue.size(); } protected int busyConnectionQuantity() { return busyConnectionVector.size(); } private void ensureCapacity() throws SQLException { int minIdle = connectionParam.getMinIdle(); int maxConnection = connectionParam.getMaxConnection(); int newCapacity = size + minIdle; newCapacity = newCapacity > maxConnection ? maxConnection : newCapacity; int growCount = 0; if (size < newCapacity) { try { for (int i = 0; i < newCapacity - size; i++) { idleConnectionQueue.put(newConnection()); growCount++; } } catch (InterruptedException e) { e.printStackTrace(); } } size = size + growCount; } protected void clear() { try { while (size-- > 0) { Connection connection = idleConnectionQueue.take(); connection.close(); } } catch (InterruptedException | SQLException e) { e.printStackTrace(); } } private String emptyMsg() { return "Database is busy, please wait..."; } @Override public Connection getConnection(String username, String password) throws SQLException { return null; } @Override public PrintWriter getLogWriter() throws SQLException { return null; } @Override public void setLogWriter(PrintWriter out) throws SQLException { } @Override public void setLoginTimeout(int seconds) throws SQLException { } @Override public int getLoginTimeout() throws SQLException { return 0; } @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; }}.ConnectionPoolFactory
package database.factory;import database.ConnectionParam;import java.sql.Connection;import java.sql.SQLException;import java.util.Map;import java.util.concurrent.ConcurrentHashMap;/** * Connection Pool Factory * Created by Michael Wong on 2016/1/18. */public class ConnectionPoolFactory { private ConnectionPoolFactory() {} private static Map<String, ConnectionPool> poolMap = new ConcurrentHashMap<>(); public static Connection getConnection(String poolName) throws SQLException { nameCheck(poolName); ConnectionPool connectionPool = poolMap.get(poolName); return connectionPool.getConnection(); } public static void registerConnectionPool(String name, ConnectionParam connectionParam) { registerCheck(name); poolMap.put(name, new ConnectionPool(connectionParam)); } // Let GC public static void unRegisterConnectionPool(String name) { nameCheck(name); final ConnectionPool connectionPool = poolMap.get(name); poolMap.remove(name); new Thread(new Runnable() { @Override public void run() { connectionPool.clear(); } }).start(); } public static int size(String poolName) { nameCheck(poolName); return poolMap.get(poolName).size(); } public static int getIdleConnectionQuantity(String poolName) { nameCheck(poolName); return poolMap.get(poolName).idleConnectionQuantity(); } public static int getBusyConnectionQuantity(String poolName) { nameCheck(poolName); return poolMap.get(poolName).busyConnectionQuantity(); } private static void registerCheck(String name) { if (name == null) { throw new IllegalArgumentException(nullName()); } } private static void nameCheck(String name) { if (name == null) { throw new IllegalArgumentException(nullName()); } if (!poolMap.containsKey(name)) { throw new IllegalArgumentException(notExists(name)); } } private static String nullName() { return "Pool name must not be null"; } private static String notExists(String name) { return "Connection pool named " + name + " does not exists"; }}四、测试
JUnit单元测试
package database.factory;import database.ConnectionParam;import org.junit.Test;import java.sql.Connection;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import static org.junit.Assert.*;/** * ConnectionPoolFactory Test * Created by Michael Wong on 2016/1/20. */public class ConnectionPoolFactoryTest { @Test public void testGetConnection() throws SQLException { String driver = "com.mysql.jdbc.Driver"; String url = "jdbc:mysql://localhost:3306/test"; String user = "root"; String password = "root"; ConnectionParam connectionParam = new ConnectionParam.ConnectionParamBuilder(driver, url, user, password).build(); ConnectionPoolFactory.registerConnectionPool("test", connectionParam); List<Connection> connectionList = new ArrayList<>(); for(int i = 0; i < 12; i++) { connectionList.add(ConnectionPoolFactory.getConnection("test")); } print(); close(connectionList); print(); connectionList.clear(); for(int i = 0; i < 12; i++) { connectionList.add(ConnectionPoolFactory.getConnection("test")); } print(); close(connectionList); ConnectionPoolFactory.unRegisterConnectionPool("test"); } @Test(expected = IllegalArgumentException.class) public void testException() { try { ConnectionPoolFactory.getConnection("test"); } catch (SQLException e) { e.printStackTrace(); } } private void close(List<Connection> connectionList) throws SQLException { for(Connection conn : connectionList) { if (conn != null) { conn.close(); } } } private void print() { System.out.println("idle: " + ConnectionPoolFactory.getIdleConnectionQuantity("test")); System.out.println("busy: " + ConnectionPoolFactory.getBusyConnectionQuantity("test")); System.out.println("size: " + ConnectionPoolFactory.size("test")); }}以上就是本文的全部内容，希望对大家的学习有所帮助。