Java -- JDBC 数据库连接池

1. 原理代码示例

public class JdbcPool implements DataSource {

	private static LinkedList<Connection> list = new LinkedList<Connection>();

	static{
		try{
			InputStream in = JdbcPool.class.getClassLoader().getResourceAsStream("db.properties");
			Properties prop = new Properties();
			prop.load(in);

			String driver = prop.getProperty("driver");
			String url = prop.getProperty("url");
			String username = prop.getProperty("username");
			String password = prop.getProperty("password");

			Class.forName(driver);

			for(int i=0;i<10;i++){
				Connection conn = DriverManager.getConnection(url, username, password);
				System.out.println("获取到了链接" + conn);
				list.add(conn);
			}

		}catch (Exception e) {
			throw new ExceptionInInitializerError(e);
		}
	}

	/*
	1.写一个子类，覆盖close方法
	2、写一个connection的包装类，增强close方法
	3、用动态代理，返回一个代理对象出去，拦截close方法的调用，对close进行增强
	 */

	public Connection getConnection() throws SQLException {

		//proxyConnection.commit()  proxyConnection.rollback
		if(list.size()>0){
			final Connection conn = list.removeFirst();   //myconnection.commit
			System.out.println("池大小是" + list.size());
			return (Connection) Proxy.newProxyInstance(JdbcPool.class.getClassLoader(), conn.getClass().getInterfaces(), new InvocationHandler(){

				public Object invoke(Object proxy, Method method, Object[] args)
						throws Throwable {
					if(!method.getName().equals("close")){
						return method.invoke(conn, args);
					}else{
						list.add(conn);
						System.out.println(conn + "被还给池了！！");
						System.out.println("池大小为" + list.size());
						return null;
					}

				}

			});

		}else{
			throw new RuntimeException("对不起，数据库忙");
		}

	}

	public Connection getConnection(String username, String password)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public PrintWriter getLogWriter() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	public int getLoginTimeout() throws SQLException {
		// TODO Auto-generated method stub
		return 0;
	}

	public void setLogWriter(PrintWriter arg0) throws SQLException {
		// TODO Auto-generated method stub

	}

	public void setLoginTimeout(int arg0) throws SQLException {
		// TODO Auto-generated method stub

	}
}

/*
用包装设计模式对某个对象进行增强
1.写一个类，实现与被增强对象(mysql的connection)相同的接口
2、定义一个变量，指向被增强对象
3、定义一个构造方法，接收被增强对象
4、覆盖想增强的方法
5、对于不想增强的方法，直接调用被增强对象的方法
 */

class MyConnection implements Connection{

	private Connection conn;
	private List pool;
	public MyConnection(Connection conn,List pool){
		this.conn = conn;
		this.pool = pool;
	}

	public void close() throws SQLException {
		pool.add(conn);
	}

	public void clearWarnings() throws SQLException {
		this.conn.clearWarnings();

	}

	public void commit() throws SQLException {
		this.conn.commit();

	}
	public Statement createStatement() throws SQLException {
		return this.conn.createStatement();
	}
	public Statement createStatement(int resultSetType, int resultSetConcurrency)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public Statement createStatement(int resultSetType,
			int resultSetConcurrency, int resultSetHoldability)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public boolean getAutoCommit() throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}
	public String getCatalog() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public int getHoldability() throws SQLException {
		// TODO Auto-generated method stub
		return 0;
	}
	public DatabaseMetaData getMetaData() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public int getTransactionIsolation() throws SQLException {
		// TODO Auto-generated method stub
		return 0;
	}
	public Map<String, Class<?>> getTypeMap() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public SQLWarning getWarnings() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public boolean isClosed() throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}
	public boolean isReadOnly() throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}
	public String nativeSQL(String sql) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public CallableStatement prepareCall(String sql) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public CallableStatement prepareCall(String sql, int resultSetType,
			int resultSetConcurrency) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public CallableStatement prepareCall(String sql, int resultSetType,
			int resultSetConcurrency, int resultSetHoldability)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public PreparedStatement prepareStatement(String sql) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public PreparedStatement prepareStatement(String sql, int[] columnIndexes)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public PreparedStatement prepareStatement(String sql, String[] columnNames)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public PreparedStatement prepareStatement(String sql, int resultSetType,
			int resultSetConcurrency) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public PreparedStatement prepareStatement(String sql, int resultSetType,
			int resultSetConcurrency, int resultSetHoldability)
			throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public void releaseSavepoint(Savepoint savepoint) throws SQLException {
		// TODO Auto-generated method stub

	}
	public void rollback() throws SQLException {
		// TODO Auto-generated method stub

	}
	public void rollback(Savepoint savepoint) throws SQLException {
		// TODO Auto-generated method stub

	}
	public void setAutoCommit(boolean autoCommit) throws SQLException {
		// TODO Auto-generated method stub

	}
	public void setCatalog(String catalog) throws SQLException {
		// TODO Auto-generated method stub

	}
	public void setHoldability(int holdability) throws SQLException {
		// TODO Auto-generated method stub

	}
	public void setReadOnly(boolean readOnly) throws SQLException {
		// TODO Auto-generated method stub

	}
	public Savepoint setSavepoint() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public Savepoint setSavepoint(String name) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}
	public void setTransactionIsolation(int level) throws SQLException {
		// TODO Auto-generated method stub

	}
	public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
		// TODO Auto-generated method stub

	}

}

2. 开源连接池  •DBCP
数据库连接池

加入dbcp链接池

1.导入jar包

 commons-dbcp-1.2.2.jar  commons-pool.jar

2、在类目录下加入dbcp的配置文件：dbcpconfig.properties

3、在jdbcUtils的静态代码块中创建池

private static DataSource ds = null;
	static{
		try{
			InputStream in = JdbcUtils_DBCP.class.getClassLoader().getResourceAsStream("dbcpconfig.properties");
			Properties prop = new Properties();
			prop.load(in);

			BasicDataSourceFactory factory = new BasicDataSourceFactory();

			ds = factory.createDataSource(prop);
			System.out.println(ds);
		}catch (Exception e) {
			throw new ExceptionInInitializerError(e);
		}
	}

重写后的工具类

public class JdbcUtils_DBCP {

	private static DataSource ds = null;
	static{
		try{
			InputStream in = JdbcUtils_DBCP.class.getClassLoader().getResourceAsStream("dbcpconfig.properties");
			Properties prop = new Properties();
			prop.load(in);

			BasicDataSourceFactory factory = new BasicDataSourceFactory();

			ds = factory.createDataSource(prop);
			System.out.println(ds);
		}catch (Exception e) {
			throw new ExceptionInInitializerError(e);
		}
	}

	public static Connection getConnection() throws SQLException{

		return ds.getConnection();
	}

	public static void release(Connection conn,Statement st,ResultSet rs){

		if(rs!=null){
			try{
				rs.close();
			}catch (Exception e) {
				e.printStackTrace();
			}
			rs = null;

		}
		if(st!=null){
			try{
				st.close();
			}catch (Exception e) {
				e.printStackTrace();
			}

		}

		if(conn!=null){
			try{
				conn.close();
			}catch (Exception e) {
				e.printStackTrace();
			}

		}
	}

}

配置文档dbcpconfig.properties

#连接设置
driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/jdbc
username=root
password=root

#<!-- 初始化连接 -->
initialSize=10

#最大连接数量
maxActive=50

#<!-- 最大空闲连接 -->
maxIdle=20

#<!-- 最小空闲连接 -->
minIdle=5

#<!-- 超时等待时间以毫秒为单位 6000毫秒/1000等于60秒 -->
maxWait=60000

#JDBC驱动建立连接时附带的连接属性属性的格式必须为这样：[属性名=property;]
#注意："user" 与 "password" 两个属性会被明确地传递，因此这里不需要包含他们。
connectionProperties=useUnicode=true;characterEncoding=UTF8

#指定由连接池所创建的连接的自动提交（auto-commit）状态。
defaultAutoCommit=true

#driver default 指定由连接池所创建的连接的只读（read-only）状态。
#如果没有设置该值，则“setReadOnly”方法将不被调用。（某些驱动并不支持只读模式，如：Informix）
defaultReadOnly=

#driver default 指定由连接池所创建的连接的事务级别（TransactionIsolation）。
#可用值为下列之一：（详情可见javadoc。）NONE,READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ, SERIALIZABLE
defaultTransactionIsolation=REPEATABLE_READ

3.开源数据库连接池  •C3P0
数据库连接池

配置文档 c3p0-config.xml 需要放在 src目录下，自动搜索

<?xml version="1.0" encoding="UTF-8"?>

<!--
c3p0-config.xml
private static ComboPooledDataSource ds;
static{
	try {
		ds = new ComboPooledDataSource("c3p0config");
	} catch (Exception e) {
		throw new ExceptionInInitializerError(e);
	}
}

-->

<c3p0-config>
	<default-config>
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="jdbcUrl">jdbc:mysql://localhost:3306/transaction</property>
		<property name="user">root</property>
		<property name="password">123456</property>

		<property name="acquireIncrement">5</property>
		<property name="initialPoolSize">10</property>
		<property name="minPoolSize">5</property>
		<property name="maxPoolSize">100</property>

	</default-config>

	<named-config name="c3p0config">
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="jdbcUrl">jdbc:mysql://localhost:3306/transaction</property>
		<property name="user">root</property>
		<property name="password">123456</property>
		<property name="acquireIncrement">5</property>
		<property name="initialPoolSize">10</property>
		<property name="minPoolSize">5</property>
		<property name="maxPoolSize">100</property><!-- intergalactoApp adopts a different approach to configuring statement caching -->
	</named-config>

</c3p0-config>

工具类：

public class JdbcUtils_C3P0 {

	private static ComboPooledDataSource ds = null;
	static{
		try{
			ds = new ComboPooledDataSource("c3p0config");

		}catch (Exception e) {
			throw new ExceptionInInitializerError(e);
		}
	}

	public static Connection getConnection() throws SQLException{

		return ds.getConnection();
	}

	public static void release(Connection conn,Statement st,ResultSet rs){

		if(rs!=null){
			try{
				rs.close();
			}catch (Exception e) {
				e.printStackTrace();
			}
			rs = null;

		}
		if(st!=null){
			try{
				st.close();
			}catch (Exception e) {
				e.printStackTrace();
			}

		}

		if(conn!=null){
			try{
				conn.close();
			}catch (Exception e) {
				e.printStackTrace();
			}

		}
	}

}