转载
http://cuishen.iteye.com/blog/427921
大家都知道hibernate是在JDBC基础上的封装,那么它的数据库连接是怎样实现的呢?带着这个疑问最近研究了下hibernate的源代码,代码还是比较简单的,但是做的很通用,好现在一起来看下源代码
hibernate的数据库连接类都放在org.hibernate.connection包内,对于数据库连接类hibernate称其为ConnectionProvider,对!就是连接提供者,org.hibernate.connection.ConnectionProvider只是个供hibernate使用的接口,通过该接口的getConnection()方法获得数据库连接,但是这个接口到底是怎么样实现的,或者是由谁提供的,hibernate并不关心,用户在使用hibernate的时候可以在其配置文件中指定具体的实现类(hoho,这就是面向接口编程的好处),现在看看这个接口的规范:
Java代码
- package org.hibernate.connection;
- public interface ConnectionProvider {
- /** 初始化建立数据库连接所需要的配置 */
- public void configure(Properties props) throws HibernateException;
- /** 获得数据库连接 */
- public Connection getConnection() throws SQLException;
- /** 关闭数据库连接 */
- public void closeConnection(Connection conn) throws SQLException;
- /** 释放连接提供者占用的所有资源 */
- public void close() throws HibernateException;
- }
接下来要说的是org.hibernate.connection.ConnectionProviderFactory,望名会意,就是制造连接提供者的工厂,这个工厂类里面通过hibernate的配置反射获得具体的ConnectionProvider实现类的实例
Java代码
- ConnectionProvider connections;
- String providerClass = properties.getProperty(Environment.CONNECTION_PROVIDER);
- if ( providerClass!=null ) {
- try {
- log.info("Initializing connection provider: " + providerClass);
- //反射获得具体的ConnectionProvider实现类的实例
- connections = (ConnectionProvider) ReflectHelper.classForName(providerClass).newInstance();
- }
- catch ( Exception e ) {
- log.error( "Could not instantiate connection provider", e );
- throw new HibernateException("Could not instantiate connection provider: " + providerClass);
- }
- }
- else if ( properties.getProperty(Environment.DATASOURCE)!=null ) {
- connections = new DatasourceConnectionProvider();
- }
- else if ( properties.getProperty(Environment.URL)!=null ) {
- connections = new DriverManagerConnectionProvider();
- }
- else {
- connections = new UserSuppliedConnectionProvider();
- }
- ...
- return connections;
对于ConnectionProvider接口,hibernate自己提供了一套丰富的实现
1. DatasourceConnectionProvider,这是基于WEB容器提供的JNDI数据库连接池的连接实现
Java代码
- package org.hibernate.connection;
- public class DatasourceConnectionProvider implements ConnectionProvider {
- private DataSource ds;
- public void configure(Properties props) throws HibernateException {
- String jndiName = props.getProperty( Environment.DATASOURCE );
- if ( jndiName == null ) {
- String msg = "datasource JNDI name was not specified by property " + Environment.DATASOURCE;
- log.error( msg );
- throw new HibernateException( msg );
- }
- user = props.getProperty( Environment.USER );
- pass = props.getProperty( Environment.PASS );
- try {
- //通过JNDI方式获得DataSource
- ds = ( DataSource ) NamingHelper.getInitialContext( props ).lookup( jndiName );
- }
- catch ( Exception e ) {
- log.error( "Could not find datasource: " + jndiName, e );
- throw new HibernateException( "Could not find datasource", e );
- }
- if ( ds == null ) {
- throw new HibernateException( "Could not find datasource: " + jndiName );
- }
- log.info( "Using datasource: " + jndiName );
- }
- public Connection getConnection() throws SQLException {
- if (user != null || pass != null) {
- //获得连接
- return ds.getConnection(user, pass);
- }
- else {
- //获得连接
- return ds.getConnection();
- }
- }
- }
2. DriverManagerConnectionProvider,这是基于JDBC的数据库连接,当然同时也实现了自己的数据库连接缓存池
Java代码
- package org.hibernate.connection;
- public class DriverManagerConnectionProvider implements ConnectionProvider {
- private String url;
- private Properties connectionProps;
- private Integer isolation;
- private final ArrayList pool = new ArrayList();
- private int poolSize;
- private int checkedOut = 0;
- private boolean autocommit;
- private static final Logger log = LoggerFactory.getLogger(DriverManagerConnectionProvider.class);
- public void configure(Properties props) throws HibernateException {
- String driverClass = props.getProperty(Environment.DRIVER);
- //数据库连接池的大小,默认是20个
- poolSize = PropertiesHelper.getInt(Environment.POOL_SIZE, props, 20); //default pool size 20
- log.info("Using Hibernate built-in connection pool (not for production use!)");
- log.info("Hibernate connection pool size: " + poolSize);
- autocommit = PropertiesHelper.getBoolean(Environment.AUTOCOMMIT, props);
- log.info("autocommit mode: " + autocommit);
- isolation = PropertiesHelper.getInteger(Environment.ISOLATION, props);
- if (isolation!=null)
- log.info( "JDBC isolation level: " + Environment.isolationLevelToString( isolation.intValue() ) );
- if (driverClass==null) {
- log.warn("no JDBC Driver class was specified by property " + Environment.DRIVER);
- }
- else {
- try {
- // trying via forName() first to be as close to DriverManager's semantics
- Class.forName(driverClass);
- }
- catch (ClassNotFoundException cnfe) {
- try {
- ReflectHelper.classForName(driverClass);
- }
- catch (ClassNotFoundException e) {
- String msg = "JDBC Driver class not found: " + driverClass;
- log.error( msg, e );
- throw new HibernateException(msg, e);
- }
- }
- }
- url = props.getProperty( Environment.URL );
- if ( url == null ) {
- String msg = "JDBC URL was not specified by property " + Environment.URL;
- log.error( msg );
- throw new HibernateException( msg );
- }
- connectionProps = ConnectionProviderFactory.getConnectionProperties( props );
- log.info( "using driver: " + driverClass + " at URL: " + url );
- // if debug level is enabled, then log the password, otherwise mask it
- if ( log.isDebugEnabled() ) {
- log.info( "connection properties: " + connectionProps );
- }
- else if ( log.isInfoEnabled() ) {
- log.info( "connection properties: " + PropertiesHelper.maskOut(connectionProps, "password") );
- }
- }
- public Connection getConnection() throws SQLException {
- if ( log.isTraceEnabled() ) log.trace( "total checked-out connections: " + checkedOut );
- synchronized (pool) {
- if ( !pool.isEmpty() ) {
- int last = pool.size() - 1;
- if ( log.isTraceEnabled() ) {
- log.trace("using pooled JDBC connection, pool size: " + last);
- checkedOut++;
- }
- //如果连接池里有空闲的连接,则返回一个连接,并将该连接从连接池里移除
- Connection pooled = (Connection) pool.remove(last);
- if (isolation!=null) pooled.setTransactionIsolation( isolation.intValue() );
- if ( pooled.getAutoCommit()!=autocommit ) pooled.setAutoCommit(autocommit);
- return pooled;
- }
- }
- log.debug("opening new JDBC connection");
- //如果连接池里没有空闲的连接,则新建一个JDBC连接并返回
- Connection conn = DriverManager.getConnection(url, connectionProps);
- if (isolation!=null) conn.setTransactionIsolation( isolation.intValue() );
- if ( conn.getAutoCommit()!=autocommit ) conn.setAutoCommit(autocommit);
- if ( log.isDebugEnabled() ) {
- log.debug( "created connection to: " + url + ", Isolation Level: " + conn.getTransactionIsolation() );
- }
- if ( log.isTraceEnabled() ) checkedOut++;
- return conn;
- }
- public void closeConnection(Connection conn) throws SQLException {
- if ( log.isDebugEnabled() ) checkedOut--;
- synchronized (pool) {
- int currentSize = pool.size();
- if ( currentSize < poolSize ) {
- if ( log.isTraceEnabled() ) log.trace("returning connection to pool, pool size: " + (currentSize + 1) );
- //如果连接池没有满,则将该连接放进连接池
- pool.add(conn);
- return;
- }
- }
- log.debug("closing JDBC connection");
- //如果连接池已满,则关闭该连接
- conn.close();
- }
- /** 释放连接池 */
- public void close() {
- log.info("cleaning up connection pool: " + url);
- Iterator iter = pool.iterator();
- while ( iter.hasNext() ) {
- try {
- ( (Connection) iter.next() ).close();
- }
- catch (SQLException sqle) {
- log.warn("problem closing pooled connection", sqle);
- }
- }
- pool.clear();
- }
- }
3. 基于第三方项目的连接池实现,大家可以自己去看hibernate源代码:org.hibernate.connection.C3P0ConnectionProvider,以及org.hibernate.connection.ProxoolConnectionProvider。
对于hibernate的普通使用,如下代码:
Java代码
- SessionFactory sf = new Configuration().configure().buildSessionFactory();
- Session session = sf.openSession();
每次openSession()获得一个session就建立了一条数据库连接,一个session其实就对应着一条连接
如果是使用spring和hibernate进行web开发,可能你会用到下面的代码
Java代码
- Session session = org.springframework.orm.hibernate3.SessionFactoryUtils.getSession(sessionFactory, true);
可以自己去看spring的源代码,这个返回的Session对象其实已经被包装后缓存到了ThreadLocal对象里