DataSource引言用Spring进行Web应用开发时我们经常会做datasource的配置。而且datasource的配法风格各异。那么他们到底有哪些异同点呢DataSource作用DataSource是javax.sql包中的类是Java原生rt.jar包中的类。public interface DataSource extends CommonDataSource, Wrapper { Connection getConnection() throws SQLException; Connection getConnection(String username, String password) throws SQLException; }javax.sql.DataSource定义的是抽象方法通过Java JNDI的方式将具体实现开放给各个厂商、组织自己、个人自己实现。在Spring框架中通过DataSource 配置的方式来定义具体的数据库源。并向Spring框架提供数据源的Connection服务。在Spring中若想实现多数据源那么就需要在DataSource下手。javax.sql.DataSource源码注释说明/** * pA factory for connections to the physical data source that this * {code DataSource} object represents. An alternative to the * {code DriverManager} facility, a {code DataSource} object * is the preferred means of getting a connection. An object that implements * the {code DataSource} interface will typically be * registered with a naming service based on the * Javatrade; Naming and Directory (JNDI) API. * P * The {code DataSource} interface is implemented by a driver vendor. * There are three types of implementations: * OL * LIBasic implementation -- produces a standard {code Connection} * object * LIConnection pooling implementation -- produces a {code Connection} * object that will automatically participate in connection pooling. This * implementation works with a middle-tier connection pooling manager. * LIDistributed transaction implementation -- produces a * {code Connection} object that may be used for distributed * transactions and almost always participates in connection pooling. * This implementation works with a middle-tier * transaction manager and almost always with a connection * pooling manager. * /OL * P * A {code DataSource} object has properties that can be modified * when necessary. For example, if the data source is moved to a different * server, the property for the server can be changed. The benefit is that * because the data sources properties can be changed, any code accessing * that data source does not need to be changed. * P * A driver that is accessed via a {code DataSource} object does not * register itself with the {code DriverManager}. Rather, a * {code DataSource} object is retrieved though a lookup operation * and then used to create a {code Connection} object. With a basic * implementation, the connection obtained through a {code DataSource} * object is identical to a connection obtained through the * {code DriverManager} facility. * p * An implementation of {code DataSource} must include a public no-arg * constructor. * * since 1.4 */概要翻译Part - 1:DataSource是获取物理数据源连接的工厂类。作为DriverManager工具的替代方案DataSource对象是获取连接的首选方法.DataSource的实现类一般都通过JNDI的方式注册到框架中进行使用。Part - 2:DataSource一般由数据库厂商提供对应的实现类DataSource有三种实现方式基本实现生成标准连接对象。连接池实现适用于中间层连接池管理器。分布式事务实现。此实现适用于中间层事务管理器并且几乎总是使用连接池管理器。Part - 3:DataSource向Spring框架屏蔽了具体数据源的差异即当物理数据源切换时只需要更新相关的DataSource配置值即可不需要应用层修改代码。Part - 4:数据库Driver都是通过DataSource对象被注册到DriverManager中而不是由Driver直接向DriverManager注册。但是对于获取Connection先通过检索先获得DataSource再根据DataSource对象进行getConnection而不是直接从DriverManager获取Connection。Spring-JDBC的DataSource实现案例在 Spring-jdbc 下DataSource 最顶级的类是 AbstractDataSource 对 DataSource 的所有父接口方法做了实现。但保留 getConnection() 方法由子类实现。在 AbstractDriverBasedDataSource 中定义了大量的参数诸如 url, username 等这些都被用来定位并定义与数据库实例的连接。package org.springframework.jdbc.datasource; import java.sql.Connection; import java.sql.SQLException; import java.util.Properties; import org.springframework.lang.UsesJava7; import org.springframework.util.Assert; public abstract class AbstractDriverBasedDataSource extends AbstractDataSource { private String url; private String username; private String password; private String catalog; private String schema; private Properties connectionProperties; public AbstractDriverBasedDataSource() { } ......略 public Connection getConnection() throws SQLException { return this.getConnectionFromDriver(this.getUsername(), this.getPassword()); } public Connection getConnection(String username, String password) throws SQLException { return this.getConnectionFromDriver(username, password); } UsesJava7 protected Connection getConnectionFromDriver(String username, String password) throws SQLException { Properties mergedProps new Properties(); Properties connProps this.getConnectionProperties(); if(connProps ! null) { mergedProps.putAll(connProps); } ......略 return con; } protected abstract Connection getConnectionFromDriver(Properties var1) throws SQLException; }整合方案为将除 url 外的所有参数整合在同一个 Properties 对象中 (其中Properties 可以被认为是一个线程安全的 Hash Map) 。最终调用 Connection getConnectionFromDriver(Properties props) 获取连接。AbstractDriverBasedDataSource 抽象类的两个子类 DriverManagerDataSource 和 SimpleDriverDataSource 都以不同方式获得了连接(Connection)但总结而言获取连接(Connection) 的任务被委托给了 Driver 来实现。// ---------------------------- // SimpleDriverDataSource 的实现 // ---------------------------- Override protected Connection getConnectionFromDriver(Properties props) throws SQLException { Driver driver getDriver(); String url getUrl(); Assert.notNull(driver, Driver must not be null); if (logger.isDebugEnabled()) { logger.debug(Creating new JDBC Driver Connection to [ url ]); } return driver.connect(url, props); } // ----------------------------- // DriverManagerDataSource 的实现 // ----------------------------- Override protected Connection getConnectionFromDriver(Properties props) throws SQLException { String url getUrl(); Assert.state(url ! null, url not set); if (logger.isDebugEnabled()) { logger.debug(Creating new JDBC DriverManager Connection to [ url ]); } // 调了个内部函数 return getConnectionFromDriverManager(url, props); } protected Connection getConnectionFromDriverManager(String url, Properties props) throws SQLException { // 委托给 DriverManager 类来获取连接 // DriverManager 的主要操作是遍历在该管理类中注册的 Driver // 每个 Driver 实例都去尝试一下能不能获得一个连接 // 第一次在某个 Driver 中拿到一个连接即返回连接 (Connection) return DriverManager.getConnection(url, props); }