在spring中配置多数据库读取

在应对大量用户读取的系统中，对数据库的操作通常采用读写分离方式，往一个数据库写入，然后通过复制将数据同步到另外的多个数据库中，读操作都从这些数据库中操作，在采用spring来配置多数据库时，并不能直接支持从多个DataSource中获得数据库连接，为此需要开发一个DataSource的代理，代理实现javax.sql.DataSource接口。该代理根据一定的策略从已有的多个DataSource中选择一个，提供给SessionFactory，供数据访问层使用。原理如下图所示：
 
 
 
 
 
DataSource Proxy选择DataSource的方式可以根据实际进行设计，这里为简单，就采用随机方式选择一个。源代码如下：
 
 
[java] view plaincopy
package code; 
 
 
import java.io.PrintWriter; 
import java.sql.Connection; 
import java.sql.SQLException; 
 
 
import java.util.List; 
import java.util.Random; 
 
 
import javax.sql.DataSource; 
 
 
import org.apache.commons.logging.Log; 
import org.apache.commons.logging.LogFactory; 
 
 
public class RandomDataSource  implements DataSource { 
 
 
<span style="white-space:pre">    </span>private List<DataSource> dataSourcePool ; 
<span style="white-space:pre">    </span>protected Log log =  LogFactory.getLog(getClass()); 
<span style="white-space:pre">    </span> 
<span style="white-space:pre">    </span>private  static ThreadLocal<DataSource> dsHolder = new ThreadLocal<DataSource>(); 
<span style="white-space:pre">    </span> 
<span style="white-space:pre">    </span> 
<span style="white-space:pre">    </span>/**
<span style="white-space:pre">    </span> * 从已有DataSource中随机选择一个
<span style="white-space:pre">    </span> *
<span style="white-space:pre">    </span> *
<span style="white-space:pre">    </span> */ 
<span style="white-space:pre">    </span>private DataSource randomDs(){ 
<span style="white-space:pre">        </span> 
<span style="white-space:pre">        </span>int size = dataSourcePool.size(); 
<span style="white-space:pre">        </span> 
<span style="white-space:pre">        </span>Random r= new Random(); 
<span style="white-space:pre">        </span>int t = r.nextInt(size); 
<span style="white-space:pre">        </span>dsHolder.set(dataSourcePool.get(t)); 
<span style="white-space:pre">        </span>return dsHolder.get(); 
<span style="white-space:pre">        </span>  
<span style="white-space:pre">        </span> 
<span style="white-space:pre">    </span>} 
<span style="white-space:pre">    </span> 
<span style="white-space:pre">    </span> 
<span style="white-space:pre">    </span>@Override 
<span style="white-space:pre">    </span>public Connection getConnection() throws SQLException { 
<span style="white-space:pre">        </span> 
<span style="white-space:pre">        </span>Connection conn = randomDs().getConnection(); 
<span style="white-space:pre">        </span>return conn; 
<span style="white-space:pre">    </span>} 
 
 
<span style="white-space:pre">    </span>@Override 
<span style="white-space:pre">    </span>public Connection getConnection(String username, String password) 
<span style="white-space:pre">            </span>throws SQLException { 
<span style="white-space:pre">        </span>Connection conn = randomDs().getConnection(username, password); 
<span style="white-space:pre">        </span>log.info("conn URL---->"+conn.getMetaData().getURL()); 
<span style="white-space:pre">        </span> 
<span style="white-space:pre">        </span>return conn; 
<span style="white-space:pre">    </span>} 
 
 
<span style="white-space:pre">    </span>@Override 
<span style="white-space:pre">    </span>public PrintWriter getLogWriter() throws SQLException { 
<span style="white-space:pre">        </span> 
<span style="white-space:pre">        </span>return dsHolder.get().getLogWriter(); 
<span style="white-space:pre">    </span>} 
 
 
<span style="white-space:pre">    </span>@Override 
<span style="white-space:pre">    </span>public int getLoginTimeout() throws SQLException { 
<span style="white-space:pre">        </span> 
<span style="white-space:pre">        </span>return dsHolder.get().getLoginTimeout(); 
<span style="white-space:pre">    </span>} 
 
 
<span style="white-space:pre">    </span>@Override 
<span style="white-space:pre">    </span>public void setLogWriter(PrintWriter out) throws SQLException { 
<span style="white-space:pre">        </span> 
<span style="white-space:pre">        </span>dsHolder.get().setLogWriter(out); 
<span style="white-space:pre">