时间：2021-07-01 10:21:17 帮助过：4人阅读
1.不会发生经常性的跨库访问。
2.主要的业务逻辑都是围绕UserID为核心的，在一个单库事务内即可完成。
在系统中，我们使用Spring和iBatis。Spring负责数据库的事务管理AOP，以及Bean间的IOC。选择iBatis的最大原因是对Sql的性能优化，以及后期如果有分表要求的时，可以很容易实现对sql表名替换。
3.设计思路
首先，要说明一下笔者的思路，其实很简单，即“在每次数据库操作前，确定当前要选择的数据库对象”而后就如同访问单库一样的访问当前选中的数据库即可。
其次，要在每次DB访问前选择数据库，需要明确几个问题，1.iBatis在什么时候从DataSource中取得具体的数据库Connection 的，2.对取得的Connection，iBatis是否进行缓存，因为在多库情况下Connection被缓存就意味着无法及时改变数据库链接选择。 3.由于我们使用了Spring来管理DB事务，因此必须搞清Spring对DB Connction的开关拦截过程是否会影响多DataSource的情况。
幸运的是，研究源码的结果发现，iBatis和Spring都是通过标准的DataSource接口来控制
Connection的，这就为我们省去了很多的麻烦，只需要实现一个能够支持多个数据库的DataSource，就能达到我们的目标。
4.代码与实现
多数据库的DataSource实现：MultiDataSource.class
Java代码
[java] view plaincopy
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import javax.sql.DataSource;
import org.apache.log4j.Logger;
import com.xxx.sql.DataSourceRouter.RouterStrategy;
/**
* 复合多数据源（Alpha）
* @author linliangyi2005@gmail.com
* Jul 15, 2010
*/
public class MultiDataSource implements DataSource {
static Logger logger = Logger.getLogger(MultiDataSource.class);
//当前线程对应的实际DataSource
private ThreadLocal<DataSource> currentDataSourceHolder = new ThreadLocal<DataSource>();
//使用Key-Value映射的DataSource
private Map<String , DataSource> mappedDataSources;
//使用横向切分的分布式DataSource
private ArrayList<DataSource> clusterDataSources;
public MultiDataSource(){
mappedDataSources = new HashMap<String , DataSource>(4);
clusterDataSources = new ArrayList<DataSource>(4);
}
/**
* 数据库连接池初始化
* 该方法通常在web 应用启动时调用
*/
public void initialMultiDataSource(){
for(DataSource ds : clusterDataSources){
if(ds != null){
Connection conn = null;
try {
conn = ds.getConnection();
} catch (SQLException e) {
e.printStackTrace();
} finally{
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
conn = null;
}
}
}
}
Collection<DataSource> dsCollection = mappedDataSources.values();
for(DataSource ds : dsCollection){
if(ds != null){
Connection conn = null;
try {
conn = ds.getConnection();
} catch (SQLException e) {
e.printStackTrace();
} finally{
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
conn = null;
}
}
}
}
}
/**
* 获取当前线程绑定的DataSource
* @return
*/
public DataSource getCurrentDataSource() {
//如果路由策略存在，且更新过，则根据路由算法选择新的DataSource
RouterStrategy strategy = DataSourceRouter.currentRouterStrategy.get();
if(strategy == null){
throw new IllegalArgumentException("DataSource RouterStrategy No found.");
}
if(strategy != null && strategy.isRefresh()){
if(RouterStrategy.SRATEGY_TYPE_MAP.equals(strategy.getType())){
this.choiceMappedDataSources(strategy.getKey());
}else if(RouterStrategy.SRATEGY_TYPE_CLUSTER.equals(strategy.getType())){
this.routeClusterDataSources(strategy.getRouteFactor());
}
strategy.setRefresh(false);
}
return currentDataSourceHolder.get();
}
public Map<String, DataSource> getMappedDataSources() {
return mappedDataSources;
}
public void setMappedDataSources(Map<String, DataSource> mappedDataSources) {
this.mappedDataSources = mappedDataSources;
}
public ArrayList<DataSource> getClusterDataSources() {
return clusterDataSources;
}
public void setClusterDataSources(ArrayList<DataSource> clusterDataSources) {
this.clusterDataSources = clusterDataSources;
}
/**
* 使用Key选择当前的数据源
* @param key
*/
public void choiceMappedDataSources(String key){
DataSource ds = this.mappedDataSources.get(key);
if(ds == null){
throw new IllegalStateException("No Mapped DataSources Exist!");
}
this.currentDataSourceHolder.set(ds);
}
/**
* 使用取模算法，在群集数据源中做路由选择
* @param routeFactor
*/
public void routeClusterDataSources(int routeFactor){
int size = this.clusterDataSources.size();
if(size == 0){
throw new IllegalStateException("No Cluster DataSources Exist!");
}
int choosen = routeFactor % size;
DataSource ds = this.clusterDataSources.get(choosen);
if(ds == null){
throw new IllegalStateException("Choosen DataSources is null!");
}
logger.debug("Choosen DataSource No." + choosen+ " : " + ds.toString());
this.currentDataSourceHolder.set(ds);
}
/* (non-Javadoc)
* @see javax.sql.DataSource#getConnection()
*/
public Connection getConnection() throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getConnection();
}
return null;
}
/* (non-Javadoc)
* @see javax.sql.DataSource#getConnection(java.lang.String, java.lang.String)
*/
public Connection getConnection(String username, String password)
throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getConnection(username , password);
}
return null;
}
/* (non-Javadoc)
* @see javax.sql.CommonDataSource#getLogWriter()
*/
public PrintWriter getLogWriter() throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getLogWriter();
}
return null;
}
/* (non-Javadoc)
* @see javax.sql.CommonDataSource#getLoginTimeout()
*/
public int getLoginTimeout() throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getLoginTimeout();
}
return 0;
}
/* (non-Javadoc)
* @see javax.sql.CommonDataSource#setLogWriter(java.io.PrintWriter)
*/
public void setLogWriter(PrintWriter out) throws SQLException {
if(getCurrentDataSource() != null){
getCurrentDataSource().setLogWriter(out);
}
}
/* (non-Javadoc)
* @see javax.sql.CommonDataSource#setLoginTimeout(int)
*/
public void setLoginTimeout(int seconds) throws SQLException {
if(getCurrentDataSource() != null){
getCurrentDataSource().setLoginTimeout(seconds);
}
}
/* (non-Javadoc)
* 该接口方法since 1.6
* 不是所有的DataSource都实现有这个方法
* @see java.sql.Wrapper#isWrapperFor(java.lang.Class)
*/
public boolean isWrapperFor(Class<?> iface) throws SQLException {
// if(getCurrentDataSource() != null){
// return getCurrentDataSource().isWrapperFor(iface);
// }
return false;
}
/* (non-Javadoc)
* 该接口方法since 1.6
* 不是所有的DataSource都实现有这个方法
* @see java.sql.Wrapper#unwrap(java.lang.Class)
*/
public <T> T unwrap(Class<T> iface) throws SQLException {
// if(getCurrentDataSource() != null){
// return getCurrentDataSource().unwrap(iface);
// }
return null;
}
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import javax.sql.DataSource;
import org.apache.log4j.Logger;
import com.xxx.sql.DataSourceRouter.RouterStrategy;
/**
* 复合多数据源（Alpha）
* @author linliangyi2005@gmail.com
* Jul 15, 2010
*/
public class MultiDataSource implements DataSource {
static Logger logger = Logger.getLogger(MultiDataSource.class);
//当前线程对应的实际DataSource
private ThreadLocal<DataSource> currentDataSourceHolder = new ThreadLocal<DataSource>();
//使用Key-Value映射的DataSource
private Map<String , DataSource> mappedDataSources;
//使用横向切分的分布式DataSource
private ArrayList<DataSource> clusterDataSources;
public MultiDataSource(){
mappedDataSources = new HashMap<String , DataSource>(4);
clusterDataSources = new ArrayList<DataSource>(4);
}
/**
* 数据库连接池初始化
* 该方法通常在web 应用启动时调用
*/
public void initialMultiDataSource(){
for(DataSource ds : clusterDataSources){
if(ds != null){
Connection conn = null;
try {
conn = ds.getConnection();
} catch (SQLException e) {
e.printStackTrace();
} finally{
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
conn = null;
}
}
}
}
Collection<DataSource> dsCollection = mappedDataSources.values();
for(DataSource ds : dsCollection){
if(ds != null){
Connection conn = null;
try {
conn = ds.getConnection();
} catch (SQLException e) {
e.printStackTrace();
} finally{
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
conn = null;
}
}
}
}
}
/**
* 获取当前线程绑定的DataSource
* @return
*/
public DataSource getCurrentDataSource() {
//如果路由策略存在，且更新过，则根据路由算法选择新的DataSource
RouterStrategy strategy = DataSourceRouter.currentRouterStrategy.get();
if(strategy == null){
throw new IllegalArgumentException("DataSource RouterStrategy No found.");
}
if(strategy != null && strategy.isRefresh()){
if(RouterStrategy.SRATEGY_TYPE_MAP.equals(strategy.getType())){
this.choiceMappedDataSources(strategy.getKey());
}else if(RouterStrategy.SRATEGY_TYPE_CLUSTER.equals(strategy.getType())){
this.routeClusterDataSources(strategy.getRouteFactor());
}
strategy.setRefresh(false);
}
return currentDataSourceHolder.get();
}
public Map<String, DataSource> getMappedDataSources() {
return mappedDataSources;
}
public void setMappedDataSources(Map<String, DataSource> mappedDataSources) {
this.mappedDataSources = mappedDataSources;
}
public ArrayList<DataSource> getClusterDataSources() {
return clusterDataSources;
}
public void setClusterDataSources(ArrayList<DataSource> clusterDataSources) {
this.clusterDataSources = clusterDataSources;
}
/**
* 使用Key选择当前的数据源
* @param key
*/
public void choiceMappedDataSources(String key){
DataSource ds = this.mappedDataSources.get(key);
if(ds == null){
throw new IllegalStateException("No Mapped DataSources Exist!");
}
this.currentDataSourceHolder.set(ds);
}
/**
* 使用取模算法，在群集数据源中做路由选择
* @param routeFactor
*/
public void routeClusterDataSources(int routeFactor){
int size = this.clusterDataSources.size();
if(size == 0){
throw new IllegalStateException("No Cluster DataSources Exist!");
}
int choosen = routeFactor % size;
DataSource ds = this.clusterDataSources.get(choosen);
if(ds == null){
throw new IllegalStateException("Choosen DataSources is null!");
}
logger.debug("Choosen DataSource No." + choosen+ " : " + ds.toString());
this.currentDataSourceHolder.set(ds);
}
/* (non-Javadoc)
* @see javax.sql.DataSource#getConnection()
*/
public Connection getConnection() throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getConnection();
}
return null;
}
/* (non-Javadoc)
* @see javax.sql.DataSource#getConnection(java.lang.String, java.lang.String)
*/
public Connection getConnection(String username, String password)
throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getConnection(username , password);
}
return null;
}
/* (non-Javadoc)
* @see javax.sql.CommonDataSource#getLogWriter()
*/
public PrintWriter getLogWriter() throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getLogWriter();
}
return null;
}
/* (non-Javadoc)
* @see javax.sql.CommonDataSource#getLoginTimeout()
*/
public int getLoginTimeout() throws SQLException {
if(getCurrentDataSource() != null){
return getCurrentDataSource().getLoginTimeout();
}
return 0;
}
/* (non-Javadoc)
* @see javax.sql.CommonDataSource#setLogWriter(java.io.PrintWriter)
*/
public void setLogWriter(PrintWriter out) throws SQLException {
if(getCurrentDataSource() != null){
getCurrentDataSource().setLogWriter(out);
}
}
/* (non-Javadoc)
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