简单的翻译, 也算是一篇笔记.
原文:http://blog.springsource.com/2007/01/23/dynamic-datasource-routing/
在Spring 2.0.1中引入了AbstractRoutingDataSource, 该类充当了DataSource的路由中介, 能有在运行时, 根据某种key值来动态切换到真正的DataSource上, 同时对于不支持事务隔离级别的JTA事务来说, Spring还提供了另外一个类IsolationLevelDataSourceRouter来处理这个问题. 下面的例子将通过context来切换不同的数据源.
首先定义一个Catalog的Dao:
Java代码
package blog.datasource;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import org.springframework.jdbc.core.simple.ParameterizedRowMapper;
import org.springframework.jdbc.core.simple.SimpleJdbcDaoSupport;
public class Catalog extends SimpleJdbcDaoSupport {
public List<Item> getItems() {
String query = "select name, price from item";
return getSimpleJdbcTemplate().query(query, new ParameterizedRowMapper<Item>() {
public Item mapRow(ResultSet rs, int row) throws SQLException {
String name = rs.getString(1);
double price = rs.getDouble(2);
return new Item(name, price);
}
});
}
}
然后定义一个Item的JavaBean
Java代码
package blog.datasource;
public class Item {
private String name;
private double price;
public Item(String name, double price) {
this.name = name;
this.price = price;
}
public String getName() {
return name;
}
public double getPrice() {
return price;
}
public String toString() {
return name + " (" + price + ")";
}
}
接着定义一个枚举类型, 用来表示不同的用户级别, 通过该类型将映射到不同的数据源
Java代码
public enum CustomerType {
BRONZE,
SILVER,
GOLD
}
下面是DataSource定义:
Xml代码
<bean id="parentDataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource"
abstract="true">
<property name="driverClassName" value="org.hsqldb.jdbcDriver"/>
<property name="username" value="sa"/>
</bean>
<bean id="goldDataSource" parent="parentDataSource">
<property name="url" value="jdbc:hsqldb:hsql://localhost:${db.port.gold}/blog"/>
</bean>
<bean id="silverDataSource" parent="parentDataSource">
<property name="url" value="jdbc:hsqldb:hsql://localhost:${db.port.silver}/blog"/>
</bean>
<bean id="bronzeDataSource" parent="parentDataSource">
<property name="url" value="jdbc:hsqldb:hsql://localhost:${db.port.bronze}/blog"/>
</bean>
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="location" value="classpath:/blog/datasource/db.properties"/>
</bean>
AbstractRoutingDataSource 实现类
Java代码
package blog.datasource;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
public class CustomerRoutingDataSource extends AbstractRoutingDataSource {
@Override
protected Object determineCurrentLookupKey() {
return CustomerContextHolder.getCustomerType();
}
}
CustomerContextHolder 是一个和LocalThread绑定的类, 定义如下:
Java代码
public class CustomerContextHolder {
private static final ThreadLocal<CustomerType> contextHolder =
new ThreadLocal<CustomerType>();
public static void setCustomerType(CustomerType customerType) {
Assert.notNull(customerType, "customerType cannot be null");
contextHolder.set(customerType);
}
public static CustomerType getCustomerType() {
return (CustomerType) contextHolder.get();
}
public static void clearCustomerType() {
contextHolder.remove();
}
}
将dao bean和datasource bean结合起来, 至于dao和真正的datasource如何关联这个可以根据需要指定相关的策略和规则来实现:
Xml代码
<bean id="catalog" class="blog.datasource.Catalog">
<property name="dataSource" ref="dataSource"/>
</bean>
<bean id="dataSource" class="blog.datasource.CustomerRoutingDataSource">
<property name="targetDataSources">
<map key-type="blog.datasource.CustomerType">
<entry key="GOLD" value-ref="goldDataSource"/>
<entry key="SILVER" value-ref="silverDataSource"/>
</map>
</property>
<property name="defaultTargetDataSource" ref="bronzeDataSource"/>
</bean>
下面通过一个TestCase来看看如何使用:
Java代码
public class CatalogTests extends AbstractDependencyInjectionSpringContextTests {
private Catalog catalog;
public void setCatalog(Catalog catalog) {
this.catalog = catalog;
}
public void testDataSourceRouting() {
CustomerContextHolder.setCustomerType(CustomerType.GOLD);
List<Item> goldItems = catalog.getItems();
assertEquals(3, goldItems.size());
System.out.println("gold items: " + goldItems);
CustomerContextHolder.setCustomerType(CustomerType.SILVER);
List<Item> silverItems = catalog.getItems();
assertEquals(2, silverItems.size());
System.out.println("silver items: " + silverItems);
CustomerContextHolder.clearCustomerType();
List<Item> bronzeItems = catalog.getItems();
assertEquals(1, bronzeItems.size());
System.out.println("bronze items: " + bronzeItems);
}
protected String[] getConfigLocations() {
return new String[] {"/blog/datasource/beans.xml"};
}
}