Spring动态数据源路由兑现

Spring动态数据源路由实现

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??

1. ?package?blog.datasource;??
2. ??
3. import?java.sql.ResultSet;??
4. import?java.sql.SQLException;??
5. import?java.util.List;??
6. ??
7. import?org.springframework.jdbc.core.simple.ParameterizedRowMapper;??
8. import?org.springframework.jdbc.core.simple.SimpleJdbcDaoSupport;??
9. ??
10. public?class?Catalog?extends?SimpleJdbcDaoSupport?{??
11. ??????????
12. ???public?List<Item>?getItems()?{??
13. ??????String?query?=?"select?name,?price?from?item";??
14. ??????return?getSimpleJdbcTemplate().query(query,?new?ParameterizedRowMapper<Item>()?{??
15. ????????????public?Item?mapRow(ResultSet?rs,?int?row)?throws?SQLException?{??
16. ???????????????String?name?=?rs.getString(1);??
17. ???????????????double?price?=?rs.getDouble(2);??
18. ???????????????return?new?Item(name,?price);??
19. ????????????}??
20. ??????});??
21. ???}??
22. }??

然后定义一个Item的JavaBean?
Java代码??

1. package?blog.datasource;??
2. ??
3. public?class?Item?{??
4. ??
5. ???private?String?name;??
6. ???private?double?price;??
7. ??????????
8. ???public?Item(String?name,?double?price)?{??
9. ??????this.name?=?name;??
10. ??????this.price?=?price;??
11. ???}??
12. ??
13. ???public?String?getName()?{??
14. ??????return?name;??
15. ???}??
16. ??
17. ???public?double?getPrice()?{??
18. ??????return?price;??
19. ???}??
20. ??
21. ???public?String?toString()?{??
22. ??????return?name?+?"?("?+?price?+?")";??
23. ???}??
24. ??
25. }??

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??

1. public?enum?CustomerType?{??
2. ???BRONZE,???
3. ???SILVER,???
4. ???GOLD??
5. }??

下面是DataSource定义:?
Xml代码??

1. <bean?id="parentDataSource"??
2. ?????????class="org.springframework.jdbc.datasource.DriverManagerDataSource"??
3. ?????????abstract="true">??
4. ???<property?name="driverClassName"?value="org.hsqldb.jdbcDriver"/>??
5. ???<property?name="username"?value="sa"/>??
6. </bean>??
7. ??????????????????
8. <bean?id="goldDataSource"?parent="parentDataSource">??
9. ???<property?name="url"?value="jdbc:hsqldb:hsql://localhost:${db.port.gold}/blog"/>??
10. </bean>??
11. ??
12. <bean?id="silverDataSource"?parent="parentDataSource">??
13. ???<property?name="url"?value="jdbc:hsqldb:hsql://localhost:${db.port.silver}/blog"/>??
14. </bean>??
15. ??
16. <bean?id="bronzeDataSource"?parent="parentDataSource">??
17. ???<property?name="url"?value="jdbc:hsqldb:hsql://localhost:${db.port.bronze}/blog"/>??
18. </bean>??
19. ??
20. <bean?class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">??
21. ???<property?name="location"?value="classpath:/blog/datasource/db.properties"/>??
22. </bean>??

AbstractRoutingDataSource 实现类?
Java代码??

1. package?blog.datasource;??
2. ??
3. import?org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;??
4. ??
5. public?class?CustomerRoutingDataSource?extends?AbstractRoutingDataSource?{??
6. ??
7. ???@Override??
8. ???protected?Object?determineCurrentLookupKey()?{??
9. ??????return?CustomerContextHolder.getCustomerType();??
10. ???}??
11. }??

CustomerContextHolder 是一个和LocalThread绑定的类, 定义如下:?
Java代码??

1. public?class?CustomerContextHolder?{??
2. ??
3. ???private?static?final?ThreadLocal<CustomerType>?contextHolder?=???
4. ????????????new?ThreadLocal<CustomerType>();??
5. ??????????
6. ???public?static?void?setCustomerType(CustomerType?customerType)?{??
7. ??????Assert.notNull(customerType,?"customerType?cannot?be?null");??
8. ??????contextHolder.set(customerType);??
9. ???}??
10. ??
11. ???public?static?CustomerType?getCustomerType()?{??
12. ??????return?(CustomerType)?contextHolder.get();??
13. ???}??
14. ??
15. ???public?static?void?clearCustomerType()?{??
16. ??????contextHolder.remove();??
17. ???}??
18. }??

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??

1. <bean?id="catalog"?class="blog.datasource.Catalog">??
2. ???<property?name="dataSource"?ref="dataSource"/>??
3. </bean>??
4. ??
5. <bean?id="dataSource"?class="blog.datasource.CustomerRoutingDataSource">??
6. ???<property?name="targetDataSources">??
7. ??????<map?key-type="blog.datasource.CustomerType">??
8. ?????????<entry?key="GOLD"?value-ref="goldDataSource"/>??
9. ?????????<entry?key="SILVER"?value-ref="silverDataSource"/>??
10. ??????</map>??
11. ???</property>??
12. ???<property?name="defaultTargetDataSource"?ref="bronzeDataSource"/>??
13. </bean>??

下面通过一个TestCase来看看如何使用:?
Java代码??

1. public?class?CatalogTests?extends?AbstractDependencyInjectionSpringContextTests?{??
2. ??
3. ???private?Catalog?catalog;??
4. ??
5. ???public?void?setCatalog(Catalog?catalog)?{??
6. ??????this.catalog?=?catalog;??
7. ???}??
8. ??
9. ???public?void?testDataSourceRouting()?{??
10. ??????CustomerContextHolder.setCustomerType(CustomerType.GOLD);??
11. ??????List<Item>?goldItems?=?catalog.getItems();??
12. ??????assertEquals(3,?goldItems.size());??
13. ??????System.out.println("gold?items:?"?+?goldItems);??
14. ??
15. ??????CustomerContextHolder.setCustomerType(CustomerType.SILVER);??
16. ??????List<Item>?silverItems?=?catalog.getItems();??
17. ??????assertEquals(2,?silverItems.size());??
18. ??????System.out.println("silver?items:?"?+?silverItems);??
19. ??????????
20. ??????CustomerContextHolder.clearCustomerType();??
21. ??????List<Item>?bronzeItems?=?catalog.getItems();??
22. ??????assertEquals(1,?bronzeItems.size());??
23. ??????System.out.println("bronze?items:?"?+?bronzeItems);????????????????
24. ???}??
25. ??
26. ???protected?String[]?getConfigLocations()?{??
27. ??????return?new?String[]?{"/blog/datasource/beans.xml"};??
28. ???}??????
29. } ?

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