繼續(xù)上篇文章如何使用mybatis3+spring3并且配置多數(shù)據(jù)源呢?

先上代碼在講解吧?
替換上一篇中spring中datasource的配置?
Java代碼??

<!--?數(shù)據(jù)源配置?-->??

<bean?id="ds1"?class="org.apache.commons.dbcp.BasicDataSource"??

????destroy-method="close">??

????<property?name="driverClassName"?value="com.mysql.jdbc.Driver"?/>??

????<property?name="url"??

????????value="jdbc:mysql://localhost:3306/payoffdatabase?useUnicode=true&amp;characterEncoding=UTF-8"?/>??

????<property?name="username"?value="root"?/>??

????<property?name="password"?value="root"?/>??

????<property?name="defaultAutoCommit"?value="true"></property>??

</bean>??

??

<bean?id="ds2"?class="org.apache.commons.dbcp.BasicDataSource"??

????destroy-method="close">??

????<property?name="driverClassName"?value="com.mysql.jdbc.Driver"?/>??

????<property?name="url"??

????????value="jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=UTF-8"?/>??

????<property?name="username"?value="root"?/>??

????<property?name="password"?value="root"?/>??

????<property?name="defaultAutoCommit"?value="true"></property>??

</bean>??

??

??

?<bean?id="dataSource"?class="a.b.router.DynamicDataSource">??

????<property?name="targetDataSources">??

????????<map?key-type="java.lang.String">??

????????????<entry?value-ref="ds1"?key="ds1"></entry>??

????????????<entry?value-ref="ds2"?key="ds2"></entry>??

????????</map>??

????</property>??

????<property?name="defaultTargetDataSource"?ref="ds1"></property>??

</bean>??

新的類DynamicDataSource?
Java代碼??

package?a.b.router;??

??

import?org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;??

??

public?class?DynamicDataSource?extends?AbstractRoutingDataSource?{??

????@Override??

????protected?Object?determineCurrentLookupKey()?{??

????????return?DataSourceContextHolder.getDbType();??

????}??

}??

新的類DataSourceContextHolder?
Java代碼??

package?a.b.router;??

??

public?class?DataSourceContextHolder?{??

??

????private?static?final?ThreadLocal<String>?contextHolder?=?new?ThreadLocal<String>();??

??

????public?static?void?setDbType(String?dbType)?{??

????????contextHolder.set(dbType);??

????}??

??

????public?static?String?getDbType()?{??

????????return?((String)?contextHolder.get());??

????}??

??

????public?static?void?clearDbType()?{??

????????contextHolder.remove();??

????}??

}??

原來的單元測試新添加一行信息，修改為?
Java代碼??

@Test??

public?void?addTest()?throws?Exception?{??

????UserLogin?userLogin?=?new?UserLogin();??

????userLogin.setPassword("102");??

????userLogin.setUsername("102");??

????DataSourceContextHolder.setDbType("ds2");??

??

????service.add(userLogin);??

}??

最主要的變化是DynamicDataSource 類，這個類繼承了AbstractRoutingDataSource，我們再繼續(xù)考察，發(fā)現(xiàn)這個類實現(xiàn)了datasource這個接口。?

再仔細研究，發(fā)現(xiàn)我配置了多個數(shù)據(jù)源給DynamicDataSource，默認的數(shù)據(jù)源是ds1。?
我們研究下AbstractRoutingDataSource類的代碼，主要是兩個實現(xiàn)datasource的方法?
Java代碼??

public?Connection?getConnection()?throws?SQLException?{??

????return?determineTargetDataSource().getConnection();??

}??

??

public?Connection?getConnection(String?username,?String?password)?throws?SQLException?{??

????return?determineTargetDataSource().getConnection(username,?password);??

}??

根據(jù)這段代碼發(fā)現(xiàn)主要玄機都在determineTargetDataSource()方法上。?

Java代碼??

protected?DataSource?determineTargetDataSource()?{??

????????Assert.notNull(this.resolvedDataSources,?"DataSource?router?not?initialized");??

????????Object?lookupKey?=?determineCurrentLookupKey();??

????????DataSource?dataSource?=?this.resolvedDataSources.get(lookupKey);??

????????if?(dataSource?==?null?&&?(this.lenientFallback?||?lookupKey?==?null))?{??

????????????dataSource?=?this.resolvedDefaultDataSource;??

????????}??

????????if?(dataSource?==?null)?{??

????????????throw?new?IllegalStateException("Cannot?determine?target?DataSource?for?lookup?key?["?+?lookupKey?+?"]");??

????????}??

????????return?dataSource;??

????}??

根據(jù)這段代碼發(fā)現(xiàn)，首先在使用數(shù)據(jù)源之前，首先判斷使用數(shù)據(jù)源的key，也就是我們配置給?
Java代碼??

private?Map<Object,?Object>?targetDataSources;??

這個map中的key值，找到key值之后再找到對應的datasource然后并使用這個數(shù)據(jù)源。?


從上面我們發(fā)現(xiàn)，實際上DynamicDataSource只是在內部封裝了數(shù)據(jù)源，然后調用它，只不過在內部他加了一些控制而已。（此處不知道是否可以理解為代理模式）?

再深一步想想，此處使用的orm層是mybatis，如果換成hibernate呢，或者jdbctemplate呢。?
實際上這個方法都適用。

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