spring - 更改数据源连接 url 运行时

Question

我正在开发一个使用 spring + hibernate + mysql 和 c3p0 进行连接池的项目。

目前，连接池的属性是通过在 src 之外定义的属性加载的。 (例如:${db_uname})

当我们创建 spring bean 时，一切都很好。

可能会发生我们连接的数据库由于某种原因无法访问，并且我们想切换主机。

需要实现回调，在那里它应该连接到新主机并重新初始化池

关于如何优雅地覆盖现有数据源/连接池的任何指示都会有很大帮助。

这是我的 spring 配置文件的样子

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="
    http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/tx 
    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
    http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-3.0.xsd
    http://www.springframework.org/schema/util
    http://www.springframework.org/schema/util/spring-util-3.0.xsd">

<!-- Component scans -->
<import resource="component-scans-1.xml" />
<import resource="component-scans-2.xml" />


<util:properties id="serviceManagerProperties" 
    location="classpath:servicemanagers.properties" />

<!-- Properties file -->
<context:property-placeholder location="classpath:database.config.properties,classpath:framework.properties" />

<!-- context:annotation-config / -->
<tx:annotation-driven transaction-manager="transactionManager" />

<bean id="dataSource"
    class="org.springframework.jdbc.datasource.DriverManagerDataSource">
</bean>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>

<context:mbean-server id="mbeanServer" />
<context:mbean-export server="mbeanServer" default-domain="a.b.c" />

<bean id="cacheManager" factory-method="getInstance"
    class="net.sf.ehcache.CacheManager" />

<bean class="net.sf.ehcache.management.ManagementService" init-method="init">
    <constructor-arg ref="cacheManager" />
    <constructor-arg ref="mbeanServer" />
    <constructor-arg value="false" />
    <constructor-arg value="false" />
    <constructor-arg value="false" />
    <constructor-arg value="true" />
</bean>

<bean id="entityManagerFactory"
    class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="jpaVendorAdapter" ref="jpaAdapter" />
    <property name="persistenceXmlLocation" value="classpath*:META-INF/framework-persistence.xml" />
    <property name="persistenceUnitName" value="PU-NAME" />
    <property name="jpaProperties">
        <props>
            <prop key="hibernate.format_sql">true</prop>
            <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
            <prop key="hibernate.cache.use_query_cache">${hibernate.cache.use_query_cache}</prop>
            <prop key="hibernate.cache.use_second_level_cache">${hibernate.cache.use_second_level_cache}</prop>
            <prop key="hibernate.cache.region.factory_class">
                org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory
            </prop>

            <prop key="hibernate.ejb.cfgfile">hibernate.cfg.xml</prop>
            <prop key="hibernate.generate_statistics">true</prop>


            <!-- CONNECTION SETTINGS -->
            <prop key="hibernate.connection.driver_class">
                com.mysql.jdbc.Driver
            </prop>
            <prop key="hibernate.connection.url">
                jdbc:mysql://${dbhost}/${dbschema}?zeroDateTimeBehavior=convertToNull&amp;useUnicode=true&amp;characterEncoding=UTF-8
            </prop>
            <prop key="hibernate.connection.username">${dbuser}</prop>
            <prop key="hibernate.connection.password">${dbpass}</prop>

            <!-- CONNECTION POOLING -->
            <prop key="hibernate.connection.provider_class">
                org.hibernate.connection.C3P0ConnectionProvider
            </prop>
            <prop key="hibernate.c3p0.maxPoolSize">${hibernate.c3p0.maxSize}</prop>
            <prop key="hibernate.c3p0.minPoolSize">${hibernate.c3p0.minSize}</prop>
            <prop key="hibernate.c3p0.acquireIncrement">${hibernate.c3p0.acquireIncrement}</prop>
            <prop key="hibernate.c3p0.idleConnectionTestPeriod">${hibernate.c3p0.idleTestPeriod}</prop>
            <prop key="hibernate.c3p0.maxStatements">${hibernate.c3p0.maxStatements}</prop>
            <prop key="hibernate.c3p0.timeout">${hibernate.c3p0.timeout}</prop>

        </props>
    </property>
</bean>

<bean id="jpaAdapter"
    class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />

假设数据库模式是正确的，假设我在事件中获得了数据库凭据和主机信息，我需要“重新设置”连接池。

Answer 1

AbstractRoutingDataSource是个不错的选择。

像这样使用的 XML 或注释:

<bean id="ds1" class="..c3p0.DataSource">
    ...
</bean>

<bean id="ds2" class="..c3p0.DataSource">
    ...
</bean>

<bean id="dataSource" class="..xxx.RoutingDataSource">
   <property name="targetDataSources">
      <map key-type="java.lang.String">
         <entry key="ds1" value-ref="ds1"/>
         <entry key="ds2" value-ref="ds2"/>             
      </map>
   </property>
   <property name="defaultTargetDataSource" ref="ds1"/>
</bean>



<bean id="sessionFactory"
    class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
    <property name="dataSource" ref="dataSource" /> 
...
</bean>

然后构建一个类来确定当前的数据源。

public class RoutingDataSource extends AbstractRoutingDataSource {
    private static final ThreadLocal<String> holder = new ThreadLocal<String>();

    protected Object determineCurrentLookupKey()
    {
        return holder.get();
    }

    public static void clear(){
        holder.remove();
    }

    public static void setDataSourceKey(String key){
        holder.set(key);
    }

}

顺便说一句，'try-finally' 语句很无聊!

try{
    RoutingDataSource.setDataSourceKey("ds1");
    myDao.doXXX();
}finally{
    RoutingDataSource.clear();
}