Spring默认PropertyPlaceholderConfigurer只能加载properties格风格简介，现在，我们需要能够从类的完整支持允许似hadoop格风格xml配置文件读取配置信息，并更换相关bean占位符，对其进行了扩展，详细扩展例如以下：
public class CustomPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {
private Resource[] locations;
public void loadProperties(Properties props) throws IOException {
if (this.locations != null) {
PropertiesPersister propertiesPersister = new DefaultPropertiesPersister();
for (int i = 0; i < this.locations.length; i++) {
Resource location = this.locations[i];
if (logger.isInfoEnabled()) {
logger.info("Loading properties file from " + location);
}
InputStream is = null;
try {
is = location.getInputStream();
propertiesPersister.load(props, is);
Configuration conf = SquirrelConfiguration.create();
Map<String, String> map = conf.listAllConfEntry(); // 从squirrel-site.xml中读取配置信息
for (Map.Entry<String, String> entry : map.entrySet()) {
props.put(entry.getKey(), entry.getValue());
}
} finally {
if (is != null) is.close();
}
}
}
}
public void setLocations(Resource[] locations) {
super.setLocations(locations);
this.locations = locations;
}
}
可是执行却一直报错，${jdbc_driver_name}没有被替换。通过查询发现。原来是在spring里使用org.mybatis.spring.mapper.MapperScannerConfigurer 进行自己主动扫描的时候。设置了sqlSessionFactory 的话。可能会导致PropertyPlaceholderConfigurer失效，也就是用${jdbc_driver_name}这样之类的表达式，将无法获取到properties文件中的内容。 导致这一原因是由于。MapperScannerConigurer实际是在解析载入bean定义阶段的，这个时候要是设置sqlSessionFactory的话，会导致提前初始化一些类。这个时候，
PropertyPlaceholderConfigurer还没来得及替换定义中的变量。导致把表达式当作字符串复制了。 但假设不设置sqlSessionFactory 属性的话，就必需要保证sessionFactory在spring中名称一定要是sqlSessionFactory 。否则就无法自己主动注入。又或者直接定义MapperFactoryBean 。再或者放弃自己主动代理接口方式。
能够例如以下方式改动：
<bean id="propertyConfigurer" class="com.yowu.common.CustomPropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>classpath:important.properties</value>
</list>
</property>
</bean> <!-- 配置线程池 -->
<bean id="taskExecutor"
class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
<!-- 线程池维护线程的最少数量 -->
<property name="corePoolSize" value="10" />
<!-- 线程池维护线程所同意的空暇时间 -->
<property name="keepAliveSeconds" value="0" />
<!-- 线程池维护线程的最大数量 -->
<property name="maxPoolSize" value="10" />
<!-- 线程池所使用的缓冲队列 -->
<property name="queueCapacity" value="0" />
</bean> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName" value="${squirrel_jdbc_driver}" />
<property name="url" value="${squirrel_jdbc_url}" />
<property name="username" value="${squirrel_jdbc_username}" />
<property name="password" value="${squirrel_jdbc_password}" />
<property name="validationQuery" value="select 1" />
<property name="initialSize" value="5" />
<property name="testWhileIdle" value="true" />
<property name="maxIdle" value="20" />
<property name="minIdle" value="5" />
<property name="maxActive" value="50" />
<property name="removeAbandonedTimeout" value="180" />
<property name="maxWait" value="30000" />
</bean> <bean id="ysqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource"/>
<property name="mapperLocations" >
<list>
<value>classpath*:mybatis/*.xml</value>
</list>
</property>
</bean>
<bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
<constructor-arg index="0" ref="ysqlSessionFactory"></constructor-arg>
<constructor-arg index="1" value="BATCH"></constructor-arg>
</bean> <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.yowu.dao, com.yowu.app.repository.dao"/>
<!--核心就是加入以下一句。 后面那个属性是value。不是ref，切记-->
<property name="sqlSessionFactoryBeanName" value="ysqlSessionFactory" />
</bean>
通过查看MapperScannerConfigurer源代码发现，事实上有这么一段代码：
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
if (this.processPropertyPlaceHolders) {
processPropertyPlaceHolders();
}
Scanner scanner = new Scanner(beanDefinitionRegistry);
scanner.setResourceLoader(this.applicationContext);
scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
/*
* BeanDefinitionRegistries are called early in application startup, before
* BeanFactoryPostProcessors. This means that PropertyResourceConfigurers will not have been
* loaded and any property substitution of this class' properties will fail. To avoid this, find
* any PropertyResourceConfigurers defined in the context and run them on this class' bean
* definition. Then update the values.
*/
private void processPropertyPlaceHolders() {
大概意思是能够设置processPropertyPlaceHolders为true，强制让PropertyResourceConfigure运行下替换工作。大家最好还是试一下，不一个优雅的解决方案亏损。
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