spring配置文件<import>标签中使用${}占位符获得配置文件的属性值

一般情况下我们在spring的配置文件中使用<import>标签是这样的，<import resource="spring-other.xml">，但是最近项目中使用到其他工程的依赖jar包，在自己的spring配置文件中需要这样写

<context:property-placeholder location="classpath:eoa/eoa_config.properties" />

<import resource="classpath:spring-fs-db-${env}.xml" />

其中env的值是从eoa_config.properties里面获取。

如果是以上这种写法，在启动时spring报错，无法解析env，原因很简单，在import动作时在属性文件加载之前。

没办法只能翻spring源码，ContextLoader

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 protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {  
        if (ObjectUtils.identityToString(wac).equals(wac.getId())) {  
// The application context id is still set to its original default value  
// -> assign a more useful id based on available information  
            String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);  
            if (idParam != null) {  
                wac.setId(idParam);  
            }  
            else {  
// Generate default id...  
                wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +  
                        ObjectUtils.getDisplayString(sc.getContextPath()));  
            }  
        }  
        wac.setServletContext(sc);  
        String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);  
        if (configLocationParam != null) {  
            wac.setConfigLocation(configLocationParam);  
        }  
  
// The wac environment‘s #initPropertySources will be called in any case when the context  
// is refreshed; do it eagerly here to ensure servlet property sources are in place for  
// use in any post-processing or initialization that occurs below prior to #refresh  
        ConfigurableEnvironment env = wac.getEnvironment();  
        if (env instanceof ConfigurableWebEnvironment) {  
            ((ConfigurableWebEnvironment) env).initPropertySources(sc, null);  
        }  
        customizeContext(sc, wac);  
        wac.refresh();  
    }  
    //initPropertySources这个方法可以自己定义属性文件的加载时机。  
    @Override  
    public void initPropertySources(ServletContext servletContext, ServletConfig servletConfig) {  
        WebApplicationContextUtils.initServletPropertySources(getPropertySources(), servletContext, servletConfig);  
    }  

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
wac.setServletContext(sc);
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}

// The wac environment‘s #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
customizeContext(sc, wac);
wac.refresh();
}
//initPropertySources这个方法可以自己定义属性文件的加载时机。
@Override
public void initPropertySources(ServletContext servletContext, ServletConfig servletConfig) {
WebApplicationContextUtils.initServletPropertySources(getPropertySources(), servletContext, servletConfig);
}

也就是说我们需要在getPropertySources()方法调用之前，就已经做好属性文件的加载顺序。

spring提供了ApplicationContextInitializer这个接口，实现该接口

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public class CustomerApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext>{  
    private static Logger logger = LoggerFactory.getLogger(CustomerApplicationContextInitializer.class);  
    @Override  
    public void initialize(ConfigurableApplicationContext applicationContext) {  
        ResourcePropertySource propertySource = null;  
        try {  
            propertySource = new ResourcePropertySource("classpath:eoa/eoa_config.properties");  
        } catch (IOException e) {  
            logger.error("eoa_config.properties is not exists");  
        }  
        applicationContext.getEnvironment().getPropertySources().addFirst(propertySource);  
    }  
}  

public class CustomerApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext>{
private static Logger logger = LoggerFactory.getLogger(CustomerApplicationContextInitializer.class);
@Override
public void initialize(ConfigurableApplicationContext applicationContext) {
ResourcePropertySource propertySource = null;
try {
propertySource = new ResourcePropertySource("classpath:eoa/eoa_config.properties");
} catch (IOException e) {
logger.error("eoa_config.properties is not exists");
}
applicationContext.getEnvironment().getPropertySources().addFirst(propertySource);
}
}

此外，还需要在web.xml中配置这个类

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<context-param>  
    <param-name>contextInitializerClasses</param-name>  
    <param-value>com.lfex.eoa.base.CustomerApplicationContextInitializer</param-value>  
</context-param>  

<context-param>
<param-name>contextInitializerClasses</param-name>
<param-value>com.lfex.eoa.base.CustomerApplicationContextInitializer</param-value>
</context-param>

因为在customizeContext(sc, wac);会调用所有的contextInitializerClasses中的initialize方法。

至此，问题解决了，总结一下分为以下几步

提供实现ApplicationContextInitializer接口的实现类

在web.xml中配置，见上

在spring的主配置文件中使用<import resource="spring-${env}.xml">