spring配置文件標籤中使用${}佔位符得到配置文件的屬性值

通常狀況下咱們在Spring的配置文件中使用<import>標籤是這樣的，<import resource="spring-other.xml">，可是最近項目中使用到其餘工程的依賴jar包，在本身的spring配置文件中須要這樣寫

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

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

其中env的值是從eoa_config.properties裏面獲取。

若是是以上這種寫法，在啓動時spring報錯，沒法解析env，緣由很簡單，在import動做時在屬性文件加載以前。

沒辦法只能翻spring源碼，ContextLoader

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這個方法能夠本身定義屬性文件的加載時機。

@Override

public void initPropertySources(ServletContext servletContext, ServletConfig servletConfig) {

WebApplicationContextUtils.initServletPropertySources(getPropertySources(), servletContext, servletConfig);

}

也就是說咱們須要在getPropertySources()方法調用以前，就已經作好屬性文件的加載順序。

spring提供了ApplicationContextInitializer這個接口，實現該接口

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，還須要在web.xml中配置這個類

<context-param>

<param-name>contextInitializerClasses</param-name>

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

</context-param>

由於在customizeContext(sc, wac);會調用全部的contextInitializerClasses中的initialize方法。

至此，問題解決了，總結一下分爲如下幾步

1. 提供實現ApplicationContextInitializer接口的實現類

2. 在web.xml中配置，見上

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