properties文件读取-Spring方式

一、properties文件读取思路

在web环境下，Spring的ApplicationContext是容器管理的（不仅管理been，还有properties属性文件），通过ContextLoaderListener载入。要获取ApplicationContext需要先得到ServletContext，而得到ServletContext又要先获取session。而且每一个要使用ApplicationContext的地方都要这么做。

但是，通过扩展ContextLoaderListener，我们可以很方便的获取到ApplicationContext。

原理十分简单，ContextLoaderListener类里面有一个叫做contextlnitialized的方法，这个方法用于初始化context。

二、操作步骤

我们自己写一个SpringPropertyResourceReader工具类，里面有一个静态变量applicationContext，用来存放web环境下的ApplicationContext的引用，getProperty(key)的方法就可以读取Spring中加载属性文件的内容了。

1、先写SpringPropertyResourceReader类：

public class SpringPropertyResourceReader {
    private static ApplicationContext applicationContext;

    //private static ApplicationContext applicationContext=new ClassPathXmlApplicationContext("applicationContext.xml");
    static Properties properties = new Properties();

    public static ApplicationContext getContext() {
        return applicationContext;
    }

    public static void setContext(ApplicationContext aContext) {
        applicationContext = aContext;
    }

    private static void init() {
        AbstractApplicationContext abstractContext = (AbstractApplicationContext) applicationContext;

        try {
            // get the names of BeanFactoryPostProcessor
            String[] postProcessorNames = abstractContext.getBeanNamesForType(BeanFactoryPostProcessor.class,
                    true, true);

            for (String ppName : postProcessorNames) {
                // get the specified BeanFactoryPostProcessor
                BeanFactoryPostProcessor beanProcessor = (BeanFactoryPostProcessor) abstractContext.getBean(ppName,
                        BeanFactoryPostProcessor.class);

                // check whether the beanFactoryPostProcessor is 
                // instance of the PropertyResourceConfigurer
                // if it is yes then do the process otherwise continue
                if (beanProcessor instanceof PropertyResourceConfigurer) {
                    PropertyResourceConfigurer propertyResourceConfigurer = (PropertyResourceConfigurer) beanProcessor;

                    // get the method mergeProperties 
                    // in class PropertiesLoaderSupport
                    Method mergeProperties = PropertiesLoaderSupport.class.getDeclaredMethod(
                            "mergeProperties");
                    // get the props
                    mergeProperties.setAccessible(true);

                    Properties props = (Properties) mergeProperties.invoke(propertyResourceConfigurer);

                    // get the method convertProperties 
                    // in class PropertyResourceConfigurer
                    Method convertProperties = PropertyResourceConfigurer.class.getDeclaredMethod("convertProperties",
                            Properties.class);
                    // convert properties
                    convertProperties.setAccessible(true);
                    convertProperties.invoke(propertyResourceConfigurer, props);
                    properties.putAll(props);
                }
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static String getProperty(String propertyName) {
        if ((applicationContext != null) && properties.isEmpty()) {
            init();
        }

        if (applicationContext == null) {
            return null;
        }

        return properties.getProperty(propertyName);
    }
}

2、然后再写ContextLoaderListener的扩展类MyContextLoaderListener

public class MyContextLoaderListener extends ContextLoaderListener {
    @Override
    public void contextInitialized(ServletContextEvent event) {
        super.contextInitialized(event);

        ServletContext context = event.getServletContext();

        // 获取web环境下的ApplicationContext
        ApplicationContext ctx = WebApplicationContextUtils.getRequiredWebApplicationContext(context);
        //  将ApplicationContext，set到SpringPropertyResourceReader的静态变量context
        SpringPropertyResourceReader.setContext(ctx);
    }
}

3、在web.xml里面配置spring监听器，用我们刚刚扩展好的MyContextLoaderListener替换以前的ContextLoaderListener：

yourpackage.MyContextLoaderListener

4、在applicationContext.xml中配置加载属性文件的代码

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <list>
            <value>classpath:scan/job.properties</value> 
        </list>
    </property>
</bean>