Cut Down on System Properties with the Spring Framework

原文参见这里:
处理关于不同环境下不同配置的
http://www.jroller.com/comments/kbaum/Weblog/cut_down_on_system_properties

因为PropertyOverrideConfigurer的语法只能beanName.beanProperties,不适合下面比如说属性是Properties的，

<bean id="sessionFactory" class="org.springframework.orm.hibernate.LocalSessionFactoryBean">
        <!--<property name="configLocation">
            <value>classpath:hibernate.cfg.xml</value>
        </property>-->
        <property name="dataSource">
            <ref local="dataSource"/>
        </property>
        <property name="mappingResources">
            <list>
                <value>com/jason/organization/domain/Organization.hbm.xml</value>
                <value>com/jason/organization/domain/User.hbm.xml</value>
                <value>com/jason/entapps/install/Constant.hbm.xml</value>

                <value>com/jason/hire/domain/Position.hbm.xml</value>

            </list>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">${hibernate.dialect}</prop>
                <prop key="hibernate.cache.provider_class">net.sf.ehcache.hibernate.Provider</prop>
                <!--<prop key="hibernate.cache.use_query_cache">true</prop>-->
                <prop key="hibernate.show_sql">true</prop>
                <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}</prop>

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

于是干脆，扩展PropertyPlaceholderConfigurer
public class EnvPropertyResourceConfigurer extends PropertyPlaceholderConfigurer
        implements InitializingBean {

    private String env;


    private String defaultEnv = "prod";

    private String basePropertyFile;

    private String envSystemProperty = "env";

    /**
     * @return Returns the basePropertyFile.
     */
    public String getBasePropertyFile() {
        return basePropertyFile;
    }

    /**
     * @param basePropertyFile The basePropertyFile to set.
     */
    public void setBasePropertyFile(String basePropertyFile) {
        this.basePropertyFile = basePropertyFile;
    }

    /**
     * @return Returns the envSystemProperty.
     */
    public String getEnvSystemProperty() {
        return envSystemProperty;
    }

    /**
     * @param envSystemProperty The envSystemProperty to set.
     */
    public void setEnvSystemProperty(String envSystemProperty) {
        this.envSystemProperty = envSystemProperty;
    }

    /*
     * (non-Javadoc)
     *
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet()
     */
    public void afterPropertiesSet() throws Exception {

        if (basePropertyFile == null) {
            return;
        }
        String env = getEnv();

        String fileName = basePropertyFile;

        if (TextUtils.stringSet(env)) {
            fileName += "." + env;
        }
        setLocation(new DefaultResourceLoader().getResource(fileName));

    }

    /**
     * @return Returns the defaultEnv.
     */
    public String getDefaultEnv() {
        return defaultEnv;
    }

    /**
     * @param defaultEnv The defaultEnv to set.
     */
    public void setDefaultEnv(String defaultEnv) {
        this.defaultEnv = defaultEnv;
    }


    /**
     * @return Returns the env.
     */
    public String getEnv() {
        return env;
    }

    /**
     * @param env The env to set.
     */
    public void setEnv(String env) {
        this.env = env;
    }
}

原文的SystemPropertyFactoryBean,在无值时返回null spring会报错,
于是我改了一下
public class SystemPropertyFactoryBean implements FactoryBean {

private String propertyName;

/**
* @return Returns the propertyName.
*/
public String getPropertyName() {
return propertyName;
}
/**
* @param propertyName The propertyName to set.
*/
public void setPropertyName(String propertyName) {
this.propertyName = propertyName;
}
/* (non-Javadoc)
* @see org.springframework.beans.factory.FactoryBean#getObject()
*/
public Object getObject() throws Exception {
String value = System.getProperty(getPropertyName());
        if(value == null) {
            value = "";
        }
        return value;
}

/* (non-Javadoc)
* @see org.springframework.beans.factory.FactoryBean#getObjectType()
*/
public Class getObjectType() {
return String.class;
}

/* (non-Javadoc)
* @see org.springframework.beans.factory.FactoryBean#isSingleton()
*/
public boolean isSingleton() {
return true;
}

}

spring中的配置
<bean id="propertyConfigurer" class="com.jason.core.EnvPropertyResourceConfigurer">
        <property name="basePropertyFile">
            <value>classpath:jdbc.properties</value>
        </property>
        <property name="env">
            <ref local="env"/>
        </property>
    </bean>
    <bean id="env" class="com.jason.core.SystemPropertyFactoryBean">
        <property name="propertyName">
            <value>env</value>
        </property>
    </bean>

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <property name="driverClassName">
            <value>${jdbc.driverClassName}</value>
        </property>
        <property name="url">
            <value>${jdbc.url}</value>
        </property>
        <property name="username">
            <value>${jdbc.username}</value>
        </property>
        <property name="password">
            <value>${jdbc.password}</value>
        </property>
    </bean>