springmvc加載xml文件讀取本地properties配置文件

org.springframework.beans.factory.config.PropertyPlaceholderConfigurer。由這個類別，您能夠將一些組態設定，移出至.properties檔案中，如此的安排可讓XML定義檔負責系統相關設定，而.properties檔可 以做爲客戶根據需求，自定義一些相關的參數。實際上，PropertyPlaceholderConfigurer起的做用就是將佔位符指向的數據庫配置 信息放在bean中定義的工具。

（1）使用如下方式讀取單個本地文件到xml中：

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">      
     <property name="location">  
               <value>file:/opt/config/config1.properties</value>        
    </property> 
 </bean>        

（2）使用如下方式讀取多個本地文件到xml中：

  <!-- 使用spring提供的PropertyPlaceholderConfigurer讀取properties -->
  <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
       <!-- 屬性名是 locations，使用子標籤<list></list>能夠指定多個數據庫的配置文件，這裏指定了一個-->
　　　　 <property name="locations">
            <list>
                <value>file:/opt/config/config1.properties</value>
　　　　　　　　　 <value>file:/opt/config/config2.properties</value>
            </list>
        </property>
        <property name="ignoreUnresolvablePlaceholders" value="true"/>
    </bean>
    <dubbo:application name="lease-risk-consumer"/>
    <!-- 讀取本地配置文件 -->
    <dubbo:registry address="${dubbo.registry.address}"/>

注意讀取單個配置文件，使用location，多個使用locations

上面是介紹org.springframework.beans.factory.config.PropertyPlaceholderConfigurer工具類的具體使用，下面淺析Spring框架下PropertyPlaceholderConfigurer類

package org.springframework.beans.factory.config;

import java.util.Properties;
import java.util.Set;

import org.springframework.beans.BeansException;
import org.springframework.core.Constants;
import org.springframework.util.PropertyPlaceholderHelper;
import org.springframework.util.PropertyPlaceholderHelper.PlaceholderResolver;
import org.springframework.util.StringValueResolver;

public class PropertyPlaceholderConfigurer extends PlaceholderConfigurerSupport {

    /** 是否覆蓋proprties文件 */
    public static final int SYSTEM_PROPERTIES_MODE_NEVER = 0;

    /**
     * 默認值，不存在時覆蓋
     */
    public static final int SYSTEM_PROPERTIES_MODE_FALLBACK = 1;

    /**覆蓋proprties文件*/
    public static final int SYSTEM_PROPERTIES_MODE_OVERRIDE = 2;


    private static final Constants constants = new Constants(PropertyPlaceholderConfigurer.class);

    private int systemPropertiesMode = SYSTEM_PROPERTIES_MODE_FALLBACK;

    private boolean searchSystemEnvironment = true;


    public void setSystemPropertiesModeName(String constantName) throws IllegalArgumentException {
        this.systemPropertiesMode = constants.asNumber(constantName).intValue();
    }
   
    public void setSystemPropertiesMode(int systemPropertiesMode) {
        this.systemPropertiesMode = systemPropertiesMode;
    }

    public void setSearchSystemEnvironment(boolean searchSystemEnvironment) {
        this.searchSystemEnvironment = searchSystemEnvironment;
    }
   
    protected String resolvePlaceholder(String placeholder, Properties props, int systemPropertiesMode) {
        String propVal = null;
        if (systemPropertiesMode == SYSTEM_PROPERTIES_MODE_OVERRIDE) {
            propVal = resolveSystemProperty(placeholder);
        }
        if (propVal == null) {
            propVal = resolvePlaceholder(placeholder, props);
        }
        if (propVal == null && systemPropertiesMode == SYSTEM_PROPERTIES_MODE_FALLBACK) {
            propVal = resolveSystemProperty(placeholder);
        }
        return propVal;
    }
  
    protected String resolvePlaceholder(String placeholder, Properties props) {
        return props.getProperty(placeholder);
    }
  
    protected String resolveSystemProperty(String key) {
        try {
            String value = System.getProperty(key);
            if (value == null && this.searchSystemEnvironment) {
                value = System.getenv(key);
            }
            return value;
        }
        catch (Throwable ex) {
            if (logger.isDebugEnabled()) {
                logger.debug("Could not access system property '" + key + "': " + ex);
            }
            return null;
        }
    }


    @Override
    protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
            throws BeansException {

        StringValueResolver valueResolver = new PlaceholderResolvingStringValueResolver(props);

        this.doProcessProperties(beanFactoryToProcess, valueResolver);
    }
   
    @Deprecated
    protected String parseStringValue(String strVal, Properties props, Set<?> visitedPlaceholders) {
        PropertyPlaceholderHelper helper = new PropertyPlaceholderHelper(
                placeholderPrefix, placeholderSuffix, valueSeparator, ignoreUnresolvablePlaceholders);
        PlaceholderResolver resolver = new PropertyPlaceholderConfigurerResolver(props);
        return helper.replacePlaceholders(strVal, resolver);
    }


    private class PlaceholderResolvingStringValueResolver implements StringValueResolver {

        private final PropertyPlaceholderHelper helper;

        private final PlaceholderResolver resolver;

        public PlaceholderResolvingStringValueResolver(Properties props) {
            this.helper = new PropertyPlaceholderHelper(
                    placeholderPrefix, placeholderSuffix, valueSeparator, ignoreUnresolvablePlaceholders);
            this.resolver = new PropertyPlaceholderConfigurerResolver(props);
        }

        public String resolveStringValue(String strVal) throws BeansException {
            String value = this.helper.replacePlaceholders(strVal, this.resolver);
            return (value.equals(nullValue) ? null : value);
        }
    }


    private class PropertyPlaceholderConfigurerResolver implements PlaceholderResolver {

        private final Properties props;

        private PropertyPlaceholderConfigurerResolver(Properties props) {
            this.props = props;
        }

        public String resolvePlaceholder(String placeholderName) {
            return PropertyPlaceholderConfigurer.this.resolvePlaceholder(placeholderName, props, systemPropertiesMode);
        }
    }

}

 

首先看下PropertyPlaceholderConfigurer類的結構

一、注入會初始化property的location屬性

 

public void setLocation(Resource location) {
    this.locations = new Resource[] {location};
}

public void setLocations(Resource[] locations) {
    this.locations = locations;
}

 

二、SystemPropertiesModeName：SystemPropertiesModeName屬性用來指定系統變量（System.getProperty）是否覆蓋proprties文件。默認是在配置文件裏找不到時使用。三個選項分別是：

 

　　SYSTEM_PROPERTIES_MODE_NEVER（不覆蓋）

　　SYSTEM_PROPERTIES_MODE_FALLBACK（默認值，不存在時覆蓋）

　　SYSTEM_PROPERTIES_MODE_OVERRIDE（覆蓋）

　　從源碼中能夠看出searchSystemEnvironment屬性的默認值爲true，即容許環境變量覆蓋properties中的值。