Spring PropertyPlaceholderConfigurer解析Java Properties属性文件值

Spring中PropertyPlaceholderConfigurer这个类，它是用来解析Java Properties属性文件值，并提供在spring配置期间替换使用属性值。接下来让我们逐渐的深入其配置。

基本的使用方法是:

<bean id="propertyConfigurerForAnalysis"
      class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> 
    <property name="location"> 
        <value>classpath:/spring/include/dbQuery.properties</value> 
    </property> 
</bean>



其中classpath是引用src目录下的文件写法。

也可以这么写:

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>/WEB-INF/config/jdbc/jdbc.properties</value>
</list>
</property>
</bean>


2.多个Properties文件的配置



当存在多个Properties文件时，配置就需使用locations了：(2)

<bean id="propertyConfigurer"
      class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> 
    <property name="locations"> 
       <list> 
          <value>classpath:/spring/include/jdbc-parms.properties</value> 
          <value>classpath:/spring/include/base-config.properties</value> 
        </list> 
    </property> 
</bean>  


3.多个PropertyPlaceholderConfigurer来分散配置



接下来我们要使用多个PropertyPlaceholderConfigurer来分散配置，达到整合多工程下的多个分散的Properties文件，其配置如下：(3)

<bean id="propertyConfigurerForProject1"
      class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> 
    <property name="order" value="1" /> 
    <property name="ignoreUnresolvablePlaceholders" value="true" />
    <property name="locations"> 
      <list>  
        <value>classpath:/spring/include/dbQuery.properties</value>    
      </list>
    </property>  
</bean> 

<bean id="propertyConfigurerForProject2"
      class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">  
    <property name="order" value="2" />  
    <property name="ignoreUnresolvablePlaceholders" value="true" />  
    <property name="locations">  
      <list>  
        <value>classpath:/spring/include/jdbc-parms.properties</value>  
        <value>classpath:/spring/include/base-config.properties</value>  
      </list>  
    </property>  
</bean>



其中order属性代表其加载的顺序,如果没有设置就按照加载xml文件时的顺序，而ignoreUnresolvablePlaceholders为是否忽略不可解析的Placeholder，如果配置了多个PropertyPlaceholderConfigurer，则该属性必须设置且为true,否则propertyConfigurerForProject2的properties文件不会被加载.

至此你已经了解到了如何使用PropertyPlaceholderConfigurer，如何使用多个Properties文件，以及如何配置多个PropertyPlaceholderConfigurer来分解工程中分散的Properties文件。

注意事项:
(1)如果上面的dbQuery.properties与jdbc-parms.properties文件中有相同的参数配置名称,dbQuery.properties中配置的参数值不会被后面的覆盖;
(2)如果jdbc-parms.properties,base-config.properties彼此有相同参数名配置,jdbc-parms.properties中的配置的值会被覆盖;


4.自定义扩展PropertyPlaceholderConfigurer实现



例如:配置文件的路径,需要动态确定的,就需要自己扩展PropertyPlaceholderConfigurer的实现,自己获取文件路径,load properties文件,然后将load后的properties加入PropertyPlaceholderConfigurer

package com.common.spring.ext;

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

import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;

import com.common.exception.ApplicationException;
import com.common.util.GlobalProperties;
import com.common.util.PropertiesUtil;


public class GollfPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {

    public void setGollfPropFiles(Set<String> gollfPropFiles) {
        String propPath = GlobalProperties.getProperty(GlobalProperties.PROPERTIES_FOLDER_PATH); //通过其他配置获取路径
        String fileSeparator = System.getProperty("file.separator");

        Properties properties = new Properties();
        for (String gollfPropFile : gollfPropFiles) {

            String nodeName = System.getProperty("weblogic.Name");
            gollfPropFile = gollfPropFile.replaceAll("\\[NODE_NAME\\]", nodeName); //NODE_NAME 是根据不同weblogic server确定

            String file = propPath + fileSeparator + gollfPropFile;

            try {
                logger.info("Loading properites file from " + file);
                Properties prop = PropertiesUtil.loadProperties(file); //返回properties文件
                logger.debug("Properties -> " + prop);
                if(prop != null) {
                    properties.putAll(prop);
                }
            } catch (Exception e) {
                logger.fatal(new ApplicationException("Properties file " + gollfPropFile +
" cannot be found. All related functionalities may be unavailable", e, true));
            }
        }

        this.setProperties(properties); //关键方法,调用的PropertyPlaceholderConfigurer中的方法,
   //通过这个方法将自定义加载的properties文件加入spring中
    }

}





xml配置

<bean id="auditJmsProperties"
       class="com.common.spring.ext.GollfPropertyPlaceholderConfigurer">
        <property name="gollfPropFiles">
            <set>
                <value>[NODE_NAME]_jms.properties</value>
            </set>
        </property>
    </bean>



PropertyPlaceholderConfigurer中加载properties文件时,实际调用的:org.springframework.core.io.support.PropertiesLoaderSupport中的mergeProperties

Spring源码



protected Properties mergeProperties() throws IOException {
  Properties result = new Properties();

  if (this.localOverride) {
   // Load properties from file upfront, to let local properties override.
   loadProperties(result);
  }

  if (this.localProperties != null) {
   for (Properties localProp : this.localProperties) {
       //将用户自定义加载的属性值,与spring加载的合并
       CollectionUtils.mergePropertiesIntoMap(localProp, result);
     }
  }

  if (!this.localOverride) {
   // Load properties from file afterwards, to let those properties override.
   loadProperties(result);
  }

  return result;
}





将多个properties文件中的配置加载以后合并成一个Properties对象返回.
上面的this.setProperties(properties)方法,就是设置localProperties的引用,localProperties不为空的话,将用户自定义加载的properties属性合并到Spring加载的result Properties对象中
localOverride参数:为true的话,表示用户自定义加载的属性值覆盖spring系统加载的,如果同名的话.

自定义使用注意:用户自定义方法的调用务必在spring 初始化调用PropertyPlaceholderConfigurer的mergeProperties()方法之前调用,否则配置文件就没有合并.一般就set值的时候调用.