Spring如何使用PropertyPlaceholderConfigurer读取文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">
  <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <!-- 对于读取一个配置文件采取的方案 -->
    <!--<property name="location" value="classpath:db.properties"/>-->

    <!--对于读取多个配置文件采取的方案-->
    <property name="locations">
      <list>
        <value>classpath:db.properties</value>
        <value>classpath:db2.properties</value>
      </list>
    </property>
  </bean>
</beans>

#db.properties 
jdbc.driverClass==net.sourceforge.jtds.jdbc.Driver 
jdbc.url=jdbc:mysql://localhost:3306/test? 
jdbc.username=anqi 
jdbc.password=123456 

#db2.properties 
name=anqi 
age=23 

import org.junit.Test; import org.junit.runner.RunWith; 
import org.springframework.beans.factory.annotation.Value; 
import org.springframework.test.context.ContextConfiguration; 
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; 

@RunWith(SpringJUnit4ClassRunner.class) 
@ContextConfiguration("classpath:spring-context.xml") 
public class TestPropertyPlaceHoder2 {   
 @Value("${jdbc.username}")   
 private String username;   
 @Value("${jdbc.password}")   
 private String password;   
 @Value("${name}")   
 private String name;   
 @Value("${age}")   
 private int age;   
 
 @Test   
 public void testResource() {     
  System.out.println("username: " + username);     
  System.out.println("password: " + password);     
  System.out.println("name: " + name);     
  System.out.println("age: " + age);   
 } 
} 
/* username: anqi   password: 123456   name: anqi   age: 23 */ 

<?xml version="1.0" encoding="UTF-8"?> 
<beans xmlns="http://www.springframework.org/schema/beans"      
  <context:property-placeholder location="classpath:db.properties,classpath:db2.properties"/> 

</beans> 

<context:property-placeholder location="classpath:db.properties,classpath:db2.properties"   
     system-properties-mode="NEVER"/>

<bean>
  <!-- 配置 preoperties文件的加载类 -->
  <bean class="com.anqi.testPropertyPlaceHoder.PropertiesUtil">
    <!-- 配置方案1 优先级更高 配置方案1找不到 key 才会去配置方案 2 里面找--> 
    <property name="locations">
      <list>
        <!-- 这里支持多种寻址方式：classpath 和 file -->
        <!-- 推荐使用file的方式引入，这样可以将配置和代码分离 -->
        <!--<value>file:/conf/localpro.properties</value>-->
        <value>classpath:db.properties</value>
        <value>classpath:db2.properties</value>
      </list>
    </property>
    <!-- 配置方案2 -->
    <property name="programConfig">
      <list>
        <value>classpath:db3.properties</value>
      </list>
    </property>
  </bean>
</beans>

jdbc.driverClass==net.sourceforge.jtds.jdbc.Driver 
jdbc.url=jdbc:mysql://localhost:3306/test? 
jdbc.username=anqi jdbc.
password=123456 
pro=1 
version=db1

name=anqi 
age=23 
pro=2 
version=db2

pro=3 

company=abc version=dev.config 

import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.core.io.FileSystemResource;
import org.springframework.core.io.Resource;

import java.io.File;
import java.io.IOException;
import java.util.*;

public class PropertiesUtil extends PropertyPlaceholderConfigurer {

  private static Resource electResource;

  private static Properties configProperties = new Properties();
  private static Properties programProperties = new Properties();

  public PropertiesUtil() {}

    /**
   * 根据 spring-context 配置文件中的配置,来将项目下对应的 properties 文件加载到系统中
   * 并且经过特殊处理 db2.properties 不允许覆盖掉 db1.properties 中相同的 key
   * @param locations
    */
   public void setLocations(Resource... locations) {
        List<Resource> existResourceList = new ArrayList<>();

        Resource devConfig = getDevConfig();
     if (devConfig != null) {
       existResourceList.add(devConfig);
     }

     Resource resource;
     for(int i = 0; i < locations.length; ++i) {
       resource = locations[i];
       if (resource.exists()) {
         existResourceList.add(resource);
         //dev db.properties db2.properties 
       }
     }

    Collections.reverse(existResourceList);
    //db2.properties db.properties dev

    if (!existResourceList.isEmpty()) {
      electResource = existResourceList.get(existResourceList.size() - 1);
      //dev
    }

    try {
      configProperties.load(electResource.getURL().openStream());
      if (existResourceList != null && existResourceList.size() > 1) {
      for(int i = existResourceList.size() - 2; i >= 0; --i) {
        Properties backupConfig = new Properties();
        //从后往前加载 db1 db2
       backupConfig.load(((Resource)existResourceList.get(i)).getURL().openStream());

       Iterator iterator = backupConfig.keySet().iterator();

       //通过后面新添加的 db3.properties、db4.peoperties 进行更新 db.properties
       //添加没有的 key 不能覆盖前面的 key
       while(iterator.hasNext()) {
         Object key = iterator.next();
         if (!configProperties.containsKey(key)) {
           configProperties.put(key, backupConfig.get(key));
         }
       }
      }
      }
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

    /**
    * 将 programConfig 的配置方案加载到 programeConfig 中
    * （即将 db3.properties 加载到 programeConfig）
    * 包含运行时方案（运行时配置优先级最高）会覆盖 key 相同的 value
    * @param locations
    */
   public void setProgramConfig (Resource... locations){

     List<Resource> existResourceList = new ArrayList<>();

     Resource resource;
     for(int i = 0; i < locations.length; ++i) {
       resource = locations[i];
       if (resource.exists()) {
         existResourceList.add(resource);
       }
     }

    if (!existResourceList.isEmpty()) {
      try {
        Iterator<Resource> iterator = existResourceList.iterator();
        while (iterator.hasNext()) {
          resource = iterator.next();
          programProperties.load(resource.getURL().openStream());
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }

    Resource devConfig = getDevConfig();
    if (devConfig != null) {
      try {
        Properties devProperties = new Properties();
        devProperties.load(devConfig.getURL().openStream());
        Iterator iterator = devProperties.keySet().iterator();

        while(iterator.hasNext()) {
          Object key = iterator.next();
          programProperties.put(String.valueOf(key), 
              devProperties.getProperty(String.valueOf(key), ""));
        }
      } catch (Exception e) {
        e.printStackTrace();
      }
    }
  }

  /**
      * 在运行期间传入配置参数（可以将配置文件放在本机或服务器上）
      * @return
    */
   private static Resource getDevConfig() {
     String s = System.getProperty("dev.config", "");
     File devConfig = new File(s);
     return !s.trim().equals("") && devConfig.exists() && devConfig.isFile() ? 
           new FileSystemResource(s) : null;
   }

  /**
   * 外部访问 properties 配置文件中的某个 key
   * @param key
   * @return
      */
   public static String get(String key){
        return programProperties.containsKey(key) ? 
       programProperties.getProperty(key) : configProperties.getProperty(key);
   }

    public static void show() {
    System.out.println("db_1 keys: "+configProperties.keySet());
    System.out.println("db_2 keys: "+programProperties.keySet());
  }
}

package com.anqi.testPropertyPlaceHoder; 
import org.springframework.context.ApplicationContext; 
import org.springframework.context.support.ClassPathXmlApplicationContext;  
public class TestPropertyPlaceHoder {   
  public static void main(String[] args) {     
    ApplicationContext al = new ClassPathXmlApplicationContext("classpath:spring-context.xml");     
    PropertiesUtil.show();     
    System.out.println(PropertiesUtil.get("version")); 

    //-Ddev.config=/dev.properties 传入运行时参数
    System.out.println(PropertiesUtil.get("company"));
    System.out.println(PropertiesUtil.get("pro"));
    //db_1 keys: [name, jdbc.password, version, company, jdbc.url, pro, jdbc.driverClass, jdbc.username, age] 
    //db_2 keys: [company, version, pro] 
    //dev.config 
    //abc 
    //3   
  } 
}