远程财产来源

Question

有没有人幸运地构造了一个使用远程源（例如数据库）来检索属性值的 PropertySource。这个想法是构建一个 PropertySource（需要一些连接信息，例如主机/端口）并将其插入 PropertySourcePlaceholderConfigurer。

问题似乎是先有鸡还是先有蛋的问题。如何将连接信息向下传递到 PropertySource？我可以首先使用配置实例化 PropertySourcePlaceholderConfigurer，以加载具有远程主机和端口属性的属性文件，然后再实例化 PropertySource 并将其注入配置器。但是，我似乎无法确保第一个要实例化（并快速注入配置器）的 bean 是我的属性源。我需要这个，因为当然，我所有的其他 bean 都依赖于远程属性。

Answer 1

Commons Configuration 支持通过org.apache.commons.configuration.ConfigurationBuilder 将来自各种源（包括JDBC 数据源）的属性加载到org.apache.commons.configuration.Configuration 对象中。

使用org.apache.commons.configuration.ConfiguratorConverter，您可以将Configuration 对象转换为可以传递给PropertySourcesPlaceholderConfigurer 的java.util.Properties 对象。

至于如何配置ConfigurationBuilder这个鸡与蛋的问题，我推荐使用org.springframework.core.env.Environment查询系统属性、命令行属性或JNDI属性。

在本例中：

@Configuration
public class RemotePropertyConfig {

   @Bean
   public static PropertySourcesPlaceholderConfigurer propertyPlaceholderConfigurer(Environment environment)
    throws Exception {
    final PropertySourcesPlaceholderConfigurer props = new PropertySourcesPlaceholderConfigurer();
    final ConfigurationBuilder configurationBuilder = new DefaultConfigurationBuilder(environment.getProperty("configuration.definition.file"));
    props.setProperties(ConfigurationConverter.getProperties(configurationBuilder.getConfiguration()));
    return props;
}

您需要指定环境属性configuration.definition.file，它指向配置Commons Configuration所需的文件：

Answer 2

与上面 Recardo 的回答类似，我使用 Spring 的 PropertiesLoaderUtils 而不是 Apache 的，但它相当于同一件事。这并不完全理想.. 硬编码的依赖注入，但是，它有效！

/**
 * This method must remain static as it's part of spring's initialization effort.
 * @return
 **/
@Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
  PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();

  String dbHost = null;
  Integer dbPort = null;

  // check system / environment properties first
  Environment environment = new StandardEnvironment();
  if (environment.containsProperty(DB_HOST_KEY)) {
    dbHost = environment.getProperty(DB_HOST_KEY);
  }
  if (environment.containsProperty(DB_PORT_KEY)) {
    dbPort = Integer.valueOf(environment.getProperty(DB_PORT_KEY));
  }

  if (dbHost == null || dbPort == null) {
    // ok one or (probably) both properties null, let's go find the database.properties file
    Properties dbProperties;
    try {
      dbProperties = PropertiesLoaderUtils.loadProperties(new EncodedResource(new ClassPathResource("database.properties"), "UTF-8"));
    }
    catch (IOException e) {
      throw new RuntimeException("Could not load database.properties.  Please confirm the file is in the classpath");
    }

    if (dbHost == null) {
      dbHost = dbProperties.getProperty(DB_HOST_KEY);
    }
    if (dbPort == null) {
      dbPort = Integer.valueOf(dbProperties.getProperty(DB_PORT_KEY));
    }
  }

  PropertySourceService propertySourceService = new DBPropertySourceService(dbHost, dbPort);
  PropertySource<PropertySourceService> propertySource = new DBPropertySource(propertySourceService);
  MutablePropertySources propertySources = new MutablePropertySources();
  propertySources.addFirst(propertySource);
  configurer.setPropertySources(propertySources);

  return configurer;
}

每个请求，这里是远程属性源的来源。它取决于一个“服务”类，它可能会做......好吧......任何事情......通过套接字远程访问属性，与数据库交谈，等等。

/**
 * Property source for use with spring's PropertySourcesPlaceholderConfigurer where the source is a service
 * that connects to remote server for property values.
 **/
public class RemotePropertySource extends PropertySource<PropertySourceService> {

  private final Environment environment;
  /**
   * Constructor...
   * @param name
   * @param source
   **/
  public RemotePropertySource(PropertySourceService source) {
    super("RemotePropertySource", source);
    environment = new StandardEnvironment();
  }

  /* (non-Javadoc)
   * @see org.springframework.core.env.PropertySource#getProperty(java.lang.String)
   */
  @Override
  public Object getProperty(String name) {

    // check system / environment properties first
    String value;
    if (environment.containsProperty(name)) {
      value = environment.getProperty(name);
    }
    else {
      value = source.getProperty(name);
    }
    return value;
  }
}