java - 如何在 Java EE 和 Spring Boot 中热重载属性？

Question

我想到了许多内部解决方案。就像在数据库中拥有属性并每 N 秒轮询一次一样。然后还检查 .properties 文件的时间戳修改并重新加载它。

但是我在查看 Java EE 标准和 Spring Boot 文档，但似乎找不到最好的方法。

我需要我的应用程序读取属性文件(或环境变量或数据库参数)，然后能够重新读取它们。生产中使用的最佳实践是什么？

正确的答案至少可以解决一个场景(Spring Boot 或 Java EE)，并提供如何使其在另一个场景中工作的概念线索

Answer 1

经过进一步研究，reloading properties must be carefully considered 。例如，在 Spring 中，我们可以重新加载属性的“当前”值，而不会出现太大问题。但是，当在上下文初始化时根据 application.properties 文件中存在的值(例如数据源、连接池、队列等)初始化资源时，必须特别小心。

注意:

用于 Spring 和 Java EE 的抽象类并不是干净代码的最佳示例。但它很容易使用，并且确实满足了这些基本的初始要求:

• 不使用除 Java 8 类之外的外部库。
• 只需一个文件即可解决问题(Java EE 版本约为 160 行)。
• 使用文件系统中可用的标准 Java Properties UTF-8 编码文件。
• 支持加密属性。

对于 Spring Boot

此代码有助于热重载 application.properties 文件，而无需使用 Spring Cloud Config 服务器(这对于某些用例来说可能有点过分)

这个抽象类你可以复制和粘贴(太棒了:D)它是一个 code derived from this SO answer

// imports from java/spring/lombok
public abstract class ReloadableProperties {
  
  @Autowired
  protected StandardEnvironment environment;
  private long lastModTime = 0L;
  private Path configPath = null;
  private PropertySource<?> appConfigPropertySource = null;

  @PostConstruct
  private void stopIfProblemsCreatingContext() {
    System.out.println("reloading");
    MutablePropertySources propertySources = environment.getPropertySources();
    Optional<PropertySource<?>> appConfigPsOp =
        StreamSupport.stream(propertySources.spliterator(), false)
            .filter(ps -> ps.getName().matches("^.*applicationConfig.*file:.*$"))
            .findFirst();
    if (!appConfigPsOp.isPresent())  {
      // this will stop context initialization 
      // (i.e. kill the spring boot program before it initializes)
      throw new RuntimeException("Unable to find property Source as file");
    }
    appConfigPropertySource = appConfigPsOp.get();

    String filename = appConfigPropertySource.getName();
    filename = filename
        .replace("applicationConfig: [file:", "")
        .replaceAll("\\]$", "");

    configPath = Paths.get(filename);

  }

  @Scheduled(fixedRate=2000)
  private void reload() throws IOException {
      System.out.println("reloading...");
      long currentModTs = Files.getLastModifiedTime(configPath).toMillis();
      if (currentModTs > lastModTime) {
        lastModTime = currentModTs;
        Properties properties = new Properties();
        @Cleanup InputStream inputStream = Files.newInputStream(configPath);
        properties.load(inputStream);
        environment.getPropertySources()
            .replace(
                appConfigPropertySource.getName(),
                new PropertiesPropertySource(
                    appConfigPropertySource.getName(),
                    properties
                )
            );
        System.out.println("Reloaded.");
        propertiesReloaded();
      }
    }

    protected abstract void propertiesReloaded();
}

然后创建一个 bean 类，允许从使用抽象类的 applicatoin.properties 检索属性值

@Component
public class AppProperties extends ReloadableProperties {

    public String dynamicProperty() {
        return environment.getProperty("dynamic.prop");
    }
    public String anotherDynamicProperty() {
        return environment.getProperty("another.dynamic.prop");    
    }
    @Override
    protected void propertiesReloaded() {
        // do something after a change in property values was done
    }
}

确保将 @EnableScheduling 添加到您的 @SpringBootApplication

@SpringBootApplication
@EnableScheduling
public class MainApp  {
   public static void main(String[] args) {
      SpringApplication.run(MainApp.class, args);
   }
}

现在您可以在任何需要的地方自动连接 AppProperties Bean。只需确保始终调用其中的方法，而不是将其值保存在变量中。并确保重新配置使用可能不同的属性值初始化的任何资源或 bean。

目前，我仅使用外部默认找到的 ./config/application.properties 文件对此进行了测试。

对于 Java EE

我创建了一个通用的 Java SE 抽象类来完成这项工作。

您可以复制并粘贴此内容:

// imports from java.* and javax.crypto.*
public abstract class ReloadableProperties {

  private volatile Properties properties = null;
  private volatile String propertiesPassword = null;
  private volatile long lastModTimeOfFile = 0L;
  private volatile long lastTimeChecked = 0L;
  private volatile Path propertyFileAddress;

  abstract protected void propertiesUpdated();

  public class DynProp {
    private final String propertyName;
    public DynProp(String propertyName) {
      this.propertyName = propertyName;
    }
    public String val() {
      try {
        return ReloadableProperties.this.getString(propertyName);
      } catch (Exception e) {
        e.printStackTrace();
        throw new RuntimeException(e);
      }
    }
  }

  protected void init(Path path) {
    this.propertyFileAddress = path;
    initOrReloadIfNeeded();
  }

  private synchronized void initOrReloadIfNeeded() {
    boolean firstTime = lastModTimeOfFile == 0L;
    long currentTs = System.currentTimeMillis();

    if ((lastTimeChecked + 3000) > currentTs)
      return;

    try {

      File fa = propertyFileAddress.toFile();
      long currModTime = fa.lastModified();
      if (currModTime > lastModTimeOfFile) {
        lastModTimeOfFile = currModTime;
        InputStreamReader isr = new InputStreamReader(new FileInputStream(fa), StandardCharsets.UTF_8);
        Properties prop = new Properties();
        prop.load(isr);
        properties = prop;
        isr.close();
        File passwordFiles = new File(fa.getAbsolutePath() + ".key");
        if (passwordFiles.exists()) {
          byte[] bytes = Files.readAllBytes(passwordFiles.toPath());
          propertiesPassword = new String(bytes,StandardCharsets.US_ASCII);
          propertiesPassword = propertiesPassword.trim();
          propertiesPassword = propertiesPassword.replaceAll("(\\r|\\n)", "");
        }
      }

      updateProperties();

      if (!firstTime)
        propertiesUpdated();

    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  private void updateProperties() {
    List<DynProp> dynProps = Arrays.asList(this.getClass().getDeclaredFields())
        .stream()
        .filter(f -> f.getType().isAssignableFrom(DynProp.class))
        .map(f-> fromField(f))
        .collect(Collectors.toList());

    for (DynProp dp :dynProps) {
      if (!properties.containsKey(dp.propertyName)) {
        System.out.println("propertyName: "+ dp.propertyName + " does not exist in property file");
      }
    }

    for (Object key : properties.keySet()) {
      if (!dynProps.stream().anyMatch(dp->dp.propertyName.equals(key.toString()))) {
        System.out.println("property in file is not used in application: "+ key);
      }
    }

  }

  private DynProp fromField(Field f) {
    try {
      return (DynProp) f.get(this);
    } catch (IllegalAccessException e) {
      e.printStackTrace();
    }
    return null;
  }

  protected String getString(String param) throws Exception {
    initOrReloadIfNeeded();
    String value = properties.getProperty(param);
    if (value.startsWith("ENC(")) {
      String cipheredText = value
          .replace("ENC(", "")
          .replaceAll("\\)$", "");
      value =  decrypt(cipheredText, propertiesPassword);
    }
    return value;
  }

  public static String encrypt(String plainText, String key)
      throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, InvalidKeySpecException {
    SecureRandom secureRandom = new SecureRandom();
    byte[] keyBytes = key.getBytes(StandardCharsets.US_ASCII);
    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
    KeySpec spec = new PBEKeySpec(key.toCharArray(), new byte[]{0,1,2,3,4,5,6,7}, 65536, 128);
    SecretKey tmp = factory.generateSecret(spec);
    SecretKey secretKey = new SecretKeySpec(tmp.getEncoded(), "AES");
    byte[] iv = new byte[12];
    secureRandom.nextBytes(iv);
    final Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
    GCMParameterSpec parameterSpec = new GCMParameterSpec(128, iv); //128 bit auth tag length
    cipher.init(Cipher.ENCRYPT_MODE, secretKey, parameterSpec);
    byte[] cipherText = cipher.doFinal(plainText.getBytes(StandardCharsets.UTF_8));
    ByteBuffer byteBuffer = ByteBuffer.allocate(4 + iv.length + cipherText.length);
    byteBuffer.putInt(iv.length);
    byteBuffer.put(iv);
    byteBuffer.put(cipherText);
    byte[] cipherMessage = byteBuffer.array();
    String cyphertext = Base64.getEncoder().encodeToString(cipherMessage);
    return cyphertext;
  }
  public static String decrypt(String cypherText, String key)
      throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, InvalidKeySpecException {
    byte[] cipherMessage = Base64.getDecoder().decode(cypherText);
    ByteBuffer byteBuffer = ByteBuffer.wrap(cipherMessage);
    int ivLength = byteBuffer.getInt();
    if(ivLength < 12 || ivLength >= 16) { // check input parameter
      throw new IllegalArgumentException("invalid iv length");
    }
    byte[] iv = new byte[ivLength];
    byteBuffer.get(iv);
    byte[] cipherText = new byte[byteBuffer.remaining()];
    byteBuffer.get(cipherText);
    byte[] keyBytes = key.getBytes(StandardCharsets.US_ASCII);
    final Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
    KeySpec spec = new PBEKeySpec(key.toCharArray(), new byte[]{0,1,2,3,4,5,6,7}, 65536, 128);
    SecretKey tmp = factory.generateSecret(spec);
    SecretKey secretKey = new SecretKeySpec(tmp.getEncoded(), "AES");
    cipher.init(Cipher.DECRYPT_MODE, secretKey, new GCMParameterSpec(128, iv));
    byte[] plainText= cipher.doFinal(cipherText);
    String plain = new String(plainText, StandardCharsets.UTF_8);
    return plain;
  }
}

然后你可以这样使用它:

public class AppProperties extends ReloadableProperties {

  public static final AppProperties INSTANCE; static {
    INSTANCE = new AppProperties();
    INSTANCE.init(Paths.get("application.properties"));
  }


  @Override
  protected void propertiesUpdated() {
    // run code every time a property is updated
  }

  public final DynProp wsUrl = new DynProp("ws.url");
  public final DynProp hiddenText = new DynProp("hidden.text");

}

如果您想使用编码属性，您可以将其值包含在 ENC() 内，并且将在添加了 .key 扩展名的属性文件的相同路径和名称中搜索解密密码。在此示例中，它将在 application.properties.key 文件中查找密码。

应用程序属性->

ws.url=http://some webside
hidden.text=ENC(AAAADCzaasd9g61MI4l5sbCXrFNaQfQrgkxygNmFa3UuB9Y+YzRuBGYj+A==)

application.properties.key ->

password aca

对于 Java EE 解决方案的属性值加密，我查阅了 Patrick Favre-Bulle 的优秀文章 Symmetric Encryption with AES in Java and Android 。然后检查了这个SO问题中的密码、 block 模式和填充 AES/GCM/NoPadding 。最后，我使 AES 位从 @erickson 的密码中派生出来，关于 AES Password Based Encryption 的优秀答案。关于Spring中值属性的加密，我认为它们与Java Simplified Encryption集成在一起

这是否符合最佳实践的资格可能超出了范围。这个答案展示了如何在 Spring Boot 和 Java EE 中拥有可重新加载的属性。