如何在Java EE和Spring Boot中热重新加载属性？

经过进一步的研究,reloading properties must be carefully considered.例如,在Spring中,我们可以重新加载属性的“当前”值而没有太多问题.但.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的抽象类不是清洁代码的最佳示例.但它易于使用,它确实满足了这个基本的初始要求：

>不使用Java 8 Classes以外的外部库.
>只有一个文件可以解决问题(Java EE版本约为160行).
>使用文件系统中可用的标准Java属性UTF-8编码文件.
>支持加密属性.

对于Spring Boot

此代码有助于在不使用Spring Cloud Config服务器的情况下热重新加载application.properties文件(对于某些用例可能过度杀毒)

这个抽象类你可以复制&粘贴(SO好吃的东西：D)这是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中检索属性值

@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@SpringBootApplication中

@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,我只使用外部和默认找到的./config/application.properties文件对此进行了测试.

对于Java EE

我做了一个普通的Java SE抽象类来完成这项工作.

你可以复制&粘贴这个：

// 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,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(),"AES");
    cipher.init(Cipher.DECRYPT_MODE,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()中,并且将在具有添加的.key扩展名的属性文件的相同路径和名称中搜索用于解密的密码.在此示例中,它将在application.properties.key文件中查找密码.

application.properties – >

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

aplication.properties.key – >

password aca

为了加密Java EE解决方案的属性值,我在Symmetric Encryption with AES in Java and Android上查阅了Patrick Favre-Bulle的优秀文章.然后在这个SO问题中检查了密码,块模式和填充,关于AES/GCM/NoPadding.最后我将AES位从密码中导出来自@erickson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

这个有资格作为最佳实践的资格可能超出范围.这个答案显示了如何在Spring Boot和Java EE中使用可重新加载的属性.