Spring 引导 2 - 在 bean 初始化之前做一些事情

Question

Problem Statement

I want to load properties from a properties file in a classpath or at an external location before the beans are initialized. These properties are also a part of Bean initialization. I cannot autowire the properties from Spring's standard application.properties or its customization because the same properties file must be accessible by multiple deployables.

What I Tried

I'm aware about Spring Application Events ; in fact, I'm already hooking ContextRefreshedEvent to perform some tasks after the Spring Context is initialized (Beans are also initialized at this stage).

For my problem statement, from the description of Spring Docs ApplicationEnvironmentPreparedEvent looked promising, but the hook did not work.

@SpringBootApplication
public class App {

    public static void main(String[] args) throws IOException {
        SpringApplication.run(App.class, args);
    }


    @EventListener
    public void onStartUp(ContextRefreshedEvent event) {
        System.out.println("ContextRefreshedEvent");    // WORKS
    }

    @EventListener
    public void onShutDown(ContextClosedEvent event) {
        System.out.println("ContextClosedEvent");   // WORKS
    }

    @EventListener
    public void onEvent6(ApplicationStartedEvent event) {
        System.out.println("ApplicationStartedEvent");  // WORKS BUT AFTER ContextRefreshedEvent
    }


    @EventListener
    public void onEvent3(ApplicationReadyEvent event) {
        System.out.println("ApplicationReadyEvent");    // WORKS WORKS BUT AFTER ContextRefreshedEvent
    }


    public void onEvent1(ApplicationEnvironmentPreparedEvent event) {
        System.out.println("ApplicationEnvironmentPreparedEvent");  // DOESN'T WORK
    }


    @EventListener
    public void onEvent2(ApplicationContextInitializedEvent event) {
        System.out.println("ApplicationContextInitializedEvent");   // DOESN'T WORK
    }


    @EventListener
    public void onEvent4(ApplicationContextInitializedEvent event) {
        System.out.println("ApplicationContextInitializedEvent");
    }

    @EventListener
    public void onEvent5(ContextStartedEvent event) {
        System.out.println("ContextStartedEvent");
    }

}

Update

As suggested by M.Deinum in the comments, I tried adding an application context initializer like below. It doesn't seem to be working either.

    public static void main(String[] args) {
        new SpringApplicationBuilder()
                .sources(App.class)
                .initializers(applicationContext -> {
                    System.out.println("INSIDE CUSTOM APPLICATION INITIALIZER");
                })
                .run(args);

    }

Update #2

While my problem statement is regarding loading properties, my question/curiosity is really about how to run some code before the classes are initialized as beans and put into Spring IoC container . Now, these beans require some property values during initialization and I can't/don't want to Autowire them because of the following reason:

As stated in comments and answers, the same can be done using Spring Boot's externalized configuration and profiles. However, I need to maintain application properties and domain-related properties separately. A base domain properties should have at least 100 properties, and the number grows over time. Both application properties and domain-related properties have a property file for different environments (dev, SIT, UAT, Production). Property files override one or more of the base properties. That's 8 property files. Now, the same app needs to be deployed into multiple geographies. That makes it 8 * n property files where n is the number of geographies. I want all the property files stored in a common module so that they can be accessed by different deployables. Environment and geography would be known in run-time as system properties.

While these might be achieved by using Spring profiles and precedence order, I want to have a programmatic control over it ( I also would maintain my own property repository ). Eg. I would write a convenience utility called MyPropUtil and access them like:

public class MyPropUtil {
     private static Map<String, Properties> repository;

     public static initialize(..) {
         ....
     }

     public static String getDomainProperty(String key) {
        return repository.get("domain").getProperty(key);
     }

     public static String getAppProperty(String key) {
         return repository.get("app").getProperty(key);
     }

     public static String getAndAddBasePathToAppPropertyValue(String key) {
        ...
     }

}

@Configuration
public class MyComponent {

    @Bean
    public SomeClass getSomeClassBean() {
        SomeClass obj = new SomeClass();
        obj.someProp1(MyPropUtil.getDomainProperty('domainkey1'));
        obj.someProp2(MyPropUtil.getAppProperty('appkey1'));
        // For some properties
         obj.someProp2(MyPropUtil.getAndAddBasePathToAppPropertyValue('some.relative.path.value'));
        ....
        return obj;
    }

}

From the docs, it seems like ApplicationEvents and ApplicationInitializers fit my need, but I am not able to get them to work for my problem statement.

Answer 1

Bit late to the party but hopefully I can offer a solution to your updated problem statement.

This will focus on problem of how to run some code before the classes are initialized as beans and put into Spring IoC container

One issue I notice is that you're defining your application events via the @EventListener annotation.

These are only called once all beans are initiated since these annotations are processed by EventListenerMethodProcessor which is only triggered when the context is ready (see SmartInitializingSingleton#afterSingletonsInstantiated)

As such, some of the events that occur before the context is ready. eg ContextStartedEvent, ApplicationContextInitializedEvent won't make it to your listener.

Instead, what you can do is extend the interface for these events directly.

@Slf4j
public class AllEvent implements ApplicationListener<ApplicationEvent> {

    @Override
    public void onApplicationEvent(final ApplicationEvent event) {
        log.info("I am a {}", event.getClass().getSimpleName());
    }

Note the missing @Component. Even bean instantiation can occur after some of these events. If you use @Component, then you'll get the following logs

I am a DataSourceSchemaCreatedEvent
I am a ContextRefreshedEvent
I am a ServletWebServerInitializedEvent
I am a ApplicationStartedEvent
I am a ApplicationReadyEvent

Still better and more instant than the annotative listeners but will still not receive the initialization events. For that, what you need to do is follow the instructions found here

To summarize,

• Create directory resources/META-INF
• Create file spring.factories
• org.springframework.context.ApplicationListener=full.path.to.my.class.AllEvent

The result:-

I am a ApplicationContextInitializedEvent
I am a ApplicationPreparedEvent
I am a DataSourceSchemaCreatedEvent
I am a ContextRefreshedEvent
I am a ServletWebServerInitializedEvent
I am a ApplicationStartedEvent
I am a ApplicationReadyEvent

In particular, ApplicationContextInitializedEvent should allow you to perform whatever per-instantiation tasks you need.

Answer 2

I think Spring Cloud Config is a perfect solution for your problem statement. Detailed documentation Here

Spring Cloud Config provides server-side and client-side support for externalized configuration in a distributed system.

So you can easily manage the configurations outside of the app, as well as all the instances will use same configurations.

Answer 3

Create a bean that will be a properties repository and inject it in other beans requiring properties.

In your example, instead of having static methods in MyPropUtil , make the class a bean itself with instance methods. Initialize Map<String, Properties> repository in the initialize method annotated with @PostConstruct .

@Component
public class MyPropUtil {

  private static final String DOMAIN_KEY = "domain";
  private static final String APP_KEY = "app";

  private Map<String, Properties> repository;

  @PostConstruct
  public void init() {
    Properties domainProps = new Properties();
    //domainProps.load();
    repository.put(DOMAIN_KEY, domainProps);

    Properties appProps = new Properties();
    //appProps.load();
    repository.put(APP_KEY, appProps);
  }

  public String getDomainProperty(String key) {
    return repository.get(DOMAIN_KEY).getProperty(key);
  }

  public String getAppProperty(String key) {
    return repository.get(APP_KEY).getProperty(key);
  }

  public String getAndAddBasePathToAppPropertyValue(String key) {
    //...
  }
}

and

@Configuration
public class MyComponent {

  @Autowired
  private MyPropUtil myPropUtil;

  @Bean
  public SomeClass getSomeClassBean() {
    SomeClass obj = new SomeClass();
    obj.someProp1(myPropUtil.getDomainProperty("domainkey1"));
    obj.someProp2(myPropUtil.getAppProperty("appkey1"));
    // For some properties
    obj.someProp2(myPropUtil.getAndAddBasePathToAppPropertyValue("some.relative.path.value"));
      //...
      return obj;
  }
}

Or you can inject MyPropUtil directly to the SomeClass :

@Component
public class SomeClass {

  private final String someProp1;
  private final String someProp2;

  @Autowired
  public SomeClass(MyPropUtil myPropUtil) {
    this.someProp1 = myPropUtil.getDomainProperty("domainkey1");
    this.someProp2 = myPropUtil.getAppProperty("appkey1");
  }
  //...
}

Answer 4

As explaned in this post you can add external property files like this;

public PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    PropertySourcesPlaceholderConfigurer properties = new PropertySourcesPlaceholderConfigurer();
    properties.setLocation(new FileSystemResource("/Users/home/conf.properties"));
    properties.setIgnoreResourceNotFound(false);
    return properties;
}

If you don't want to use this, just read the property file with jackson and set the properties to System.setProperty("key","value") in the main method before spring starts.

If you don't want to use this too, take a look at the BeanPostProcessor#postProcessBeforeInitialization method. It runs before bean properties initialized by spring.

Answer 5

I might be missing what exactly do you mean by "Beans initialization", probably an example of such a bean in a question could be beneficial.

I think you should differentiate between properties reading part and bean initialization. By the time of bean initialization, properties are already read and available. Thats a part of spring magic, if you wish.

That's why the following code works for example:

@Component
public class MySampleBean {

    public MySampleBean(@Value("${some.prop}" String someProp) {...}
}

It doesn't matter from where do these property come (spring boot defines many different ways of these places with precedence between them), it will happen before the initialization of beans happens.

Now, lets get back to your original question:

I want to load properties from a properties file in a classpath or at external location (before the beans are initialized - irrelevant).

In spring / spring-boot there is a concept of profiles that basically allows to create a file application-foo.properties (or yaml) and when you load with --spring.profiles.active=foo it will automatically load properties defined in this application-foo.properties in addition to the regular application.properties

So you can place the stuff that you want to "load from classpath" into application-local.properties (the word local is for the sake of example only) and start the application with --spring.profiles.active=local (in the deployment script, docker file or whatever)

If you want to run the property from external location (outside the classpath) you can use: --spring.config.location=<Full-path-file>

Note that even if you put some properties into a regular application.properties and still use --spring.config.location with the same key-value pairs they will take precedence over the properties in the classpath.

Alternatively you can use only --sring.profiles.active=local or remote and do not use config locations at all.

Answer 6

You can configure external location directly in the command line:

java -jar app.jar --spring.config.location=file:///Users/home/config/external.properties

Answer 7

You can use WebApplicationInitializer to execute code before classes are initialized as beans

public class MyWebInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext servletContext) throws ServletException { var ctx = new AnnotationConfigWebApplicationContext(); ctx.register(WebConfig.class); ctx.setServletContext(servletContext);

We create an AnnotationConfigWebApplicationContext and register a web configuration file with register().

Answer 8

You can check if PropertySource may help you.

Example:

@PropertySource({"classpath:persistence/persistence.properties"})

You can use this annotation on every @Configuration or @SpringBootApplication bean

Answer 9

It sounds like you want to take some ownership of a part of the bean initialization. Typically people think of Spring completing the bean configuration, but in your case it might be easier to consider Spring as starting it.

So, your bean has some properties you want to configure, and some that you want Spring to configure. Just annotate the ones you want Spring to configure (with @Autowire or @Inject , or whatever flavour you prefer), and then take over the control from there, using @PostConstruct or InitializingBean .

class MyMultiStageBoosterRocket {

  private Foo foo;
  private Bar bar;
  private Cat cat;

  @Autowire
  public MyMultiStageBoosterRocket(Foo foo, Bar bar) {
    this.foo = foo;
    this.bar = bar'
  }

  // called *after* Spring has done its injection, but *before* the bean
  // is registered in the context
  @PostConstruct
  public void postConstruct() {
    // your magic property injection from whatever source you happen to want
    ServiceLoader<CatProvider> loader = ServiceLoader.load(CatProvider.class);
    // etc...
  }
}

Of course your mechanism for property resolution would need to be available statically somehow, but that seems to fit with you MyPropUtil example.

Getting far more involved, you start looking at Bean Post Processors directly ( @PostConstruct is a simple variant of sorts).

There's a previous question, with a useful answer, here How exactly does the Spring BeanPostProcessor work? , but for simplicity, you'd do something like

public class CustomBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName)
            throws BeansException {

        // fixme: detect if this bean needs fancy initialization

        return bean;
    }
}

Clearly @PostProcess , or InitializingBean are simpler, but the custom post processor has a big advantage... it can be injected with other Spring managed beans. That means you can Spring manage your property injection whatever-thing, and still manually manage the actual injection process.

Answer 10

Just try to load everything you need in main before

SpringApplication.run()

call

public static void main(String[] args) {
    // before spring initialization
    TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
    SpringApplication.run(CyberRiskApplication.class, args);
}

Answer 11

You can use ApplicationEnvironmentPreparedEvent but it can't be configured using EventListener annotation. Because by this time Bean drfinitions are not loaded. See the below link on how to cofigure this event. https://www.thetechnojournals.com/2019/10/spring-boot-application-events.html

Answer 12

I feel like your main issue is that you need to maintain application properties and domain-related properties separately. From spring's perspective, it doesn't really matter since all properties files are kinda merged together after they have been loaded in memory. So for example, you have two files that contain some properties:

application.related=property1 # this is in application.properties

domain.related=property2 # this is in domain-specific.properties

After they have been loaded, you will get one big thing that contains all properties, if I am not mistaken, it is a org.springframework.core.env.ConfigurableEnvironment instance.

Then what you need to do is just inject the property you need using something like @Value .

For the main issue, to separate properties into different files, you just need to specify spring's spring.config.name property (via environment variable, command line or programmatically). Following the above example, it should be spring.config.name=application,domain-specific .

Furthermore, if you really want to have programmatic control , you can add a custom EnvironmentPostProcessor which exposes the ConfigurableEnvironment instance.