Configuration handling & implementation is racy

[snazy]

Describe the bug

Polaris currently uses Dropwizard and relies on Jackson for configuration, but also ties initialization/setup/business logic into configuration objects.

For example in PolarisApplicationConfig there are:

  @JsonProperty("realmContextResolver")
  @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")
  public void setRealmContextResolver(RealmContextResolver realmContextResolver) {
    this.realmContextResolver = realmContextResolver;
  }

  @JsonProperty("defaultRealm")
  public void setDefaultRealm(String defaultRealm) {
    this.defaultRealm = defaultRealm;
    realmContextResolver.setDefaultRealm(defaultRealm);
  }

These code constructs are racy/error-prone, because literally nothing guarantees that realmContextResolver is set to != null when setDefaultRealm() is invoked.

[snazy]

Example stack trace:

io.dropwizard.configuration.ConfigurationParsingException: default configuration has an error:
  * Failed to parse configuration at: defaultRealm; Cannot invoke "org.apache.polaris.service.context.RealmContextResolver.setDefaultRealm(String)" because "this.realmContextResolver" is null (through reference chain: org.apache.polaris.service.dropwizard.config.PolarisApplicationConfig["defaultRealm"])

	at io.dropwizard.configuration.ConfigurationParsingException$Builder.build(ConfigurationParsingException.java:277)
	at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:177)
	at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:121)
	at io.dropwizard.core.cli.ConfiguredCommand.parseConfiguration(ConfiguredCommand.java:141)
	at io.dropwizard.core.cli.ConfiguredCommand.run(ConfiguredCommand.java:85)
	at io.dropwizard.core.cli.Cli.run(Cli.java:78)
	at io.dropwizard.core.Application.run(Application.java:94)
	at org.apache.polaris.service.dropwizard.PolarisApplication.main(PolarisApplication.java:153)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Cannot invoke "org.apache.polaris.service.context.RealmContextResolver.setDefaultRealm(String)" because "this.realmContextResolver" is null (through reference chain: org.apache.polaris.service.dropwizard.config.PolarisApplicationConfig["defaultRealm"])
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:402)
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:361)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.wrapAndThrow(BeanDeserializerBase.java:1964)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:275)
	at com.fasterxml.jackson.module.blackbird.deser.SuperSonicBeanDeserializer.deserialize(SuperSonicBeanDeserializer.java:155)
	at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:342)
	at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:4893)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3036)
	at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:148)
	... 6 more
Caused by: java.lang.NullPointerException: Cannot invoke "org.apache.polaris.service.context.RealmContextResolver.setDefaultRealm(String)" because "this.realmContextResolver" is null
	at org.apache.polaris.service.dropwizard.config.PolarisApplicationConfig.setDefaultRealm(PolarisApplicationConfig.java:307)
	at com.fasterxml.jackson.module.blackbird.deser.SettableStringProperty.set(SettableStringProperty.java:56)
	at com.fasterxml.jackson.module.blackbird.deser.SettableStringProperty.deserializeAndSet(SettableStringProperty.java:41)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:273)
	... 11 more