com.hazelcast.spi.discovery

## Class AbstractDiscoveryStrategy

- java.lang.Object
- - com.hazelcast.spi.discovery.AbstractDiscoveryStrategy

- All Implemented Interfaces:
    DiscoveryStrategy
  Direct Known Subclasses:
    MulticastDiscoveryStrategy

      public abstract class AbstractDiscoveryStrategy
      extends Object
      implements DiscoveryStrategy

  An common abstract superclass for `DiscoveryStrategy` implementations, offering convenient access to configuration properties (which may be overridden on the system's environment or JVM properties), as well as a `ILogger` instance.
  Since:
    3.6

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `AbstractDiscoveryStrategy(ILogger logger, Map<String,Comparable> properties)`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `destroy()` The `stop` method is used to stop internal services, sockets or to destroy any kind of internal state.
    `Map<String,Object>` | `discoverLocalMetadata()` Returns a map with discovered metadata provided by the runtime environment.
    `protected ILogger` | `getLogger()` Returns a `ILogger` instance bound to the current class.
    `protected <T extends Comparable> T` | `getOrDefault(PropertyDefinition property, T defaultValue)` Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), otherwise it will return the given `defaultValue`.
    `protected <T extends Comparable> T` | `getOrDefault(String prefix, PropertyDefinition property, T defaultValue)` Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), can be found in the system's environment, or passed as a JVM property.
    `protected <T extends Comparable> T` | `getOrNull(PropertyDefinition property)` Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), otherwise it will return `null`.
    `protected <T extends Comparable> T` | `getOrNull(String prefix, PropertyDefinition property)` Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), can be found in the system's environment, or passed as a JVM property.
    `PartitionGroupStrategy` | `getPartitionGroupStrategy()` Returns a custom implementation of a `PartitionGroupStrategy` to override default behavior of zone aware backup strategies `PartitionGroupMetaData` or to provide a specific behavior in case the discovery environment does not provide information about the infrastructure to be used for automatic configuration.
    `protected Map<String,Comparable>` | `getProperties()` Returns an immutable copy of the configuration properties.
    `void` | `start()` The `start` method is used to initialize internal state and perform any kind of startup procedure like multicast socket creation.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

    - ### Methods inherited from interface com.hazelcast.spi.discovery.DiscoveryStrategy

      `discoverNodes`

- - ### Constructor Detail

    - #### AbstractDiscoveryStrategy

          public AbstractDiscoveryStrategy(ILogger logger,
                                           Map<String,Comparable> properties)

  - ### Method Detail

    - #### destroy

          public void destroy()

      Description copied from interface: `DiscoveryStrategy`
      The `stop` method is used to stop internal services, sockets or to destroy any kind of internal state.
      Specified by:
        `destroy` in interface `DiscoveryStrategy`

    - #### start

          public void start()

      Description copied from interface: `DiscoveryStrategy`
      The `start` method is used to initialize internal state and perform any kind of startup procedure like multicast socket creation. The behavior of this method might change based on the `DiscoveryNode` instance passed to the `DiscoveryStrategyFactory`.
      Specified by:
        `start` in interface `DiscoveryStrategy`

    - #### getPartitionGroupStrategy

          public PartitionGroupStrategy getPartitionGroupStrategy()

      Description copied from interface: `DiscoveryStrategy`
      Returns a custom implementation of a `PartitionGroupStrategy` to override default behavior of zone aware backup strategies `PartitionGroupMetaData` or to provide a specific behavior in case the discovery environment does not provide information about the infrastructure to be used for automatic configuration.
      Specified by:
        `getPartitionGroupStrategy` in interface `DiscoveryStrategy`
      Returns:
        a custom implementation of a `PartitionGroupStrategy` otherwise `null` in case of the default implementation is to be used

    - #### discoverLocalMetadata

          public Map<String,Object> discoverLocalMetadata()

      Description copied from interface: `DiscoveryStrategy`
      Returns a map with discovered metadata provided by the runtime environment. Those information may include, but are not limited, to location information like datacenter, rack, host or additional tags to be used for custom purpose.

      Information discovered from this method are shaded into the `Member`s attributes. Existing attributes will not be overridden, that way local attribute configuration overrides provided metadata.

      The default implementation provides an empty map with no further metadata configured. Returning `null` is not permitted and will most probably result in an `NullPointerException` inside the cluster system.
      Specified by:
        `discoverLocalMetadata` in interface `DiscoveryStrategy`
      Returns:
        a map of discovered metadata as provided by the runtime environment

    - #### getProperties

          protected Map<String,Comparable> getProperties()

      Returns an immutable copy of the configuration properties.
      Returns:
        the configuration properties

    - #### getLogger

          protected ILogger getLogger()

      Returns a `ILogger` instance bound to the current class.
      Returns:
        a ILogger instance

    - #### getOrNull

          protected <T extends Comparable> T getOrNull(PropertyDefinition property)

      Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), otherwise it will return `null`.

      This method overload won't do environment or JVM property lookup. A call to this overload is equivalent to `getOrNull(String, PropertyDefinition)` with `null` passed as the first parameter.
      Type Parameters:
        `T` - the type of the property, must be compatible with the conversion result of `PropertyDefinition.typeConverter()`
      Parameters:
        `property` - the PropertyDefinition to lookup
      Returns:
        the value of the given property if available in the configuration, otherwise null

    - #### getOrNull

          protected <T extends Comparable> T getOrNull(String prefix,
                                                       PropertyDefinition property)

      Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), can be found in the system's environment, or passed as a JVM property. Otherwise it will return `null`.

      This overload will resolve the requested property in the following order, whereas the higher priority is from top to bottom:
      - `System.getProperty(String)`: JVM properties
      - `System.getenv(String)`: System environment
      - Configuration properties of this `DiscoveryStrategy`
      To resolve JVM properties or the system environment the property's key is prefixed with given `prefix`, therefore a prefix of com.hazelcast.discovery and a property key of hostname will result in a property lookup of com.hazelcast.discovery.hostname in the system environment and JVM properties.
      Type Parameters:
        `T` - the type of the property, must be compatible with the conversion result of `PropertyDefinition.typeConverter()`
      Parameters:
        `prefix` - the property key prefix for environment and JVM properties lookup
        `property` - the PropertyDefinition to lookup
      Returns:
        the value of the given property if available in the configuration, system environment or JVM properties, otherwise null

    - #### getOrDefault

          protected <T extends Comparable> T getOrDefault(PropertyDefinition property,
                                                          T defaultValue)

      Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), otherwise it will return the given `defaultValue`.

      This method overload won't do environment or JVM property lookup. A call to this overload is equivalent to `getOrDefault(String, PropertyDefinition, Comparable)` with `null` passed as the first parameter.
      Type Parameters:
        `T` - the type of the property, must be compatible with the conversion result of `PropertyDefinition.typeConverter()`
      Parameters:
        `property` - the PropertyDefinition to lookup
      Returns:
        the value of the given property if available in the configuration, otherwise the given default value

    - #### getOrDefault

          protected <T extends Comparable> T getOrDefault(String prefix,
                                                          PropertyDefinition property,
                                                          T defaultValue)

      Returns the value of the requested `PropertyDefinition` if available in the declarative or programmatic configuration (XML or Config API), can be found in the system's environment, or passed as a JVM property. otherwise it will return the given `defaultValue`.

      This overload will resolve the requested property in the following order, whereas the higher priority is from top to bottom:
      - `System.getProperty(String)`: JVM properties
      - `System.getenv(String)`: System environment
      - Configuration properties of this `DiscoveryStrategy`
      To resolve JVM properties or the system environment the property's key is prefixed with given `prefix`, therefore a prefix of com.hazelcast.discovery and a property key of hostname will result in a property lookup of com.hazelcast.discovery.hostname in the system environment and JVM properties.
      Type Parameters:
        `T` - the type of the property, must be compatible with the conversion result of `PropertyDefinition.typeConverter()`
      Parameters:
        `prefix` - the property key prefix for environment and JVM properties lookup
        `property` - the PropertyDefinition to lookup
      Returns:
        the value of the given property if available in the configuration, system environment or JVM properties, otherwise the given default value

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