Package io.helidon.service.configuration.api

Class System

java.lang.Object

io.helidon.service.configuration.api.System

Direct Known Subclasses:

LocalhostSystem

public abstract class System
extends Object

A service provider that represents some kind of system in which the current program is running.

The meaning of system is deliberately loose. A system might be a laptop, a platform-as-a-service such as the Oracle Application Container Cloud Service or Heroku, a generic Linux-like ecosystem running as part of a Kubernetes cluster, and so on.

System instances provide access to their environment as well as to their properties.

In an arbitrary collection of System instances, zero or one of them may be marked as being authoritative. An authoritative System holds sway, and its properties and environment values are to be preferred over all others.

See Also:

getSystems(), getenv(), getProperties(), isAuthoritative()

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	System(String name, boolean authoritative) Creates a new System.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object other) Returns true if this System is equal to the supplied Object.
Map<String,String>	getenv() Returns the environment of this System as a non-null, unchanging and unmodifiable Map.
String	getName() Returns the name of this System.
Properties	getProperties() Returns the properties of this System as a non-null, unchanging and unmodifiable Properties object.
static Set<System>	getSystems() Returns a non-null, unchanging and unmodifiable Set of System instances as found by the Java service provider mechanism.
int	hashCode() Returns a hashcode for this System that varies with only its name, enablement and authority.
boolean	isAuthoritative() Returns true if this System is authoritative.
abstract boolean	isEnabled() Returns true if this System is enabled.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

System

protected System(String name,
                 boolean authoritative)

Creates a new System.

Parameters:

name - the name of the System; must not be null

authoritative - whether the System will be authoritative

Throws:

NullPointerException - if name is null

See Also:

getName(), isAuthoritative()

Method Detail

getName

public final String getName()

Returns the name of this System.

This method never returns null.

Multiple invocations of this method will return identical String instances.

Returns:

the name of this System; never null

See Also:

System(String, boolean)

isEnabled

public abstract boolean isEnabled()

Returns true if this System is enabled.

If a System is enabled, then its environment values and properties may be used. If a System is not enabled, then usage of its environment values and properties may result in undefined behavior.

Returns:

true if this System is enabled; false otherwise

See Also:

System(String, boolean)

isAuthoritative

public boolean isAuthoritative()

Returns true if this System is authoritative.

If a System is authoritative, then its environment values and properties are to be preferred over any others that might be present.

In the presence of an authoritative System, usage of a non-authoritative System may lead to undefined behavior.

Returns:

true if this System is authoritative; false otherwise

See Also:

System(String, boolean)

getenv

public Map<String,String> getenv()

Returns the environment of this System as a non-null, unchanging and unmodifiable Map.

This method never returns null.

Overrides of this method must not return null.

Overrides of this method must ensure that the Map returned may be used without requiring the user to perform synchronization.

Multiple invocations of this method or any overridden variants of it are not guaranteed to return equal or identical Map instances.

The default implementation of this method returns the result of invoking System.getenv().

Returns:

the environment of this System as a non-null, unchanging and unmodifiable Map; never null

See Also:

getProperties(), System.getenv()

getProperties

public Properties getProperties()

Returns the properties of this System as a non-null, unchanging and unmodifiable Properties object.

This method never returns null.

Overrides of this method must not return null.

Callers must not mutate the Properties object that is returned. Attempts to do so may result in an UnsupportedOperationException.

Multiple invocations of this method or any overridden variants of it are not guaranteed to return equal or identical Properties instances.

The default implementation of this method returns the result of invoking System.getProperties().

Returns:

the properties of this System as a non-null, unchanging and unmodifiable Properties object; never null

See Also:

getenv(), System.getProperties()

hashCode

public int hashCode()

Returns a hashcode for this System that varies with only its name, enablement and authority.

Overrides:

hashCode in class Object

Returns:

a hashcode for this System

See Also:

equals(Object)

equals

public boolean equals(Object other)

Returns true if this System is equal to the supplied Object.

This System is deemed to be equal to an Object passed to this method if the supplied Object is an instance of System and has a name equal to the name of this System and has an enabled status equal to that of this System and has an authoritative status equal to that of this System.

Overrides:

equals in class Object

Parameters:

other - the Object to test; may be null in which case false will be returned

Returns:

true if this System is equal to the supplied Object; false otherwise

See Also:

hashCode()

getSystems

public static final Set<System> getSystems()

Returns a non-null, unchanging and unmodifiable Set of System instances as found by the Java service provider mechanism.

This method never returns null but may return an empty Set.

If one of the System instances so discovered is authoritative, then it will be the only member of the returned Set.

Multiple invocations of this method are not guaranteed to return equal or identical Set instances.

Returns:

a non-null unmodifiable Set of System instances as found by the Java service provider mechanism; never null

See Also:

isAuthoritative(), ServiceLoader.load(Class)