Module io.helidon.common

Package io.helidon.common

Class HelidonServiceLoader<T>

java.lang.Object

io.helidon.common.HelidonServiceLoader<T>

Type Parameters:

T - Type of the service to be loaded

All Implemented Interfaces:

Iterable<T>

public final class HelidonServiceLoader<T>
extends Object
implements Iterable<T>

Helidon specific support for Java Service Loaders.

This service loader:

• Can have additional implementations added
• Uses weights defined either by Weighted or by Weight
• Can have exclusions defined by an exact implementation class name, either in HelidonServiceLoader.Builder.addExcludedClass(Class) or HelidonServiceLoader.Builder.addExcludedClassName(String) or by a system property "io.helidon.common.serviceloader.exclude"<T> that defines a comma separated list of fully qualified class names to be excluded. Note that if a class implements more than one service, it would be excluded from all.

Note on weight handling

Service weight is defined by:

• Value provided in HelidonServiceLoader.Builder.addService(Object, double) (if used)
• then by Weighted.weight() if service implements it
• then by Weight annotation if present
• otherwise a default weight 100.0 from Weighted.DEFAULT_WEIGHT is used

Example:

 @Weight(4500)
 public class MyServiceImpl implements Service, Weighted {
     public double weight() {
         return 6200;
     }
 }
 

Such a service would have a weight of 6200 as that is more significant than the annotation.

A service with higher weight is returned before a service with a lower weight number. Services with the same weight have order defined by the order they are in the configured services and then as they are loaded from the ServiceLoader. Negative weights are not allowed. A service with weight 2 will be returned before a service with weight 2.

See Also:

• ServiceLoader
• builder(java.util.ServiceLoader)

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	HelidonServiceLoader.Builder<T>	Fluent api builder for HelidonServiceLoader.

Field Summary

Fields

Modifier and Type	Field	Description
static final String	SYSTEM_PROPERTY_EXCLUDE	System property used to exclude some implementation from the list of services that are configured for Java Service loader or services that are registered using HelidonServiceLoader.Builder.

Method Summary

Modifier and Type	Method	Description
List<T>	asList()	Provides a list of service implementations in weighted order.
static <T> HelidonServiceLoader.Builder<T>	builder(ServiceLoader<T> serviceLoader)	Create a builder for customizable service loader.
static <T> HelidonServiceLoader<T>	create(ServiceLoader<T> serviceLoader)	Create a weighted service loader from a Java Service loader.
void	forEach(Consumer<? super T> action)
Iterator<T>	iterator()
Stream<T>	stream()	Provides a stream of service implementations, in weighted order.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.lang.Iterable

spliterator

Field Details

SYSTEM_PROPERTY_EXCLUDE

public static final String SYSTEM_PROPERTY_EXCLUDE

System property used to exclude some implementation from the list of services that are configured for Java Service loader or services that are registered using HelidonServiceLoader.Builder.

See Also:

• Constant Field Values

Method Details

builder

public static <T> HelidonServiceLoader.Builder<T> builder(ServiceLoader<T> serviceLoader)

Create a builder for customizable service loader.

Type Parameters:

T - type of the service

Parameters:

serviceLoader - the Java Service loader used to get service implementations

Returns:

a new fluent API builder

create

public static <T> HelidonServiceLoader<T> create(ServiceLoader<T> serviceLoader)

Create a weighted service loader from a Java Service loader.

Type Parameters:

T - type of the service

Parameters:

serviceLoader - the Java service loader

Returns:

service loader with exclusions defined by system properties and no custom services

iterator

public Iterator<T> iterator()

Specified by:

iterator in interface Iterable<T>

forEach

public void forEach(Consumer<? super T> action)

Specified by:

forEach in interface Iterable<T>

asList

public List<T> asList()

Provides a list of service implementations in weighted order.

Returns:

list of service implementations

stream

public Stream<T> stream()

Provides a stream of service implementations, in weighted order.

Returns:

stream os service implementations