Module io.helidon.common.serviceloader

Package io.helidon.common.serviceloader

Class HelidonServiceLoader<T>

java.lang.Object

io.helidon.common.serviceloader.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 priorities defined either by Prioritized or by Priority
• 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" 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 priority handling

Service priority is defined by:

• Value provided in HelidonServiceLoader.Builder.addService(Object, int) (if used)
• then by Prioritized.priority() if service implements it
• then by Priority annotation if present
• otherwise a default priority 5000 from Prioritized.DEFAULT_PRIORITY is used

Example:

 @Priority(4500)
 public class MyServiceImpl implements Service, Prioritized {
     public int priority() {
         return 6200;
     }
 }
 

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

A service with lower priority number is returned before a service with a higher priority number. Services with the same priority have order defined by the order they are in the configured services and then as they are loaded from the ServiceLoader. Negative priorities are not allowed. A service with priority 1 will be returned before a service with priority 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 prioritized 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 prioritized service loader from a Java Service loader.
void	forEach(Consumer<? super T> action)
Iterator<T>	iterator()

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 prioritized 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 prioritized order.

Returns:

list of service implementations