ServiceLoader

Class Overview

A service-provider loader.

A service provider is a factory for creating all known implementations of a particular class or interface S . The known implementations are read from a configuration file in META-INF/services/ . The file's name should match the class' binary name (such as java.util.Outer$Inner ).

The file format is as follows. The file's character encoding must be UTF-8. Whitespace is ignored, and # is used to begin a comment that continues to the next newline. Lines that are empty after comment removal and whitespace trimming are ignored. Otherwise, each line contains the binary name of one implementation class. Duplicate entries are ignored, but entries are otherwise returned in order (that is, the file is treated as an ordered set).

Given these classes:

        package a.b.c;
 public interface MyService { ... }
 public class MyImpl1 implements MyService { ... }
 public class MyImpl2 implements MyService { ... }
       

        # Known MyService providers.
 a.b.c.MyImpl1  # The original implementation for handling "bar"s.
 a.b.c.MyImpl2  # A later implementation for "foo"s.
       

        for (MyService service : ServiceLoader
        
         .load(MyService.class)) {
     if (service.supports(o)) {
       return service.handle(o);
     }
   }
        
       

Note that each iteration creates new instances of the various service implementations, so any heavily-used code will likely want to cache the known implementations itself and reuse them. Note also that the candidate classes are instantiated lazily as you call next on the iterator: construction of the iterator itself does not instantiate any of the providers.

Summary

[Expand] Inherited Methods
From class java.lang.Object Object clone () Creates and returns a copy of this Object . boolean equals ( Object o) Compares this instance with the specified object and indicates if they are equal. void finalize () Invoked when the garbage collector has detected that this instance is no longer reachable. final Class <?> getClass () Returns the unique instance of Class that represents this object's class. int hashCode () Returns an integer hash code for this object. final void notify () Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll () Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString () Returns a string containing a concise, human-readable description of this object. final void wait () Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait (long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait (long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
From interface java.lang.Iterable abstract Iterator <T> iterator () Returns an Iterator for the elements in this object.