package com.mogujie.uni.sl;
/**
 * Created by laibao
 */
public interface Animal {
    void eat();
}  

package com.mogujie.uni.sl;
/**
 * Created by laibao
 */
public class Pig implements Animal {
  @Override
  public void eat() {
    System.out.println("Pig eating...");
  }
}

package com.mogujie.uni.sl;
/**
 * Created by laibao
 */
public class Dog implements Animal {
  @Override
  public void eat() {
    System.out.println("Dog eating...");
  }
}

com.mogujie.uni.sl.Pig
com.mogujie.uni.sl.Dog

package com.mogujie.uni;
import com.mogujie.uni.sl.Animal;
import java.util.Iterator;
import java.util.ServiceLoader;
/**
 * Created by laibao
 */
public class TestServiceLoader {
  public static void main(String[] args) {
    ServiceLoader<Animal> serviceLoader = ServiceLoader.load(Animal.class);
    Iterator<Animal> animalIterator = serviceLoader.iterator();
    while(animalIterator.hasNext()){
      Animal animal = animalIterator.next();
      animal.eat();
    }
  }
}

Pig eating...
Dog eating...

package com.mogujie.uni;

import org.apache.commons.io.IOUtils;
import java.net.URL;
import java.util.Enumeration;
import java.util.LinkedList;
import java.util.List;

/**
 * Created by laibao
 */
public class CustomServiceLoader {

  public static final String MAPPING_CONFIG_PREFIX = "META-INF/services";

  public static <S> List<S> loade(Class<S> service) throws Exception{
    String mappingConfigFile = MAPPING_CONFIG_PREFIX + "/" + service.getName() ;
    //由于一个接口的实现类可能存在多个jar包中的META-INF目录下，所以下面使用getResources返回一个URL数组
    Enumeration<URL> configFileUrls = CustomServiceLoader.class.getClassLoader().getResources(mappingConfigFile);
    if(configFileUrls == null){
      return null ;
    }
    List<S> services = new LinkedList<S>();
    while(configFileUrls.hasMoreElements()){
      URL configFileUrl = configFileUrls.nextElement();
      String configContent = IOUtils.toString(configFileUrl.openStream());
      String[] serviceNames = configContent.split("\n");
      for(String serviceName : serviceNames){
        Class serviceClass = CustomServiceLoader.class.getClassLoader().loadClass(serviceName);
        Object serviceInstance = serviceClass.newInstance();
        services.add((S)serviceInstance);
      }
    }
    return services ;
  }

}

package com.mogujie.uni;
import com.mogujie.uni.sl.Animal;
import java.util.List;
/**
 * Created by laibao
 */
public class CustomServiceLoaderTest {
  public static void main(String[] args) throws Exception {
    List<Animal> animals = CustomServiceLoader.loade(Animal.class);
    for (Animal animal : animals){
      animal.eat();
    }
  }
}

Pig eating...
Dog eating...