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(yu)一個(ge)接口的實現類可能(neng)存在(zai)多個(ge)jar包(bao)中的META-INF目錄(lu)下(xia)，所以下(xia)面使用getResources返回(hui)一個(ge)URL數組
        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...