基础积累：Java SPI机制

什么是SPI

SPI 全称为 (Service Provider Interface) ，是JDK内置的一种服务提供发现机制。SPI是一种动态替换发现的机制， 比如有个接口，想运行时动态的给它添加实现，你只需要添加一个实现。我们经常遇到的就是java.sql.Driver接口，其他不同厂商可以针对同一接口做出不同的实现，mysql和postgresql都有不同的实现提供给用户，而Java的SPI机制可以为某个接口寻找服务实现。

简单示例

SPI接口

public interface ObjectSerializer {

    byte[] serialize(Object obj) throws ObjectSerializerException;

    <T> T deSerialize(byte[] param, Class<T> clazz) throws ObjectSerializerException;

    String getSchemeName();
}

SPI具体实现

public class KryoSerializer implements ObjectSerializer {

    @Override
    public byte[] serialize(Object obj) throws ObjectSerializerException {
        byte[] bytes;
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        try {
            //获取kryo对象
            Kryo kryo = new Kryo();
            Output output = new Output(outputStream);
            kryo.writeObject(output, obj);
            bytes = output.toBytes();
            output.flush();
        } catch (Exception ex) {
            throw new ObjectSerializerException("kryo serialize error" + ex.getMessage());
        } finally {
            try {
                outputStream.flush();
                outputStream.close();
            } catch (IOException e) {

            }
        }
        return bytes;
    }

    @Override
    public <T> T deSerialize(byte[] param, Class<T> clazz) throws ObjectSerializerException {
        T object;
        try (ByteArrayInputStream inputStream = new ByteArrayInputStream(param)) {
            Kryo kryo = new Kryo();
            Input input = new Input(inputStream);
            object = kryo.readObject(input, clazz);
            input.close();
        } catch (Exception e) {
            throw new ObjectSerializerException("kryo deSerialize error" + e.getMessage());
        }
        return object;
    }

    @Override
    public String getSchemeName() {
        return "kryoSerializer";
    }

}

public class JavaSerializer implements ObjectSerializer {
    @Override
    public byte[] serialize(Object obj) throws ObjectSerializerException {
        ByteArrayOutputStream arrayOutputStream;
        try {
            arrayOutputStream = new ByteArrayOutputStream();
            ObjectOutput objectOutput = new ObjectOutputStream(arrayOutputStream);
            objectOutput.writeObject(obj);
            objectOutput.flush();
            objectOutput.close();
        } catch (IOException e) {
            throw new ObjectSerializerException("JAVA serialize error " + e.getMessage());
        }
        return arrayOutputStream.toByteArray();
    }

    @Override
    public <T> T deSerialize(byte[] param, Class<T> clazz) throws ObjectSerializerException {
        ByteArrayInputStream arrayInputStream = new ByteArrayInputStream(param);
        try {
            ObjectInput input = new ObjectInputStream(arrayInputStream);
            return (T) input.readObject();
        } catch (IOException | ClassNotFoundException e) {
            throw new ObjectSerializerException("JAVA deSerialize error " + e.getMessage());
        }
    }

    @Override
    public String getSchemeName() {
        return "javaSerializer";
    }

}

增加META-INF目录文件

Resource下面创建META-INF/services 目录里创建一个以服务接口命名的文件com.skipper.ObjectSerializer
内容为

com.skipper.KryoSerializer
com.skipper.JavaSerializer

Service类

@Service
public class SerializerService {


    public ObjectSerializer getObjectSerializer() {
        ServiceLoader<ObjectSerializer> serializers = ServiceLoader.load(ObjectSerializer.class);

        final Optional<ObjectSerializer> serializer = StreamSupport.stream(serializers.spliterator(), false)
                .findFirst();

        return serializer.orElse(new JavaSerializer());
    }
}

测试类

@Autowired
    private SerializerService serializerService;

    @Test
    public void serializerTest() throws ObjectSerializerException {
        ObjectSerializer objectSerializer = serializerService.getObjectSerializer();
        System.out.println(objectSerializer.getSchemeName());
        byte[] arrays = objectSerializer.serialize(Arrays.asList("1", "2", "3"));
        ArrayList list = objectSerializer.deSerialize(arrays, ArrayList.class);
        Assert.assertArrayEquals(Arrays.asList("1", "2", "3").toArray(), list.toArray());
    }

结果为 kryoSerializer