diff --git a/src/main/java/io/github/ehlxr/extension/ExtensionLoader.java b/src/main/java/io/github/ehlxr/extension/ExtensionLoader.java
new file mode 100644
index 0000000..05f963c
--- /dev/null
+++ b/src/main/java/io/github/ehlxr/extension/ExtensionLoader.java
@@ -0,0 +1,379 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2020 xrv <xrg@live.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package io.github.ehlxr.extension;
+
+import io.netty.util.internal.StringUtil;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.regex.Pattern;
+
+/**
+ * 加载和管理扩展（简化版 Dubbo SPI）
+ *
+ * @author ehlxr
+ */
+@SuppressWarnings("unused")
+public class ExtensionLoader<T> {
+    private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);
+
+    private static final String EXTENSIONS_DIRECTORY = "META-INF/extensions/";
+    private static final String EXTENSIONS_INTERNAL_DIRECTORY = "META-INF/extensions/internal/";
+
+    private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*,+\\s*");
+
+    private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<>();
+    private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<>();
+
+    private final Class<T> type;
+    private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<>();
+    private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<>();
+    private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<>();
+    private final Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<>();
+    private String defaultExtension;
+
+    private ExtensionLoader(Class<T> type) {
+        this.type = type;
+    }
+
+    /**
+     * {@link ExtensionLoader} 的工厂方法。
+     *
+     * @param type 扩展点接口类型
+     * @param <T>  扩展点类型
+     * @return {@link ExtensionLoader} 实例
+     * @throws IllegalArgumentException 参数为 <code>null</code>；
+     *                                  或是扩展点接口上没有 {@link SPI} 注解。
+     */
+    @SuppressWarnings("unchecked")
+    public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
+        if (type == null) {
+            throw new IllegalArgumentException("SPI type == null");
+        }
+        if (!type.isInterface()) {
+            throw new IllegalArgumentException("SPI type(" + type.getName() + ") is not interface!");
+        }
+        if (!type.isAnnotationPresent(SPI.class)) {
+            throw new IllegalArgumentException("type(" + type.getName() +
+                    ") is not a extension, because WITHOUT @SPI Annotation!");
+        }
+
+        ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
+        if (loader == null) {
+            EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<>(type));
+            loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
+        }
+        return loader;
+    }
+
+    /**
+     * Get the String of Throwable, like the output of {@link Throwable#printStackTrace()}.
+     *
+     * @param throwable the input throwable.
+     */
+    private static String throwable2String(Throwable throwable) {
+        StringWriter w = new StringWriter(1024);
+        try (PrintWriter p = new PrintWriter(w)) {
+            throwable.printStackTrace(p);
+            return w.toString();
+        }
+    }
+
+    public T getExtension(String name) {
+        if (StringUtil.isNullOrEmpty(name)) {
+            throw new IllegalArgumentException("SPI name == null");
+        }
+
+        Holder<Object> holder = cachedInstances.get(name);
+        if (holder == null) {
+            cachedInstances.putIfAbsent(name, new Holder<>());
+            holder = cachedInstances.get(name);
+        }
+
+        Object instance = holder.get();
+        if (instance == null) {
+            synchronized (cachedInstances) {
+                instance = holder.get();
+                if (instance == null) {
+                    instance = createExtension(name);
+                    holder.set(instance);
+                }
+            }
+        }
+        //noinspection unchecked
+        return (T) instance;
+    }
+
+    /**
+     * 返回缺省的扩展。
+     *
+     * @throws IllegalStateException 指定的扩展没有设置缺省扩展点
+     */
+    public T getDefaultExtension() {
+        loadExtensionClasses0();
+
+        if (null == defaultExtension || defaultExtension.length() == 0) {
+            throw new IllegalStateException("No default extension on extension " + type.getName());
+        }
+        return getExtension(defaultExtension);
+    }
+
+    /**
+     * 获取扩展点实现的所有扩展点名。
+     *
+     * @since 0.1.0
+     */
+    public Set<String> getSupportedExtensions() {
+        Map<String, Class<?>> classes = getExtensionClasses();
+        return Collections.unmodifiableSet(new HashSet<>(classes.keySet()));
+    }
+
+    public String getExtensionName(Class<?> spi) {
+        getExtensionClasses();
+        return cachedNames.get(spi);
+    }
+
+    private T createExtension(String name) {
+        Class<?> clazz = getExtensionClasses().get(name);
+        if (clazz == null) {
+            throw findExtensionClassLoadException(name);
+        }
+        try {
+            //noinspection unchecked
+            T instance = (T) EXTENSION_INSTANCES.get(clazz);
+            if (instance == null) {
+                EXTENSION_INSTANCES.putIfAbsent(clazz, clazz.newInstance());
+                //noinspection unchecked
+                instance = (T) EXTENSION_INSTANCES.get(clazz);
+            }
+
+            return instance;
+        } catch (Throwable t) {
+            throw new IllegalStateException("SPI instance(name: " + name + ", class: " +
+                    type + ")  could not be instantiated: " + t.getMessage(), t);
+        }
+    }
+
+    private Map<String, Class<?>> getExtensionClasses() {
+        Map<String, Class<?>> classes = cachedClasses.get();
+        if (classes == null) {
+            synchronized (cachedClasses) {
+                classes = cachedClasses.get();
+                if (classes == null) {
+                    loadExtensionClasses0();
+                    classes = cachedClasses.get();
+                }
+            }
+        }
+        return classes;
+    }
+
+    private IllegalStateException findExtensionClassLoadException(String name) {
+        for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
+            if (entry.getKey().toLowerCase().contains(name.toLowerCase())) {
+                return entry.getValue();
+            }
+        }
+
+        int i = 1;
+        StringBuilder buf = new StringBuilder("No such extension " + type.getName() + " by name " + name);
+        for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
+            if (i == 1) {
+                buf.append(", possible causes: ");
+            }
+
+            buf.append("\r\n(");
+            buf.append(i++);
+            buf.append(") ");
+            buf.append(entry.getKey());
+            buf.append(":\r\n");
+            buf.append(throwable2String(entry.getValue()));
+        }
+        return new IllegalStateException(buf.toString());
+    }
+
+    private void loadExtensionClasses0() {
+        final SPI annotation = type.getAnnotation(SPI.class);
+        if (annotation != null) {
+            String value = annotation.value();
+            if ((value = value.trim()).length() > 0) {
+                String[] names = NAME_SEPARATOR.split(value);
+                if (names.length > 1) {
+                    throw new IllegalStateException("more than 1 default extension name on extension " +
+                            type.getName() + ": " + Arrays.toString(names));
+                }
+                if (names.length == 1 && names[0].trim().length() > 0) {
+                    defaultExtension = names[0].trim();
+                }
+            }
+        }
+
+        Map<String, Class<?>> extensionClasses = new HashMap<>();
+        loadFile(extensionClasses, EXTENSIONS_DIRECTORY);
+        loadFile(extensionClasses, EXTENSIONS_INTERNAL_DIRECTORY);
+        cachedClasses.set(extensionClasses);
+    }
+
+    private void loadFile(Map<String, Class<?>> extensionClasses, String dir) {
+        String fileName = dir + type.getName();
+        try {
+            Enumeration<URL> urls;
+            ClassLoader classLoader = ExtensionLoader.class.getClassLoader();
+            if (classLoader != null) {
+                urls = classLoader.getResources(fileName);
+            } else {
+                urls = ClassLoader.getSystemResources(fileName);
+            }
+
+            if (urls != null) {
+                while (urls.hasMoreElements()) {
+                    URL url = urls.nextElement();
+
+                    try (
+                            BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), StandardCharsets.UTF_8))
+                    ) {
+                        String line;
+                        while ((line = reader.readLine()) != null) {
+                            // delete comments
+                            final int ci = line.indexOf('#');
+                            if (ci >= 0) {
+                                line = line.substring(0, ci);
+                            }
+                            line = line.trim();
+                            if (line.length() == 0) {
+                                continue;
+                            }
+
+                            try {
+                                String name = null;
+                                int i = line.indexOf('=');
+
+                                if (i > 0) {
+                                    name = line.substring(0, i).trim();
+                                    line = line.substring(i + 1).trim();
+                                }
+
+                                if (line.length() > 0) {
+                                    Class<? extends T> clazz = Class.forName(line, true, classLoader).asSubclass(type);
+                                    if (!type.isAssignableFrom(clazz)) {
+                                        throw new IllegalStateException("Error when load extension class(interface: " +
+                                                type.getName() + ", class line: " + clazz.getName() + "), class "
+                                                + clazz.getName() + "is not subtype of interface.");
+                                    }
+
+                                    if (name == null || name.length() == 0) {
+                                        // clazz: xxx.xxx.ZfyAPI
+                                        // type: xxx.xxx.API
+                                        // -> name: zfy
+                                        if (clazz.getSimpleName().length() > type.getSimpleName().length()
+                                                && clazz.getSimpleName().endsWith(type.getSimpleName())) {
+                                            name = clazz.getSimpleName().substring(0, clazz.getSimpleName().length()
+                                                    - type.getSimpleName().length()).toLowerCase();
+                                        } else {
+                                            throw new IllegalStateException("No such extension name for the class "
+                                                    + clazz.getName() + " in the config " + url);
+                                        }
+                                    }
+
+
+                                    if (!cachedNames.containsKey(clazz)) {
+                                        cachedNames.put(clazz, name);
+                                    }
+
+                                    Class<?> c = extensionClasses.get(name);
+                                    if (c == null) {
+                                        extensionClasses.put(name, clazz);
+                                    } else if (c != clazz) {
+                                        throw new IllegalStateException("Duplicate extension "
+                                                + type.getName() + " name " + name + " on " + c.getName()
+                                                + " and " + clazz.getName());
+                                    }
+                                }
+                            } catch (Throwable t) {
+                                IllegalStateException e = new IllegalStateException("Failed to load extension class(interface: "
+                                        + type + ", class line: " + line + ") in " + url + ", cause: " + t.getMessage(), t);
+                                exceptions.put(line, e);
+                            }
+                        }
+                    } catch (Throwable t) {
+                        logger.error("Exception when load extension class(interface: " +
+                                type + ", class file: " + url + ") in " + url, t);
+                    }
+                }
+            }
+        } catch (Throwable t) {
+            logger.error("Exception when load extension class(interface: " +
+                    type + ", description file: " + fileName + ").", t);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return this.getClass().getName() + "[" + type.getName() + "]";
+    }
+
+    /**
+     * Holds a value of type <code>T</code>.
+     */
+    @SuppressWarnings("unused")
+    private static final class Holder<T> {
+        /**
+         * The value contained in the holder.
+         */
+        private volatile T value;
+
+        /**
+         * Creates a new holder with a <code>null</code> value.
+         */
+        Holder() {
+        }
+
+        /**
+         * Create a new holder with the specified value.
+         *
+         * @param value The value to be stored in the holder.
+         */
+        public Holder(T value) {
+            this.value = value;
+        }
+
+        public T get() {
+            return value;
+        }
+
+        public void set(T value) {
+            this.value = value;
+        }
+    }
+}
diff --git a/src/main/java/io/github/ehlxr/extension/SPI.java b/src/main/java/io/github/ehlxr/extension/SPI.java
new file mode 100644
index 0000000..69fdfb5
--- /dev/null
+++ b/src/main/java/io/github/ehlxr/extension/SPI.java
@@ -0,0 +1,48 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2020 xrv <xrg@live.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package io.github.ehlxr.extension;
+
+import io.github.ehlxr.did.extension.ExtensionLoader;
+
+import java.lang.annotation.*;
+
+/**
+ * 把一个接口标识成扩展点。
+ * <p>
+ * 没有此注释的接口 {@link ExtensionLoader} 会拒绝接管
+ *
+ * @author ehlxr
+ * @see ExtensionLoader
+ */
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.TYPE})
+public @interface SPI {
+
+    /**
+     * the default extension name.
+     */
+    String value() default "";
+}