nosum-gateway/src/main/java/cn/nosum/common/extension/ExtensionLoader.java

package cn.nosum.common.extension;

import cn.nosum.common.annotation.Adaptive;
import cn.nosum.common.annotation.DisableInject;
import cn.nosum.common.annotation.SPI;
import cn.nosum.common.util.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
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;

/**
 * Load gateway ExtensionLoader
 * @param <T>
 */
public class ExtensionLoader<T> {
    private static final Logger logger= LoggerFactory.getLogger(ExtensionLoader.class);

    // 需要扫描的路径
    private static final String GATEWAY_DIRECTORY = "META-INF/gateway/";

    private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");

    // 缓存
    private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<>();
    private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<>();
    private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<>();
    private final Holder<Object> cachedAdaptiveInstance = new Holder<>();
    private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<>();
    private Set<Class<?>> cachedWrapperClasses;

    private final ExtensionFactory objectFactory;
    private volatile Class<?> cachedAdaptiveClass = null;
    private final Class<?> type;
    private String cachedDefaultName;
    // 记录错误信息
    private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<>();
    private volatile Throwable createAdaptiveInstanceError;

    private ExtensionLoader(Class<?> type) {
        this.type = type;
        objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
    }

    @SuppressWarnings("unchecked")
    public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
        if (type == null) {
            throw new IllegalArgumentException("Extension type == null");
        }
        if (!type.isInterface()) {
            throw new IllegalArgumentException("Extension type (" + type + ") is not an interface!");
        }
        if (!withExtensionAnnotation(type)) {
            throw new IllegalArgumentException("Extension type (" + type +
                    ") is not an extension, because it is NOT annotated with @" + SPI.class.getSimpleName() + "!");
        }

        ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
        if (loader == null) {
            EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
            loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
        }
        return loader;
    }

    @SuppressWarnings("unchecked")
    public T getExtension(String name) {
        if (StringUtils.isEmpty(name)) {
            throw new IllegalArgumentException("Extension name == null");
        }
        if ("true".equals(name)) {
            return getDefaultExtension();
        }
        final Holder<Object> holder = getOrCreateHolder(name);
        Object instance = holder.get();
        if (instance == null) {
            synchronized (holder) {
                instance = holder.get();
                if (instance == null) {
                    instance = createExtension(name);
                    holder.set(instance);
                }
            }
        }
        return (T) instance;
    }

    private Holder<Object> getOrCreateHolder(String name) {
        Holder<Object> holder = cachedInstances.get(name);
        if (holder == null) {
            cachedInstances.putIfAbsent(name, new Holder<>());
            holder = cachedInstances.get(name);
        }
        return holder;
    }

    private T createExtension(String name) {
        Class<?> clazz = getExtensionClasses().get(name);
        if (clazz == null) {
            throw new NullPointerException(name);
        }
        try {
            T instance = (T) EXTENSION_INSTANCES.get(clazz);
            if (instance == null) {
                EXTENSION_INSTANCES.putIfAbsent(clazz, clazz.newInstance());
                instance = (T) EXTENSION_INSTANCES.get(clazz);
            }
            injectExtension(instance);
            Set<Class<?>> wrapperClasses = cachedWrapperClasses;
            if (CollectionUtils.isNotEmpty(wrapperClasses)) {
                for (Class<?> wrapperClass : wrapperClasses) {
                    instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
                }
            }
            return instance;
        } catch (Throwable t) {
            throw new IllegalStateException("Extension instance (name: " + name + ", class: " +
                    type + ") couldn't be instantiated: " + t.getMessage(), t);
        }
    }

    /**
     * 实现依赖注入
     * @param instance 需要进行依赖注入的实例
     */
    private T injectExtension(T instance) {
        try {
            if (objectFactory != null) {
                for (Method method : instance.getClass().getMethods()) {
                    if (isSetter(method)) {
                        // 存在 @DisableInject 则跳过
                        if (method.getAnnotation(DisableInject.class) != null) {
                            continue;
                        }
                        Class<?> pt = method.getParameterTypes()[0];
                        if (ReflectUtils.isPrimitives(pt)) {
                            continue;
                        }
                        try {
                            String property = getSetterProperty(method);
                            Object object = objectFactory.getExtension(pt, property);
                            if (object != null) {
                                method.invoke(instance, object);
                            }
                        } catch (Exception e) {
                            logger.error("Failed to inject via method " + method.getName()
                                    + " of interface " + type.getName() + ": " + e.getMessage(), e);
                        }
                    }
                }
            }
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
        }
        return instance;
    }


    /**
     * @return 根据默认扩展名获取到的实例
     */
    public T getDefaultExtension() {
        getExtensionClasses();
        if (StringUtils.isEmpty(cachedDefaultName) || "true".equals(cachedDefaultName)) {
            return null;
        }
        return getExtension(cachedDefaultName);
    }

    /**
     * @return 获取自适应扩展点
     */
    @SuppressWarnings("unchecked")
    public T getAdaptiveExtension() {
        Object instance = cachedAdaptiveInstance.get();
        if (instance == null) {
            if (createAdaptiveInstanceError == null) {
                synchronized (cachedAdaptiveInstance) {
                    instance = cachedAdaptiveInstance.get();
                    if (instance == null) {
                        try {
                            instance = createAdaptiveExtension();
                            cachedAdaptiveInstance.set(instance);
                        } catch (Throwable t) {
                            createAdaptiveInstanceError = t;
                            throw new IllegalStateException("Failed to create adaptive instance: " + t.toString(), t);
                        }
                    }
                }
            } else {
                throw new IllegalStateException("Failed to create adaptive instance: " + createAdaptiveInstanceError.toString(), createAdaptiveInstanceError);
            }
        }

        return (T) instance;
    }

    @SuppressWarnings("unchecked")
    private T createAdaptiveExtension() {
        try {
            return injectExtension((T) getAdaptiveExtensionClass().newInstance());
        } catch (Exception e) {
            throw new IllegalStateException("Can't create adaptive extension " + type + ", cause: " + e.getMessage(), e);
        }
    }

    /**
     * 获取自适应扩展点
     */
    private Class<?> getAdaptiveExtensionClass() {
        getExtensionClasses();
        if (cachedAdaptiveClass != null) {
            return cachedAdaptiveClass;
        }
        return null;
    }

    private Map<String, Class<?>> getExtensionClasses() {
        Map<String, Class<?>> classes = cachedClasses.get();
        if (classes == null) {
            synchronized (cachedClasses) {
                classes = cachedClasses.get();
                if (classes == null) {
                    classes = loadExtensionClasses();
                    cachedClasses.set(classes);
                }
            }
        }
        return classes;
    }


    /**
     * 如果存在默认扩展名，提取并且缓存
     */
    private void cacheDefaultExtensionName() {
        String value;
        if (StringUtils.isEmpty(value=PropertiesUtil.getProperty(type.getName()))){
            final SPI defaultAnnotation = type.getAnnotation(SPI.class);
            if (defaultAnnotation != null) {
                value = defaultAnnotation.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) {
                        cachedDefaultName = names[0];
                    }
                }
            }
        }else{
            cachedDefaultName=value;
        }
    }

    // synchronized in getExtensionClasses
    private Map<String, Class<?>> loadExtensionClasses() {
        cacheDefaultExtensionName();
        Map<String, Class<?>> extensionClasses = new HashMap<>();
        loadDirectory(extensionClasses, GATEWAY_DIRECTORY, type.getName());
        return extensionClasses;
    }

    private void loadDirectory(Map<String, Class<?>> extensionClasses, String dir, String type) {
        String fileName = dir + type;
        try {
            Enumeration<URL> urls;
            ClassLoader classLoader = findClassLoader();
            if (classLoader != null) {
                urls = classLoader.getResources(fileName);
            } else {
                urls = ClassLoader.getSystemResources(fileName);
            }
            if (urls != null) {
                while (urls.hasMoreElements()) {
                    java.net.URL resourceURL = urls.nextElement();
                    loadResource(extensionClasses, classLoader, resourceURL);
                }
            }
        } catch (Throwable t) {
            logger.error("Exception occurred when loading extension class (interface: " +
                    type + ", description file: " + fileName + ").", t);
        }
    }

    private void loadResource(Map<String, Class<?>> extensionClasses, ClassLoader classLoader, java.net.URL resourceURL) {
        try {
            try (BufferedReader reader = new BufferedReader(new InputStreamReader(resourceURL.openStream(), StandardCharsets.UTF_8))) {
                String line;
                while ((line = reader.readLine()) != null) {
                    final int ci = line.indexOf('#');
                    if (ci >= 0) {
                        line = line.substring(0, ci);
                    }
                    line = line.trim();
                    if (line.length() > 0) {
                        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) {
                                loadClass(extensionClasses, resourceURL, Class.forName(line, true, classLoader), name);
                            }
                        } catch (Throwable t) {
                            IllegalStateException e = new IllegalStateException("Failed to load extension class (interface: " + type + ", class line: " + line + ") in " + resourceURL + ", cause: " + t.getMessage(), t);
                            exceptions.put(line, e);
                        }
                    }
                }
            }
        } catch (Throwable t) {
            logger.error("Exception occurred when loading extension class (interface: " +
                    type + ", class file: " + resourceURL + ") in " + resourceURL, t);
        }
    }

    private void loadClass(Map<String, Class<?>> extensionClasses, java.net.URL resourceURL, Class<?> clazz, String name) throws NoSuchMethodException {
        if (!type.isAssignableFrom(clazz)) {
            throw new IllegalStateException("Error occurred when loading extension class (interface: " +
                    type + ", class line: " + clazz.getName() + "), class "
                    + clazz.getName() + " is not subtype of interface.");
        }
        if (clazz.isAnnotationPresent(Adaptive.class)) {
            cacheAdaptiveClass(clazz,name);
        } else if (isWrapperClass(clazz)) {
            cacheWrapperClass(clazz);
        }
    }

    private void cacheAdaptiveClass(Class<?> clazz,String name) {
        // 只有名称匹配时才会进行保存
        if (cachedAdaptiveClass == null && name.equals(cachedDefaultName)) {
            cachedAdaptiveClass = clazz;
        } else if (!cachedAdaptiveClass.equals(clazz)) {
            throw new IllegalStateException("More than 1 adaptive class found: "
                    + cachedAdaptiveClass.getClass().getName()
                    + ", " + clazz.getClass().getName());
        }
    }

    private void cacheWrapperClass(Class<?> clazz) {
        if (cachedWrapperClasses == null) {
            cachedWrapperClasses = new HashSet<>();
        }
        cachedWrapperClasses.add(clazz);
    }

    private boolean isWrapperClass(Class<?> clazz) {
        try {
            clazz.getConstructor(type);
            return true;
        } catch (NoSuchMethodException e) {
            return false;
        }
    }

    private boolean isSetter(Method method) {
        return method.getName().startsWith("set")
                && method.getParameterTypes().length == 1
                && Modifier.isPublic(method.getModifiers());
    }

    private static ClassLoader findClassLoader() {
        return ClassUtils.getClassLoader(ExtensionLoader.class);
    }

    private static <T> boolean withExtensionAnnotation(Class<T> type) {
        return type.isAnnotationPresent(SPI.class);
    }

    private String getSetterProperty(Method method) {
        return method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";
    }

    public Set<String> getSupportedExtensions() {
        Map<String, Class<?>> clazzes = getExtensionClasses();
        return Collections.unmodifiableSet(new TreeSet<>(clazzes.keySet()));
    }
}