半日闲

因过竹院逢僧话，又得浮生半日闲

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发表于 分类于 ， ，

逻辑解析

  1. 判断SPI类信息是否符合扩展点规范， 判断是否为空， 判断是否为接口， 判断是否被SPI注解修饰
  2. 在扩展点实例缓存中获取类的扩展实例，如果存在，直接返回；如果不存在，则为该SPI接口创建一个扩展点类实例，在返回。
  3. 在创建SPI接口的扩展点类实例的时候，需要判断该SPI是否为ExtensionFactory，如果是，则成员变量ObjectFactory不赋值， 否则，创建一个objectFactory的适配实例 实例化过程。

    相关代码

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    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() + "!");
        }
        //如果存在，直接返回，如果不存在，创建一个再返回
        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;
    }
    //实例化
    private ExtensionLoader(Class<?> type) {
        this.type = type;
        objectFactory =
                (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
    }
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发表于 分类于 ， ， 
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//名称分隔器正则
private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");

//扩展点加载器缓存
private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<>(64);

//扩展点实例缓存
private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<>(64);

//SPI接口
private final Class<?> type;


private final ExtensionFactory objectFactory;

//单个SPI接口缓存到的扩展点名称
private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<>();

//单个SPI接口实现类缓存
private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<>();

//activate实现类缓存
private final Map<String, Object> cachedActivates = new ConcurrentHashMap<>();
//SPI实现类实例缓存
private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<>();
//adaptive实例缓存
private final Holder<Object> cachedAdaptiveInstance = new Holder<>();
//adaptive包装类缓存
private volatile Class<?> cachedAdaptiveClass = null;
//默认扩展名缓存
private String cachedDefaultName;
//创建adaptive适配实例异常错误
private volatile Throwable createAdaptiveInstanceError;

//SPI实现类包装类缓存
private Set<Class<?>> cachedWrapperClasses;

//异常集合
private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<>();


/**
 * Record all unacceptable exceptions when using SPI
 */
private Set<String> unacceptableExceptions = new ConcurrentHashSet<>();

//扩展点加载策略 采用传统spi技术加载
private static volatile LoadingStrategy[] strategies = loadLoadingStrategies();