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扩展点加载机制 - ExtensionLoader
例子
@Bean
public ObjectSerializer objectSerializer() {
return ExtensionLoader.getExtensionLoader(ObjectSerializer.class)
.getActivateExtension(env.getProperty("recover.serializer.support"));
}public final class ExtensionLoader<T> {
private Class<T> type;
private ExtensionLoader(final Class<T> type) {
this.type = type;
}
private static <T> boolean withExtensionAnnotation(final Class<T> type) {
return type.isAnnotationPresent(NickSPI.class);
}
/**
* Gets extension loader.
*
* @param <T> the type parameter
* @param type the type
* @return the extension loader
*/
public static <T> ExtensionLoader<T> getExtensionLoader(final Class<T> type) {
if (type == null) {
throw new NickException("type == null");
}
if (!type.isInterface()) {
throw new NickException("Extension type(" + type + ") not interface!");
}
if (!withExtensionAnnotation(type)) {
throw new NickException("type" + type.getName() + "not exist");
}
return new ExtensionLoader<>(type);
}
/**
* Gets activate extension.
*
* @param value the value
* @return the activate extension
*/
public T getActivateExtension(final String value) {
ServiceLoader<T> loader = ServiceBootstrap.loadAll(type);
return StreamSupport.stream(loader.spliterator(), false)
.filter(e -> Objects.equals(e.getClass()
.getAnnotation(NickSPI.class).value(), value))
.findFirst().orElseThrow(() -> new NickException("Please check your configuration"));
}
}public class ServiceBootstrap {
/**
* Load first s.
*
* @param <S> the type parameter
* @param clazz the clazz
* @return the s
*/
public static <S> S loadFirst(final Class<S> clazz) {
final ServiceLoader<S> loader = loadAll(clazz);
final Iterator<S> iterator = loader.iterator();
if (!iterator.hasNext()) {
throw new IllegalStateException(String.format(
"No implementation defined in /META-INF/services/%s, please check whether the file exists and has the right implementation class!",
clazz.getName()));
}
return iterator.next();
}
/**
* Load all service loader.
*
* @param <S> the type parameter
* @param clazz the clazz
* @return the service loader
*/
public static <S> ServiceLoader<S> loadAll(final Class<S> clazz) {
return ServiceLoader.load(clazz);
}
}