一个实现类里需要依赖另一个 @SPI 接口的实例,怎么办?
如下示例,你需要写一个 set 方法:
public class OrderServiceImpl implements OrderService {
private InfoService infoService;//是dubbo的扩展点,是spring的bean接口
public void setInfoService(InfoService infoService) {
this.infoService = infoService;
}
}
Dubbo 源码阅读(一)getExtensionLoader 和 getExtension 里,看 createExtension 方法,可以看到,里面有一步是 injectExtension(instance);
为什么要写一个 setXX 方法,原因就在这里面:
private T injectExtension(T instance) {
try {
if (objectFactory != null) {
for (Method method : instance.getClass().getMethods()) {
//如果有一个方法以set开头,入参长度为1
if (method.getName().startsWith("set")
&& method.getParameterTypes().length == 1
&& Modifier.isPublic(method.getModifiers())) {
/**
* Check {@link DisableInject} to see if we need auto injection for this property
*/
if (method.getAnnotation(DisableInject.class) != null) {
continue;
}
Class<?> pt = method.getParameterTypes()[0];
try {
//拿到入参方法set后面的字符串,首字母小写
String property = method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";
//先拿property的Extension
Object object = objectFactory.getExtension(pt, property);
if (object != null) {
method.invoke(instance, object);
}
} catch (Exception e) {
logger.error("fail to inject via method " + method.getName()
+ " of interface " + type.getName() + ": " + e.getMessage(), e);
}
}
}
}
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
return instance;
}
跟 getExtension:
@SPI
public interface ExtensionFactory {
/**
* Get extension.
*
* @param type object type.
* @param name object name.
* @return object instance.
*/
<T> T getExtension(Class<T> type, String name);
}
它有3个实现:
其中,AdaptiveExtensionFactory 是打了 @Adaptive 注解的,说明它是被优先实现的,但是在。
@Adaptive
public class AdaptiveExtensionFactory implements ExtensionFactory {
private final List<ExtensionFactory> factories;
public AdaptiveExtensionFactory() {
//拿到所有的ExtensionFactory实例
ExtensionLoader<ExtensionFactory> loader = ExtensionLoader.getExtensionLoader(ExtensionFactory.class);
List<ExtensionFactory> list = new ArrayList<ExtensionFactory>();
for (String name : loader.getSupportedExtensions()) {
list.add(loader.getExtension(name));
}
factories = Collections.unmodifiableList(list);
}
@Override
public <T> T getExtension(Class<T> type, String name) {
//SpiExtensionFactory SpringExtensionFactory
for (ExtensionFactory factory : factories) {
T extension = factory.getExtension(type, name);
if (extension != null) {
//如果能通过SpiExtensionFactory得到直接返回
return extension;
}
}
return null;
}
}
AdaptiveExtensionFactory 在哪里创建的呢? 在创建 ExtensionLoader 的时候
private ExtensionLoader(Class<?> type) {
this.type = type;
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}
回到上一段代码,跟 getSupportedExtensions:
public Set<String> getSupportedExtensions() {
//别名
Map<String, Class<?>> clazzes = getExtensionClasses();
//按别名排序
return Collections.unmodifiableSet(new TreeSet<String>(clazzes.keySet()));
//SpiExtensionFactory 在前面
//SpringExtensionFactory 在后面
}
再看看 SpiExtensionFactory 和 SpringExtensionFactory 的 getExtension:
类 SpiExtensionFactory
public class SpiExtensionFactory implements ExtensionFactory {
@Override
public <T> T getExtension(Class<T> type, String name) {
if (type.isInterface() && type.isAnnotationPresent(SPI.class)) {
ExtensionLoader<T> loader = ExtensionLoader.getExtensionLoader(type);
if (!loader.getSupportedExtensions().isEmpty()) {
return loader.getAdaptiveExtension();
}
}
return null;
}
}
类 SpringExtensionFactory
@Override
@SuppressWarnings("unchecked")
public <T> T getExtension(Class<T> type, String name) {
for (ApplicationContext context : contexts) {
if (context.containsBean(name)) {
Object bean = context.getBean(name);
if (type.isInstance(bean)) {
return (T) bean;
}
}
}
logger.warn("No spring extension (bean) named:" + name + ", try to find an extension (bean) of type " + type.getName());
if (Object.class == type) {
return null;
}
for (ApplicationContext context : contexts) {
try {
return context.getBean(type);
} catch (NoUniqueBeanDefinitionException multiBeanExe) {
logger.warn("Find more than 1 spring extensions (beans) of type " + type.getName() + ", will stop auto injection. Please make sure you have specified the concrete parameter type and there's only one extension of that type.");
} catch (NoSuchBeanDefinitionException noBeanExe) {
if (logger.isDebugEnabled()) {
logger.debug("Error when get spring extension(bean) for type:" + type.getName(), noBeanExe);
}
}
}
logger.warn("No spring extension (bean) named:" + name + ", type:" + type.getName() + " found, stop get bean.");
return null;
}