Dubbo拓展点加载机制
Java SPI(Service Provider Interface)
(1)接口
public interface SPIService {
public void printService();
}
(2)接口实现1
public class SPIServiceImpl implements SPIService {
public void printService() {
System.out.println("Hello World");
}
}
(3)接口实现2
public class SPIServiceImpl2 implements SPIService {
public void printService() {
System.out.println("Hello World2");
}
}
(4)接口实现2
public class SPIServiceImpl3 implements SPIService {
public void printService() {
System.out.println("Hello World3");
}
}
(5)在resource目录下建立META-INF/services目录，建立接口的全路径名文件(这里是gdut.ff.spi.SPIService)，在文件里以分行符分隔接口实现类的全路径名。
(6)Main方法
import java.util.ServiceLoader;
public class SPIServiceMain {
public static void main(String[] args) {
ServiceLoader<SPIService> serviceLoader = ServiceLoader.load(SPIService.class);
for (SPIService spiService:serviceLoader) {
spiService.printService();
}
}
}
java.util.ServiceLoader可以获取接口的全部实现，具体调用哪个实现是用户在META-INF/services中配置。
Dubbo SPI
(1)在接口上添加注解@SPI
import org.apache.dubbo.common.extension.SPI;
@SPI("spiServiceImpl")
public interface SPIService {
public void printService();
}
(2)在META-INF/dubbo/internal文件夹下建立全路径名配置文件，内容如下
spiServiceImpl=gdut.ff.spi.SPIServiceImpl
(3)Main方法:通过ExtensionLoader获取接口SPIService.class的默认实现
public class SPIServiceMain {
public static void main(String[] args) {
SPIService defaultExtension = ExtensionLoader.getExtensionLoader(SPIService.class).getDefaultExtension();
defaultExtension.printService();
}
}
Java SPI 和 Dubbo SPI 对比
(1) Java SPI会一次性实例化所有拓展点的实现，而Dubbo SPI并不会立即全部初始化。
(2) Dubbo SPI实现了IoC和AOP机制。
(3) Dubbo SPI兼容Java SPI的配置方式和配置内容，在Dubbo启动的时候，会扫描META-INF/services/,META-INF/dubbo/,META-INF/dubbo/internal/三个目录
拓展点注解 @SPI
(1)@SPI可以使用在类、接口和枚举类上。
(2)标志这是Dubbo SPI接口。
(3)SPI注解有一个value属性，可以通过这个属性设置这个接口的默认实现类。
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface SPI {
/**
* 默认实现类名称
*/
String value() default "";
}
拓展点自适应注解 @Adaptive
(1)@Adaptive注解可以标记在类、接口、枚举和方法上。
(2)使用@Adaptive注解，可以动态地通过URL中的参数来确定具体使用的实现类，从而解决了自动加载中的实例注入问题。
(3)当传递的参数URL没有参数key可以匹配@Adaptive的value数组的某一个值，就会使用@SPI("XXX")默认实现。
(4)当传递的参数URL有参数key可以匹配@Adaptive的value数组的某一个值(顺序是key依次匹配)，就使用该key对应的value值。查找该value值在配置文件(META-INF/dubbo/internal/目录下)对应的实现类。
(5)当在某个实现类上加了@Adaptive注解，优先级最高，无论默认实现@SPI的值是什么和URL传递了什么参数，都会直接调用带有@Adaptive注解的类。
(6)方法级别注解会生成和编译动态实现类，而类级别的注解不会生成动态类。
(7)会缓存两个与@Adaptive有关的对象，Adaptive具体实现类的Class类型缓存在cachedAdaptiveClass中；Class的具体实例化对象缓存在cachedAdaptiveInstance中。
@SPI("spiServiceImpl")
public interface SPIService {
@Adaptive({"test"})
public void printService(URL url);
}
spiServiceImpl=gdut.ff.spi.SPIServiceImpl spiServiceImpl2=gdut.ff.spi.SPIServiceImpl2 spiServiceImpl3=gdut.ff.spi.SPIServiceImpl3
public class SPIServiceMain {
public static void main(String[] args) {
SPIService defaultExtension = ExtensionLoader.getExtensionLoader(SPIService.class).getAdaptiveExtension();
//这里设置@Adaptive的参数test的值是spiServiceImpl2，表示调用gdut.ff.spi.SPIServiceImpl2
URL url = URL.valueOf("file://localhost/hello?test=spiServiceImpl2");
defaultExtension.printService(url);
}
}
输出是：Hello World2
(8)如果在多个实现类上面都加了@Adaptive注解，会抛出“发现多于一个Adaptive类”错误。
拓展点自适应激活注解 @Activate
(1)可以标记在类、枚举、接口和方法上。主要使用在有多个拓展点，需要根据不同的应用场景激活。
ExtensionLoader工作原理
public class SPIServiceMain {
public static void main(String[] args) {
URL url = URL.valueOf("file://localhost/hello");
SPIService defaultService = ExtensionLoader.getExtensionLoader(SPIService.class).getExtension("true");
defaultService.printService(url);
}
}
(1)getExtension
private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<String, Holder<Object>>();
public T getExtension(String name) {
if (name == null || name.length() == 0)
throw new IllegalArgumentException("Extension name == null");
if ("true".equals(name)) {
//加载返回默认拓展类
return getDefaultExtension();
}
//先在缓存实例中获取
Holder<Object> holder = cachedInstances.get(name);
if (holder == null) {
cachedInstances.putIfAbsent(name, new Holder<Object>());
holder = cachedInstances.get(name);
}
Object instance = holder.get();
if (instance == null) {
synchronized (holder) {
instance = holder.get();
if (instance == null) {
//缓存中没有再创建
instance = createExtension(name);
holder.set(instance);
}
}
}
return (T) instance;
}
private T createExtension(String name) {
Class<?> clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(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 (wrapperClasses != null && !wrapperClasses.isEmpty()) {
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 + ") could not be instantiated: " + t.getMessage(), t);
}
}
private Map<String, Class<?>> getExtensionClasses() {
//从缓存类中查找
Map<String, Class<?>> classes = cachedClasses.get();
if (classes == null) {
synchronized (cachedClasses) {
classes = cachedClasses.get();
if (classes == null) {
classes = loadExtensionClasses();
cachedClasses.set(classes);
}
}
}
return classes;
}
private Map<String, Class<?>> loadExtensionClasses() {
//获取接口上的注解SPI
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
if (defaultAnnotation != null) {
//@SPI注解的value值
String 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];
}
}
Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
// META-INF/dubbo/internal/接口全路径名
loadDirectory(extensionClasses, DUBBO_INTERNAL_DIRECTORY, type.getName());
// META-INF/dubbo/internal/接口全路径名
loadDirectory(extensionClasses, DUBBO_INTERNAL_DIRECTORY, type.getName().replace("org.apache", "com.alibaba"));
// META-INF/dubbo/接口全路径名
loadDirectory(extensionClasses, DUBBO_DIRECTORY, type.getName());
// META-INF/dubbo/接口全路径名
loadDirectory(extensionClasses, DUBBO_DIRECTORY, type.getName().replace("org.apache", "com.alibaba"));
// META-INF/services/接口全路径名
loadDirectory(extensionClasses, SERVICES_DIRECTORY, type.getName());
// META-INF/services/接口全路径名
loadDirectory(extensionClasses, SERVICES_DIRECTORY, type.getName().replace("org.apache", "com.alibaba"));
return extensionClasses;
}
private void loadDirectory(Map<String, Class<?>> extensionClasses, String dir, String type) {
String fileName = dir + type;
try {
Enumeration<java.net.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 when load extension class(interface: " +
type + ", description file: " + fileName + ").", t);
}
}
private void loadResource(Map<String, Class<?>> extensionClasses, ClassLoader classLoader, java.net.URL resourceURL) {
try {
//IO流读取META-INF文件夹的配置文件
BufferedReader reader = new BufferedReader(new InputStreamReader(resourceURL.openStream(), "utf-8"));
try {
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);
}
}
}
} finally {
reader.close();
}
} catch (Throwable t) {
logger.error("Exception when load 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 {
//判断clazz是否是type的子类
if (!type.isAssignableFrom(clazz)) {
throw new IllegalStateException("Error when load extension class(interface: " +
type + ", class line: " + clazz.getName() + "), class "
+ clazz.getName() + "is not subtype of interface.");
}
//判断实现类clazz是否有@Adaptive注解
if (clazz.isAnnotationPresent(Adaptive.class)) {
if (cachedAdaptiveClass == null) {
cachedAdaptiveClass = clazz;
} else if (!cachedAdaptiveClass.equals(clazz)) {
throw new IllegalStateException("More than 1 adaptive class found: "
+ cachedAdaptiveClass.getClass().getName()
+ ", " + clazz.getClass().getName());
}
//判断是否是包装拓展类，如果是，缓存起来
} else if (isWrapperClass(clazz)) {
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
} else {
clazz.getConstructor();
if (name == null || name.length() == 0) {
name = findAnnotationName(clazz);
if (name.length() == 0) {
throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + resourceURL);
}
}
String[] names = NAME_SEPARATOR.split(name);
if (names != null && names.length > 0) {
//判断是否有@Activate注解，如果有，缓存起来
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) {
cachedActivates.put(names[0], activate);
} else {
// support com.alibaba.dubbo.common.extension.Activate
com.alibaba.dubbo.common.extension.Activate oldActivate = clazz.getAnnotation(com.alibaba.dubbo.common.extension.Activate.class);
if (oldActivate != null) {
cachedActivates.put(names[0], oldActivate);
}
}
//普通拓展类，缓存起来
for (String n : names) {
if (!cachedNames.containsKey(clazz)) {
cachedNames.put(clazz, n);
}
Class<?> c = extensionClasses.get(n);
if (c == null) {
extensionClasses.put(n, clazz);
} else if (c != clazz) {
throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName());
}
}
}
}
}
(2)getAdaptiveExtension
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("fail to create adaptive instance: " + t.toString(), t);
}
}
}
} else {
throw new IllegalStateException("fail to create adaptive instance: " + createAdaptiveInstanceError.toString(), createAdaptiveInstanceError);
}
}
return (T) instance;
}
private T createAdaptiveExtension() {
try {
return injectExtension((T) getAdaptiveExtensionClass().newInstance());
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extension " + type + ", cause: " + e.getMessage(), e);
}
}
private Class<?> getAdaptiveExtensionClass() {
getExtensionClasses();
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}
ExtensionFactory
package org.apache.dubbo.common.extension;
@SPI
public interface ExtensionFactory {
<T> T getExtension(Class<T> var1, String var2);
}
有三种实现：
(1)SpiExtensionFactory
(2)SpringExtensionFactory
(3)AdaptiveExtensionFactory
代码编译器
(1)JDK编译器JdkCompiler
(2)Javassist编译器JavassistCompiler
(3)Adaptive编译器AdaptiveCompiler
参考资料
《深入理解Apache Dubbo与实战》
Dubbo SPI之Adaptive详解正文到此结束
- 本文标签： spring IDE value http AOP HashSet 目录 https UI key src 工作原理 stream struct 配置 实例 lib IO 缓存 ip map URLs 自适应 cache synchronized 编译 cat Document provider ioc equals ssl description App dubbo Service ConcurrentHashMap apache find CTO final message HashMap java tar 代码 参数 ACE id
- 版权声明： 本文为互联网转载文章，出处已在文章中说明(部分除外)。如果侵权，请联系本站长删除，谢谢。
- 本文海报： 生成海报一 生成海报二
热门推荐
相关文章
近期评论
-
666
-
文章和留言都翻到11页了 没有OOM
-
-
朋友，翻页到11页，及以后，会出现OOM，无法访问
-
-
-
-
版本号是多少，你可以下载哪个代码仓库，jdk选1.8 直接跑就行
-
-
Loading...
![[HBLOG]公众号](https://www.liuhaihua.cn/img/qrcode_gzh.jpg)
