package com.taobao.tddl.common.utils.extension;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Enumeration;
import java.util.List;
import java.util.Map;
import java.util.ServiceLoader;
import org.apache.commons.lang.exception.ExceptionUtils;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
/**
* 包装{@linkplain ServiceLoader}，提供SPI的获取方式 <br/>
* jdk自带的{@linkplain ServiceLoader}
* 存在一些局限，无法为SPI扩展定义排序规则，如果classpath存在多个SPI配置时，加载无法确定，所以包装一下允许以后替换实现
*
* @see <a
* href="http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Service%20Provider">JDK5.0的自动发现机制实现</a>
* @author jianghang 2013-9-13 下午3:38:30
* @since 5.0.0
*/
public class ExtensionLoader<S> {
private static final String SERVICES_DIRECTORY = "META-INF/services/";
private static final String TDDL_DIRECTORY = "META-INF/tddl/";
private static Map<Class, Class> providers = Maps.newConcurrentMap();
/**
* 指定classloader加载server provider
*
* @param service
* @param loader
* @return
* @throws ExtensionNotFoundException
*/
public static <S> S load(Class<S> service, ClassLoader loader) throws ExtensionNotFoundException {
return loadFile(service, null, loader);
}
/**
* 加载server provider
*
* @param service
* @return
* @throws ExtensionNotFoundException
*/
public static <S> S load(Class<S> service) throws ExtensionNotFoundException {
return loadFile(service, null, findClassLoader());
}
/**
* 加载server provider
*
* @param service
* @return
* @throws ExtensionNotFoundException
*/
public static <S> S load(Class<S> service, String activateName) throws ExtensionNotFoundException {
return loadFile(service, activateName, findClassLoader());
}
/**
* 指定classloader加载server provider
*
* @param service
* @param loader
* @return
* @throws ExtensionNotFoundException
*/
public static <S> S load(Class<S> service, String activateName, ClassLoader loader)
throws ExtensionNotFoundException {
return loadFile(service, activateName, loader);
}
/**
* 获取所有的扩展类，按照{@linkplain Activate}定义的order顺序进行排序
*
* @return
*/
public static <S> List<Class> getAllExtendsionClass(Class<S> service) {
return findAllExtensionClass(service, null, findClassLoader());
}
/**
* 获取所有的扩展类，按照{@linkplain Activate}定义的order顺序进行排序
*
* @return
*/
public static <S> List<Class> getAllExtendsionClass(Class<S> service, ClassLoader loader) {
return findAllExtensionClass(service, null, loader);
}
private static <S> S loadFile(Class<S> service, String activateName, ClassLoader loader) {
Class<?> extension = providers.get(service);
if (extension == null) {
synchronized (service) {
extension = providers.get(service);
if (extension == null) {
List<Class> extensions = findAllExtensionClass(service, activateName, loader);
if (extensions.isEmpty()) {
throw new ExtensionNotFoundException("not found service provider for : " + service.getName());
}
extension = extensions.get(extensions.size() - 1);// 最大的一个
}
}
}
try {
return service.cast(extension.newInstance());
} catch (InstantiationException e) {
throw new ExtensionNotFoundException("not found service provider for : " + service.getName()
+ " caused by " + ExceptionUtils.getFullStackTrace(e));
} catch (IllegalAccessException e) {
throw new ExtensionNotFoundException("not found service provider for : " + service.getName()
+ " caused by " + ExceptionUtils.getFullStackTrace(e));
}
}
private static <S> List<Class> findAllExtensionClass(Class<S> service, String activateName, ClassLoader loader) {
List<Class> extensions = Lists.newArrayList();
try {
loadFile(service, SERVICES_DIRECTORY, loader, extensions);
loadFile(service, TDDL_DIRECTORY, loader, extensions);
} catch (IOException e) {
throw new ExtensionNotFoundException("not found service provider for : " + service.getName()
+ " caused by " + ExceptionUtils.getFullStackTrace(e));
}
if (extensions.isEmpty()) {
return extensions;
}
// 做一下排序
Collections.sort(extensions, new Comparator<Class>() {
public int compare(Class c1, Class c2) {
Integer o1 = 0;
Integer o2 = 0;
Activate a1 = (Activate) c1.getAnnotation(Activate.class);
Activate a2 = (Activate) c2.getAnnotation(Activate.class);
if (a1 != null) {
o1 = a1.order();
}
if (a2 != null) {
o2 = a2.order();
}
return o1.compareTo(o2);
}
});
if (activateName != null) { // 如果有激活条件
for (int i = extensions.size() - 1; i >= 0; i--) {
Class clz = extensions.get(i);
Activate activate = (Activate) clz.getAnnotation(Activate.class);
if (activate != null && activateName.equals(activate.name())) {
return Arrays.asList(clz);
}
}
throw new ExtensionNotFoundException("not found service provider for : " + service.getName()
+ " activateName : " + activateName);
} else {
return extensions;
}
}
private static void loadFile(Class<?> service, String dir, ClassLoader classLoader, List<Class> extensions)
throws IOException {
String fileName = dir + service.getName();
Enumeration<java.net.URL> urls;
if (classLoader != null) {
urls = classLoader.getResources(fileName);
} else {
urls = ClassLoader.getSystemResources(fileName);
}
if (urls != null) {
while (urls.hasMoreElements()) {
java.net.URL url = urls.nextElement();
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
String line = null;
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) {
extensions.add(Class.forName(line, true, classLoader));
}
}
} catch (Throwable e) {
// ignore
}
}
}
}
private static ClassLoader findClassLoader() {
return Thread.currentThread().getContextClassLoader();
}
}