单仁做的网站,青岛外贸网站设计,龙华新区做网站,做排行榜的网站//ServiceLoader实现了Iterable接口#xff0c;可以遍历所有的服务实现者public final class ServiceLoaderimplements Iterable{//查找配置文件的目录private static final String PREFIX META-INF/services/;//表示要被加载的服务的类或接口private final Clas…//ServiceLoader实现了Iterable接口可以遍历所有的服务实现者public final class ServiceLoaderimplements Iterable{//查找配置文件的目录private static final String PREFIX META-INF/services/;//表示要被加载的服务的类或接口private final Classservice;//这个ClassLoader用来定位加载实例化服务提供者private finalClassLoader loader;//访问控制上下文private finalAccessControlContext acc;//缓存已经被实例化的服务提供者按照实例化的顺序存储private LinkedHashMap providers new LinkedHashMap();//The current lazy-lookup iteratorprivateLazyIterator lookupIterator;//重新加载就相当于重新创建ServiceLoader了用于新的服务提供者安装到正在运行的Java虚拟机中的情况public voidreload() {//清空缓存中所有已实例化的服务提供者providers.clear();//新建一个迭代器该迭代器会从头查找和实例化服务提供者lookupIterator newLazyIterator(service, loader);}//私有构造器//使用指定的类加载器和服务创建服务加载器//如果没有指定类加载器使用系统类加载器就是应用类加载器。private ServiceLoader(Classsvc, ClassLoader cl) {service Objects.requireNonNull(svc, Service interface cannot be null);loader (cl null) ?ClassLoader.getSystemClassLoader() : cl;acc (System.getSecurityManager() ! null) ? AccessController.getContext() : null;reload();}//解析失败处理的方法private static void fail(Classservice, String msg, Throwable cause)throwsServiceConfigurationError{throw new ServiceConfigurationError(service.getName() : msg,cause);}private static void fail(Classservice, String msg)throwsServiceConfigurationError{throw new ServiceConfigurationError(service.getName() : msg);}private static void fail(Class service, URL u, intline, String msg)throwsServiceConfigurationError{fail(service, u : line : msg);}//解析服务提供者配置文件中的一行//首先去掉注释校验然后保存//返回下一行行号//重复的配置项和已经被实例化的配置项不会被保存private int parseLine(Class service, URL u, BufferedReader r, intlc,Listnames)throwsIOException, ServiceConfigurationError{//读取一行String ln r.readLine();if (ln null) {return -1;}//#号代表注释行int ci ln.indexOf(#);if (ci 0) ln ln.substring(0, ci);lnln.trim();int n ln.length();if (n ! 0) {if ((ln.indexOf( ) 0) || (ln.indexOf(\t) 0))fail(service, u, lc,Illegal configuration-file syntax);int cp ln.codePointAt(0);if (!Character.isJavaIdentifierStart(cp))fail(service, u, lc,Illegal provider-class name: ln);for (int i Character.charCount(cp); i n; i Character.charCount(cp)) {cpln.codePointAt(i);if (!Character.isJavaIdentifierPart(cp) (cp ! .))fail(service, u, lc,Illegal provider-class name: ln);}if (!providers.containsKey(ln) !names.contains(ln))names.add(ln);}return lc 1;}//解析配置文件解析指定的url配置文件//使用parseLine方法进行解析未被实例化的服务提供者会被保存到缓存中去private Iterator parse(Classservice, URL u)throwsServiceConfigurationError{InputStream in null;BufferedReader r null;ArrayList names new ArrayList();try{inu.openStream();r new BufferedReader(new InputStreamReader(in, utf-8));int lc 1;while ((lc parseLine(service, u, r, lc, names)) 0);}catch(IOException x) {fail(service,Error reading configuration file, x);}finally{try{if (r ! null) r.close();if (in ! null) in.close();}catch(IOException y) {fail(service,Error closing configuration file, y);}}returnnames.iterator();}//Private inner class implementing fully-lazy provider lookup//服务提供者查找的迭代器private classLazyIteratorimplements Iterator{//服务提供者接口Classservice;//类加载器ClassLoader loader;//保存实现类的urlEnumeration configs null;//保存实现类的全名Iterator pending null;//迭代器中下一个实现类的全名String nextName null;private LazyIterator(Classservice, ClassLoader loader) {this.service service;this.loader loader;}private booleanhasNextService() {if (nextName ! null) {return true;}if (configs null) {try{String fullName PREFIX service.getName();if (loader null)configsClassLoader.getSystemResources(fullName);elseconfigsloader.getResources(fullName);}catch(IOException x) {fail(service,Error locating configuration files, x);}}while ((pending null) || !pending.hasNext()) {if (!configs.hasMoreElements()) {return false;}pendingparse(service, configs.nextElement());}nextNamepending.next();return true;}privateS nextService() {if (!hasNextService())throw newNoSuchElementException();String cnnextName;nextName null;Class c null;try{c Class.forName(cn, false, loader);}catch(ClassNotFoundException x) {fail(service,Provider cn not found);}if (!service.isAssignableFrom(c)) {fail(service,Provider cn not a subtype);}try{S pservice.cast(c.newInstance());providers.put(cn, p);returnp;}catch(Throwable x) {fail(service,Provider cn could not be instantiated,x);}throw new Error(); //This cannot happen}public booleanhasNext() {if (acc null) {returnhasNextService();}else{PrivilegedAction action new PrivilegedAction() {public Boolean run() { returnhasNextService(); }};returnAccessController.doPrivileged(action, acc);}}publicS next() {if (acc null) {returnnextService();}else{PrivilegedAction action new PrivilegedAction() {public S run() { returnnextService(); }};returnAccessController.doPrivileged(action, acc);}}public voidremove() {throw newUnsupportedOperationException();}}//获取迭代器//返回遍历服务提供者的迭代器//以懒加载的方式加载可用的服务提供者//懒加载的实现是解析配置文件和实例化服务提供者的工作由迭代器本身完成public Iteratoriterator() {return new Iterator() {//按照实例化顺序返回已经缓存的服务提供者实例IteratorknownProvidersproviders.entrySet().iterator();public booleanhasNext() {if(knownProviders.hasNext())return true;returnlookupIterator.hasNext();}publicS next() {if(knownProviders.hasNext())returnknownProviders.next().getValue();returnlookupIterator.next();}public voidremove() {throw newUnsupportedOperationException();}};}//为指定的服务使用指定的类加载器来创建一个ServiceLoaderpublic static ServiceLoader load(Classservice,ClassLoader loader){return new ServiceLoader(service, loader);}//使用线程上下文的类加载器来创建ServiceLoaderpublic static ServiceLoader load(Classservice) {ClassLoader clThread.currentThread().getContextClassLoader();returnServiceLoader.load(service, cl);}//使用扩展类加载器为指定的服务创建ServiceLoader//只能找到并加载已经安装到当前Java虚拟机中的服务提供者应用程序类路径中的服务提供者将被忽略public static ServiceLoader loadInstalled(Classservice) {ClassLoader clClassLoader.getSystemClassLoader();ClassLoader prev null;while (cl ! null) {prevcl;clcl.getParent();}returnServiceLoader.load(service, prev);}/*** Returns a string describing this service.**returnA descriptive string*/publicString toString() {return java.util.ServiceLoader[ service.getName() ];}}
