远程服务调用（RMI）

模块概念的引入，是本框架的一大优势，而跨JVM的远程服务调用则是另一个最有价值的功能。

《本地服务调用》一文中我们讲解了跨模块间的服务调用可以是这样的：

ServiceHelper.invoke("pas","AuthService:auth",new Data("principal",principalInstance,"url","http://localhost:8080/pas/index.shtml"));

如果这个pas不是本地模块，而是远程模块，又该如何调用呢？

正如你期望的那样，还是上面这样调用，这意味着，无论这个pas模块部署在什么地方，你得代码复杂度没有变化。可怜了那些靠代码量体现工作量的程序猿们，处理了一个如此复杂的工作，还是这么简单的两行代码。

远程服务的实现方法

flying中是通过hessian来实现远程调用的，主要是因为hessian简单、功能够用。

服务提供端代码：

1、定义Hessian服务提供接口

public interface RemoteService {

RemoteValue invoke(Principal principal, String moduleId, String serviceId, RemoteValue request) throws Exception;

}

2、定义Hessian的Servlet

@WebServlet(value="/remoting")

public class HessianRemoteService extends HessianServlet implements RemoteService{

private final static Logger logger = Logger.getLogger(HessianRemoteService.class);

public void init(ServletConfig servletConfig) throws ServletException {

super.init(servletConfig);

}

public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws IOException, ServletException {

HttpServletRequest req = (HttpServletRequest)servletRequest;

long start = System.currentTimeMillis();

final String requestURI = req.getRequestURI() + (req.getQueryString() == null?"":"?" + req.getQueryString());

try {

super.service(servletRequest, servletResponse);

} finally {

logger.info("Access(" + (System.currentTimeMillis() - start) + ")\tURI:" + requestURI);

}

}

public RemoteValue invoke(Principal principal, String moduleId, String serviceId, RemoteValue remoteData) throws Exception {

long start = System.currentTimeMillis();

try {

Data req = remoteData.getValue();

LocalModule module = Application.getInstance().getModules().getLocalModule(moduleId);

ThreadContext.getContext().reset(module, serviceId, req, principal);

ThreadContext.getContext().setInvokeType(ThreadContext.InvokeType.Remote);

Data result = module.invoke(serviceId, req);

remoteData.setValue(result);

} catch (Exception e){

remoteData.setException(e);

} finally {

logger.info("RemoteInvoker(" + (System.currentTimeMillis() - start) + ")\tModuleId:" + moduleId+";ServiceId:" + serviceId);

}

return remoteData;

}

}

3、实现Hessian调用的客户端

public class HessianRemoteServiceInvoker implements RemoteServiceInvoker {

@Override

public Data invoke(Principal principal, LocalModule localModule, String remoteModuleId, String serviceId, Data request)

throws Exception {

if (localModule == null) {

localModule = ThreadContext.getContext().getModule();

}

if (localModule != null) {

Thread.currentThread().setContextClassLoader(localModule.getClassLoader());

}

String url = Application.getInstance().getModules().getRemoteModule(remoteModuleId).getPath();

RemoteService remoteService = getRemoteService(url);

Map<String, Object> nonSerializable = request.filterValues(new DataFilter(){

@Override

public boolean isValid(String key, Object value) {

return key != null && value != null && (value instanceof Serializable);

}

});

final RemoteValue res = remoteService.invoke(principal, remoteModuleId, serviceId, new RemoteValue(request));

if (res.getException() != null) {

throw (Exception) res.getException();

} else {

return res.getValue().putAll(nonSerializable);

}

}

private static Map<String,RemoteService> remoteServiceMap = new ConcurrentHashMap<String, RemoteService>();

private static Object lock = new Object();

private RemoteService getRemoteService(String url) throws Exception {

RemoteService remoteService = remoteServiceMap.get(url);

if(remoteService==null){

synchronized (lock) {

remoteService = remoteServiceMap.get(url);

if(remoteService==null){

HessianProxyFactory factory = new HessianProxyFactory(Thread.currentThread().getContextClassLoader());

HttpClientHessianConnectionFactory hessianConnectionFactory = HttpClientHessianConnectionFactory.getInstance();

//hessianConnectionFactory.addHeader("authorization", "admin");

factory.setConnectionFactory(hessianConnectionFactory);

final Data config = Application.getInstance().getConfigs("hessian");

if (config != null) {

factory.setConnectTimeout(config.getLong("connectTimeout", 10000l));

factory.setReadTimeout(config.getLong("readTimeout", 10000l));

factory.setHessian2Reply(config.getBoolean("hessian2Reply", true));

factory.setHessian2Request(config.getBoolean("hesian2Request", false));

factory.setChunkedPost(config.getBoolean("chunkedPost", true));

factory.setDebug(config.getBoolean("debug", false));

}

remoteService = (RemoteService) factory.create(RemoteService.class, url);

remoteServiceMap.put(url, remoteService);

}

}

}

return remoteService;

}

}

4、实现RemoteModule中的invoke方法：

public Data invoke(String serviceId, Data request) throws Exception {

return RemoteServiceInvokerHelper.invoke(remoteServiceInvoker, id, serviceId, request);

}

框架源码：https://github.com/hifong/flying

博客空间：http://www.cnblogs.com/hifong/

Demo应用：https://github.com/hifong/pas

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