Jini/JavaSpaces发现错误

Question

本文简介：http://java.sun.com/developer/technicalArticles/tools/JavaSpaces/是一个如何运行JavaSpaces客户端的教程。我用Eclipse编写了这些类，启动了Launch-All脚本和Run example。它起作用了。之后，我将这些类导出到可执行jar ( JavaSpaceClient.jar )中，并使用以下命令尝试该jar : java -jar JavaSpaceClient.jar它运行良好，给我的结果是:搜索JavaSpace...已发现JavaSpace。正在向空间中写入邮件...正在从太空中读取消息...这条消息是:ЗдравоJavaSpaceсвете！

我的问题是，当我在另一台局域网计算机上移动这个jar文件时，当我键入相同的命令时，它会显示错误。下面是错误：

cica@cica-System-Name:~/Desktop$ java -jar JavaSpaceClient.jar 
Searching for a JavaSpace...
Jul 27, 2011 11:20:54 PM net.jini.discovery.LookupDiscovery$UnicastDiscoveryTask run
INFO: exception occurred during unicast discovery to biske-Inspiron-1525:4160 with constraints InvocationConstraints[reqs: {}, prefs: {}]
java.net.UnknownHostException: biske-Inspiron-1525
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:175)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:384)
at java.net.Socket.connect(Socket.java:546)
at java.net.Socket.connect(Socket.java:495)
at com.sun.jini.discovery.internal.MultiIPDiscovery.getSingleResponse(MultiIPDiscovery.java:134)
at com.sun.jini.discovery.internal.MultiIPDiscovery.getResponse(MultiIPDiscovery.java:75)
at net.jini.discovery.LookupDiscovery$UnicastDiscoveryTask.run(LookupDiscovery.java:1756)
at net.jini.discovery.LookupDiscovery$DecodeAnnouncementTask.run(LookupDiscovery.java:1599)
at com.sun.jini.thread.TaskManager$TaskThread.run(TaskManager.java:331)

我只写了“搜索JavaSpace...”并在一段时间后打印这些错误消息。有人能帮我纠正这个错误吗？

编辑:为了发现，我使用了我在互联网上找到的LookupDiscovery类：

import java.io.IOException;

import java.rmi.RemoteException;

import net.jini.core.lookup.ServiceRegistrar;
import net.jini.core.lookup.ServiceTemplate;

import net.jini.discovery.LookupDiscovery;
import net.jini.discovery.DiscoveryListener;
import net.jini.discovery.DiscoveryEvent;

/**
   A class which supports a simple JINI multicast lookup.  It doesn't register
   with any ServiceRegistrars it simply interrogates each one that's
   discovered for a ServiceItem associated with the passed interface class.
   i.e. The service needs to already have registered because we won't notice
   new arrivals. [ServiceRegistrar is the interface implemented by JINI
   lookup services].

   @todo Be more dynamic in our lookups - see above

   @author  Dan Creswell (dan@dancres.org)
   @version 1.00, 7/9/2003
 */
public class Lookup implements DiscoveryListener {
    private ServiceTemplate theTemplate;
    private LookupDiscovery theDiscoverer;

    private Object theProxy;

    /**
       @param aServiceInterface the class of the type of service you are
       looking for.  Class is usually an interface class.
     */
    public Lookup(Class aServiceInterface) {
        Class[] myServiceTypes = new Class[] {aServiceInterface};
        theTemplate = new ServiceTemplate(null, myServiceTypes, null);
    }

    /**
       Having created a Lookup (which means it now knows what type of service
       you require), invoke this method to attempt to locate a service
       of that type.  The result should be cast to the interface of the
       service you originally specified to the constructor.

       @return proxy for the service type you requested - could be an rmi
       stub or an intelligent proxy.
     */
    Object getService() {
        synchronized(this) {
            if (theDiscoverer == null) {

                try {
                    theDiscoverer =
                        new LookupDiscovery(LookupDiscovery.ALL_GROUPS);
                    theDiscoverer.addDiscoveryListener(this);
                } catch (IOException anIOE) {
                    System.err.println("Failed to init lookup");
                    anIOE.printStackTrace(System.err);
                }
            }
        }

        return waitForProxy();
    }

    /**
       Location of a service causes the creation of some threads.  Call this
       method to shut those threads down either before exiting or after a
       proxy has been returned from getService().
     */
    void terminate() {
        synchronized(this) {
            if (theDiscoverer != null)
                theDiscoverer.terminate();
        }
    }

    /**
       Caller of getService ends up here, blocked until we find a proxy.

       @return the newly downloaded proxy
     */
    private Object waitForProxy() {
        synchronized(this) {
            while (theProxy == null) {

                try {
                    wait();
                } catch (InterruptedException anIE) {
                }
            }

            return theProxy;
        }
    }

    /**
       Invoked to inform a blocked client waiting in waitForProxy that
       one is now available.

       @param aProxy the newly downloaded proxy
     */
    private void signalGotProxy(Object aProxy) {
        synchronized(this) {
            if (theProxy == null) {
                theProxy = aProxy;
                notify();
            }
        }
    }

    /**
       Everytime a new ServiceRegistrar is found, we will be called back on
       this interface with a reference to it.  We then ask it for a service
       instance of the type specified in our constructor.
     */
    public void discovered(DiscoveryEvent anEvent) {
        synchronized(this) {
            if (theProxy != null)
                return;
        }

        ServiceRegistrar[] myRegs = anEvent.getRegistrars();

        for (int i = 0; i < myRegs.length; i++) {
            ServiceRegistrar myReg = myRegs[i];

            Object myProxy = null;

            try {
                myProxy = myReg.lookup(theTemplate);

                if (myProxy != null) {
                    signalGotProxy(myProxy);
                    break;
                }
            } catch (RemoteException anRE) {
                System.err.println("ServiceRegistrar barfed");
                anRE.printStackTrace(System.err);
            }
        }
    }

    /**
       When a ServiceRegistrar "disappears" due to network partition etc.
       we will be advised via a call to this method - as we only care about
       new ServiceRegistrars, we do nothing here.
     */
    public void discarded(DiscoveryEvent anEvent) {
    }
}

我的客户机程序只是尝试搜索JavaSpaces服务，将MessageEntry写入其中，然后检索消息并将其打印出来。以下是客户端程序：

import net.jini.space.JavaSpace;

public class SpaceClient {
   public static void main(String argv[]) {
      try {
         MessageEntry msg = new MessageEntry();
         msg.content = "Hello JavaSpaces wordls!";
         System.out.println("Searching for JavaSpaces...");
         Lookup finder = new Lookup(JavaSpace.class);
         JavaSpace space = (JavaSpace) finder.getService();
         System.out.println("JavaSpaces discovered.");
         System.out.println("Writing into JavaSpaces...");
         space.write(msg, null, 60*60*1000);
         MessageEntry template = new MessageEntry();
         System.out.println("Reading message from JavaSpaces...");
         MessageEntry result = (MessageEntry) space.read(template, null, Long.MAX_VALUE);
         System.out.println("Message: "+result.content);
      } catch(Exception e) {
         e.printStackTrace();
      }
   }
}

当然，这是MessageEntry类：

import net.jini.core.entry.*;

public class MessageEntry implements Entry {
   public String content;

   public MessageEntry() {
   }

   public MessageEntry(String content) {
     this.content = content;
   }

   public String toString() {
     return "MessageContent: " + content;
   }
}

EDIT2:我在两台Windows机上做了发现。在那之后，我尝试了Windows - Ubuntu组合，但它不起作用。也许有一些网络问题？当我互相ping的时候，一切都很好。也许在Ubuntu上有一些DNS问题..

EDIT3:如果JavaSpaces服务在Windows上启动，客户端程序在Ubuntu上，则Windows - Ubuntu组合有效。当我尝试反向操作时，在Ubuntu上运行JavaSpaces服务和在Windows上运行客户端时出现错误。显然，Ubuntu存在一些问题。Ubuntu默认安装了OpenJDK。我安装了Oracle JDK，设置了JAVA_HOME，并将JAVA_HOME/bin放入PATH变量。我想知道也许不同版本的Java有一些问题，也许我用的不对。

Answer 1

我找到解决方案了！这是dns问题。在Ubuntu上，我的/etc/hosts文件是：

192.168.1.3 biske-Inspiron-1525 # Added by NetworkManager
127.0.0.1   localhost.localdomain   localhost
::1 biske-Inspiron-1525 localhost6.localdomain6 localhost6
127.0.1.1   biske-Inspiron-1525

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

我刚刚删除了行127.0.1.1 biske-Inspiron-1525，现在它工作得很好。一件小事毁了我上百万的神经:)

Answer 2

您运行的服务注册器(在主机biske-Inspiron-1525的端口4160上)可能发现其主机名不正确(没有域名)，因此使用短主机名发送通告。因此，在发现服务注册商之后，客户端有可能随后尝试与服务注册商建立连接，如果它在不同的域上，则无法解析主机名。

要确保服务注册器使用正确的主机名运行，请尝试使用以下命令行属性启动它：

-Dcom.sun.jini.reggie.unicastDiscoveryHost="biske-Inspiron-1525.and.its.domain"

Answer 3

您似乎正在对特定主机和端口执行单播发现，并且无法查找该主机。

假设您可以使用DNS解析名称biske-Inspiron-1525，尝试删除":4160“部分，然后查看单播查找是否成功。

下面是我用来查找服务的代码示例。这有点复杂，因为我实现了ServiceDiscoveryListener并以这种方式处理服务发现。我实际上保留了一个服务列表，并在其中一个服务失败时动态切换，但我在示例中去掉了这一部分。我还使用了Jini的配置部分，稍后我将对其进行解释。我在这里使用的服务接口称为"TheService"：

public class JiniClient implements ServiceDiscoveryListener {

private TheService service = null;

private Class[] serviceClasses;
private ServiceTemplate serviceTemplate;

public JiniClient(String[] configFiles) throws ConfigurationException {

    Configuration config = ConfigurationProvider.getInstance(configFiles,
            getClass().getClassLoader());


    // Set the security manager
    System.setSecurityManager(new RMISecurityManager());        

    // Define the service we are interested in.
    serviceClasses = new Class[] {TheService.class};
    serviceTemplate = new ServiceTemplate(null, serviceClasses, null);

    // Build a cache of all discovered services and monitor changes
    ServiceDiscoveryManager serviceMgr = null;

    DiscoveryManagement mgr = null;
    try {
        mgr = (DiscoveryManagement)config.getEntry(
                getClass().getName(), // component
                "discoveryManager",                 // name
                DiscoveryManagement.class);          // type

        if (null == mgr) {
            throw new ConfigurationException("entry for component " +
                    getClass().getName() + " name " +
                    "discoveryManager must be non-null");
        }
    } catch (Exception e) {
        /* This will catch both NoSuchEntryException and 
         * ConfigurationException. Putting them both
         * below just to make that clear.
         */
        if( (e instanceof NoSuchEntryException) || 
                (e instanceof ConfigurationException)) {
            // default value
            try {
                System.err.println("Warning, using default multicast discover.");
                mgr = new LookupDiscoveryManager(LookupDiscovery.ALL_GROUPS,
                        null,  // unicast locators
                        null); // DiscoveryListener
            } catch(IOException ioe) {
                e.printStackTrace();
        throw new RuntimeException("Unable to create lookup discovery manager: " + e.toString());
            }
        } 
    }

    try {
        serviceMgr = new ServiceDiscoveryManager(mgr, new LeaseRenewalManager());
    } catch (IOException e) {
        e.printStackTrace();
        throw new RuntimeException("Unable to create service discovery manager: " + e.toString());
    }

    try {
        serviceMgr.createLookupCache(serviceTemplate, 
                                                null,  // no filter
                                                this); // listener
    } catch(Exception e) {
        e.printStackTrace();
        throw new RuntimeException("Unable to create serviceCache: " + e.getMessage());
    }
}

public void serviceAdded(ServiceDiscoveryEvent evt) {
       /* Called when a service is discovered */
    ServiceItem postItem = evt.getPostEventServiceItem();
    //System.out.println("Service appeared: " +
    //         postItem.service.getClass().toString());

    if(postItem.service instanceof TheService) {
        /* You may be looking for multiple services. 
                     * The serviceAdded method will be called for each
                     * so you can use instanceof to figure out if 
                     * this is the one you want.
                     */
        service = (TheService)postItem.service;

    }       
}

public void serviceRemoved(ServiceDiscoveryEvent evt) {
/* This notifies you of when a service goes away. 
     * You could keep a list of services and then remove this 
     * service from the list. 
 */ 
}

public void serviceChanged(ServiceDiscoveryEvent evt) {
/* Likewise, this is called when a service changes in some way. */  

}

配置系统允许您动态配置发现方法，以便您可以切换到发现特定单播系统或组播，而无需更改应用程序。下面是一个单播发现配置文件的示例，您可以将其传递给上述对象构造函数：

import net.jini.core.discovery.LookupLocator;
import net.jini.discovery.LookupDiscoveryManager;
import net.jini.discovery.LookupDiscovery;

com.company.JiniClient {
    discoveryManager = new LookupDiscoveryManager(
        LookupDiscovery.ALL_GROUPS,
        new LookupLocator[] { new LookupLocator("jini://biske-Inspiron-1525.mycompany.com")},
        null,
        this); // the current config
}