使用Jini连接代理

### 使用Jini连接代理 #### 1. 背景与Jini连接器概述 在远程访问JMX代理时，RMI连接器能让我们调用MBean服务器方法并接收通知，但它有个缺点，即必须知道RMI连接器服务器的地址。为解决这个问题，可以构建Jini连接器。Jini能让开发者编写可自我描述且可被客户端发现的服务，使用Jini连接器，无需客户端知道代理的确切位置就能分发JMX代理。 例如，想要与JMX代理交互的客户端可以构建一个Jini连接器客户端，输入一些搜索参数，就能定位到最近匹配的代理。Jini连接器会使用其注册所在的MBean服务器的默认域名来宣传自己，Jini连接器客户端则使用该域名作为搜索参数来搜索代理。 Jini连接器由三个组件组成： - **MBean**：允许通过MBean服务器管理连接器，就像RMI连接器和HTML适配器MBean一样。 - **Jini服务**：由MBean创建，允许客户端连接到代理。 - **Jini客户端**：用于定位代理的Jini服务。 #### 2. Jini连接器组件详细介绍 ##### 2.1 MBean MBean在连接器中的作用是设置和管理Jini服务，它让代理能够控制Jini服务，包括设置其描述以及决定何时使服务可被发现。MBean包含对其MBean服务器的引用，这使得Jini服务可以回调MBean服务器的方法。MBean组件由`JINIServerMBean`接口和`JINIServer`类（实现`JINIServerMBean`接口）定义。 `JINIServerMBean`接口暴露的属性和操作如下表所示： | 属性/操作 | 描述 | | --- | --- | | Domain | 只读属性，指示包含此连接器的代理的域。 | | EntryName | 读写属性，为MBean启动的Jini服务提供一个标识符。此属性可选，但提供值能让客户端更精确地搜索服务。 | | Groups | 读写属性，指示Jini服务将向哪些查找服务组注册。 | | enableConnections | 操作，告诉MBean启动Jini服务。 | `JINIServerMBean`接口代码如下： ```java package jmxbook.ch9; public interface JINIServerMBean { public String getDomain(); public String getEntryName(); public void setEntryName( String name ); public String[] getGroups(); public void setGroups( String[] groups ); public void enableConnections(); } ``` `JINIServer`类实现了`JINIServerMBean`、`MBeanRegistration`和`ServiceIDListener`三个接口，其代码如下： ```java package jmxbook.ch9; import javax.management.*; import java.rmi.*; import java.util.*; import net.jini.discovery.*; import net.jini.core.lookup.*; import net.jini.lookup.*; import net.jini.lease.*; import net.jini.core.discovery.*; import net.jini.lookup.entry.*; import net.jini.core.entry.*; public class JINIServer implements JINIServerMBean, MBeanRegistration, ServiceIDListener { private MBeanServer mbs = null; private JoinManager jm = null; private ServiceID id = null; private String domain = null; private ObjectName name = null; private String[] groups; private Name entry = null; private boolean enabled = false; public JINIServer() { groups = new String[ 1 ]; groups[ 0 ] = "public"; } public String getDomain() { return domain; } public String getEntryName() { return entry.name; } public void serviceIDNotify( ServiceID id ) { this.id = id; } public ObjectName preRegister( MBeanServer server, ObjectName name) throws Exception { this.mbs = server; if( name == null ) { name = new ObjectName( mbs.getDefaultDomain() + ":connectorType=JINI" ); } this.domain = name.getDomain(); return name; } public void postRegister (Boolean registrationDone) {} public void preDeregister() throws Exception {} public void postDeregister(){} public void setGroups( String groups[] ) { if( groups != null ) this.groups = groups; } public String[] getGroups() { return groups; } public void enableConnections() { createService(); } public void setEntryName( String name ) { Entry old = entry; this.entry = new Name( name ); if( enabled ) { Entry[] newlabels = { entry }; Entry[] labels = { old }; jm.modifyAttributes( labels, newlabels ); } } private void createService() { try { JINIConnector connector = new JINIConnectorImpl( this ); Entry[] labels = { entry }; LookupDiscoveryManager mgr = new LookupDiscoveryManager( groups, null, null ); jm = new JoinManager(connector, labels, this, mgr, new LeaseRenewalManager()); enabled = true; } catch( Exception e ) { e.printStackTrace(); } } /* call back methods */ public Integer getMBeanCount() throws Exception { return mbs.getMBeanCount(); } public ObjectInstance createMBean(String className, ObjectName name) throws Exception { return mbs.createMBean( className, name ); } } ``` 这个类使用了Jini工具包中的多个包，用于查找查找服务以及管理和描述Jini服务。`createService()`方法负责创建Jini服务类`JINIConnectorImpl`并将其注册到可用的Jini查找服务中。 ##### 2.2 Jini服务 Jini服务实现了与MBean服务器接口中每个方法对应的方法，这使得Jini客户端可以通过Jini服务将其方法调用转发到MBean服务器。Jini服务由`JINIConnectorImpl`类定义，该类实现了`JINIConnector`接口。 `JINIConnector`接口代码如下： ```java package jmxbook.ch9; import java.rmi.*; import javax.management.*; public interface JINIConnector extends Remote { public Integer getMBeanCount() throws JINIConnectorException; public ObjectInstance createMBean(String className, ObjectName name) throws JINIConnectorException; } ``` `JINIConnectorImpl`类代码如下： ```java package jmxbook.ch9; import java.rmi.*; import java.rmi.server.*; import javax.management.*; public class JINIConnectorImpl extends UnicastRemoteObject implements JINIConnector { private JINIServer server = null; public JINIConnectorImpl( JINIServer server ) throws RemoteException { this.server = server; } public Integer getMBeanCount() throws JINIConnectorException { try { return server.getMBeanCount(); } catch( Exception e ) { throw new JINIConnectorException( "getMBeanCount", e ); } } public ObjectInstance createMBean(String className, ObjectName name) throws JINIConnectorException { try { return server.createMBean( className, name ); } catch( Exception e ) { throw new JINIConnectorException( "createMBean", e ); } } } ``` 为了成为Jini服务，`JINIConnectorImpl`类必须是一个远程类，因此它扩展了`UnicastRemoteObject`类，并实现了`JINIConnector`接口。该类包含对`JINIServer` MBean的引用，以便服务可以回调MBean来执行服务客户端所需的调用。 `JINIConnectorException`类用于包装服务器端异常，代码如下： ```java package jmxbook.ch9; import java.rmi.*; public class JINIConnectorException extends RemoteException { private Exception exception = null; public JINIConnectorException( String message, Exception ex ) { super( message, ex ); this.exception = ex; } public Exception getWrappedException() { return exception; } } ``` #### 3. Jini连接器客户端 Jini连接器客户端用于发现和使用Jini连接器服务，从而使用JMX代理。客户端实现了`MBeanServer`接口，为客户端用户提供服务器端可用的所有方法。由于篇幅原因，除了`getMBeanCount()`和`createMBean()`方法外，其他方法都被存根化。 `JINIConnectorClient`类代码如下： ```java package jmxbook.ch9; import javax.management.*; import java.rmi.*; import java.util.*; import net.jini.discovery.*; import net.jini.core.lookup.*; import net.jini.lookup.*; import java.io.*; public class JINIConnectorClient implements DiscoveryListener, MBeanServer { private ServiceTemplate template = null; private LookupDiscovery reg = null; private JINIConnector server =null; public JINIConnectorClient() { System.setSecurityManager( new RMISecurityManager() ); Class[] cls = { JINIConnector.class }; template = new ServiceTemplate( null, cls, null ); try { reg = new LookupDiscovery( new String[] { "" } ); reg.addDiscoveryListener( this ); while( server == null ) Thread.sleep( 1000 ); } catch( Exception e ) { e.printStackTrace(); } } public void discovered( DiscoveryEvent event ) { if( server != null ) return; ServiceRegistrar[] lookups = event.getRegistrars(); try { ServiceMatches items = lookups[0].lookup( template, Integer.MAX_VALUE ); server = ( JINIConnector ) items.items[ 0 ].service; System.out.println( "service found" ); } catch( Exception e ) { e.printStackTrace(); } } public void discarded( DiscoveryEvent event ){} public Integer getMBeanCount() { try { return server.getMBeanCount(); } catch( JINIConnectorException e ) { return null; } } public ObjectInstance createMBean(String className, ObjectName name) throws ReflectionException, InstanceAlreadyExistsException, MBeanRegistrationException, MBeanException, NotCompliantMBeanException { try { return server.createMBean( className, name ); } catch( JINIConnectorException e ) { Exception ex = e.getWrappedException(); if( ex instanceof ReflectionException ) throw ( ReflectionException ) ex; else if( ex instanceof InstanceAlreadyExistsException ) throw ( InstanceAlreadyExistsException ) ex; else if( ex instanceof MBeanRegistrationException ) throw ( MBeanRegistrationException ) ex; else if( ex instanceof MBeanException ) throw ( MBeanException ) ex; else throw ( NotCompliantMBeanException ) ex; } } /* UNIMPLEMENTED METHODS BELOW */ public Object instantiate(String className) throws ReflectionException, MBeanException { return null; } public Object instantiate(String className, ObjectName loaderName) throws ReflectionException, MBeanException, InstanceNotFoundException { return null; } public Object instantiate(String className, Object params[], String signature[]) throws ReflectionException, MBeanException { return null; } public Object instantiate(String className, ObjectName loaderName, Object params[], String signature[]) throws ReflectionException, MBeanException, InstanceNotFoundException { return null; } public ObjectInstance createMBean(String className, ObjectName name ```