For RMI on server-side, do we need to start rmiregistry
program, or just call LocateRegistry.createRegistry
?
If both are possible, what are the advantages and disadvantages?
DESCRIPTION. A remote object registry is a bootstrap naming service that is used by RMI servers on the same host to bind remote objects to names. Clients on local and remote hosts can then look up remote objects and make remote method invocations.
An RMI server is a program that hosts remote objects. An RMI registry is a separate program that binds remote object names to instances. An RMI server makes remote objects accessible to clients by registering them in the registry; clients then obtain access via that same registry.
By default, the RMI Registry uses port 1099. Client and server (stubs, remote objects) communicate over random ports unless a fixed port has been specified when exporting a remote object.
A Java RMI registry is a simplified name service that allows clients to get a reference (a stub) to a remote object. In general, a registry is used (if at all) only to locate the first remote object a client needs to use.
They're the same thing... rmiregistry
is a separate program, which you can run from a command line or a script, while LocateRegistry.createRegistry
does the same thing programatically.
In my experience, for "real" servers you will want to use rmiregistry
so that you know it's always running regardless of whether or not the client application is started. createRegistry
is very useful for testing, as you can start and stop the registry from your test as necessary.
If we start rmiregistry first, RmiServiceExporter would register itself to the running rmiregistry. In this case, we have to set the system property 'java.rmi.server.codebase' to where the 'org.springframework.remoting.rmi.RmiInvocationWrapper_Stub' class can be found. Otherwise, the RmiServiceExporter would not be started and got the exception " ClassNotFoundException class not found: org.springframework.remoting.rmi.RmiInvocationWrapper_Stub; nested exception is: ..."
If your rmi server, rmi client and rmiregistry can access the same filesystem, you may want the system property to be automatically configured to where the spring.jar can be found on the shared filesystem. The following utility classes and spring configuration show how this can be achieved.
abstract public class CodeBaseResolver {
static public String resolveCodeBaseForClass(Class<?> clazz) {
Assert.notNull(clazz);
final CodeSource codeSource = clazz.getProtectionDomain().getCodeSource();
if (codeSource != null) {
return codeSource.getLocation().toString();
} else {
return "";
}
}
}
public class SystemPropertyConfigurer {
private Map<String, String> systemProperties;
public void setSystemProperties(Map<String, String> systemProperties) {
this.systemProperties = systemProperties;
}
@PostConstruct
void init() throws BeansException {
if (systemProperties == null || systemProperties.isEmpty()) {
return;
}
for (Map.Entry<String, String> entry : systemProperties.entrySet()) {
final String key = entry.getKey();
final String value = SystemPropertyUtils.resolvePlaceholders(entry.getValue());
System.setProperty(key, value);
}
}
}
<bean id="springCodeBase" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="staticMethod" value="xx.CodeBaseResolver.resolveCodeBaseForClass" />
<property name="arguments">
<list>
<value>org.springframework.remoting.rmi.RmiInvocationWrapper_Stub</value>
</list>
</property>
</bean>
<bean id="springCodeBaseConfigurer" class="xx.SystemPropertyConfigurer"
depends-on="springCodeBase">
<property name="systemProperties">
<map>
<entry key="java.rmi.server.codebase" value-ref="springCodeBase" />
</map>
</property>
</bean>
<bean id="rmiServiceExporter" class="org.springframework.remoting.rmi.RmiServiceExporter" depends-on="springCodeBaseConfigurer">
<property name="serviceName" value="XXX" />
<property name="service" ref="XXX" />
<property name="serviceInterface" value="XXX" />
<property name="registryPort" value="${remote.rmi.port}" />
</bean>
The above example shows how system property be set automatically only when rmi server, rmi client and rmi registry can access the same filesystem. If that is not true or spring codebase is shared via other method (e.g. HTTP), you may modify the CodeBaseResolver to fit your need.
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