RMI之所以使用的范围受限制主要有两方面原因,其一:必须要是java,平台的异构性受到限制;其二:穿越防火墙不方便。这里主要谈谈RMI如何通过固定分配端口来穿越防火墙。 RMI穿越防火墙不方便主要是因为除了RMI服务注册的端口(默认1099)外,与RMI的通讯还需要另外的端口来传送数据,而另外的端口是随机分配的,所以要想RMI的客户能通过防火墙来与RMI服务通讯,则需要能让随机分配的端口固定下来,具体做法如下:
1、增加一个文件SMRMISocket.java
import java.rmi.server.*;
import java.io.*;
import java.net.*;
public class SMRMISocket extends RMISocketFactory {
public Socket createSocket(String host, int port) throws IOException{
return new Socket(host,port);
}
public ServerSocket createServerSocket(int port) throws IOException {
if (port == 0)
port = 10990; //不指定就随机分配了
return new ServerSocket(port);
}
}
2、在实例化UnicastRemoteObject的子类前加入一下代码:
[java] view plaincopyprint?
try {
RMISocketFactory.setSocketFactory(new SMRMISocket());
} catch (Exception ex) {
}
这样的话RMI分配的端口就被固定了,防火墙只需要打开1099和10990端口即可。
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在用RMI做服务监控的时候碰到两个问题:
1. InetAddress.getLocalHost().getHostAddress(); 报错UnknowHost
linux /etc/hosts 加主机名以及映射
hostname hostname -i 能正确获取到就ok
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2. 先记录问题
1) 服务端重启客户端报错的问题
http://forum.springsource.org/showthread.php?t=61575
at monitor.SendHeartBeatThread.run(SendHeartBeatThread.java:32)
Caused by: java.rmi.NoSuchObjectException: no such object in table
at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:275)
at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:252)
at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:161)
at org.springframework.remoting.rmi.RmiInvocationWrapper_Stub.invoke(Unknown Source)
at org.springframework.remoting.rmi.RmiClientInterceptor.doInvoke(RmiClientInterceptor.java:397)
at org.springframework.remoting.rmi.RmiClientInterceptor.doInvoke(RmiClientInterceptor.java:343)
... 5 more
<bean id="beanId" class="org.springframework.remoting.rmi.RmiProxyFa ctoryBean">
<property name="serviceUrl" value="rmi://127.0.0.1:6666/appName"/>
<property name="serviceInterface" value="test.HelloI"/>
<!--property name="cacheStub" value="false"/-->
<property name="lookupStubOnStartup" value="false"/>
<property name="refreshStubOnConnectFailure" value="true"/>
</bean>
因为RMI stub被连接到特定的端点,不仅仅是为每个调用打开一个给定的目标地址的连接,所以如果重新启动RMI端点主机的服务器,那么就需要重新注册这些stub,并且客户端需要再次查询它们。
class="org.springframework.remoting.rmi.RmiProxyFactoryBean">
<property name="serviceUrl">
<value>${showcasewiz.report.serviceurl}</value>
</property>
<property name="serviceInterface">
<value>com.meetexpo.showcase.backend.service.ReportService</value>
</property>
</bean>
class="org.springframework.remoting.rmi.RmiProxyFactoryBean">
<property name="serviceUrl">
<value>${showcasewiz.report.serviceurl}</value>
</property>
<property name="serviceInterface">
<value>com.meetexpo.showcase.backend.service.ReportService</value>
</property>
</bean>
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2) 内网(局域网)间访问明明指定一个ip确变成另一个ip的情况)
Exception in thread "main" org.springframework.remoting.RemoteConnectFailureException: Cannot connect to remote service [rmi://218.206.203.3:9902/cmpayNotice]; nested exception is java.rmi.ConnectException: Connection refused to host: 10.97.164.26; nested exception is:
java.net.ConnectException: Connection timed out: connect
Caused by: java.rmi.ConnectException: Connection refused to host: 10.97.164.26; nested exception is:
java.net.ConnectException: Connection timed out: connect
以下from:http://dd2086.iteye.com/blog/362995
出错堆栈:
org.springframework.remoting.RemoteConnectFailureException: Cannot connect to remote service [rmi://192.168.2.61/Service]; nested exception is java.rmi.ConnectException: Connection refused to host: 192.168.7.11; nested exception is:
java.net.ConnectException: Connection timed out: connect
很奇怪,rmi访问的url是对的,但是后续的访问得到的IP却是双网卡中的另外一个无法访问的。
在本机做个简单试验:
System.out.println(UnicastRemoteObject.exportObject(new Remote(){},0));
输出:
Proxy[Remote,RemoteObjectInvocationHandler[UnicastRef [liveRef: [endpoint:[192.168.2.3:2339](local),objID:[0]]]]]
说明对象在没有注册出去的时候其IP就已经决定,绑定出去以后客户端就按照这个IP按图索骥。Server端有两个网卡,乱找一个就Over了。
这种方式对分布式对象注册很有用,但是碰到多IP的情况下就比较弱智了。sun的faq上给出一个简单答案:
http://java.sun.com/j2se/1.5.0/docs/guide/rmi/faq.html#netmultihomed
一句话:
System.setProperty("java.rmi.server.hostname","192.168.2.3");//建议从配置文件加载。
或
java -Djava.rmi.server.hostname=xxx -jar xxx.jar
http://yangwencan2002.iteye.com/blog/284249
http://hi.baidu.com/wolf55/item/1676aa0b41184417cd34ea52