(初级)HDFS中的RPC
RPC采用客户机/服务器模式。请求程序就是一个客户机，而服务提供程序就是一个服务器。首先，客户机调用进程发送一个有进程参数的调用信息到服务进程，然后等待应答信息。在服务器端，进程保持睡眠状态直到调用信息的到达为止。当一个调用信息到达，服务器获得进程参数，计算结果，发送答复信息，然后等待下一个调用信息，最后，客户端调用进程接收答复信息，获得进程结果，然后调用执行继续进行。
hadoop的整个体系结构就是构建在RPC之上的(见org.apache.hadoop.ipc)
package rpc;
import org.apache.hadoop.ipc.VersionedProtocol;
public interface MyBizable extends VersionedProtocol{
long VERSION = 2345245L;
public abstract String hello(String name);
}
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package rpc;
import java.io.IOException;
import org.apache.hadoop.ipc.VersionedProtocol;
public class MyBiz implements VersionedProtocol, MyBizable{
/* (non-Javadoc)
* @see rpc.MyBizable#hello(java.lang.String)
*/
@Override
public String hello(String name) {
System.out.println("服务器端，我被调用了");
return "hello "+name;
}
/* (non-Javadoc)
* @see rpc.MyBizable#getProtocolVersion(java.lang.String, long)
*/
@Override
public long getProtocolVersion(String protocol, long clientVersion) throws IOException {
return VERSION;
}
}
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package rpc;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.ipc.RPC;
import org.apache.hadoop.ipc.RPC.Server;
public class MyServer {
static final String ADDRESS="localhost";
static final int PORT=12345;
public static void main(String[] args) throws Exception {
/**
* @param instance the instance whose methods will be called此实例中的方法会被调用
* @param conf the configuration to use
* @param bindAddress the address to bind on to listen for connection用于监听链接的地址
* @param port the port to listen for connections on
* @param numHandlers the number of method handler threads to run
* @param verbose whether each call should be logged
*/
Server server = RPC.getServer(new MyBiz(), ADDRESS, PORT, new Configuration());
server.start();
}
}
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package rpc;
import java.net.InetSocketAddress;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.ipc.RPC;
public class MyClient {
public static void main(String[] args) throws Exception{
/**
* 构造一个客户端代理对象，该对象实现了命名的协议
* 代理对象会与指定地址的服务端通话
*/
MyBizable proxy = (MyBizable)RPC.waitForProxy(
MyBizable.class,//Class protocol,
MyBizable.VERSION,
new InetSocketAddress(MyServer.ADDRESS,MyServer.PORT),
new Configuration());
//hello()的调用，在RPC的环境下，是发生在server端，而非client端
String result = proxy.hello("yanxin");
System.out.println("客户端:"+result);
//关闭网络连接
RPC.stopProxy(proxy);
}
}
