Hadoop technology insider HDFS-Notes 6 RPC

1.1 hadoop remote process call

1. remote interface call (versionedprotocol interface must be implemented)

There is a method in it. During IPC communication, the version numbers of the client and server interfaces are compared. Must be consistent.

Package RPC; import Org. apache. hadoop. IPC. versionedprotocol; public interface mybizable extends versionedprotocol {// must have a public static final long version = 100l; // The actual call method public abstract string Hello (string name );}

 

2. Define the implementation class of remote objects

Package RPC; import Java. io. ioexception; public class mybiz implements mybizable {// obtain the version number @ overridepublic long getprotocolversion (string protocol, long clientversion) throws ioexception {// todo auto-generated method stubreturn version ;} @ overridepublic string Hello (string name) {system. out. println ("I was called"); Return "Hello:" + name ;}}

 

3. Build servers

Package RPC;

 

Import org. Apache. hadoop. conf. configuration;

Import org. Apache. hadoop. IPC. RPC;

Import org. Apache. hadoop. IPC. rpc. server;

 

Public class myserver {

Public static final string server_address = "localhost ";

Public static final int server_port = 12344;

Public static void main (string [] ARGs) throws exception {

// Public static server getserver (final object instance, final string bindaddress, final int port, configuration conf)

/** Construct an RPC server.

* @ Param instance the instance whose methods will be called client calls remote interface

* @ Param bindaddress the address to bind on to listen for connection listening connection address

* @ Param port the port to listen for connections on port

* @ Param conf configuration file

*/

Final server Server = rpc. getserver (New mybiz (), server_address, server_port, new configuration ());

Server. Start ();

}

}

4. Client implementation

Package RPC; import Java. io. ioexception; import java.net. inetsocketaddress; import Org. apache. hadoop. conf. configuration; import Org. apache. hadoop. IPC. RPC; import Org. apache. hadoop. IPC. versionedprotocol; public class myclient {public static void main (string [] ARGs) throws exception {/** construct a client-side proxy object that implements the named protocol, * talking to a server at the named address. */FINAL mybizable proxy = (mybizable) RPC. waitforproxy (mybizable. class
, Mybizable. Version
, New inetsocketaddress (myserver. server_address, myserver. server_port)
, New configuration (); // normal test string result = proxy. hello ("hello"); system. out. println (result); RPC. stopproxy (proxy );}}

 

Principle: (do not pay attention to it for the time being. You can review it when necessary)

Summary: hadoop's namenode, secondarynamenode, datanode, jobtrack and other processes all implement remote call interfaces. That is to say, each of them is a server waiting for the client to call. They act as clients and servers.

To start hadoop is to start the RPC server.