ObjectOutputStream送出的物件指向舊的物件?

假設我在Server端有以下的Code

HashMap<String,String> map=new HashMap<String,String> ();
ObjectOutputStream oos=new ObjectOutputStream(clientsocket.getOutputStream);
while(true){
       map.put(Long.toString(System.currentTimeMillis()),Long.toString(System.currentTimeMillis()));
       oos.writeObject(map);
}

另外一端收到的會發現後面收到的物件都跟第一次收到的物件一樣，Why?因為在送出的時候都是指向同一個位址，因此必須要加上oos.reset();結果才會正確。

File Transfer via Network using C vs. JAVA

這次的測試分別比較了使用gcc /gcc -O2 編譯而成的與javac 1.6.0_23 的版本編譯而成的執行檔來做比較，測試的兩台機器是在Lan環境下。測試的設備與程式碼如下:

CPU	Intel(R) Core(TM) i7 CPU         950  @ 3.07GHz
MEMERY	6G
NETWORK	1G
TEST FILE	466819755 byte (tar.bz2 file)

測試程式如下:
C (copy from http://content.edu.tw/primary/info_edu/cy_sa/report/more/8611a8.htm)
server.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#define TRUE 1
main()
{
int sock, msgsock, length;
struct sockaddr_in name;
FILE *fp;
int rval,wrval;
char buf[1024],filename[1024];

sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
/*-------------------------------------------------------*/
/* Create the acceptable connection host with Wildcard */
/*-------------------------------------------------------*/
name.sin_family = AF_INET;
name.sin_addr.s_addr = INADDR_ANY;
name.sin_port = 5000;
if (bind(sock, (struct sockaddr *)&name, sizeof name) < 0) {
perror ("binding stream socket");
exit(1);
}
listen(sock,5);
do{
msgsock = accept(sock,(struct sockaddr *)0, (int *)0);
if (msgsock == -1)
perror("accept error !\\n ");
else do {
bzero(buf, sizeof(buf) );
/*--------------------------------------------------*/
/* Read filename from msgsock (sent from client) */
/*--------------------------------------------------*/
if ((rval = read(msgsock, buf,1024)) < 0)
perror("reading stream message");
if (rval == 0)
printf("Ending connection\\n");
else {
if ((fp=fopen(buf,"r")) == NULL) {
printf("file not found : %s !\\n ",buf);
break;
}
printf("opening [%s] !!\\n ",buf);
bzero(filename,sizeof(filename));
strcpy(filename, buf);
/*--------------------------------------------------*/
/* Read file content & sent to msgsock ...> client */
/*--------------------------------------------------*/
while (fgets(buf,sizeof(buf),fp) != (char*)NULL) {
if ((wrval=write(msgsock,buf,sizeof(buf))) <0)
break;
//printf(".");
}
fclose(fp);
printf("\\n\\n closing [%s] ! \\n",filename);
rval=0;
}
}while (rval != 0);
close(msgsock);
printf(" [%s]finish* !! \\n ",filename);
}while (TRUE);
close(sock);
exit(0);
}

client.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#define DATA "The sea is clam ...."
main(int argc, char *argv[] )
{
int sock, rval, wrval;
char buf[1024];
struct sockaddr_in server;
struct hostent *hp, *gethostbyname();
FILE *fp;

sock = socket(AF_INET,SOCK_STREAM,0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
server.sin_family=AF_INET;
hp=gethostbyname(argv[1]);
if (hp == 0 ) {
printf( "%s : unknown host\\n", argv[1]);
exit(2);
}
bcopy((char*)hp->h_addr, (char *)&server.sin_addr, hp->h_length);
server.sin_port = 5000;
if (connect(sock, (struct sockaddr *)&server, sizeof server) < 0)
{
perror ("connecting stream socket");
exit(1);
}

if (write(sock, argv[3],strlen(argv[3])) < 0)
perror ("writing stream socket");
sleep(1);
printf("requiring [%s], ...\\n",argv[3]);
fp=fopen(argv[4],"w+");
/*---------------------------------------------------------*/
/* Read file content from sock (sent from ftp_serv ) */
/* and Write to local file */
/*---------------------------------------------------------*/
while ( (rval=read(sock,buf,sizeof(buf) )) >1) {
//printf(".");
fputs(buf,fp);
}
fclose(fp);
close(sock);
printf("finish !! \\n");
printf("closing connection !! \\n");
exit(0);
}

JAVA
server.java

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class server {
  public static void main(String[] args) throws IOException {
    ServerSocket servsock = new ServerSocket(5000);
    File myFile = new File("hadoop.tar.bz2");
    while (true) {
      Socket sock = servsock.accept();
      byte[] mybytearray = new byte[(int) myFile.length()];
      BufferedInputStream bis = new BufferedInputStream(new FileInputStream(myFile));
      bis.read(mybytearray, 0, mybytearray.length);
      OutputStream os = sock.getOutputStream();
      os.write(mybytearray, 0, mybytearray.length);
      os.flush();
      sock.close();
    }
  }
}

client.java

import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.Socket;

public class client {
  public static void main(String[] argv) throws Exception {
    Socket sock = new Socket("192.168.254.1", 5000);
    byte[] mybytearray = new byte[1024];
    InputStream is = sock.getInputStream();
    FileOutputStream fos = new FileOutputStream("hadoop.tar.bz2");
    BufferedOutputStream bos = new BufferedOutputStream(fos);
    int bytesRead ;
   while((bytesRead= is.read(mybytearray, 0, mybytearray.length))!=-1){
    bos.write(mybytearray, 0, bytesRead);
    }
    bos.close();
    sock.close();
  }
}

測試結果如下:

Test Case	Time(s)
C with -O2	20.539(s)
C without -O2	20.286(s)
JAVA	4.923(s)

很詭異的結果，再研究看看。