为什么我在socket接受的数据是乱码

server端
import java.io.*;
import java.net.*;
public class EchoServer1 extends Thread {
   Socket socket1;
   public EchoServer1( Socket s) {
      socket1=s;
      start();
   }
   public void run() {
      try {
         BufferedReader in=new BufferedReader(new InputStreamReader(socket1.getInputStream()));
         PrintWriter out =new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket1.getOutputStream())), true);
         byte[] sa=new byte[50];
         String stra=null;
String str=null;
str = new String(sa,0,5,"gb2312");
//stra = new String(straa.getBytes("iso8859-1"),"gb2312");
           // String str=in.readLine();
            System.out.println("Server receives " +str);
            out.write("Server returns back "+str);

out.flush();
in.close();
out.close();
      }
        
   catch (IOException e) {
      System.err.println("IO Exception");
   }
   finally {
      try {
         socket1.close();
      }
      catch (IOException e) {
         System.err.println("Socket not closed");
      }
   }
}static final int PORT = 8082;
public static void main(String[] args) throws IOException {
   ServerSocket s = new ServerSocket(PORT);
      System.out.println("Server Started");
      try {
         while(true) {
            Socket socket1 = s.accept();
            try {
               new EchoServer1(socket1);
            }
            catch(Exception e) {
                socket1.close();
            }
         }
      }
      finally {
         s.close();
      }
   }
}client端
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
public class client1 extends Thread{ int threadNumber;
Socket socket1;
public client1(int i,Socket s){
System.out.println("making:"+i);
threadNumber=i;
socket1=s;
start();

}
public void run(){
try{
PrintWriter out=new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket1.getOutputStream())),true);
int i=0;
out.print("datafrom client:"+threadNumber+"="+i);
out.flush();


BufferedReader in=new BufferedReader(new InputStreamReader(socket1.getInputStream()));

System.out.println(in.readLine()+"liu");

}
catch(IOException e){
try {
socket1.close();
} catch (IOException e1) {
// TODO 自动生成 catch 块
e1.printStackTrace();
}
}
}
public static void main(String[] args) throws IOException{
new client1(1,new Socket("10.0.1.75",8082));
new client1(2,new Socket("10.0.1.75",8082));
new client1(3,new Socket("10.0.1.75",8082)); }}
请问怎么办  谢谢