英文:
Client cannot get date from Server in Java
问题
我正在编写代码，从服务器获取日期传输到客户端。但是当我运行时，结果为 `null`。<br>
我无法理解为什么会这样，而且我在从服务器到客户端的日期格式方面也遇到了问题。
我可以同步时钟，但无法同步日期。<br>
**我需要帮助：** 我想要从服务器同步客户端的日期和时钟。
**服务器：**
```java
public class ServerDemo{
public static void main(String []args) throws IOException{
ServerSocket s = new ServerSocket(50555);
int server_timeout = 10000;
s.setSoTimeout(server_timeout);
displayBanner();
System.out.println("|\n|-Server is running...");
try{
while(true){
Socket s1 = s.accept();
System.out.println("|\n|-Connection Received : " + s1);
BufferedWriter dos = new BufferedWriter(new OutputStreamWriter(s1.getOutputStream()));
SimpleDateFormat outDate = new SimpleDateFormat("dd/MM/yyyy");
//DateFormat timeFormat = new SimpleDateFormat("HH:mm:ss");
Date dt = new Date();
System.out.println(" |\n |-Sent to client : " + dt);
dos.write(outDate.format(dt) + " ");
//dos.writeChars(timeFormat.format(dt) + '\n');
System.out.println(" |\n |-Connection Terminated : " + s1);
s1.close();
dos.close();
}
} catch(SocketTimeoutException e){
System.out.println("|\nTerminating server due to timeout...");
System.out.println("Server is terminated!");
s.close();
}
}
System.out.println("[+]--Clock Synchronization Server v1.0.1--- initializing...");
}
客户端：
public class ClientDemo{
public static void main(String []args) throws Exception{
Socket s = new Socket("192.168.1.190", 50555);
BufferedReader InFromServer = new BufferedReader(new InputStreamReader(s.getInputStream()));
BufferedWriter OutToServer = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
String date = InFromServer.readLine();
System.out.println(date);
/*
DateFormat Format = new SimpleDateFormat("dd/MM/yyyy");
//parse the data from the server
Date serverDate = Format.parse(date);
//format the server for the Runtime commands
DateFormat newFormatDate = new SimpleDateFormat("dd-MM-yy");
String sysdate = "" + newFormatDate.format(serverDate);
System.out.println(sysdate);
*/
InFromServer.close();
s.close();
}
}
<details>
<summary>英文:</summary>
I'm writing code to get date from server to client. But when I run, result is `null`.<br>
I can't understand why and I also have trouble in format day from Server to Client.
I can sync clock, but I cannot sync date.<br>
**I need a help:** I want to sync date and clock on client from server
**Server:**
public class ServerDemo{
public static void main(String []args) throws IOException{
ServerSocket s = new ServerSocket(50555);
int server_timeout = 10000;
s.setSoTimeout(server_timeout);
displayBanner();
System.out.println("|\n|-Server is running...");
try{
while(true){
Socket s1 = s.accept();
System.out.println("|\n|-Connection Received : " + s1);
BufferedWriter dos = new BufferedWriter(new OutputStreamWriter(s1.getOutputStream()));
SimpleDateFormat outDate = new SimpleDateFormat("dd/MM/yyyy");
//DateFormat timeFormat = new SimpleDateFormat("HH:mm:ss");
Date dt = new Date();
System.out.println(" |\n |-Sent to client : " + dt);
dos.write(outDate.format(dt) + " ");
//dos.writeChars(timeFormat.format(dt) + '\n');
System.out.println(" |\n |-Connection Terminated : " + s1);
s1.close();
dos.close();
}
} catch(SocketTimeoutException e){
System.out.println("|\nTerminating server due to timeout...");
System.out.println("Server is terminated!");
s.close();
}
}
System.out.println("[+]--Clock Synchronization Server v1.0.1--- initializing...");
}
**Client:**
public class ClientDemo{
public static void main(String []args) throws Exception{
Socket s = new Socket("192.168.1.190", 50555);
BufferedReader InFromServer = new BufferedReader(new InputStreamReader(s.getInputStream()));
BufferedWriter OutToServer = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
String date = InFromServer.readLine();
System.out.println(date);
/*
DateFormat Format = new SimpleDateFormat("dd/MM/yyyy");
//parse the data from the server
Date serverDate = Format.parse(date);
//format the server for the Runtime commands
DateFormat newFormatDate = new SimpleDateFormat("dd-MM-yy");
String sysdate = "" + newFormatDate.format(serverDate);
System.out.println(sysdate);
*/
InFromServer.close();
s.close();
}
</details>
# 答案1
**得分**: 0
`dos.flush();` 是关键。以下是已稍作修改的工作类：
服务器端：
```java
public class ServerDemo {
public static void main(String[] args) throws IOException {
ServerSocket s = new ServerSocket(50555);
int server_timeout = 30000;
s.setSoTimeout(server_timeout);
System.out.println("|\n|-服务器正在运行...");
try {
while (true) {
Socket s1 = s.accept();
System.out.println("|\n|-已接收连接 : " + s1);
BufferedWriter dos = new BufferedWriter(new OutputStreamWriter(s1.getOutputStream()));
SimpleDateFormat outDate = new SimpleDateFormat("dd/MM/yyyy");
Date dt = new Date();
System.out.println(" |\n |-发送给客户端 : " + dt);
dos.write(outDate.format(dt) + " ");
dos.flush(); // <- 这是关键
dos.close();
s1.close();
}
} catch (SocketTimeoutException e) {
System.out.println("|\n因超时终止服务器...");
System.out.println("服务器已终止!");
s.close();
}
}
}
客户端：
package serverClient;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;
public class ClientDemo {
public static void main(String[] args) throws Exception {
Socket s = new Socket("127.0.0.1", 50555);
BufferedReader InFromServer = new BufferedReader(new InputStreamReader(s.getInputStream()));
String date = InFromServer.readLine();
System.out.println(date);
InFromServer.close();
s.close();
}
}
英文:
dos.flush(); is the key. Here are the working classes (slightly changed):
Server side:
public class ServerDemo {
public static void main(String[] args) throws IOException {
ServerSocket s = new ServerSocket(50555);
int server_timeout = 30000;
s.setSoTimeout(server_timeout);
System.out.println("|\n|-Server is running...");
try {
while (true) {
Socket s1 = s.accept();
System.out.println("|\n|-Connection Received : " + s1);
BufferedWriter dos = new BufferedWriter(new OutputStreamWriter(s1.getOutputStream()));
SimpleDateFormat outDate = new SimpleDateFormat("dd/MM/yyyy");
Date dt = new Date();
System.out.println(" |\n |-Sent to client : " + dt);
dos.write(outDate.format(dt) + " ");
dos.flush(); //<- this is essential
dos.close();
s1.close();
}
} catch (SocketTimeoutException e) {
System.out.println("|\nTerminating server due to timeout...");
System.out.println("Server is terminated!");
s.close();
}
}
}
Client side:
package serverClient;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;
public class ClientDemo {
public static void main(String[] args) throws Exception {
Socket s = new Socket("127.0.0.1", 50555);
BufferedReader InFromServer = new BufferedReader(new InputStreamReader(s.getInputStream()));
String date = InFromServer.readLine();
System.out.println(date);
InFromServer.close();
s.close();
}
}
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