Android客户端Socket无法接收Windows Java服务端数据求助

我在家庭WiFi环境下严格按规范实现客户端-服务端通信，但一直出现异常，急需技术建议。已经在Android Manifest中配置了INTERNET、ACCESS_NETWORK_STATE权限（还有MANAGE_EXTERNAL...权限，不过这个和当前问题不直接相关），怀疑是不是ISP的问题？

Java服务端代码 #

try {
    FileInputStream fIS = new FileInputStream(file);
    fIS.read(array, 0, array.length);
    Socket client = serverSocket.accept();
    if (!(client.getInetAddress().getHostAddress().equals("192.168.1.2"))) client.close();
        System.out.println(client.getInetAddress().getHostAddress() + " HAS CONNECTED, PORT "
            + client.getPort());
    if (client.isOutputShutdown()) {
        System.out.println("CLIENT SOCKET HAS BEEN SHUT!!!!!!");
        return;
    }
    OutputStream clientOut = client.getOutputStream();
    System.out.println("SENDING FILE CHUNKS...");
    System.out.println("0000000000000000");
    clientOut.write(array, 0, array.length);
    clientOut.flush();
    System.out.println("111111111111111111");
    client.close();
    System.out.println("333333333333333333");
    System.out.println("FINISHED!");
    }
catch(SocketException se){
        System.err.println(se.getMessage());
        se.printStackTrace();
    }
catch(FileNotFoundException ex){
        System.err.println(ex.getMessage());
    }
catch(IOException ex){
        System.err.println(ex.getMessage());
    }

Android客户端代码 #

try {
    clientSocket = new Socket("192.168.1.4",65001,thisLocalAddr,64999);
    clientSocket.setSoTimeout(15000);
    array = new byte[13574867];
    InputStream realIS =  clientSocket.getInputStream();
    if (clientSocket.isInputShutdown()) return;
    realIS.read(array,0,array.length);
    fiOS = new FileOutputStream(Environment.getExternalStorageDirectory() +
            "/Share/file.pdf");
    fiOS.write(array,0, array.length);

    realIS.close();
    clientSocket.close();
    fiOS.close();
}
catch (SocketException se) {
      Log.e("MainActivity ", se.getStackTrace().toString());

}
catch (NumberFormatException nfn) {
    Log.d("MainActivity", nfn.getStackTrace().toString());}
catch (UnknownHostException uhe) {
    Log.d("MainActivity", "Unknown Host Exception");
    Log.d("FileReceiver: ","dumbo =  " + dumbo.length()) ;
}

控制台输出 #

192.168.1.2 HAS CONNECTED, PORT 64999
SENDING FILE CHUNKS...
0000000000000000
Connection reset by peer
java.net.SocketException: Connection reset by peer
    at java.base/sun.nio.ch.SocketDispatcher.write0(Native Method)
    at java.base/sun.nio.ch.SocketDispatcher.write(SocketDispatcher.java:54)
    at java.base/sun.nio.ch.NioSocketImpl.tryWrite(NioSocketImpl.java:394)
    at java.base/sun.nio.ch.NioSocketImpl.implWrite(NioSocketImpl.java:410)
    at java.base/sun.nio.ch.NioSocketImpl.write(NioSocketImpl.java:440)
    at java.base/sun.nio.ch.NioSocketImpl$2.write(NioSocketImpl.java:819)
    at java.base/java.net.Socket$SocketOutputStream.implWrite(Socket.java:1223)
    at java.base/java.net.Socket$SocketOutputStream.write(Socket.java:1210)
    at Main.sendFile(Main.java:53)
    at Main.main(Main.java:15)

问题排查与解决建议 #

1. 排除ISP影响：家庭WiFi内设备通信走局域网，不经过ISP骨干网，所以该异常和ISP无关，优先排查代码和本地网络配置。

2. 修复服务端核心问题

   • IP校验逻辑漏洞：当前代码在关闭非指定IP的客户端Socket后，没有终止后续流程，会导致对已关闭的Socket执行写入操作，直接触发连接重置。修改为：

     if (!(client.getInetAddress().getHostAddress().equals("192.168.1.2"))) {
         client.close();
         return; // 终止后续代码执行
     }
     

   • 文件读取不完整：fIS.read(array, 0, array.length)无法保证一次性读满整个数组，大文件会出现数据截断，改成循环读取：

     int bytesRead;
     while ((bytesRead = fIS.read(array)) != -1) {
         clientOut.write(array, 0, bytesRead);
     }
     clientOut.flush();
     

   • 资源自动回收：用try-with-resources语法自动关闭流和Socket，避免资源泄漏：

     try (Socket client = serverSocket.accept();
          OutputStream clientOut = client.getOutputStream();
          FileInputStream fIS = new FileInputStream(file)) {
         // 业务逻辑代码
     } catch (Exception e) {
         e.printStackTrace();
     }
     

3. 修复客户端核心问题

   • 移除固定本地端口：指定固定本地端口64999可能导致端口冲突，让系统自动分配端口即可：

     clientSocket = new Socket("192.168.1.4",65001);
     

   • 处理实际读取字节数：realIS.read(array)返回实际读取的字节数，直接写入整个数组会导致文件冗余，修改为：

     int bytesRead = realIS.read(array,0,array.length);
     if (bytesRead > 0) {
         fiOS.write(array,0, bytesRead);
     }
     

   • 完善异常日志：SocketException只打印栈轨迹字符串无法定位问题，改成打印完整异常信息：

     Log.e("MainActivity ", se.getMessage(), se);
     

4. 本地网络排查点

   • 关闭路由器的AP隔离功能：部分路由器默认开启该功能，会阻止局域网内设备互相通信
   • 检查Android设备的后台网络权限：部分国产ROM会限制后台App的网络访问，确保你的App在后台能正常联网
   • 测试小文件传输：先尝试传输几KB的小文件，排除大文件传输时的超时或缓冲区问题

内容的提问来源于stack exchange，提问作者Huang