Socket常见异常场景模拟实战

前言：

如标题所示，本文主要罗列下Socket编程中的那些常见异常，通过实战的方式来模拟这些异常。

1.java.net.BindException: Address already in use: JVM_Bind

原因：就是当前端口号已经被其他进程占用了。

模拟：创建两个ServerSocket，以相同的端口号启动。

ServerSocket serverSocket = new ServerSocket();
serverSocket.bind(new InetSocketAddress("localhost", 9999));ServerSocket serverSocket2 = new ServerSocket();
serverSocket2.bind(new InetSocketAddress("localhost", 9999));

此时就会出现该异常

2.java.net.ConnectException: Connection refused: connect

原因：当客户端通过Socket(ip,port)创建对远端ip:port的连接时，当对应的ip或port并不存在时（或者ip存在但是在执行port上没有进程在监听），则会报当前错

模拟：服务端以9999端口启动，客户端以8888端口连接

// 服务端启动
ServerSocket serverSocket = new ServerSocket();
serverSocket.bind(new InetSocketAddress("localhost", 9999));// 客户端启动
Socket socket = new Socket("localhost", 8888);

3.java.net.SocketTimeoutException: connect timed out

原因：客户端在规定时间内没有连接上服务端。这个报错的具体原因有很多种

模拟：笔者在Mac上启动ServerSocket，并打开防火墙，阻止所有传入连接；然后在Windows电脑上开启Socket连接

服务端代码

SocketAddress address = new InetSocketAddress("localhost", 9999);
ServerSocket ss = new ServerSocket();
ss.bind(address);
// 接收请求
Socket s = ss.accept();// 直接sleep
Thread.sleep(1000000);

客户端代码

public class Client {static SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");public static void main(String[] args) {connectTime();}public static void connectTime() {Socket socket =  new Socket();try {System.out.println("begin time:" + format.format(new Date()));// 连接服务端ip:portsocket.connect(new InetSocketAddress("192.168.3.18", 9999), 3000);System.out.println(socket.isConnected());} catch (IOException e) {e.printStackTrace();} finally {System.out.println("end time:" + format.format(new Date()));}}
}

测试：

先启动服务端，再启动客户端，可以看到客户端的控制台信息如下

begin time:2022-06-18 11:54:19
java.net.SocketTimeoutException: connect timed outat java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)at java.net.Socket.connect(Socket.java:589)at sockettimeout.Client.connectTime(Client.java:27)at sockettimeout.Client.main(Client.java:19)
end time:2022-06-18 11:54:22

连接花费时间为3秒，就是我们设置的连接超时时间

4.java.net.SocketTimeoutException: Read timed out

原因：客户端或服务端Socket设置了读超时时间，在指定时间内没有获取到结果，则会抛出该异常

模拟：服务端监听到连接后直接sleep，客户端在连接成功后从InputStream中获取数据，一直等待到超时

服务端代码

SocketAddress address = new InetSocketAddress("localhost", 9999);
ServerSocket ss = new ServerSocket();
ss.bind(address);
// 接收请求
Socket s = ss.accept();// 直接sleep
Thread.sleep(1000000);

客户端代码

static SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");public static void main(String[] args) {try {Socket socket = new Socket("localhost", 9999);// 设置超时时间为5秒socket.setSoTimeout(5000);socket.setKeepAlive(true);InputStream inputStream = socket.getInputStream();byte[] bytes = new byte[1024];System.out.println("begin time:" + format.format(new Date()));// 在这里阻塞read方法，一直到超时为止while (inputStream.read() != -1) {inputStream.read(bytes);}} catch (Exception e) {e.printStackTrace();} finally {System.out.println("end time:" + format.format(new Date()));}
}

测试：

先启动服务端，再启动客户端，可以看到客户端的控制台信息如下

begin time:2022-06-18 11:16:04
java.net.SocketTimeoutException: Read timed outat java.net.SocketInputStream.socketRead0(Native Method)at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)at java.net.SocketInputStream.read(SocketInputStream.java:171)at java.net.SocketInputStream.read(SocketInputStream.java:141)at java.net.SocketInputStream.read(SocketInputStream.java:224)at sockettimeout.Client.main(Client.java:27)
end time:2022-06-18 11:16:09

end-start正好等于我们设置的Socket.setSoTimeout(5000) 5秒钟。

5.java.net.SocketException: Socket closed

原因：这种情况在客户端和服务端都有可能发生。主要原因是：在socket关闭了连接后，又发起了读写操作

模拟：客户端Socket创建完成，在调用close()方法后，再次发起写操作

5.1 服务端代码

下面展示的是一个完整的服务端代码，后续会采用该示例

public class BIOServerSocket {private String address;private int port;public BIOServerSocket(String address, int port) {this.address = address;this.port = port;}public void startServer() {try {ServerSocket serverSocket = new ServerSocket();serverSocket.bind(new InetSocketAddress(address, port));System.out.println("bio server start...");while (true) {Socket clientSocket = serverSocket.accept();System.out.println("client connect...");// 写入 threadServerWriteThread serverWriteThread = new ServerWriteThread(clientSocket);serverWriteThread.start();// 读取数据read(clientSocket);}} catch (IOException e) {e.printStackTrace();}}private void read(Socket clientSocket) {try {BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));String msg = "";while ((msg = bufferedReader.readLine()) != null) {System.out.println("receive msg: " + msg);if (msg.equals("bye")) {bufferedReader.close();clientSocket.close();}}} catch (IOException e) {try {clientSocket.close();} catch (IOException ex) {ex.printStackTrace();}e.printStackTrace();}}public static void main(String[] args) {String address = "localhost";int port = 9999;BIOServerSocket bioServerSocket = new BIOServerSocket(address, port);bioServerSocket.startServer();}
}/*** 从Scanner获取输入信息，并写回到client*/
class ServerWriteThread extends Thread {private Socket socket;private PrintWriter writer;private Scanner scanner;public ServerWriteThread(Socket socket) throws IOException{this.socket = socket;scanner = new Scanner(System.in);this.writer = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()), true);}@Overridepublic void run() {String msg = "";try {while ((msg = scanner.nextLine()) != null) {if (msg.equals("bye")) {socket.close();break;}writer.println(msg);}} catch (Exception e) {e.printStackTrace();}}
}

客户端代码

try {Socket socket =  new Socket("localhost", 9999);OutputStream outputStream = socket.getOutputStream();// 第一次写数据outputStream.write(11);// 关闭socketsocket.close();// 第二次写数据outputStream.write(12);
} catch (IOException e) {e.printStackTrace();
}

测试：

先启动服务端，再启动客户端，可以看到客户端的控制台输出如下信息

java.net.SocketException: Socket closedat java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:118)at java.net.SocketOutputStream.write(SocketOutputStream.java:134)at sockettimeout.Client.socketClose(Client.java:32)at sockettimeout.Client.main(Client.java:20)

6.java.net.SocketException: Software caused connection abort: socket write error

原因：该问题有可能发生在客户端或服务端。主要因为：当一端的socket被关闭后，另一端仍进行数据读写

注意：与5的不同在于，5中的示例是当前socket关闭后又继续发送数据，而6该问题是对端关闭了socket，当前端仍进行数据读写

模拟：服务端接收到连接后，等待一段时间则关闭该socket，而此时客户端继续读写

服务端代码

SocketAddress address = new InetSocketAddress("localhost", 9999);
ServerSocket ss = new ServerSocket();
ss.bind(address);// 接收连接
Socket s = ss.accept();Thread.sleep(3000);s.close();

客户端代码：

try {System.out.println("begin time:" + format.format(new Date()));Socket socket =  new Socket("localhost", 9999);OutputStream outputStream = socket.getOutputStream();outputStream.write(11);System.out.println("send 11");Thread.sleep(1000);outputStream.write(12);System.out.println("send 12");Thread.sleep(1000);outputStream.write(13);System.out.println("send 13");Thread.sleep(1000);outputStream.write(14);System.out.println("send 14");Thread.sleep(1000);outputStream.write(15);System.out.println("send 15");
} catch (Exception e) {e.printStackTrace();
} finally {System.out.println("end time:" + format.format(new Date()));
}

测试：先启动服务端，再启动客户端，控制台结果如下：

begin time:2022-06-18 12:16:14
send 11
send 12
send 13
java.net.SocketException: Software caused connection abort: socket write errorat java.net.SocketOutputStream.socketWrite0(Native Method)at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:111)at java.net.SocketOutputStream.write(SocketOutputStream.java:134)at sockettimeout.Client.connectReset(Client.java:38)at sockettimeout.Client.main(Client.java:20)
end time:2022-06-18 12:16:17

注意：还有可能遇到些别的异常信息，如connect reset by peer，实际是与当前场景类似的。

参考：

java.net.SocketException四大异常解决方案_hzp666的博客-CSDN博客_socketexception

Java SDK报错：SocketTimeoutException - 表格存储 - 阿里云 SocketTimeoutException的一些场景