面试题：Java Socket编程异常处理中的资源管理

Question

假设你正在开发一个基于Java Socket的多线程网络应用，在处理Socket异常时，如何有效地管理网络连接等相关资源，避免资源泄漏？请结合具体代码示例进行说明。

Answer 1

在Java Socket多线程网络应用中处理异常并避免资源泄漏，可以通过以下方式实现：

1. 使用try - catch - finally块：在使用Socket、ServerSocket以及相关的InputStream、OutputStream时，将操作放在try块中，在catch块处理异常，在finally块关闭资源。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class SocketServer {
    private static final int PORT = 12345;

    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        Socket clientSocket = null;
        BufferedReader in = null;
        PrintWriter out = null;

        try {
            serverSocket = new ServerSocket(PORT);
            System.out.println("Server started on port " + PORT);

            clientSocket = serverSocket.accept();
            System.out.println("Client connected: " + clientSocket);

            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            out = new PrintWriter(clientSocket.getOutputStream(), true);

            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Received from client: " + inputLine);
                out.println("Echo: " + inputLine);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (in != null) in.close();
                if (out != null) out.close();
                if (clientSocket != null) clientSocket.close();
                if (serverSocket != null) serverSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

2. 使用try - with - resources（Java 7及以上）：这是Java 7引入的更简洁的资源管理方式，会自动关闭实现了AutoCloseable接口的资源。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class SocketServerTryWithResources {
    private static final int PORT = 12345;

    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(PORT);
             Socket clientSocket = serverSocket.accept();
             BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
             PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true)) {

            System.out.println("Server started on port " + PORT);
            System.out.println("Client connected: " + clientSocket);

            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Received from client: " + inputLine);
                out.println("Echo: " + inputLine);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

无论是使用传统的try - catch - finally还是try - with - resources，关键在于确保在异常发生时，所有打开的网络连接（Socket、ServerSocket）以及相关的输入输出流（InputStream、OutputStream及其包装类）都能被正确关闭，从而避免资源泄漏。