java - Java中同一个类的继承和组合

Question

我在 github 上找到了以下代码:

public class DummySSLSocketFactory extends SSLSocketFactory {

    private static final Logger LOG = LoggerFactory.getLogger(DummySSLSocketFactory.class);
    private SSLSocketFactory factory;

    public DummySSLSocketFactory() {
        try {
            SSLContext sslContext = SSLContext.getInstance("TLS");
            TrustManager[] trustManagers = new TrustManager[] {new DummyTrustManager()};
            sslContext.init(null, trustManagers, new java.security.SecureRandom());
            factory = sslContext.getSocketFactory();
        } catch (Exception e) {
            throw new RuntimeCamelException("Error creating DummySSLSocketFactory: " + e.getMessage(), e);
        }
    }

    /**
     * Must provide this getDefault operation for JavaMail to be able to use this factory.
     */
    public static SocketFactory getDefault() {
        LOG.warn("Camel is using DummySSLSocketFactory as SSLSocketFactory (only to be used for testing purpose)");
        return new DummySSLSocketFactory();
    }

    public String[] getDefaultCipherSuites() {
        return factory.getDefaultCipherSuites();
    }

    public String[] getSupportedCipherSuites() {
        return factory.getSupportedCipherSuites();
    }

    public Socket createSocket(Socket socket, String host, int port, boolean autoClose) throws IOException {
        return factory.createSocket(socket, host, port, autoClose);
    }

    public Socket createSocket(String host, int port) throws IOException {
        return factory.createSocket(host, port);
    }

    public Socket createSocket(String host, int port, InetAddress localAddress, int localPort)
        throws IOException {
        return factory.createSocket(host, port, localAddress, localPort);
    }

    public Socket createSocket(InetAddress host, int port) throws IOException {
        return factory.createSocket(host, port);
    }

    public Socket createSocket(InetAddress address, int port, InetAddress localAddress, int localPort)
        throws IOException {
        return factory.createSocket(address, port, localAddress, localPort);
    }

    public Socket createSocket() throws IOException {
        // must have this createSocket method
        return factory.createSocket();
    }

}

类似的实现广泛应用于不同的项目。我试图弄清楚同时使用继承和组合的目的是什么。看起来只要有一个返回 sslContext.getSocketFactory(); 结果的工厂方法就足够了，因为它根本不扩展该类。

Answer 1

我不知道编写这段代码的确切意图是什么，但是在这种类组织中，很明显，使用组合和继承，DummySSLSocketFactory可以使用 protected 方法 在 SSLSocketFactory 中实现，甚至在它上面的类中实现(使用 super)。
这是可能的，因为 DummySSLSocketFactory 具有对其父类 SSLSocketFactory

的引用

 private SSLSocketFactory factory;

在 DummySSLSocketFactory 的构造函数中设置

factory = sslContext.getSocketFactory();

如果没有此引用，您将能够使用 super 访问 SSLSocketLayer，但不能使用更高的类。