import org.apache.sshd.common.keyprovider.AbstractKeyPairProvider; //导入依赖的package包/类
public KeyCapture() {
    sshd.setPort(9422);

    sshd.setPublickeyAuthenticator((username, key, session) -> {
        final String expectedKey;
        final String fingerprint = fingerprint(key);

        synchronized (KeyCapture.this) {
            final String newUser = issuedTokens.get(username);
            if (null != newUser) {
                userDatabase.put(newUser, fingerprint);
                session.setAttribute(JUST_ADDED, true);
                session.setAttribute(ACCOUNT_NAME, username);
                return true;
            }

            expectedKey = userDatabase.get(username);
        }

        logger.info("{} trying to authenticate with {}, db contains {}", username, fingerprint, expectedKey);

        if (null == expectedKey || !expectedKey.equals(fingerprint)) {
            return false;
        }

        session.setAttribute(ACCOUNT_NAME, username);
        session.setAttribute(JUST_ADDED, false);
        return true;
    });

    sshd.setKeyPairProvider(new AbstractKeyPairProvider() {
        @Override
        public Iterable<KeyPair> loadKeys() {
            return Collections.singleton(serverKeyPair);
        }
    });

    sshd.setShellFactory(CommandWrapper.wrap((in, out, err, session) -> {
        try (final PrintStream ps = new PrintStream(out)) {
            final String whom = session.getAttribute(ACCOUNT_NAME);

            if (session.getAttribute(JUST_ADDED)) {
                ps.println("Added successfully!  You can now log-in normally.\r");
                synchronized (KeyCapture.this) {
                    issuedTokens.remove(whom);
                }
                return 0;
            }
            ps.println("Hi!  You've successfully authenticated as " + whom + "\r");
            ps.println("Bye!\r");
        }
        return 0;
    }));
}