用java和MySQL实现访客管理系统的黑名单功能代码，要求黑名单功能里有增删改查功能

这里给出一个简单的访客管理系统的黑名单功能代码，使用Java和MySQL实现。其中，访客表的结构为id、name、phone、email、is_blacklist，is_blacklist字段表示是否在黑名单中（0表示不在，1表示在）。

增加黑名单：

public void addToBlacklist(int visitorId) throws SQLException {
    Connection conn = null;
    PreparedStatement ps = null;
    try {
        conn = getConnection();
        String sql = "UPDATE visitors SET is_blacklist = 1 WHERE id = ?";
        ps = conn.prepareStatement(sql);
        ps.setInt(1, visitorId);
        ps.executeUpdate();
    } finally {
        close(conn, ps, null);
    }
}

移出黑名单：

public void removeFromBlacklist(int visitorId) throws SQLException {
    Connection conn = null;
    PreparedStatement ps = null;
    try {
        conn = getConnection();
        String sql = "UPDATE visitors SET is_blacklist = 0 WHERE id = ?";
        ps = conn.prepareStatement(sql);
        ps.setInt(1, visitorId);
        ps.executeUpdate();
    } finally {
        close(conn, ps, null);
    }
}

修改黑名单状态：

public void updateBlacklistStatus(int visitorId, int status) throws SQLException {
    Connection conn = null;
    PreparedStatement ps = null;
    try {
        conn = getConnection();
        String sql = "UPDATE visitors SET is_blacklist = ? WHERE id = ?";
        ps = conn.prepareStatement(sql);
        ps.setInt(1, status);
        ps.setInt(2, visitorId);
        ps.executeUpdate();
    } finally {
        close(conn, ps, null);
    }
}

查询黑名单列表：

public List<Visitor> getBlacklist() throws SQLException {
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet rs = null;
    List<Visitor> list = new ArrayList<>();
    try {
        conn = getConnection();
        String sql = "SELECT * FROM visitors WHERE is_blacklist = 1";
        ps = conn.prepareStatement(sql);
        rs = ps.executeQuery();
        while (rs.next()) {
            Visitor visitor = new Visitor();
            visitor.setId(rs.getInt("id"));
            visitor.setName(rs.getString("name"));
            visitor.setPhone(rs.getString("phone"));
            visitor.setEmail(rs.getString("email"));
            visitor.setIsBlacklist(rs.getInt("is_blacklist"));
            list.add(visitor);
        }
    } finally {
        close(conn, ps, rs);
    }
    return list;
}

其中，getConnection()和close()方法为获取数据库连接和关闭资源的通用方法，这里不再赘述。