null connection returned

As an AI language model, I do not have the context to provide a specific answer. However, a "null connection returned" error message typically means that a connection to a database or server was attempted but was unsuccessful, resulting in a null value being returned. This could be due to various reasons such as incorrect login credentials, network issues, or server maintenance. More information about the specific context and error message would be required to provide a more accurate answer.

相关问题

org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection: DataSource returned null

org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection: DataSource returned null是由于无法获取到JDBC连接而引起的异常。这可能是由于配置文件中的数据库连接信息错误导致的。根据引用和引用，可以看出其中的错误信息显示了两种不同的情况。引用中的错误信息显示了访问数据库时使用的用户名为空，而引用中的错误信息没有明确指出具体的原因。可能是由于数据库连接配置文件中的密码写错或为空导致的。根据引用，可以看出在application.properties文件中找到了将密码写错或留空的情况。因此，解决这个问题的方法是在配置文件中正确配置数据库连接的用户名和密码。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
- *1* [Springboot+MySQL，出现Could not get JDBC Connection](https://download.csdn.net/download/weixin_38732425/13688000)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 50%"]
- *2* *3* [【解决报错】Failed to obtain JDBC Connection](https://blog.csdn.net/weixin_43883815/article/details/109122690)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 50%"]
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constructing new movegroup connection for group 'manipulator' in namespace

引用\[1\]:出现如下报错信息： \[ INFO\] \[1564730909.628248268\]: Constructing new MoveGroup connection for group 'arm_group' in namespace '' \[ INFO\] \[1564730910.984667942\]: MoveItSimpleControllerManager: Waiting for redwall_arm/follow_joint_trajectory to come up \[ERROR\] \[1564730915.984849668\]: MoveItSimpleControllerManager: Action client not connected: redwall_arm/follow_joint_trajectory \[ INFO\] \[1564730916.087709422\]: Returned 0 controllers in list \[ INFO\] \[1564730916.107154984\]: Trajectory execution is managing controllers 。
引用\[2\]:发现竟然没有找到follow_joint_trajectory消息，难道move_group没有发布吗？纠结了一天，终于找到原因了，之前虚拟机械臂有gazebo的ros_control插件自动帮我们获取了follow_joint_trajectory的动作action信息，现在到真实机器人了，需要我们自己写程序了。问题找到了，最重要的是要理解一点，move_group此时是follow_joint_trajectory的client端，动作消息是client端的move_group发布的，听起来有点绕，但是千万不要把报错信息的action client not connect搞混淆了，我们现在client是存在且被感知的(就是move_group)，而之所以报错是因为我缺少了action server端，我们需要添加一个server订阅这个action。
引用\[3\]:Animation Blueprints Exposed types on SkeletalControlBase to allow creation of derived classes.Added support for creating sub-classes of FAnimNode_StateMachine outside Engine module.Allowed UAnimNotify_PlayMontageNotify to be inherited by other modules.Bug Fix:Fixed sub-classes of FAnimNode_SkeletalControlBase not having deprecated CacheBones called。

问题:constructing new movegroup connection for group 'manipulator' in namespace
回答: 根据提供的引用内容，报错信息中显示正在构建一个新的MoveGroup连接，连接的组是'manipulator'，命名空间为空。\[1\]这个报错信息表明正在尝试建立一个名为'manipulator'的组的MoveGroup连接。然而，报错信息中还显示了一个错误，即Action client 'redwall_arm/follow_joint_trajectory'未连接。\[2\]这可能是因为缺少一个action server端，需要添加一个server来订阅这个action。根据提供的信息，还无法确定是否已经在命名空间中找到了'manipulator'组的相关信息。
#### 引用[.reference_title]
- *1* *2* [通过ROS控制真实机械臂(5)---Moveit!真实机械臂(move_group和demo.launch修改)](https://blog.csdn.net/qq_34935373/article/details/95916111)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insert_down28v1,239^v3^insert_chatgpt"}} ] [.reference_item]
- *3* [Unreal Engine 4.20 Release Notes](https://blog.csdn.net/pizi0475/article/details/81636150)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insert_down28v1,239^v3^insert_chatgpt"}} ] [.reference_item]
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