Maven 解决 MySQL JDBC 驱动版本解析错误

Could not find artifact mysql:mysql-connector-java:pom:unknown in nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public)

The error 

Could not find artifact mysql:mysql-connector-java:pom:unknown means that Maven cannot resolve the version of the MySQL JDBC driver specified in your pom.xml. This is often due to one of three main issues: a missing version number, an incorrect Group ID and Artifact ID combination, or a problem with your Maven repository configuration. 

1. Missing version number

The most common cause is that the version number is missing from the dependency declaration in your pom.xml. Maven cannot guess which version you want to use. 

Solution
Add a specific, valid version number to your dependency. You can find the latest versions on the Maven Central Repository website. 

xml

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.32</version>
</dependency>

Use code with caution.

2. Old dependency coordinates with Spring Boot 3+

If you are using Spring Boot 3.x or newer, the Group ID and Artifact ID for the MySQL Connector have changed. This can cause the "unknown" version error. 

Solution
Use the new coordinates for the dependency. 

Old (for Spring Boot 2.x and earlier):

xml

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

Use code with caution.

New (for Spring Boot 3.x and later):

xml

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
</dependency>

Use code with caution.

3. Repository or cache issues

The problem could also be a misconfigured mirror, a corrupt local repository, or an issue with the remote repository itself (in this case, nexus-aliyun). 

Solutions

• Forcibly update Maven: Instruct Maven to check the remote repositories for updates by running mvn clean install -U from your project's root directory.
• Clear the local cache: If your local Maven repository (~/.m2/repository/) has become corrupted, you can delete the mysql/mysql-connector-java directory to force a fresh download.
• Check the AliYun repository: Verify that the version you are requesting is actually available on the AliYun repository. If it's not present, you may need to switch to the official Maven Central repository or explicitly declare a repository in your pom.xml. 

Example of declaring Maven Central in your pom.xml:

xml

<repositories>
    <repository>
        <id>central</id>
        <name>Maven Central</name>
        <url>https://repo.maven.apache.org/maven2</url>
    </repository>
</repositories>

Use code with caution.

错误 “Could not find artifact mysql:mysql-connector-java:pom:unknown” 意味着 Maven 无法解析你的 pom.xml 中指定的 MySQL JDBC 驱动版本。这通常是由以下三个主要问题之一导致的：缺少版本号、groupId 和 artifactId 组合不正确，或者 Maven 仓库配置有问题。

1. 缺少版本号

最常见的原因是 pom.xml 中的依赖声明缺少版本号。Maven 无法猜测你想要使用哪个版本。

解决方案：

为依赖添加一个具体、有效的版本号。你可以在 Maven 中央仓库网站上找到最新版本。

1. Spring Boot 3 + 使用了旧的依赖坐标

如果你使用的是 Spring Boot 3.x 或更新版本，MySQL 连接器的 groupId 和 artifactId 已经更改。这可能会导致 “unknown” 版本错误。

解决方案：

使用新的依赖坐标。

旧版本（适用于 Spring Boot 2.x 及更早版本）：

新版本（适用于 Spring Boot 3.x 及更高版本）：

1. 仓库或缓存问题

问题也可能出在镜像配置错误、本地仓库损坏，或者远程仓库本身有问题（在本例中是阿里云 Nexus）。

解决方案：

• 强制更新 Maven：通过在项目根目录运行mvn clean install -U命令，指示 Maven 检查远程仓库以获取更新。
• 清理本地缓存：如果你的本地 Maven 仓库（~/.m2/repository/）已损坏，可以删除mysql/mysql-connector-java目录，强制重新下载。
• 检查阿里云仓库：确认你请求的版本在阿里云仓库中是否实际存在。如果不存在，你可能需要切换到官方 Maven 中央仓库，或者在 pom.xml 中显式声明仓库。

在 pom.xml 中声明 Maven 中央仓库的示例：