Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransien,换句话说，就是电脑的mysql版本要和电脑的版本一样

        当遇到如下问题

### Error querying database.  Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
### The error may exist in com/itheima/mapper/BrandMapper.java (best guess)
### The error may involve com.itheima.mapper.BrandMapper.selectAll
### The error occurred while executing a query
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.

可能就是我们的mysql版本太高，但是pom.xml里面的配置文件的版本太低了，导致连接不上我么的数据库，我们可以点击Dependencies,将MySQL-connect-Java的版本提高

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>brand-demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <packaging>war</packaging>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>


    <dependencies>
        <!-- mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.13</version>
        </dependency>

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

        <!--servlet-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>

        <!--jsp-->

        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.2.1-b03</version>
            <scope>provided</scope>
        </dependency>

        <!--jstl-->
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>


    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
            </plugin>
        </plugins>
    </build>


</project>