【数据库连接异常】MySQLNonTransientConnectionException: Could not create connection to database server.

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一、报错内容

在JDBC连接数据库时，代码没有错，运行却出现报错信息：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)atjava.lang.reflect.Constructor.newInstance(Constructor.java:423)atorg.junit.runners.ParentRunner.run(ParentRunner.java:363)atcom.mysql.jdbc.Util.handleNewInstance(Util.java:404)atorg.junit.runner.JUnitCore.run(JUnitCore.java:137)atcom.mysql.jdbc.Util.getInstance(Util.java:387)atcom.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)atcom.mysql.jdbc.SQLError.createSQLException(SQLError.java:919)atcom.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)atcom.mysql.jdbc.SQLError.createSQLException(SQLError.java:898)atcom.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)atcom.mysql.jdbc.SQLError.createSQLException(SQLError.java:887)atcom.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:862)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2331)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2084)
Caused by: java.lang.NullPointerException: null

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二、分析与解决

我出现这个问题后，找到的原因是：Maven添加管理的mysql-connector-java依赖版本与下载使用的MySQL版本不一致导致的无法获取数据库连接对象。

• Maven添加的版本：5.1.37

<dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>5.1.37version>
dependency>

…

• 实际下载使用的MySQL版本：8.0.31

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解决方案：

• 将IDEA项目中Maven的pom.xml配置文件中添加的依赖版本改为自己正在使用的MySQL版本即可：

        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>8.0.31version>
        dependency>

**改完后记得重启IDEA**

测试：

    @Test
    public void testGetConnection(){
        Connection connection = JDBCUtils.getConnection();
        System.out.println("connection = " + connection);
    }
}

成功获取连接对象，问题解决：

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