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Maven项目管理时，连接数据库报错

• 一、报错内容
• 二、分析与解决

  ---

  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. e v a l u a t e ( P a r e n t R u n n e r . j a v a : 268 ) a t j a v a . l a n g . r e f l e c t . C o n s t r u c t o r . n e w I n s t a n c e ( C o n s t r u c t o r . j a v a : 423 ) a t o r g . j u n i t . r u n n e r s . P a r e n t R u n n e r . r u n ( P a r e n t R u n n e r . j a v a : 363 ) a t c o m . m y s q l . j d b c . U t i l . h a n d l e N e w I n s t a n c e ( U t i l . j a v a : 404 ) a t o r g . j u n i t . r u n n e r . J U n i t C o r e . r u n ( J U n i t C o r e . j a v a : 137 ) a t c o m . m y s q l . j d b c . U t i l . g e t I n s t a n c e ( U t i l . j a v a : 387 ) a t c o m . i n t e l l i j . j u n i t 4. J U n i t 4 I d e a T e s t R u n n e r . s t a r t R u n n e r W i t h A r g s ( J U n i t 4 I d e a T e s t R u n n e r . j a v a : 69 ) a t c o m . m y s q l . j d b c . S Q L E r r o r . c r e a t e S Q L E x c e p t i o n ( S Q L E r r o r . j a v a : 919 ) a t c o m . i n t e l l i j . r t . j u n i t . I d e a T e s t R u n n e r 2.evaluate(ParentRunner.java:268) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at com.mysql.jdbc.Util.handleNewInstance(Util.java:404) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.mysql.jdbc.Util.getInstance(Util.java:387) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:919) at com.intellij.rt.junit.IdeaTestRunner 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.IdeaTestRunnerRepeater 1. e x e c u t e ( I d e a T e s t R u n n e r . j a v a : 38 ) a t c o m . m y s q l . j d b c . S Q L E r r o r . c r e a t e S Q L E x c e p t i o n ( S Q L E r r o r . j a v a : 898 ) a t c o m . i n t e l l i j . r t . e x e c u t i o n . j u n i t . T e s t s R e p e a t e r . r e p e a t ( T e s t s R e p e a t e r . j a v a : 11 ) a t c o m . m y s q l . j d b c . S Q L E r r o r . c r e a t e S Q L E x c e p t i o n ( S Q L E r r o r . j a v a : 887 ) a t c o m . i n t e l l i j . r t . j u n i t . I d e a T e s t R u n n e r 1.execute(IdeaTestRunner.java:38) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:898) at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:887) at com.intellij.rt.junit.IdeaTestRunner 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.IdeaTestRunnerRepeater.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

  ---

  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

    
                mysql
                mysql-connector-java
                5.1.37
    
    

    …

    • 实际下载使用的MySQL版本：8.0.31

      

      ---

      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：

                
                    mysql
                    mysql-connector-java
                    8.0.31
                
        

        **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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