项目中链接mysql的问题，该怎么解决

Question

[2018-05-26 21:48:32] [ERROR] [com.alibaba.druid.pool.DruidDataSource:1217] create connection error
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
at sun.reflect.GeneratedConstructorAccessor62.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2575)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2311)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.GeneratedConstructorAccessor59.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:347)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:142)
at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:211)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:136)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1271)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1325)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:1215)
Caused by: java.lang.NullPointerException
at com.mysql.jdbc.ConnectionImpl.getServerCharacterEncoding(ConnectionImpl.java:3286)
at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1987)
at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1913)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1290)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2493)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2526)
... 15 more

Answer 1

1、检查url、用户名、密码是否正确
2、检查jar包是否冲突、网络是否畅通。

Answer 2

先通过数据库客户端登录数据库，确保地址、账密都正确。
使用druid的话，要配置好druid，springboot下的参考配置如下 ，其他框架的配置就要上网查了：
spring:
    datasource:
        type: com.alibaba.druid.pool.DruidDataSource
        #mysql
#        driverClassName:      com.mysql.jdbc.Driver       
        druid:
            #mysql
            url: jdbc:mysql://192.168.80.118:3306/xxxxxx
            username: root
            password: root            initial-size: 10
            max-active: 100
            min-idle: 10
            max-wait: 60000
            pool-prepared-statements: true
            max-pool-prepared-statement-per-connection-size: 20
            time-between-eviction-runs-millis: 60000
            min-evictable-idle-time-millis: 300000
            validation-query: SELECT 1 FROM DUAL
            test-while-idle: true
            test-on-borrow: false
            test-on-return: false
            stat-view-servlet:
                enabled: true
                url-pattern: /druid/*
                #login-username: admin
                #login-password: admin
            filter:
                stat:
                    log-slow-sql: true
                    slow-sql-millis: 1000
                    merge-sql: true
                wall:
                    config:
                      multi-statement-allow: true

Answer 3

#        driverClassName:      com.mysql.jdbc.Driver
这一段的#要去掉