MySQLNonTransientConnectionException 无法创建与数据库服务器的连接。引起：java.lang.NullPointerException答案

【问题标题】：MySQLNonTransientConnectionException Could not create connection to database server. Caused by: java.lang.NullPointerExceptionMySQLNonTransientConnectionException 无法创建与数据库服务器的连接。引起：java.lang.NullPointerException
【发布时间】：2018-10-27 05:06:50
【问题描述】：

我有一个本地 MySQL 社区服务器 (8.0.11) 在 127.0.0.1:3306 的本地主机上运行。

（我创建了一个数据库并为其注册了一个用户）。我可以使用以下终端查询来访问数据库：./mysql -u testuser -p

并且我能够访问服务器。

我正在使用 Spring 和 JDBC 使用以下代码做同样的事情：

private final String URL= "jdbc:mysql://127.0.0.1:3306/db_example?useSSL=false";
private final String DB_USERNAME = "testuser";
private final String DB_PASSWORD = "pass";


public void connectAndInsertToDB() {
    try {
        Class.forName("com.mysql.jdbc.Driver").newInstance();
    } catch (Exception e) {
        System.out.println("JAVA: Class.forName() error");
        e.printStackTrace();
    }
    try {

        conn = DriverManager.getConnection(URL, DB_USERNAME, DB_PASSWORD);
    } catch (SQLException e) {
        System.out.println("Error in initializing a connection to MYSQL DB");
        e.printStackTrace();

    }
}

然后我收到以下错误：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
23:03:28,603 ERROR [stderr] (default task-3)    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
23:03:28,603 ERROR [stderr] (default task-3)    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
23:03:28,604 ERROR [stderr] (default task-3)    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
23:03:28,607 ERROR [stderr] (default task-3)    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
23:03:28,608 ERROR [stderr] (default task-3)    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
23:03:28,608 ERROR [stderr] (default task-3)    at com.mysql.jdbc.Util.getInstance(Util.java:387)
23:03:28,608 ERROR [stderr] (default task-3)    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:917)
23:03:28,609 ERROR [stderr] (default task-3)    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896)
23:03:28,609 ERROR [stderr] (default task-3)    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885)
23:03:28,609 ERROR [stderr] (default task-3)    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
23:03:28,610 ERROR [stderr] (default task-3)    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2332)
23:03:28,611 ERROR [stderr] (default task-3)    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2085)
23:03:28,611 ERROR [stderr] (default task-3)    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795)
23:03:28,611 ERROR [stderr] (default task-3)    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
23:03:28,611 ERROR [stderr] (default task-3)    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
23:03:28,612 ERROR [stderr] (default task-3)    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
23:03:28,612 ERROR [stderr] (default task-3)    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
23:03:28,612 ERROR [stderr] (default task-3)    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
23:03:28,612 ERROR [stderr] (default task-3)    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
23:03:28,613 ERROR [stderr] (default task-3)    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)
23:03:28,613 ERROR [stderr] (default task-3)    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)
23:03:28,613 ERROR [stderr] (default task-3)    at java.sql.DriverManager.getConnection(DriverManager.java:664)
23:03:28,613 ERROR [stderr] (default task-3)    at java.sql.DriverManager.getConnection(DriverManager.java:247)
23:03:28,613 ERROR [stderr] (default task-3)    at com.voice4.spring.security.config.core.Inventory.connectAndInsertToDB(Inventory.java:41)
23:03:28,614 ERROR [stderr] (default task-3)    at com.voice4.spring.security.config.core.KomalController.indexPage(KomalController.java:36)
23:03:28,614 ERROR [stderr] (default task-3)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
23:03:28,614 ERROR [stderr] (default task-3)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
23:03:28,614 ERROR [stderr] (default task-3)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
23:03:28,614 ERROR [stderr] (default task-3)    at java.lang.reflect.Method.invoke(Method.java:497)
23:03:28,615 ERROR [stderr] (default task-3)    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
23:03:28,615 ERROR [stderr] (default task-3)    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
23:03:28,615 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
23:03:28,616 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
23:03:28,616 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
23:03:28,616 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
23:03:28,616 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
23:03:28,617 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
23:03:28,617 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
23:03:28,617 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
23:03:28,617 ERROR [stderr] (default task-3)    at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
23:03:28,618 ERROR [stderr] (default task-3)    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
23:03:28,618 ERROR [stderr] (default task-3)    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
23:03:28,618 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
23:03:28,619 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)
23:03:28,619 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)
23:03:28,620 ERROR [stderr] (default task-3)    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
23:03:28,621 ERROR [stderr] (default task-3)    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
23:03:28,621 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,622 ERROR [stderr] (default task-3)    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:115)
23:03:28,622 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,622 ERROR [stderr] (default task-3)    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
23:03:28,623 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,623 ERROR [stderr] (default task-3)    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
23:03:28,624 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,624 ERROR [stderr] (default task-3)    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:169)
23:03:28,625 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,625 ERROR [stderr] (default task-3)    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
23:03:28,625 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,625 ERROR [stderr] (default task-3)    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200)
23:03:28,625 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,626 ERROR [stderr] (default task-3)    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:121)
23:03:28,626 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,626 ERROR [stderr] (default task-3)    at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:100)
23:03:28,626 ERROR [stderr] (default task-3)    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
23:03:28,627 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,627 ERROR [stderr] (default task-3)    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66)
23:03:28,627 ERROR [stderr] (default task-3)    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
23:03:28,627 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,627 ERROR [stderr] (default task-3)    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105)
23:03:28,627 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,628 ERROR [stderr] (default task-3)    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
23:03:28,628 ERROR [stderr] (default task-3)    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
23:03:28,628 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
23:03:28,628 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:214)
23:03:28,628 ERROR [stderr] (default task-3)    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177)
23:03:28,629 ERROR [stderr] (default task-3)    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
23:03:28,629 ERROR [stderr] (default task-3)    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
23:03:28,629 ERROR [stderr] (default task-3)    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
23:03:28,629 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
23:03:28,629 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
23:03:28,630 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
23:03:28,630 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
23:03:28,630 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
23:03:28,630 ERROR [stderr] (default task-3)    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
23:03:28,630 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
23:03:28,631 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
23:03:28,631 ERROR [stderr] (default task-3)    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
23:03:28,631 ERROR [stderr] (default task-3)    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
23:03:28,631 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
23:03:28,632 ERROR [stderr] (default task-3)    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
23:03:28,632 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
23:03:28,633 ERROR [stderr] (default task-3)    at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
23:03:28,633 ERROR [stderr] (default task-3)    at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
23:03:28,633 ERROR [stderr] (default task-3)    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
23:03:28,634 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
23:03:28,634 ERROR [stderr] (default task-3)    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
23:03:28,634 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)
23:03:28,634 ERROR [stderr] (default task-3)    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
23:03:28,635 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
23:03:28,635 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81)
23:03:28,636 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138)
23:03:28,636 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135)
23:03:28,636 ERROR [stderr] (default task-3)    at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
23:03:28,636 ERROR [stderr] (default task-3)    at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
23:03:28,637 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)
23:03:28,637 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction$$Lambda$887/252834873.call(Unknown Source)
23:03:28,638 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
23:03:28,639 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction$$Lambda$888/1261718761.call(Unknown Source)
23:03:28,639 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
23:03:28,639 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction$$Lambda$888/1261718761.call(Unknown Source)
23:03:28,640 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
23:03:28,640 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction$$Lambda$888/1261718761.call(Unknown Source)
23:03:28,640 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
23:03:28,641 ERROR [stderr] (default task-3)    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction$$Lambda$888/1261718761.call(Unknown Source)
23:03:28,641 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
23:03:28,641 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
23:03:28,642 ERROR [stderr] (default task-3)    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104)
23:03:28,642 ERROR [stderr] (default task-3)    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:326)
23:03:28,642 ERROR [stderr] (default task-3)    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:812)
23:03:28,642 ERROR [stderr] (default task-3)    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
23:03:28,643 ERROR [stderr] (default task-3)    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
23:03:28,643 ERROR [stderr] (default task-3)    at java.lang.Thread.run(Thread.java:745)
23:03:28,644 ERROR [stderr] (default task-3) Caused by: java.lang.NullPointerException
23:03:28,644 ERROR [stderr] (default task-3)    at com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:3005)
23:03:28,644 ERROR [stderr] (default task-3)    at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1916)
23:03:28,644 ERROR [stderr] (default task-3)    at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1845)
23:03:28,645 ERROR [stderr] (default task-3)    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1215)
23:03:28,645 ERROR [stderr] (default task-3)    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2255)
23:03:28,645 ERROR [stderr] (default task-3)    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2286)
23:03:28,645 ERROR [stderr] (default task-3)    ... 111 more

在错误消息的底部，我得到一个提示，它是由 Null 指针异常引起的，但我无法弄清楚我的查询/代码中什么可以为 null？一切都可以在终端上完美运行，只是不能在 JDBC 上运行。

【问题讨论】：

标签： java mysql jdbc spring-data-jpa

【解决方案1】：

您的程序中使用的是哪个版本的 mysql-connector-java？我在我的电脑上运行你的代码，没有问题。但是我将 mysql-connector-java 更改为 5.1.26 版本，我得到了同样的错误。您使用的是mysql 8.0.11，所以您可以尝试使用mysql-connector-java 8.0.11。

顺便说一句，URL，你应该在版本 8 中这样写

String URL= "jdbc:mysql://127.0.0.1:3306/db_example?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=CONVERT_TO_NULL&serverTimezone=GMT";

【讨论】：

我在使用驱动程序 5.1.39 时遇到了同样的问题。我切换到版本 8.0.11 并根据您的评论修改 URL，现在我可以连接。谢谢凯文斯
很抱歉，这个答案对我没有帮助。基本相同的行为，但尝试重新连接 3 次。放弃。是错误信息。
我将 mysql-connector-java 版本更改为 8.0.16。现在它起作用了。谢谢
大家好，我的 persistence.xml 中出现验证错误，提示“对实体 'characterEncoding' 的引用必须以 ';' 结尾分隔符”。所以把它放在这里，以防有人遇到同样的错误。我不得不将 URL 中的“&”更改为“&”。因此字符串的格式如下： String URL="jdbc:mysql://127.0.0.1:3306/db_example?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=CONVERT_TO_NULL&serverTimezone=GMT";

【解决方案2】：

我遇到了同样的问题，我刚刚更新到mysql-connector-java-8.0.11，之前是mysql-connector-java-5.1.38。

改变了

Class.forName("com.mysql.jdbc.Driver");

到

Class.forName("com.mysql.cj.jdbc.Driver");

使用mysql-8.0.17.0

【讨论】：

【解决方案3】：

很遗憾，如果您的设备使用的是旧版本的 Android，即。 V6。以上将不起作用。 jdbc 驱动程序 V8+ 与旧版本的 Android 不兼容。

【讨论】：

【解决方案4】：

就 SpringBoot 应用而言，如果您的项目包含多个模块，并且每个模块都有单独的 pom.xml 文件，那么请确保所有模块都具有与 MySQL 服务器兼容的相同版本的 MySQL 连接器。

【讨论】：

【解决方案5】：

我尝试使用 mysql-connector-java-8.0.11 但这并没有解决我的问题在我下载了“mysql-connector-java-8.0.11”之后解决了我的问题我将它添加到我的项目所在的文件夹，然后我将整个文件夹（包括 src 文件夹）添加为外部库，并且由于某种原因解决了问题

【讨论】：

【解决方案6】：

我更新了mysql版本，它现在可以工作了：

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.22</version>
</dependency>

【讨论】：