Java Servlet,MySQL JDBC“无法创建与数据库服务器的连接”
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我今天搬到macOS并重新创建了一个非常简单的数据库测试项目来检查我的mySQL连接.但我得到一个SQL异常：“无法创建与数据库服务器的连接”.这是完整的日志：https://pastebin.com/iZrktVKn
我完全复制了每一步,我在Windows上做了什么.在Windows上一切都很好.我有一个context.xml,一个Servlet和一个connector.jar文件.该项目应该在Tomcat上运行.
context.xml中：
<Context>
<Resource name="jdbc/web_student_tracker"
auth="Container" type="javax.sql.DataSource"
maxActive="20" maxIdle="5" maxWait="10000"
username="webstudent" password="webstudent"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/web_student_tracker?useSSL=false"/>
</Context>
Servlet(只是重要的事情)：
@Resource(name="jdbc/web_student_tracker")
private DataSource dataSource;
Servlet中的doGet方法：
//Printwiter + content type setting
PrintWriter out = response.getWriter();
response.setContentType("text/plain");
//Get a connection to the database
Connection myConn = null;
Statement myStmt = null;
ResultSet myRs = null;
try{
myConn = dataSource.getConnection();
//Create SQL statements
String sql = "select * from student";
myStmt = myConn.createStatement();
//Execute SQL query
myRs = myStmt.executeQuery(sql);
//Process the ResultSet
while(myRs.next()) {
String email = myRs.getString("email");
out.println(email);
}
} catch(Exception ex) {
ex.printStackTrace();
}
}
我确实在数据库中添加了一个’webstudent’用户：
CREATE USER 'webstudent'@'localhost' IDENTIFIED BY 'webstudent';
GRANT ALL PRIVILEGES ON * . * TO 'webstudent'@'localhost';
一切都在运行,我错过了什么？也是我在macOS中开发的新手,也是MySQL的新手.但在Windows上,一切正常.
堆栈跟踪：
java.sql.SQLException: Cannot create PoolableConnectionFactory (Could not create connection to database server.)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:2333)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createDataSource(BasicDataSource.java:2062)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:1532)
at com.jsptanulas.web.jdbc.TestServlet.doGet(TestServlet.java:40)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1539)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1495)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
at com.mysql.jdbc.Util.getInstance(Util.java:387)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:917)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2332)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2085)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)
at org.apache.tomcat.dbcp.dbcp2.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:38)
at org.apache.tomcat.dbcp.dbcp2.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:260)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.validateConnectionFactory(BasicDataSource.java:2343)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:2329)
... 26 more
Caused by: java.lang.NullPointerException
at com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:3005)
at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1916)
at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1845)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1215)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2255)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2286)
... 40 more
解决方法:
问题是连接器版本和MySQL版本不匹配. MySQL 8需要来自JDBC连接器.jar的版本8.
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