I moved today to macOS and recreated a very simple database-test project to check my mySQL connection. But i get an SQL Exception: "Could not create connection to database server". Here is the full log: https://pastebin.com/iZrktVKn
I literally copied every step, what i did on Windows. On Windows everything was fine. I have one context.xml, one Servlet, and one connector.jar file. This project should run on Tomcat.
context.xml:
<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(just the important things):
@Resource(name="jdbc/web_student_tracker")
private DataSource dataSource;
doGet method in Servlet:
//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();
}
}
And i did add a 'webstudent'user to the DB:
CREATE USER 'webstudent'@'localhost' IDENTIFIED BY 'webstudent';
GRANT ALL PRIVILEGES ON * . * TO 'webstudent'@'localhost';
Everything is up and running, what im i missing? Also im new to developing in macOS, and also new to MySQL. But on Windows, everything worked just fine.
StackTrace:
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
The problem was the connector version and the MySQL version mismatch. MySQL 8 needs the version 8 from the JDBC connector .jar .
It is because of version mismatch of mysql connector jar. Change version or dependency of mysql
来源：https://stackoverflow.com/questions/49966834/java-servlet-mysql-jdbc-could-not-create-connection-to-database-server