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Why there is an Exception in thread "Tomcat JDBC Pool Cleaner"?

Thank you for suggesting to improve the question.
I am working on a full-stack application with a jdk1.8.0_181 and running on an apache-tomcat-8.5.34. According to project requirements I have jtds-1.3.1. For some reason I am getting run time exception from isValid() method in the JtdsConnection.class. As I am already using validation Query="Select 1" while creating the connection. I am very confused why this error persists at the first place. For better understanding here is the runtime exception-
Exception in thread "Tomcat JDBC Pool Cleaner[1694819250:1627477239682]" java.lang.AbstractMethodError
at net.sourceforge.jtds.jdbc.JtdsConnection.isValid(JtdsConnection.java:2833)
at org.apache.tomcat.jdbc.pool.PooledConnection.validate(PooledConnection.java:516)
at org.apache.tomcat.jdbc.pool.PooledConnection.validate(PooledConnection.java:454)
at org.apache.tomcat.jdbc.pool.ConnectionPool.testAllIdle(ConnectionPool.java:1084)
at org.apache.tomcat.jdbc.pool.ConnectionPool$PoolCleaner.run(ConnectionPool.java:1473)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)
Also, here is my context file-
<Resource name="jdbc/xxxx" auth="Container" driverClassName="net.sourceforge.jtds.jdbc.Driver" factory="org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory" maxTotal="100" maxIdle="30" maxWaitMillis="10000" username="xxxxxx" password="xxxxx" testOnBorrow="true" testOnReturn="true" testWhileIdle="true" type="javax.sql.DataSource" url="jdbc:jtds:sqlserver:xxxxxxx;sendStringParametersAsUnicode=false" validationQuery="SELECT 1" />
Please share your thoughts and work around to resolve the same.

It's because of the DBCP Jar issue. Make sure you should have the jar that is compatible with Tomcat 8.
Tomcat 8 supports the JDBC connection pool and I am using the DBCP connection pool. Thus, I needed to use the correct DBCP.jar. The compatible jar can be found out from below link-
http://tomcat.apache.org/tomcat-9.0-doc/jndi-datasource-examples-howto.html

Connection pool in tomcat 7

Here is my current config
<Resource
name="jdbc/data"
auth="Container"
type="javax.sql.DataSource"
factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/TABLE_NAME"
username="USER_NAME"
password="PASSWORD"
initialSize="10"
maxActive="50"
suspectTimeout="120"
minIdle="10"
maxIdle="20"
maxWait="1000"
testOnBorrow="true"
timeBetweenEvictionRunsMillis="30000"
minEvictableIdleTimeMillis="60000"
validationQuery="SELECT 1 FROM DUAL"
validationInterval="40"
removeAbandoned="true"
removeAbandonedTimeout="100"
/>
This is in global context so multiple apps can use it.
I am little confused about parameters.need some details.
What I understand is
initalSize a number of connection created when a pool started.
maxActive maximum 50 connections can active at a time.
minIdle 10 connections remain Idle when connection is not used else are closed after maxwait
maxIdle 20 connections can be store as idle.
But When I start tomcat server I can see a 30 IDLE connections which remains forever.Why this happens? Am I missing something ? According to my understanding about connection pool there should only 10 connections should created and can stay in IDLE mode. Is there any specific changes that I have to do with mysql my.cnf

When you say...
This is in global context so multiple apps can use it.
What specifically do you mean? Is it in $CATALINA_BASE/conf/server.xml in the GlobalNamingResources block or in $CATALINA_BASE/conf/context.xml?
Defining a Resource tag in the GlobalNamingResources block of $CATALINA_BASE/conf/server.xml will cause only one resource to be created across the entire server. This can then be shared to applications deployed on your system by adding a ResourceLink tag to the Context configuration.
Defining a Resource in $CATALINA_BASE/conf/context.xml will define the resource once for each application deployed to your Tomcat instance. Thus if you have three applications deployed, you'll end up with three separate resources. This is a guess, but probably why you are seeing 30 connections to your database server.

attempt to reconnect jdbc pool datasource after database restarts

I have a web-app with a Java back-end that uses Tomcat jdbc-pool for database connections. This works fine.
However I am trying to foolproof it before exporting it to other locations, and recently a scenario occurred where someone restarted the SQL Server database service but did not restart the Tomcat service. This caused a SQLException: java.sql.SQLException: I/O Error: Connection reset by peer: socket write error until I restarted Tomcat, forcing the jdbc-pool datasource to reconnect.
I looked for some kind of a configuration in the Tomcat jdbc-pool docs to tell the datasource to attempt to reconnect but I couldn't find anything.
Does anyone know if there is some kind of configuration for this or should I check this condition before each request?

Not 100% sure if this is your problem but on http://www.tomcatexpert.com/blog/2010/04/01/configuring-jdbc-pool-high-concurrency it says you can use testOnBorrow with a validationQuery.
<Resource type="javax.sql.DataSource"
...
testOnBorrow="true"
validationQuery="SELECT 1"
removeAbandoned="true"
/>

While checking for the same issue I came across this post which has the auto connect configurations for all app servers.
Below are the configuration which I used for auto connect in tomcat for reference.
<Resource auth="Container"
driverClassName="oracle.jdbc.OracleDriver"
initialSize="5"
maxActive="120"
maxIdle="5"
maxWait="5000"
name="jdbc/oracle/myds"
password="secret"
poolPreparedStatements="true"
type="javax.sql.DataSource"
url="jdbc:oracle:thin:#DBHOSTNAME:1521/ServiceName"
username="testuser"
validationQuery="select 1 from tab"
testOnBorrow="true"/>
Complete auto connect configurations for all app servers can be found here in Datasource autoreconnect in Java Application Servers.

Just to add on to Natan Cox's answer
Reference - http://tomcat.apache.org/tomcat-8.0-doc/jdbc-pool.html#Common_Attributes
<Resource type="javax.sql.DataSource"
...
testOnBorrow="true"
validationQuery="SELECT 1"
removeAbandoned="true"
/>
As against Geronimo, I would still like to use validationQuery
Database validationQuery notes
hsqldb - select 1 from INFORMATION_SCHEMA.SYSTEM_USERS
Oracle - select 1 from dual
DB2 - select 1 from sysibm.sysdummy1
mysql - select 1
microsoft SQL Server - select 1
postgresql - select 1
ingres - select 1
derby - values 1
H2 - select 1
Firebird - select 1 from rdb$database
Reference - DBCP - validationQuery for different Databases

Why is my DBCP connection pool running out of connections?

I have developed Java application using connection pooling (DBCP) with Sql Server 2005. In my configuration file I have MaxActive="500" but in some cases it will exceed more then 500 connects. Why? And database is slow that time.
<Resource
name="jdbc/tm4u"
auth="Container"
type="javax.sql.DataSource"
driverClassName="com.microsoft.sqlserver.jdbc.SQLServerDriver"
url="jdbc:sqlserver://XXXX;databaseName=XX;User=abc;Password=son;selectMethod=cursor"
username="abc"
password="son"
autoReconnect="true"
maxActive="500"
removeAbandoned="true"
logAbandoned="true"
removeAbandonedTimeout="60"
maxIdle="10"
/>

In your code, do you close the connections that were opened? By doing this the connections will be returned to the pool and re-used. There should be no performance degradation in this case. However, if we need more than 500 active connections, some of them will have to wait.
Also see other questions on SO related to pooling.

DBCP Tomcat connection pool leak

<Resource name="myConn" auth="Container"
type="javax.sql.DataSource" driverClassName="oracle.jdbc.driver.OracleDriver"
url="jdbc:oracle:thin:#10.10.10.10.:1521:mydb"
username="username" password="password" maxActive="500" maxIdle="50"
maxWait="-1" removeAbandoned="true" removeAbandonedTimeout="60" logAbandoned="true" accessToUnderlyingConnectionAllowed="true"
/>
I am trying to find out areas of the application where connections are NOT being closed. I added the removeAbandoned and logAbandoned clauses in my context file but if i check v$session on oracle it is still showing the same number of connections active even after 60 seconds. Is there something wrong in the configuration above?

I would set maxActive to smaller value like 50 and then check if the configuration is working correctly.
According to the docs the connections pool must running low to execute the check for abandoned connections:
When available db connections run low
DBCP will recover and recycle any
abandoned dB connections it finds.
I would also changed the removeAbandonedTimeout to 20 so that you won't have to wait to long to check if the detector is working fine.