com.mysql.jdbc.exceptions.jdbc4.CommunicationsException

MySQL JDBC Communications link failure

If you are getting this error intermittently most probably your MySQL connection is getting disconnected causing your SQL statement to fail.

Solution

Add the highlighted lines as shown below, basically it checks the connection using the query specified in the config validationQuery before doing the actual SQL statement specified in the program. 

<?xml version="1.0" encoding="UTF-8"?>
<Context reloadable="true">
<Resource auth="Container"
name="jdbc/mysql"
type="javax.sql.DataSource"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/world"
username="root"
password="mysql"
testWhileIdle="true"
testOnBorrow="true"
testOnReturn="false"
validationQuery="SELECT 1"
validationInterval="30000"
maxIdle="5"
maxActive="50"
maxWait="5"
removeAbandoned="true"
removeAbandonedTimeout="1200"
/>
</Context>

Sample Error log

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet successfully received from the server was 66,617 milliseconds ago.
The last packet sent successfully to the server was 0 milliseconds ago. at sun.reflect.GeneratedConstructorAccessor97.newInstance(Unknown Source) at 
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at 
com.mysql.jdbc.Util.handleNewInstance(Util.java:411) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116) at 
com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3102) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2991) at 
com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3532) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002) at 
com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624) at 
com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127) at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2293) at 
org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement.executeQuery(DelegatingPreparedStatement.java:96) at 
org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement.executeQuery(DelegatingPreparedStatement.java:96) at 
com.as400samplecode.CountryInformation.getInfo(CountryInformation.java:83) at com.as400samplecode.CountryInformation.doPost(CountryInformation.java:53) at 
javax.servlet.http.HttpServlet.service(HttpServlet.java:647) at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) at 
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269) at 
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188) at 
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172) 
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117) at 
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174) at 
org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:200) at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:291) at 
org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:775) at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:704) at 
org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:897) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689) at 
java.lang.Thread.run(Thread.java:662) Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was 
unexpectedly lost. at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2552) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3002) ... 28 more