Error: PersistenceExceptionorg.hibernate.exception.GenericJDBCException: Cannot open connection

This problem has been causing me headaches, lately. After some heavy googling, I came across the following explanation.

The biggest problem here is that at first glance in my stacktrace it totally looked like a transaction/sqlserver problem.

Here's the stacktrace:

2011-07-23 22:23:46,805 WARN [org.hibernate.util.JDBCExceptionReporter] [ ] SQL Error: 0, SQLState: null 2011-07-23 22:23:46,805 ERROR [org.hibernate.util.JDBCExceptionReporter] [ ] Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >; - nested throwable: (javax.resource.ResourceException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >) 2011-07-23 22:23:46,805 ERROR [nl.isaac.youw8.ejb.StorageServiceBean] [ ] Error: PersistenceExceptionorg.hibernate.exception.GenericJDBCException: Cannot open connection searching an DashboardUser Query: from DashboardUser WHERE id = :id ORDER BY ID DESC javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: Cannot open connection at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:629) at org.hibernate.ejb.QueryImpl.getSingleResult(QueryImpl.java:99) at nl.isaac.youw8.ejb.StorageServiceBean.findSingle(StorageServiceBean.java:673) at nl.isaac.youw8.ejb.StorageServiceBean.findSingleObjectLike(StorageServiceBean.java:136) at sun.reflect.GeneratedMethodAccessor778.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:112) at org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:166) at youw8.interceptors.DefaultInterceptor.intercept(DefaultInterceptor.java:140) at sun.reflect.GeneratedMethodAccessor220.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:118) at org.jboss.ejb3.interceptor.EJB3InterceptorsInterceptor.invoke(EJB3InterceptorsInterceptor.java:63) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.entity.TransactionScopedEntityManagerInterceptor.invoke(TransactionScopedEntityManagerInterceptor.java:54) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.tx.TxPolicy.invokeInCallerTx(TxPolicy.java:126) at org.jboss.aspects.tx.TxInterceptor$Required.invoke(TxInterceptor.java:195) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:95) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:62) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.security.RoleBasedAuthorizationInterceptor.invoke(RoleBasedAuthorizationInterceptor.java:166) at org.jboss.ejb3.security.RoleBasedAuthorizationInterceptor.invoke(RoleBasedAuthorizationInterceptor.java:115) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.security.AuthenticationInterceptor.invoke(AuthenticationInterceptor.java:77) at org.jboss.ejb3.security.Ejb3AuthenticationInterceptor.invoke(Ejb3AuthenticationInterceptor.java:110) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:46) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.asynchronous.AsynchronousInterceptor.invoke(AsynchronousInterceptor.java:106) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.stateless.StatelessContainer.localInvoke(StatelessContainer.java:240) at org.jboss.ejb3.stateless.StatelessContainer.localInvoke(StatelessContainer.java:210) at org.jboss.ejb3.stateless.StatelessLocalProxy.invoke(StatelessLocalProxy.java:84) at $Proxy157.findSingleObjectLike(Unknown Source) at youw8.services.exposed.webservices.rest.MeasurementsResource.addActivityMeasurement(MeasurementsResource.java:486) at sun.reflect.GeneratedMethodAccessor1608.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:184) at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:67) at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:276) at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:133) at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:83) at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:133) at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:71) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1171) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1103) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1053) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1043) at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:406) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:477) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:662) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at youw8.services.exposed.oauth.provider.servlets.AuthorizationServlet.doFilter(AuthorizationServlet.java:259) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175) at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:182) at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262) at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:856) at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:566) at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1508) at java.lang.Thread.run(Thread.java:619) Caused by: org.hibernate.exception.GenericJDBCException: Cannot open connection at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103) at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:29) at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:426) at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144) at org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:139) at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1547) at org.hibernate.loader.Loader.doQuery(Loader.java:673) at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:236) at org.hibernate.loader.Loader.doList(Loader.java:2220) at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2104) at org.hibernate.loader.Loader.list(Loader.java:2099) at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:378) at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:338) at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:172) at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1121) at org.hibernate.impl.QueryImpl.list(QueryImpl.java:79) at org.hibernate.ejb.QueryImpl.getSingleResult(QueryImpl.java:80) ... 75 more Caused by: org.jboss.util.NestedSQLException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >; - nested throwable: (javax.resource.ResourceException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >) at org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:95) at org.hibernate.ejb.connection.InjectedDataSourceConnectionProvider.getConnection(InjectedDataSourceConnectionProvider.java:47) at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:423) ... 89 more Caused by: javax.resource.ResourceException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY > at org.jboss.resource.connectionmanager.TxConnectionManager.getManagedConnection(TxConnectionManager.java:319) at org.jboss.resource.connectionmanager.BaseConnectionManager2.allocateConnection(BaseConnectionManager2.java:402) at org.jboss.resource.connectionmanager.BaseConnectionManager2$ConnectionManagerProxy.allocateConnection(BaseConnectionManager2.java:849) at org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:89) ... 91 more 2011-07-23 22:23:46,805 WARN [org.hibernate.util.JDBCExceptionReporter] [ ] SQL Error: 0, SQLState: null 2011-07-23 22:23:46,805 ERROR [org.hibernate.util.JDBCExceptionReporter] [ ] Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >; - nested throwable: (javax.resource.ResourceException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >) 2011-07-23 22:23:46,805 ERROR [nl.isaac.youw8.ejb.StorageServiceBean] [ ] Error: PersistenceExceptionorg.hibernate.exception.GenericJDBCException: Cannot open connection searching an Activity Query: from Activity WHERE id = :id ORDER BY ID DESC javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: Cannot open connection at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:629) at org.hibernate.ejb.QueryImpl.getSingleResult(QueryImpl.java:99) at nl.isaac.youw8.ejb.StorageServiceBean.findSingle(StorageServiceBean.java:673) at nl.isaac.youw8.ejb.StorageServiceBean.findSingleObjectLike(StorageServiceBean.java:136) at sun.reflect.GeneratedMethodAccessor778.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:112) at org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:166) at youw8.interceptors.DefaultInterceptor.intercept(DefaultInterceptor.java:140) at sun.reflect.GeneratedMethodAccessor220.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:118) at org.jboss.ejb3.interceptor.EJB3InterceptorsInterceptor.invoke(EJB3InterceptorsInterceptor.java:63) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.entity.TransactionScopedEntityManagerInterceptor.invoke(TransactionScopedEntityManagerInterceptor.java:54) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.tx.TxPolicy.invokeInCallerTx(TxPolicy.java:126) at org.jboss.aspects.tx.TxInterceptor$Required.invoke(TxInterceptor.java:195) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:95) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:62) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.security.RoleBasedAuthorizationInterceptor.invoke(RoleBasedAuthorizationInterceptor.java:166) at org.jboss.ejb3.security.RoleBasedAuthorizationInterceptor.invoke(RoleBasedAuthorizationInterceptor.java:115) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.aspects.security.AuthenticationInterceptor.invoke(AuthenticationInterceptor.java:77) at org.jboss.ejb3.security.Ejb3AuthenticationInterceptor.invoke(Ejb3AuthenticationInterceptor.java:110) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:46) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.asynchronous.AsynchronousInterceptor.invoke(AsynchronousInterceptor.java:106) at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101) at org.jboss.ejb3.stateless.StatelessContainer.localInvoke(StatelessContainer.java:240) at org.jboss.ejb3.stateless.StatelessContainer.localInvoke(StatelessContainer.java:210) at org.jboss.ejb3.stateless.StatelessLocalProxy.invoke(StatelessLocalProxy.java:84) at $Proxy157.findSingleObjectLike(Unknown Source) at youw8.services.exposed.webservices.rest.MeasurementsResource.addActivityMeasurement(MeasurementsResource.java:490) at sun.reflect.GeneratedMethodAccessor1608.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:184) at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:67) at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:276) at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:133) at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:83) at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:133) at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:71) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1171) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1103) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1053) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1043) at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:406) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:477) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:662) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at youw8.services.exposed.oauth.provider.servlets.AuthorizationServlet.doFilter(AuthorizationServlet.java:259) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175) at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:182) at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262) at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:856) at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:566) at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1508) at java.lang.Thread.run(Thread.java:619) Caused by: org.hibernate.exception.GenericJDBCException: Cannot open connection at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103) at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:29) at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:426) at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144) at org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:139) at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1547) at org.hibernate.loader.Loader.doQuery(Loader.java:673) at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:236) at org.hibernate.loader.Loader.doList(Loader.java:2220) at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2104) at org.hibernate.loader.Loader.list(Loader.java:2099) at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:378) at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:338) at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:172) at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1121) at org.hibernate.impl.QueryImpl.list(QueryImpl.java:79) at org.hibernate.ejb.QueryImpl.getSingleResult(QueryImpl.java:80) ... 75 more Caused by: org.jboss.util.NestedSQLException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >; - nested throwable: (javax.resource.ResourceException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY >) at org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:95) at org.hibernate.ejb.connection.InjectedDataSourceConnectionProvider.getConnection(InjectedDataSourceConnectionProvider.java:47) at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:423) ... 89 more Caused by: javax.resource.ResourceException: Transaction is not active: tx=TransactionImple < ac, BasicAction: 53f73f9b:8b5:4e26e1da:501d3a status: ActionStatus.ABORT_ONLY > at org.jboss.resource.connectionmanager.TxConnectionManager.getManagedConnection(TxConnectionManager.java:319) at org.jboss.resource.connectionmanager.BaseConnectionManager2.allocateConnection(BaseConnectionManager2.java:402) at org.jboss.resource.connectionmanager.BaseConnectionManager2$ConnectionManagerProxy.allocateConnection(BaseConnectionManager2.java:849) at org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:89) ... 91 more 2011-07-23 22:23:46,805 ERROR [youw8.services.exposed.webservices.rest.MeasurementsResource] [ ] error occured:null

The important part in the stack trace is: org.hibernate.exception.SQLStateConverter.handledNonSpecificException. This indicates that an exception occurred that was not handled correctly and somewhere along the line the problem was caught, the transaction was rolled back, and then the rest of the business logic started performing without having any longer a transaction context.

At least, it's probably something like that.

It turned out to be a NullPointerException.

Senior Java Developer Test

Found the following test on http://thedailywtf.com. It tickled my fancy. An interesting use for recursion.

Question 1
(a) What does the following function do?
(b) How could the function be improved?
(c) Rewrite the function with your suggested improvements.

public String funcX (String s) {
  if (s == null || s.length() == 1 || s.length() == 0) {
    return s;
  } else {
    return funcX(s.substring(1)) + s.substring(0, 1);
  }
}

Just a small javadoc addendum to clarify things:

public String substring(int beginIndex, int endIndex)

Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

Some notes on Time

Found the following link through one of the blogs I follow : Time

Decrease Indentation

And when I talk about indentation, I mean nested if statements, another one of my pet peeves.

This specific refactoring is called: Replace Nested Conditional with Guard Clauses^[1].

Preconditions (GuardClauses) are a great example of where it is okay to return early at the start of the function.

It is very convenient to prevent the ArrowAntiPattern.

Here a bad example:

public boolean getPayment(String a, Double b)
{
    boolean result = false;
    if (a != null && b != null && !a.equals("") && b >= 0.0)
    {
        User user = getUser(a);
        if (user != null && user.getAccountValue() >= b))
        {
            user.setAccountValue(user.getAccountValue() - b);
            return true;
        }
        else
        {
            log.debug("User account not found or insufficient funds.");
            result = false;
        }
    }
    else
    {
        log.debug("Bad values.");
        result = false;
    }
    return result;
}

Here a good example (bad example refactored):

public boolean getPayment(String a, Double b)
{
    // preconditions
    if (a == null || b == null)
    {
        log.debug("Null values");
        return false;
    }
    if ("".equals(a) || b <= 0.0)
    {
        log.debug("Bad values");
        return false;
    }
    User user = getUser(a);
    if (user == null)
    {
        log.debug("User account not found.");
        return false;
    }
    if (user.getAccountValue() < b)
    {
        log.debug("Insufficient funds.");
        return false;
    }
    user.setAccountValue(user.getAccountValue() - b);
    return true;
}

One important skill here is the proper negation of an expression. You'd be surprised how many people lack this skill.

References

[1] Refactoring - Improving the design of existing code

Martin Fowler

A Small Warning Regarding Hibernate

I found the following quote that struck a chord with me.

The problem is sort of cultural. Some developers come to using a tool like Hibernate because they are uncomfortable with SQL and with relational databases. We would say that this is exactly the wrong reason to use Hibernate. You should be very comfortable with SQL and JDBC before you start using Hibernate - Hibernate builds on JDBC, it does not replace it.

ref. http://www.javaperformancetuning.com/news/interview041.shtml

The Martingale System of Gambling

Just a small exercise for my edification, regarding the "Gamblers Fallacy" inherent to "The Martingale" system of gambling.

import java.util.*;
import java.io.*;
import java.text.*;

/**
 * A quick implementation of the Martingale
 * system of gambling. Run it, and it will
 * play at the roulette table, until broke.
 * How far can you make it before going
 * broke? Let me know!
 */
public class Martingale
{    

  
  public static String padLeftToTotal(long s, long n) {
    return String.format("%1$#" + (n-(s+"").length()) + 
      "s", s + "");  
  }

  public static void main(String[] stuff)
  {
    long account = 255;
    long bet = 1;
    long maxbet = 0;
    
    // 0..36
    // where red: 1, 3, 5, 7, .. 36
    // where black: 2, 4, 6, .. 35
    // where green : 0
    while (account > 0L)
    {
      long result = 
        Math.round(Math.random()*36.0);
      System.out.println("Account: " + 
        padLeftToTotal(account, 15) + 
        " Betting " + padLeftToTotal(bet, 15) + 
        " $ on red.. result is " + 
        padLeftToTotal(result, 3) + " " + 
        (result == 0 ? "green" : ((result % 2) == 0 ? "black" : "  red")));
      if (result != 0 && (result % 2) == 1)
      {
        // red, we win!
        account += bet;
        bet = 1;
      }
      else
      {
        // not red, we lose!
        account -= bet;
        bet *= 2;
        if (bet > maxbet) 
        {
          maxbet = bet;
          System.out.println("Maximum bet increased to " + maxbet + "$");
          try
          {
            Thread.sleep(1000);
          } catch (Exception e)
          {
          }
        }
      }
    }
    System.out.println("You lose, dude!");
    System.out.println("You now owe the casino " + 
      (-account) + " $");
  }

}

“Remember this well, Lady Luck has no memory.”

References

Wikipedia : Gambler's Fallacy

http://en.wikipedia.org/wiki/Gambler%27s_fallacy

What happened at Monte Carlo in 1913?

http://www.fallacyfiles.org/gamblers.html

Update: 10 February 2015, added Monte Carlo link.