JSF mysql tomcat memory leak

Question

I am a basic programmer and I meet a bug what I didn't see before. I use MySQL, Tomcat 8 and jsf. Here is my application (part):

When I write something to the text area and hit the "Mehet" button, it makes the following: (xhtml page)

<p:commandButton value="Mehet"
                        action="#{alvallalkozoBevitelBean.add()}" update="@form :alvallalkozoFrm" />

The datatable inside the "alvallalkozoFrm" form. Java code:

public void add() throws SQLException {

    String sql = "INSERT INTO alvallalkozo(Ceg_neve, Ceg_szekhelye, Kapcsolattarto_neve, Kapcsolattarto_email, Ceg_telefonsz, Ceg_megjegyzes) VALUES(?,?,?,?,?,?)";

    if (ds == null)
        throw new SQLException("Datasource nem található");
    PreparedStatement ps = null;
    Connection con = ds.getConnection();
    if (con == null)
        throw new SQLException("Nincs adatbázis kapcsolat");
    ps = con.prepareStatement(sql);

    ps.setString(1, alvallalkozo.getCegNeve());
    ps.setString(2, alvallalkozo.getCegSzekhelye());
    ps.setString(3, alvallalkozo.getKapcsolattartoNeve());
    ps.setString(4, alvallalkozo.getKapcsolattartoEmail());
    ps.setString(5, alvallalkozo.getCegTelefonsz());
    ps.setString(6, alvallalkozo.getCegMegjegyzes());
    ps.executeUpdate();

    System.out.println("Data Added Successfully");
}

I can add only 7 times some data with it, and when I want to add 8th data with "Mehet" button, Tomcat freezes, and chrome shows the following:

Then I stop Tomcat because I can not do anything with it, and I get the following exception in Tomcat:

    WARNING: The web application [eDispatcher] is still processing a request that has yet to finish. This is very likely to create a memory leak. You can control the time allowed for requests to finish by using the unloadDelay attribute of the standard Context implementation. Stack trace of request processing thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.park(Unknown Source)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
 org.apache.tomcat.dbcp.pool2.impl.LinkedBlockingDeque.takeFirst(LinkedBlockingDeque.java:582)
 org.apache.tomcat.dbcp.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:439)
 org.apache.tomcat.dbcp.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:360)
 org.apache.tomcat.dbcp.dbcp2.PoolingDataSource.getConnection(PoolingDataSource.java:118)
 org.apache.tomcat.dbcp.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:1412)
 com.dangerzone.main.IndexBean.getAlvallalkozok(IndexBean.java:51)
 sun.reflect.GeneratedMethodAccessor59.invoke(Unknown Source)
 sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
 java.lang.reflect.Method.invoke(Unknown Source)
 javax.el.BeanELResolver.getValue(BeanELResolver.java:97)
 com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
 com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
 org.apache.el.parser.AstValue.getValue(AstValue.java:167)
 org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184)
 com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
 javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
 javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
 javax.faces.component.UIData.getValue(UIData.java:732)
 org.primefaces.component.api.UIData.getDataModel(UIData.java:758)
 javax.faces.component.UIData.getRowCount(UIData.java:356)
 org.primefaces.component.api.UIData.calculateFirst(UIData.java:209)
 org.primefaces.component.datatable.DataTableRenderer.preRender(DataTableRenderer.java:115)
 org.primefaces.component.datatable.DataTableRenderer.encodeEnd(DataTableRenderer.java:83)
 javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1863)
 javax.faces.render.Renderer.encodeChildren(Renderer.java:176)
 javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
 com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:582)
 com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:183)
 javax.faces.component.UIForm.visitTree(UIForm.java:381)
 javax.faces.component.UIComponent.visitTree(UIComponent.java:1700)
 javax.faces.component.UIComponent.visitTree(UIComponent.java:1700)
 com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:403)
 com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:322)
 org.primefaces.context.PrimePartialViewContext.processPartial(PrimePartialViewContext.java:60)
 javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1004)
 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
 com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:430)
 com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
 com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
 com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
 com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
 javax.faces.webapp.FacesServlet.service(FacesServlet.java:655)
 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
 org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
 org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
 org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
 org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
 org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
 org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
 org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
 org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
 org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
 org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
 org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223)
 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1517)
 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1474)
 java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
 java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
 org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
 java.lang.Thread.run(Unknown Source)

Something stays in the memory in background, maybe the post request. My question: what creates the memory leak? How can I solve this issue? Thanks and sorry for long representation.

Answer 1

You're not closing the Connections thus generating a memory leak. This can be noted here in the stacktrace (emphasys mine):

sun.misc.Unsafe.park(Native Method) java.util.concurrent.locks.LockSupport.park(Unknown Source) java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source) org.apache.tomcat.dbcp.pool2.impl.LinkedBlockingDeque.takeFirst(LinkedBlockingDeque.java:582) org.apache.tomcat.dbcp.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:439) org.apache.tomcat.dbcp.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:360) org.apache.tomcat.dbcp.dbcp2.PoolingDataSource.getConnection(PoolingDataSource.java:118) org.apache.tomcat.dbcp.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:1412)

In short: ALWAYS close the resources.

Two ways to do it:

1. Explicitly calling method close:

   ps.close();
   con.close();
   

2. Use a try-with-resources (available since Java 7), there's no need to call close since the try will do it automatically for you:

   String sql = "...";
   try (Connection con = ds.getConnection();
       PreparedStatement ps = con.prepareStatement(sql)) {
       //...
   } catch (SQLException e) {
       //ALWAYS handle your exceptions as well
   }