Managing memory between screens?

I have a few screens. A login, a home page, and a data page. The data page has a grid that pulls data from an Access database, and displays it in a grid.

From running it on Eclipse my computer, I notice that it jumps from 300mb of ram to 800mb of ram, and it never goes back down (while the server is up). Even if I close out of the browser. Sometimes if I do multiple runs, it'll go from 1.1gb back to 800gb, but never back to 300mb... but sometimes it won't go back down at all, and just continues increasing.

I read that it might be better to use a Navigator over here

Navigator navigator = new Navigator();
navigator.addView(HomeScreen.VIEW_NAME, HomeScreen.class);
navigator.addView(DataView.VIEW_NAME, DataView.class); }

than to use

UI.getCurrent().setContent(new DataScreen());

Is this true?

Or maybe I have a memory leak in my data page? It's a big page. I'm not sure if Lazy loading will help?

This uses a lot of other libraries (HTTPUnit, UCanAccess, and HTTPClient)

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.SimpleDateFormat;
import java.util.Date;

import com.gargoylesoftware.htmlunit.BrowserVersion;
import com.gargoylesoftware.htmlunit.ElementNotFoundException;
import com.gargoylesoftware.htmlunit.FailingHttpStatusCodeException;
import com.gargoylesoftware.htmlunit.NicelyResynchronizingAjaxController;
import com.gargoylesoftware.htmlunit.WebClient;
import com.gargoylesoftware.htmlunit.html.HtmlForm;
import com.gargoylesoftware.htmlunit.html.HtmlInput;
import com.gargoylesoftware.htmlunit.html.HtmlPage;
import com.vaadin.annotations.Theme;
import com.vaadin.data.util.BeanContainer;
import com.vaadin.shared.ui.label.ContentMode;
import com.vaadin.ui.Alignment;
import com.vaadin.ui.Button;
import com.vaadin.ui.Button.ClickEvent;
import com.vaadin.ui.Button.ClickListener;
import com.vaadin.ui.DateField;
import com.vaadin.ui.Grid.MultiSelectionModel;
import com.vaadin.ui.Grid.SelectionMode;
import com.vaadin.ui.GridLayout;
import com.vaadin.ui.Grid;
import com.vaadin.ui.Label;
import com.vaadin.ui.Notification;
import com.vaadin.ui.UI;


@Theme("demotimeentrygrid")
public class DataScreen extends GridLayout{
    //Makes Class serializable
    private static final long serialVersionUID = 1L;
    //Container/Arraylist like object to hold all pulled data from Access db.
    BeanContainer<String, Bean> beanList = new BeanContainer<String, Bean>(Bean.class);
    //Where the Access db is located.
    private String logName = "\\\\server\\folder\\logging\\TextFileslog.txt";
   
    public DataScreen(){
        //Set Website URI fragment (url)
        UI.getCurrent().getPage().setUriFragment("Data");
    
        //Size of rows/columns for layout.
        setRows(4);
        setColumns(3);
        
        //Sets Unique Index for the Grid (similar to a index for a table)
        beanList.setBeanIdProperty("RID");
        
        //Creates a Header at the Top of the page, and spaces it.
        Label titleLabel = new Label("Data Entry<br></br>");
        titleLabel.setStyleName("TitleLabel");
        titleLabel.setContentMode(ContentMode.HTML);
        titleLabel.setWidth("100%");
        
        //setup DateField, user can filter entries by date.
        DateField df = new DateField();
        df.setValue(new Date());
        Button dateButton = new Button("Go");
        
        //Sets up the grid of beans.
        Grid grid = new Grid (beanList);
        
        grid.removeColumn("RID"); //Don't show this column, but it is there.
        grid.setSelectionMode(SelectionMode.MULTI); //Allows to pick multiple entries.
               
        ////////////Button Functions

        //When user picks a date and presses Go, this button loads
        //The beans straight from the acess db. Right now, it's connected to a test db.
        dateButton.addClickListener(new ClickListener() {
            private static final long serialVersionUID = 1L;

            @Override
            public void buttonClick(ClickEvent event){
                dateButton.setEnabled(false);
                //Resets beanList if it was previously populated
                beanList.removeAllItems();
                grid.setSelectionMode(SelectionMode.NONE);
                grid.setSelectionMode(SelectionMode.MULTI);

                try {
                    
                    Class.forName("net.ucanaccess.jdbc.UcanaccessDriver");
                    
                    Connection conn=DriverManager.getConnection("jdbc:ucanaccess://\\\\server\\folder\\MainLog.mdb;SingleConnection=true");
                     
                    Statement s = conn.createStatement();
                    Bean bean = new Bean();

                     ResultSet rs = s.executeQuery("SELECT [Department], [UName], [Entry-Date] from [DataTable] where  [Entry-Date] = #"+new SimpleDateFormat("MM/dd/yyyy").format(df.getValue())+"#");
                 
                     while (rs.next()) {
                         bean.setDept(rs.getString(1));
                         bean.setUName(rs.getString(2));
                         bean.setEntryDate(rs.getString(3).split("\\s")[0].split("-")[1] + rs.getString(3).split("\\s")[0].split("-")[2]+ rs.getString(3).split("\\s")[0].split("-")[0].substring(2));
                         beanList.addBean(bean);
                         bean = new Bean();
                     } //End While
                     s.close();
                     rs.close(); //Close recordset
                     conn.close(); //Close Access connection
                } catch (ClassNotFoundException | SQLException e) {
                    e.printStackTrace();
                }
                dateButton.setEnabled(true);
            } //End Click Listener
        }); //End Click Event

        //Sends the Selected Time Entries to Online db
        Button btnSendOnlineDb = new Button("Send Selected to DB");
        btnSendOnlineDb.setStyleName("submitButton");
        
       btnSendOnlineDb.addClickListener(new ClickListener() {
            private static final long serialVersionUID = 1L;

            @Override
            public void buttonClick(ClickEvent event){
                btnSendOnlineDb.setEnabled(false);
                
                //Sets up WebClient to go to online db.
                WebClient webClient = new WebClient(BrowserVersion.BEST_SUPPORTED);
                //Turns off useless logger that comes with UCanAccess
                java.util.logging.Logger.getLogger("com.gargoylesoftware").setLevel(java.util.logging.Level.OFF);
                
                try{
                //Container to hold failed posted TimeEntries.
                    BeanContainer<String, Bean> failures = new BeanContainer<String, Bean>(Bean.class);
                    failures.setBeanIdProperty("RID");
                    File log = new File(logName);
                    PrintWriter pw = new PrintWriter(new FileWriter(log,true));
                    
                   
                    String sCurrentLine;
                 
                 
                    //Navigate to Online page page, and log in.
                    HtmlPage page = (HtmlPage) webClient.getPage(onlineDbPage);
                    HtmlForm form = page.getFormByName("loginfm");
                    form.getInputByName("user").setValueAttribute(UserName);
                    HtmlInput passWordInput = form.getInputByName("password");
                    passWordInput.removeAttribute("disabled");
                    passWordInput.setValueAttribute(Pword);
                    page = form.getInputByValue("Login").click();
                    webClient.setAjaxController(new NicelyResynchronizingAjaxController());

                    //Gets which Time entries were selected by User.
                    MultiSelectionModel selection = (MultiSelectionModel) grid.getSelectionModel();
                    selection.getSelectedRows();
                    
                    //Cycles through each one and submits them to online db
                    for (Object itemId: selection.getSelectedRows()){
                        
                        //Try/Catch for following errors:
                            //Work Order Not Found
                            //Work Order Closed
                        
                        try {
                            beanList.getItem(itemId).getBean();
                            
                            if (beanList.getItem(itemId).getBean().getWo().contains("-")){
                                beanList.getItem(itemId).getBean().setWo(beanList.getItem(itemId).getBean().getWo().split("-")[0].toUpperCase());
                            }
                            
                            HtmlPage mainPage = webClient.getPage("websiteEntry");
                            form = mainPage.getFormByName("timeForm");
                            form.getInputByName("chkaction").setValueAttribute("checked");
                            form.getInputByName("E2EMPL").setValueAttribute(beanList.getItem(itemId).getBean().getDept());
                            form.getInputByName("ww_fE2WKDT").setValueAttribute(beanList.getItem(itemId).getBean().getEntryDate());

                            mainPage = form.getButtonByName("timeButton").click();
                            //usually when an entry fails, the follow page has the words "row 1" in it. This
                            //Catches it and stores it to show the user at the end. It also logs it in a text file.

                            //Catches basic errors and logs them
                                //Wrong syntax in fields, etc
                            if (mainPage.asText().contains("row 1")){
                                failures.addBean(beanList.getItem(itemId).getBean());
                            }
                            System.out.println(mainPage.asText());                
                        }catch (Exception e){
                            e.printStackTrace();    
                            
                            // Catches the major errors and logs them.
                            failures.addBean(beanList.getItem(itemId).getBean());
                            continue;
                        }
                        
                    }//End For Loop
                    h = null;
                    if (failureEntries.size() >0)
                        UI.getCurrent().addWindow(new BeanErrorWindow(failures));
                   
                    webClient.close();
                    
                
                }catch(FailingHttpStatusCodeException | ElementNotFoundException | IOException e){
                    e.printStackTrace();
                }                
                Notification.show("Completed.");
                btnSendOnlineDb.setEnabled(true);
            } // Click Event
            
            
        }); //Online db Button ClickListener

        ////////////End Button Functions

        
        //Sets up JavaScript
        
        
        
        
        ////////Sets up look of page.
        
        //Get Width and Height of Browser Window.
        int browserWidth =  UI.getCurrent().getPage().getBrowserWindowWidth();
        int browserHeight = UI.getCurrent().getPage().getBrowserWindowHeight();

        
        //Sidebar menu.
        MenuLayout menu = new MenuLayout();
        menu.setHeight("100%");
        menu.setWidth(Math.round(.15*browserWidth) + "px");
        
        setHeight(browserHeight+"px");
        addStyleName("backgroundColor");
        addComponent(menu,0,0,0,3);
        addComponent(titleLabel,1,0,2,0);
        addComponent(df,1,1);
        addComponent(dateButton,2,1);
        
        //Grid with the Time Entries
        grid.setWidth(Math.round(.85*browserWidth) + "px");
        grid.setHeight(Math.round(.70*browserHeight) + "px");
        setComponentAlignment(df, Alignment.MIDDLE_RIGHT);
        setComponentAlignment(dateButton, Alignment.MIDDLE_LEFT);
        
        addComponent(btnSendOnlineDb,1,3,2,3);
        setComponentAlignment(btnSendOnlineDb, Alignment.MIDDLE_RIGHT);
        addComponent(grid,1,2,2,2);
        setComponentAlignment(grid, Alignment.MIDDLE_CENTER);
        
    }
}

Is there a way to make sure that this page gets picked up by garbage collector when the user leaves the page? During runtime in Eclipse, if I try to filter by date more than 2-3 times, I almost always get Memory Overhead heap etc error.

After looking through the form, it looks like the problem is BeanItemContainer / BeanContainer.

So I'm trying to use ListContainer but I'm having some trouble since it's kind of hard to find examples of people using ListContainer.

So far:

ListContainer<Bean> te = new ListContainer<Bean>(Bean.class);

gives me:

Jun 16, 2016 9:44:22 AM com.vaadin.server.DefaultErrorHandler doDefault
SEVERE:
java.lang.NoClassDefFoundError: org/apache/commons/collections/FastHashMap
    at org.vaadin.viritin.ListContainer.<init>(ListContainer.java:76)
    at com.example.gridbutton.GridbuttonUI.init(GridbuttonUI.java:43)
    at com.vaadin.ui.UI.doInit(UI.java:682)
    at com.vaadin.server.communication.UIInitHandler.getBrowserDetailsUI(UIInitHandler.java:214)
    at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:74)
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1409)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:364)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.collections.FastHashMap
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1333)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1167)
    ... 30 more

And I'm not sure why. I have downloaded the apache commons beanutils and commons collections4.

Edit well ok googling some more, it appears that I need to use Commons Collections 3. So i replaced that and it worked. But to be honest, the BeanItemContainer and ListContainer didn't have any difference in memory consumption or performance.

I tried with Grid (works fine, but ListContainer had no improvements), then I tried both with MGrid (which actually gave me memory overhead problems) then I tried with MTable, which I don't really want to use because I need Multiselect and Multiselect is depreciated or doesn't work in MTable.

Grid Code:

ListContainer<Bean> te = new ListContainer<Bean>(Bean.class);
 Grid grid = new Grid(te);

MGrid Code:

ListContainer<Bean> te = new ListContainer<Bean>(Bean.class);
MGrid mgrid = new MGrid(te);

I also get this error in MTable so I really don't want to use MTable:

Jun 16, 2016 10:31:44 AM com.vaadin.server.DefaultErrorHandler doDefault

SEVERE:
com.vaadin.ui.Table$CacheUpdateException: Error during Table cache update.
    at com.vaadin.ui.Table.maybeThrowCacheUpdateExceptions(Table.java:1767)
    at com.vaadin.ui.Table.refreshRenderedCells(Table.java:1756)
    at com.vaadin.ui.Table.attach(Table.java:4290)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:619)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:675)
    at com.vaadin.ui.AbstractComponent.setParent(AbstractComponent.java:582)
    at com.vaadin.ui.AbstractSingleComponentContainer.setContent(AbstractSingleComponentContainer.java:150)
    at com.vaadin.ui.UI.setContent(UI.java:1312)
    at com.example.gridbutton.GridbuttonUI.init(GridbuttonUI.java:103)
    at com.vaadin.ui.UI.doInit(UI.java:682)
    at com.vaadin.server.communication.UIInitHandler.getBrowserDetailsUI(UIInitHandler.java:214)
    at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:74)
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1409)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:364)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.RuntimeException: java.lang.NoSuchMethodException: org.vaadin.viritin.ListContainer.getCollection()
    at org.vaadin.viritin.ListContainer$DynaBeanItem$DynaProperty.getValue(ListContainer.java:545)
    at com.vaadin.ui.Table.formatPropertyValue(Table.java:4170)
    at com.vaadin.ui.Table.getPropertyValue(Table.java:4114)
    at com.vaadin.ui.Table.parseItemIdToCells(Table.java:2386)
    at com.vaadin.ui.Table.getVisibleCellsNoCache(Table.java:2225)
    at com.vaadin.ui.Table.refreshRenderedCells(Table.java:1745)
    ... 35 more

I'm not sure where to go from here. I think I don't know what I'm doing to be honest.

Hi Alisa,
This may be found helpful for you. https://www.youtube.com/watch?v=bH2_nWxwXY8