Memory Leak Update

I have been using Hibernate with the default C3P0 connection pooling.

I have been receiving PERM GEN errors.

After reading Frank Kievet's blog about memory leaks, I started investigating.
http://frankkieviet.blogspot.com/2006/10/classloader-leaks-dreaded-permgen-space.html
http://frankkieviet.blogspot.com/2006/10/how-to-fix-dreaded-permgen-space.html

I added his code for causing a garbage collection in the perm gen and noticed that a lot of memory was being lost on each redeploy of the web app.

I downloaded the Eclipse, stand-alone Memory Analyzer (MAT).
http://www.eclipse.org/mat/

My steps to find the leak:

1. I ran the web app and used MAT to obtain a heap dump from Tomcat. 
2. I reran the web app again and obtained another heap dump. 
3. I opened the dominator tree for each dump.
4. The second dump contained the web app loader from the first dump. This class is causing the class loader memory leak.
5. In the second dominator tree, I right-clicked the stale web app loader and selected Path to GC Roots (excluding weak references).
6. The references listed are the ones causing the memory leak.

The leaks are usually for a third-party tool. It is important to close these tools properly. The tools I am using are Hibernate, C3P0 and MySQL. Each of these has to be closed properly. The best place for the code is in a SevletContextListener. I used several sites to find this information.
https://hibernate.atlassian.net/browse/HHH-7364
http://stackoverflow.com/questions/11872316/tomcat-guice-jdbc-memory-leak
http://docs.oracle.com/cd/E17952_01/connector-j-relnotes-en/news-5-1-23.html

I also had to update several jar files to newer versions:
hibernate-c3p0-4.1.1.Final.jar
mysql-connecto-java-5.1.28-bin.jar

package shared;

import com.mysql.jdbc.AbandonedConnectionCleanupThread;
import java.sql.Driver;
import java.sql.DriverManager;
import java.util.Enumeration;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class WebappListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        try {
            AbandonedConnectionCleanupThread.shutdown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        try {
            Enumeration enumer = DriverManager.getDrivers();
            while (enumer.hasMoreElements()) {
                DriverManager.deregisterDriver(enumer.nextElement());
            }
        } catch (java.sql.SQLException se) {
            se.printStackTrace();
        }
        shared.HibernateHelper.closeFactory();
    }
}

The HibernateHelper class is a helper class for using Hibernate. All the methods are static. It has a static variable for the session factory that already exists.

    static public void closeSessionFactory(SessionFactory factory) {
        if (factory != null) {
            if (factory instanceof SessionFactoryImpl) {
                SessionFactoryImpl sf = (SessionFactoryImpl) factory;
                ConnectionProvider conn = sf.getConnectionProvider();
               
                if (conn instanceof C3P0ConnectionProvider) {
                    ((C3P0ConnectionProvider) conn).close();
                }
            }
            factory.close();
        }
    }

    static public void closeFactory() {
        closeSessionFactory(sessionFactory);
    }

The relevant imports for this method are:

import org.hibernate.SessionFactory;
import org.hibernate.internal.SessionFactoryImpl;
import org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider;
import org.hibernate.service.jdbc.connections.spi.ConnectionProvider;

Starting with JSON

I am using jQuery in an application to build a user interface that creates a tree of classes. I want to use that tree as a template in another application that looks for a similar structure.

I am trying to use JSON to save the tree from the first app, read it in the second app, convert it to a Java object and then compare it to the other structure.

I took a quick look at JSON.simple, but I only looked at one post where the advice was to use either Jackson or GSON. I will try GSON first.

Download: http://code.google.com/p/google-gson/downloads/list

Tutorial: http://www.studytrails.com/java/json/java-google-json-parse-json-to-java.jsp

I have successfully completed my task.

1. Created JSON from the object structure using jQuery and javascript.
2. Added the JSON to a hidden field that is submitted to the server application.
3. In the server application using Java and GSON, I read the JSON data and created a class hierarchy from it.

These are the methods that created the JSON from my object structure. There are two structures, TextPart and Group. Group contains TextPart and other Groups. TextPart contains text and another field to indicate if the text is equivalent to another TextPart.
    
    //grab the text, replacing " with \".
    function getTextPartText(textPart) {
        return $.trim($(textPart).children('code').text()).replace(/\"/g, "\\\"");     
    }
  
    //grab the text, replacing " with \". Change to lower case, change space to underscore.
    function getTextPartEquivalent(textPart) {
        var result = $.trim($(textPart).children('var').text().toLowerCase());
        result = result.toLowerCase().replace(/\s/g,'_');
        return result.replace(/\"/g, "\\\"");     
    }
  
    function textPartToJson(textPart) {
        return '{ ' +
                '"textPart" : "' + getTextPartText(textPart) + '"' +
                ', "equivalent" : "' + getTextPartEquivalent(textPart) + '"' +
               '}';
    }
  
    function groupToJson(group) {
        var state, result, children, comma, classAttr, i, radioGroup;
      
        state = "sequential";      
        radioGroup = $(group).children('.radioGroupType');
        if (radioGroup.length > 0) {
            if (radioGroup.children(".groupTypeRandom").prop('checked')) {
                state = "random";
            }
        }
        result = '{ "groupType":"' + state + '", "children": [';
        children = $(group).children();
        comma="";
        for (i = 0; i < children.length; i++) {
            classAttr = $(children[i]).attr('class');
            if ( classAttr === 'group') {
                result += comma + groupToJson(children[i]);         
                comma = ", ";
            } else if ( classAttr === 'textPart') {
                result += comma + textPartToJson(children[i]);                
                comma = ", ";
            } else {
                console.log("warn: skipping object in groupToJson: ", classAttr);
            }
        }
        result += "]}";
        return result;
    }

In the server application, create an equivalent object structure using GSON.

Object processJsonObject(JsonObject object) {
        if (object.has("children")) {
            Group group = new Group();
            group.setGroupType(GroupType.valueOf(object.get("groupType").getAsString().toUpperCase()));
            group.setChildren(processJsonArray(object.getAsJsonArray("children")));
            System.out.print("---start group");
            System.out.println(String.format(" (%s) ---", object.get("groupType").getAsString()));     
            processJsonArray(object.getAsJsonArray("children"));
            System.out.println("---end group---");
            return group;
        } else if (object.has("textPart")) { 
            TextPart textPart = new TextPart();
            textPart.setTextPart(object.get("textPart").getAsString());
            textPart.setEquivalent(object.get("equivalent").getAsString());
            System.out.print(object.get("textPart").getAsString());       
            System.out.println(String.format(", %s", object.get("equivalent").getAsString()));
            return textPart;
        } else {
            return null;
        }
    }
   
    Object[] processJsonArray(JsonArray array) {
        ArrayList list = new ArrayList();
        for (JsonElement element : array) {
            if (element.isJsonArray()) {
                list.add(processJsonArray((JsonArray)element));
            } else if (element.isJsonObject()) {
                list.add(processJsonObject((JsonObject)element));
            } else {
                System.out.println(String.format("No object or array: %s", element));
            }
        }
        return list.toArray();
    }

I added a serialize and deserialize routine for saving the object structure. This allows the structure to be referenced by other applications.

public void serialize() {
      try
      {
         FileOutputStream fileOut =
           new FileOutputStream(context.getRealPath("/WEB-INF/templates/example.rote"));
         ObjectOutputStream out = new ObjectOutputStream(fileOut);
         out.writeObject(getRoot());
         out.close();
         fileOut.close();
         System.out.printf("Serialized data is saved in /WEB-INF/templates/example.rote");
      }catch(IOException i)
      {
         i.printStackTrace();
      }
    }
   
    public void deserialize() {
        try
      {
         FileInputStream fileIn =
           new FileInputStream(context.getRealPath("/WEB-INF/templates/example.rote"));
         ObjectInputStream in = new ObjectInputStream(fileIn);
         setRoot((Group) in.readObject());
         in.close();
         fileIn.close();
      }catch(IOException i)
      {
         i.printStackTrace();
         return;
      }catch(ClassNotFoundException c)
      {
         System.out.println("Example class not found");
         c.printStackTrace();
         return;
      }
    }

In the other application, I read the file that was created by the first application.

Using jQuery

Download jQuery form http://jquery.com/download/

Add a script tag to the HTML page for jQuery. I am using Tomcat, so I am using JSP.

    <script src="${pageContext.request.contextPath}/jquery/jquery-2.0.3.min.js">

Place some jQuery inside another script tag.

        <script>
        $( document ).ready(function() {
            console.log( "ready!" );
        });
        </script>

Found a great tool for playing with jQuery: http://jsfiddle.net/

Kiteboard Helmet Search

I am looking for a helmet for kite boarding. I have a large head. With short hair, my head is 24-1/4". My local stores do not have helmets that fit. I am looking for a helmet that fits and has good safety features.

I read this from an excellent post:

"Liner: There are three main types of insulation. Expanded Poly-Propylene (EPP) is the most common. It’s very stiff, not affected by moisture, and will take multiple impacts, according to Halstead. Expanded Poly-Styrene is "the very best" energy attenuating substance. It’s what’s used in bike helmets, but generally is only expected to be hit once, and with one exception noted below isn’t used in whitewater helmets. Finally, there are closed-cell foams. The best of these are otherwise known as Vinyl Nitrile, which is a PVC synthetic rubber, heavier in a safe density than EPS/EPP, and will absorb water, but it is usually much softer. A closed-cell foam will also absorb sweat along with water, which can make for a ‘funky’ brain bucket. A fourth insulation, Ethyl Vinyl Acetate or EVA, "isn’t a functional energy attenuator because it’s so springy," says Halstead.

Halstead says stiffer is better. "When you look at the stuff that will actually protect your head, it ought to be so stiff that you think, ‘my God, this is going to hurt.’ But you need that much stiffness to spread the impact. If you pick up a helmet with soft foam inside, the chance of it protecting you is slim." Of course, not everyone agrees with Halstead. Jay Norfleet from Grateful Heads thinks EPP is not a multiple-impact foam because it compresses. And Doug Poe of Pro-Tec believes EVA gives the same protection as closed-cell foam."

It is impossible to find a water helmet that fits a large head. My head is 62.5 cm. That is the upper limit of some helmets and above the limit for most.

Liquid Force XL 24in

ShredReady makes some helmets that are one-size-fits-all. I bought the Standard cut helmet and removed all the padding. I also cut away some of the mesh liner. It fits, barely.