Category: Java

Today we're trying to rewrite jug.bg for a third time. This time using ReactJS. Let's see how this goes this time.

I did a talk on Jigsaw at BGOUG.

The talk is for a very important new feature in Java SE 9. Code named Jigsaw, this feature modularizes the Java SE platform.
The coolest thing I do at the talk is to create a custom JRE.

Of course the jug and jPrime were mentioned.

Code: https://bitbucket.org/stybz/jigsaw.sty/src/

Video:

Presentation:

Today we had a meeting that discussed a way to automate deployments on AWS.

SDL's Behrooz Nobakht came especially for our event to explain how that is automated within their own products.

The first edition of jProfessionals is happening right now.

We managed to bring over Koshuke Kawaguchi. He's the creator of Hudson and after leaving Oracle, creator of the open source Jenkins. The topic was Jenkins 2.0.

The next speaker is Vladimir Tsanev. He'll talk about JMH with examples. Very interesting topic. He actually showed how to create a simple benchmark and to how to execute it.

Update: After the plentiful lunch Svetlin Nakov was awesome presenting HTTP/2. He was great at explaining the inner workings of the new protocol. Emil Doychev presented Groovy. There was a little bashing on JPA.

Some time for coffee and Doychin Bondzhev presented JavaFX in a very accessible way.

Trayan Iliev talked about high performance reactive programming with java 8. It was very interesting. Especially the demo at the end.

Wow.

Writing this I'm listening to Alan Bateman and Mark Reinhold deliver a session on the new Jigsaw (their third attempt?). This time it might work.

There's a lot of beer, more than I can handle (it turns out that a teenage girl handles her liquor better than I can) . A lot of awesome sessions - even one on the history of the universe.

The JUG is represented by Ivan, Krasi, Vladi and a bunch more awesome folks that make my trip here awesome.

I'm now supposed to be a java concurrency specialist:

Pretty proud of the certificate, but a lot more to learn.

So this weekend the Bulgarian Java User Group (jug.bg) organized a hackaton to try to create a JBoss Forge plugin to create Spring Boot applications.

JBoss Forge is a tool to ease development. Main traits are it can create JPA entities, It can create an example REST interface to those entities, a web interface to those entities and it integrates with Eclipse and IntelliJ IDEA:

The code is here. Here are a couple of pictures from the event:

If I want to use the latest JDK9 build in IntelliJ, I get:

To fix it, I have to fix /Applications/IntelliJ IDEA 14.app/Contents/Info.plist

Restart. Should work.

So far no issues with IDEA, but I expect to see some.

March 20th will be the start of the annual SoftUni Conf. I will present Java SE 8' s lambda feature. I expect it to be a fun event.

Today (2015.02.25) we had a bgjug sponsored "intro to nashorn" event.

Mitya, presented nashorn and avatar.js. Gave a lot of examples and had a hands-on - a node.js server working with hibernate.

So we in the Bulgarian Java User Group wanted to build Valhalla, and no IDE (Eclipse, Intellij Idea) supports it. We needed some simple text editor with some java support. And Sublime Text 3 (with Javatar) is the one we chose.

Sublime is a fancy editor written in C and Python. Javatar is a plugin that adds some Java support.

Installing Sublime Text 3 beta is straight forward. Installing Javatar is:

[openjdk@localhost valhalla]$ cd ~/.config/sublime-text-3/Packages/
[openjdk@localhost Packages]$ git clone git://github.com/spywhere/Javatar.git

Setting up the correct java is: Ctrl+Shift+P --> "javatar" --> Javatar Settings - Default

Then change the javac and java locations:

Creating projects is a bit uneasy - create new project is actually called "Project -> Save as".

And then we can run some code (fist compile, then run):

Today we had a second bgjug hackaton for the month. Its topic was Valhalla.

Project Valhalla will probably be part of Java 10 (expected 2018). Among other things it allows using primitives as generic arguments.

Here's how you can build Valhalla yourself.

Here's a virtual machine with valhalla if you're lazy (virtual box).

This is the valhalla presentation by Ivan. And this is the video of the talk (in Bulgarian).

Here are some of the code we ran:

Ivan created a simple ArrayList

public class SpecialArrayList {
	private static int INITIAL_SIZE = 10;
 
	private T[] elements = null;
	private int length = 0;
 
	public SpecialArrayList() {
		elements = new T[INITIAL_SIZE];
	}
 
	public T get(int position) {
		if(position >= length) {
			throw new ArrayIndexOutOfBoundsException();
		}
 
		return elements[position];
	}
 
	public void add(T element) {
		// Check whether array is full
		elements[length] = element;
		length++;
	}
}
public class Main {
	public static void main(String[] args) {
		SpecialArrayList intList = new SpecialArrayList<>();
		intList.add(1);intList.add(2);intList.add(3);intList.add(4);
		System.out.println(intList.get(2));
 
		SpecialArrayList stringList = new SpecialArrayList<>();
		stringList.add("1");stringList.add("2");stringList.add("3");stringList.add("4");
		System.out.println(stringList.get(3));
	}
}

Nayden tested a bit of crazy code - which is supposed to fail (IA impl = new IAImpl();):

public class B  {
   protected T t;
   protected T[] ts;
   public B(){}
 
   public B(T t){
     this.t = t;
     this.ts = new T[100];
   //  System.out.println(this.t.getClass());
   }
 
   public T[] getTs(){
     return this.ts;
   }
 
   public T getT(){
     return this.t;
   }
 
   public static void main(String[] args){
       B b = new B<>(100);
       System.out.println(b.getT());
 
       System.out.println(b.getClass());
       System.out.println((new B("dada")).getClass());
       System.out.println(c.getClass());
 
       IAImpl ludnica = new IAImpl();
       ludnica.setT(100);
       System.out.println(ludnica.getT() instanceof Object);
 
       IABase base = new IAChild();
       base.setT("dada");
       System.out.println(base.getT());
       System.out.println(base.getClass());
 
       IA impl = new IAImpl();
 
       impl.setT("dada");
       System.out.println(impl.getT());
       System.out.println(impl.getClass());
   }
}
 
 
interface IA{
 public T getT();
 public void setT(T t);
}
 
 
class IABase{
 private T t;
 public T getT(){
   return this.t;
 }
 public void setT(T t){
   this.t = t;
 }
}
 
class IAChild extends IABase {
 
}
 
class IAImpl implements IA {
 private Object t;
 public Object getT(){
   return this.t;
 }
 public void setT(Object t){
   this.t = t;
 }
}

So we had a hackaton a month ago to fix a bug in the OpenJDK. Today we continued with the fix - using streams, benchmarking different solutions, and prepared a patch to send to the jdk team.

FYI: Eclipse Luna (4.4) is currently beta.

Create new Maven Project.

Open the pom.xml

Add the following dependencies:

    <dependency>
      <groupId>net.sourceforge.htmlcleaner</groupId>
      <artifactId>htmlcleaner</artifactId>
      <version>2.6</version>
    </dependency>
    <dependency>
      <groupId>org.apache.httpcomponents</groupId>
      <artifactId>httpclient</artifactId>
      <version>4.3.4</version>
    </dependency>

The code is as follows:

package sty.qainjava.xpath.on.html;
 
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.URL;
import java.nio.charset.Charset;
 
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
 
import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.entity.ContentType;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.htmlcleaner.CleanerProperties;
import org.htmlcleaner.DomSerializer;
import org.htmlcleaner.HtmlCleaner;
import org.htmlcleaner.SimpleHtmlSerializer;
import org.htmlcleaner.TagNode;
import org.w3c.dom.Document;
 
/**
 * QAinJava: how to do an xpath on html in java.
 * 
 * We use <a href="http://htmlcleaner.sourceforge.net/">HtmlCleaner</a>
 * and <a href="https://hc.apache.org/">HttpClient</a>.
 * 
 * @author Mihail STY
 */
public class Program {
	/**
	 * We're not using any methods so that the source code is as straight
	 * forward as possible.
	 * 
	 * No exception handling at all for simplicity
	 */
	public static void main(String[] args) throws IOException,
	        ParserConfigurationException, XPathExpressionException,
	        TransformerException {
 
		String address = "https://www.google.com/";
 
		String html;
 
 
		{
			// the httpclient part
			CloseableHttpClient httpclient = HttpClients.createDefault();
			HttpGet httpGet = new HttpGet(address);
			CloseableHttpResponse response = httpclient.execute(httpGet);
			HttpEntity entity = response.getEntity();
 
			ContentType contentType = ContentType.getOrDefault(entity);
			Charset charset = contentType.getCharset();
 
			BufferedReader r = new BufferedReader(new InputStreamReader(
			        entity.getContent(), charset));
 
			// we can directly plug the input to HtmlCleaner,
			// but we put it in a string so we can print it,
			// or save it to a file
			String line = null;
			StringBuilder builder = new StringBuilder();
			while ((line = r.readLine()) != null) {
				builder.append(line);
			}
			html = builder.toString();
		}
 
		{// write html to a file
			BufferedWriter bf = new BufferedWriter(new OutputStreamWriter(
			        new FileOutputStream("google.html.xml")));
			bf.write(html);
			// exception handling is not exceptionally good, but that's not our
			// focus here
			bf.flush();
			bf.close();
		}
 
		// HtmlCleaner part
		TagNode tagNode = new HtmlCleaner().clean(html);
		String cleanHtml = new SimpleHtmlSerializer(new CleanerProperties())
		        .getAsString(tagNode);
		// System.out.println(cleanHtml);
 
		{// write cleanHtml to a file
			BufferedWriter bf = new BufferedWriter(new OutputStreamWriter(
			        new FileOutputStream("clean.html.xml")));
			bf.write(cleanHtml);
			// exception handling is not exceptionally good, but that's not our
			// focus here
			bf.flush();
			bf.close();
		}
 
		// we need a DOM document to execute xpath, HtmlCleaner helps in creating one
		Document doc = new DomSerializer(new CleanerProperties())
		        .createDOM(tagNode);
 
		{// save dom to file with a transformer (just for testing purposes)
			TransformerFactory factory = TransformerFactory.newInstance();
			Transformer transformer = factory.newTransformer();
			transformer.transform(new DOMSource(doc), new StreamResult(
			        new File("dom.html.xml")));
		}
 
		// the xpath part
		XPath xpath = XPathFactory.newInstance().newXPath();
		String imgURL = (String) xpath.evaluate("//img/@src", doc,
		        XPathConstants.STRING);
 
		//using two URLs we can make sure we get the absolute URL even if relative.
		System.out.println(new URL(new URL(address), imgURL).toString());
	}
}

• Some people, when confronted with a problem, think, "I know, I'll use regular expressions." Now they have two problems.
• Some people, when faced with a problem, think, "I know, I'll use #binary." Now they have 10 problems.
• Some people, when confronted with a problem, think, "I know, I'll use #threads," and then two they hav erpoblesms.
• Some people, when confronted with a problem, think "I know, I'll use #multithreading". Nothhw tpe yawrve o oblems.
• Some people, when confronted with a problem, think, "I know, I'll use mutexes." Now they have
• Some people, when confronted with a problem, think: "I know, I'll use caching." Now they have one problems.
• Some people see a problem and think "I know, I'll use #Java!" Now they have a ProblemFactory.
• Some programmers, when confronted with a problem, think "I know, I'll use floating point arithmetic." Now they have 1.999999999997 problems.
• Some people, wanting an escape from their full-time job, think "I know, I'll contribute to open source." Now they have two full-time jobs.
• Some people, when confronted with a problem, think: "I know, I'll think outside the box!" Now, they have 3.75 problems, an entirely new framework, and three dozen toll house cookies cooling in the kitchen.
• Some people when confronted with a desire to use pithy quotes in their presentations think "I know, I'll use something from Star Wars". Now two problems they have.
• Some people, when confronted with a problem, think, "I know, I'll use #UTF8." Now they à??????µ?ç°§ùÔ_¦Ñ?.
• "I'll use #PHP!" Now they have ("1 apple" + "1 orange") problems.
• "I'll use #Perl!" Now they have more than one way to have more than one problem....
• Some people, when confronted with a problem, think, "I know, I'll use Shareware." Now they have two trials.
• Some people, when confronted with a problem, think, "I know, I'll use delegations." Now their problem is a problem of their problem.
• Some people when confronted with a problem think "I know, I'll quote jwz". Now everyone has a problem.

Source: http://nedbatchelder.com/blog/201204/two_problems.html

CodingBat is a nice website that tests basic java and python skills.

How can one highlight (use a code color scheme) for source code or xml or html and do the following and do it in any html page?
Like this:

One can use a javascript library. Instead of explaining how it works, here's the trick:

  <pre name="code" class="xml:nogutter:nocontrols">
    <?xml version="1.0" encoding="UTF-8"?>
      <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
              xmlns:news="http://www.google.com/schemas/sitemap-news/0.9">
          <url>
              <loc>http://www.kenoshanews.com/news/on_target_archer_sets_county_fair_record_472937185.html</loc>
                <news:news>
                  <news:publication>
                      <news:name>Kenosha News</news:name>
                      <news:language>en</news:language>
                  </news:publication>
                  <news:access>Subscription</news:access>
                <news:publication_date>2013-08-18</news:publication_date>
                <news:title>On target: Archer sets county fair record</news:title>
                </news:news>
          </url>
      </urlset>
  </pre>
  <link type="text/css" rel="stylesheet" href="http://syntaxhighlighter.googlecode.com/svn-history/tags/1.5.1/Styles/SyntaxHighlighter.css" />
  <script language="javascript" src="http://syntaxhighlighter.googlecode.com/svn-history/tags/1.5.1/Scripts/shCore.js"></script>
  <script language="javascript" src="http://syntaxhighlighter.googlecode.com/svn-history/tags/1.5.1/Scripts/shBrushXml.js"></script>
  <script language="javascript">
    dp.SyntaxHighlighter.HighlightAll('code');
  </script>

The important part is:

class="xml:nogutter:nocontrols"

xml = the language
nogutter, nocontrols = options
http://syntaxhighlighter.googlecode.com/svn-history/tags/1.5.1/ = I don't want to include these in my project, so I use them remotely, you can download them locally, but download all.
Add the js libraries for the languages you use. For xml I added shBrushXml (see the code).

Supported languages: https://code.google.com/p/syntaxhighlighter/wiki/Languages
Configuration options: https://code.google.com/p/syntaxhighlighter/wiki/Configuration

public class Peshev {
    public static void main(String... args) {
        String[] fff = new String[]{"a", "b",};
        System.out.println(fff[0]+fff[1]);
    } 
}

Do you see the trailing comma after "b"? That's allowed. Unexpected from a strongly-typed lang as Java.

IDEA allows cursor placement in whitespace that is not part of the file. How to switch it off?

THEN:

Now if someone knows to move left and right with the arrow keys skipping 4 spaces at a time, not a single space.