Java 8 Examples dedicated blog

Hi, I have recently started a new blog dedicated to Java 8 examples. I will be covering a lot of topics for Java 8 there. Here is the link: Java 8 Examples

How to create Interstitial Ad for AdMob in Ionic Cordova app?

You might have encountered an error like, when requesting an ad from AdMob using Cordova AdMob Plugin: interstitialAd is null, call createInterstitialView first

Chances are you are doing it wrong. To create an Interstitial Ad you need to take of three things:

1. Use interstitialAdId as the key to pass you ad unit id in your options object
2. First create a Interstitial view using createInterstitialView
3. In success callback from createInterstitialView use requestInterstitialAd to request an ad

Below is the complete code snippet:

if (window.plugins && window.plugins.AdMob) {
    var admob_key = device.platform == "Android" ? "XXXXX" : "YYYYYYYYY";
    var admob = window.plugins.AdMob;
    var options = {
        interstitialAdId: admob_key,
        autoShow: true
    };
    admob.createInterstitialView(options, function() {
            admob.requestInterstitialAd({
                    'isTesting': false
                },
                function() {
                    admob.showAd(true);
                },
                function(error) {
                    console.log('failed to request ad ' + error);
                }
            );
        },
        function() {
            console.log('failed to create Interstitial view');
        });
} else {
    console.log("Admob plugin not available");
}

Using AmCharts in Play Framework 2 with Java

In this post, I am going to show you how you can use AmCharts in Play Framework 2 using Java.

First create a new Play Framework 2 Java project and download the Javascript libraries for AmCharts. download. After you uncompress the file, you see that there are a lot of files in that folder. You really don't need all of it. To start with, I just chose some of them and put them in the public folder in my Play Framework 2 project:

Make things easier you can also download jQuery.

<script src="@routes.Assets.at("javascripts/jquery-1.11.1.min.js")" type="text/javascript"></script>
<script src="@routes.Assets.at("javascripts/amcharts/amcharts.js")" type="text/javascript"></script>
<script src="@routes.Assets.at("javascripts/amcharts/themes/dark.js")" type="text/javascript"></script>
<script src="@routes.Assets.at("javascripts/amcharts/serial.js")" type="text/javascript"></script>
<script src="@routes.Assets.at("javascripts/amcharts/pie.js")" type="text/javascript"></script>

Now let's create a template file called graph.scala.html and add two empty divs. One for the graph itself and the other for the legend. Also, for the ease of presentation, we put the javascript to handle the graph drawing in this template, but outside the main:

@main("Graphs"){

<div id="test-chart"></div>
<div id="test-legend"></div>

}
<script type="text/javascript">
   // code to handle the graph drawing goes here
</script>

Make sure that the tag ids match. Meaning the first section of the id on both tags should be the same: xxxx-chart, xxxx-legend.

Next, I will talk show you how to draw the actual graph in Javascript. As a rule of thumb, any code related to the AmCharts should be written between:

AmCharts.ready(function(){
   // code goes here
}

Please not that you might see other variations of initialization above across other websites.

Now, let's put the actual code inside the initialization function, for now we use some fake data to show the graph:

      var chart = AmCharts.makeChart("test-chart", {
                    "type": "pie", // type of the graph
                    "theme": "dark", // the theme
                    "legend": { // settings for legend
                         "markerType": "circle",
                         "position": "right",
                         "marginRight": 80,
                         "autoMargins": false
                    },
                    "dataProvider": [{
                         "country": "Czech Republic",
                         "litres": 256.9
                    }, {
                         "country": "Ireland",
                         "litres": 131.1
                    }, {
                         "country": "Germany",
                         "litres": 115.8
                    }, 
                    "valueField": "litres", // field name to get the value from
                    "titleField": "country" // field name to get the title from
                });

Put the route in the 'routes' file, and Implement an action in a controller to show the page:

public class Application extends Controller {

    public static Result showGraph() {
            return ok(graph.render(""));
    }

}

The final and a very important step is to give an initial width size to your div. Create a css file called main.css in public/stylesheets folder and put the following in it:

   #test-chart {
 width  : 100%;
 height  : 500px;
 font-size : 11px;
  }

Make sure you add it to your header in the main.scala.html file:

 <link rel="stylesheet" media="screen" href="@routes.Assets.at("stylesheets/main.css")">

Now, run the project and go to the url that you defined in the routes file. You should see something like:

Switching between multiple JDKs on Mac OSX

Suppose you are working on a few Java projects and each of which needs a specific version of JDK.

First. make sure that you download your required JDKs: JDK 8 and JDK 7. gm

Second, look for .bash_profile in your home directory ~. If you can't find it, create it as follows:

touch ~/.bash_profile

Next, use a text editor such as vim to open this file as follows:

vim ~/.bash_profile

Now let's add some aliases that will allow us to easily switch between JDKs:

alias setJdk6='export JAVA_HOME=$(/usr/libexec/java_home -v 1.6)'
alias setJdk7='export JAVA_HOME=$(/usr/libexec/java_home -v 1.7)'
alias setJdk8='export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)'

/usr/libexec/java_home is just a command (symlink) that gives you the path for the active JDK, and using -v xx shows the path to the JDK with version xx.

After you added the above aliases to the .bash_profile file, save and close the file and run:

source ~/.bash_profile

This will set the aliases for you. Now to switch between the JDKs, just type setJdkX (replace X with the version number). Example:

setJdk8 

If you would like to know how you can prevent modification of a private field in java, see: Preventing modification of a private field in Java

How to test file upload action in Play Framework 2 in Java?

In this post, we will see how we can test an action that expects a file upload (e.g. a profile picture or an image) in Play Framework 2 for Java. First, lets create an action that accepts a file upload as below:

 public static F.Promise uploadProfileImage() {
    final Http.MultipartFormData body = request().body().asMultipartFormData();
    final Http.MultipartFormData.FilePart picture = body.getFile("picture");
    User user = // get the user from db
    
    final File imgFile = picture.getFile();
    final String imgPathToSave = "images/" + "some unique name";
    //save on disk
    final boolean success = new File("images").mkdirs();
    final byte[] bytes = IOUtils.toByteArray(new FileInputStream(imgFile));
    FileUtils.writeByteArrayToFile(new File(imgPathToSave),bytes);
    user.profileImageUrl = imgPathToSave;
    user.save();
       
}

AS you can see, the body of the request is a MultipartFormData. This makes a bit tricky to write functional tests in Play Framework 2 for Java actually. But, let's see the solution.

@Test
public void uploadProfileImageOK() throws Exception { 
   MultipartFormData.FilePart part = new MultipartFormData.FilePart<>("picture","test-image.jpg",Scala.Option("image/jpeg"),new File("test-image.jpg"));

   MultipartFormData formData = new MultipartFormData(Scala.>emptyMap(),Scala.toSeq(Arrays.asList(part)),Scala.emptySeq(),Scala. emptySeq());

   AnyContent anyContent = new AnyContentAsMultipartFormData(formData);

   Result uploadImageResult = callAction(controllers.routes.ref.UserController.uploadProfileImage(), fakeRequest().withHeader("Csrf-Token", "nocheck").withCookies(fakeCookie).withAnyContent(anyContent,"multipart/form-data", "POST"));

   assertEquals(OK, status(uploadImageResult));

   
}

To see more about functional testing in Play Framework 2 using Java see: How to test an action secure by SecureSocial in Play Framework 2 in Java

How to test an action secure by SecureSocial in Play Framework 2 in Java?

SecureSocial is an authentication module for Play Framework 2 applications supporting OAuth, OAuth2, OpenID, Username/Password and custom authentication schemes. Suppose you have an action and you have secured it with @SecureSocial.SecuredAction annotation:

public class Application extends Controller {
    @SecureSocial.SecuredAction
    public static Result index() {
        Identity user = (Identity) ctx().args.get(SecureSocial.USER_KEY);
        return ok(index.render(user));
    }
}

At the time of writing this blog post, SecureSocial only uses cookies for authentication. If you want to write a functional test for this action without taking care of a fake cookie you will get an unauthorized message. To do this we need to some provisioning before our test. Best is to use the @Befor. Below is the steps:

1. Lets assume that you save your user authentication data in the User model. Here we create a fake user before

@Before
public void setUp() throws Exception {
   User user = new User();
   User user = new User();
   user.firstName = "jack";
   user.lastName = "sparrow";
   user.email = "jack.sparrow@caribbean.com";
   user.providerId = "userpasswordid";
   user.password = "$2a$10$ywqls6dRsN4wLr.xNydi2uDVFNkOlmi9WSAfRy.RXdN5sgKKnKhau";
   user.authMethod = "userPassword";
   user.save();
}

Please note that the password that you see above is a hash produced with "Bcrypt" encryption and the value depends on how you have implemented this. See Secure Social Password Plugin for more info.
2. Now create a class named FunctionalTestHelpers and add the following method:

public static Http.Cookie getFakeCookie(String email){
        User user = User.findByEmail(email);

        SocialUser socialUser = new SocialUser(new IdentityId(user.email,user.providerId),
                user.firstName,
                user.lastName,
                String.format("%s %s", user.firstName, user.lastName),
                Option.apply(user.email),
                null,
                new AuthenticationMethod("userPassword"),
                null,
                null,
                Some.apply(new PasswordInfo("bcrypt", user.password, null))
        );

        Either either = Authenticator.create(socialUser);
        Authenticator auth = (Authenticator) either.right().get();
        Cookie scalaCookie = auth.toCookie();

        return new Http.Cookie(scalaCookie.name(),
                               scalaCookie.value(),
                               null,
                               scalaCookie.path(),
                               null,
                               scalaCookie.secure(),
                               scalaCookie.httpOnly());

    }

3. Now you can use the code below in your tests to get a fake cookie. The code above basically mimics what SecureSocial does for creating a cookie.

 
Http.Cookie fakeCookie = FunctionalTestHelpers.getFakeCookie("jack.sparrow@caribbean.com"); 

4. Now lets see it in action:

final Result deleteResult = callAction(controllers.routes.ref.TaskController.removeTask(taskId),fakeRequest().withCookies(fakeCookie).withHeader("Csrf-Token", "nocheck"));
assertThat(status(deleteResult)).isEqualTo(OK);

How to test actions annotated with @RequireCSRFCheck in Play Framework 2?

Let say you have an action as below that you want to protect against CSRF attacks, so you add the @RequireCSRFCheck annotation:

@RequireCSRFCheck
public Result saveUser() {
    // Handle body (process a form)
    return ok();
}

Now suppose you want to write some functional tests for this action. All you need to do is to add fake "nocheck" to your header in "callAction" as below:

final Result result = callAction(controllers.routes.ref.UserController.saveUser(),fakeRequest().withHeader("Csrf-Token", "nocheck"));
assertThat(status(result)).isEqualTo(OK);

For more information about CSRF checks in Play Framework 2 see: JavaCsrf

Importing a CSV file into a SQLite3 database table in Python

For this you need to import csv, sqlite3 libraries:

import csv, sqlite3

Lets use an in-memory database and create a simple table with two columns:

con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("CREATE TABLE t (col1, col2);")

Now, lets load our .csv file into a dictionary:

with open('data.csv','rb') as fin:
    dr = csv.DictReader(fin) # comma is default delimiter
    to_db = [(i['col1'], i['col2']) for i in dr]

csv.DictReader uses first line in the .csv file for column headings by default. Comma is also the default delimiter. The actual import:

cur.executemany("INSERT INTO t (col1, col2) VALUES (?, ?);", to_db)
con.commit()

If you want to play around with an example, you can try this:

#!/usr/bin/python
# -*- coding: utf-8 -*-

import sys, csv, sqlite3

def main():
    con = sqlite3.connect(sys.argv[1]) # database file input
    cur = con.cursor()
    cur.executescript("""
        DROP TABLE IF EXISTS t;
        CREATE TABLE t (COL1 TEXT, COL2 TEXT);
        """) # checks to see if table exists and makes a fresh table.

    with open(sys.argv[2], "rb") as f: # CSV file input
        reader = csv.reader(f, delimiter=',') # no header information with delimiter
        for row in reader:
            to_db = [unicode(row[0], "utf8"), unicode(row[1], "utf8")] # Appends data from CSV file representing and handling of text
            cur.execute("INSERT INTO neto (COL1, COL2) VALUES(?, ?);", to_db)
            con.commit()
    con.close() # closes connection to database

if __name__=='__main__':
    main()

Please not that the code above, we encode the input.

Preventing the modification of a private field in Java

Let's say you have a class like:

public class Test
{
  private String[] arr = new String[]{"1","2"};    

  public String[] getArr() 
  {
    return arr;
  }
}

Now, I have another class that uses the above class:

Test test = new Test();
test.getArr()[0] ="some value!"; //!!!

Bam! We were able to modify a private field outside of the class. This not what you want! To avoid this situation, you can use of the following solutions:

1. Either create a defensive copy:

public String[] getArr() {
  return arr == null ? null : Arrays.copyOf(arr, arr.length);
}

2. If you can use a List instead of an array, Collections provides an unmodifiable list:

public List getList() {
    return Collections.unmodifiableList(list);
}

What is the use of “assert” in Python?

The

assert

statement/function exists in mostly every other programming language out there. When you do...

assert a_condition

... you're telling the program to test that condition, and trigger an error if the condition is false. In Python, it's roughly equivalent to this:

if not condition:
    raise AssertionError()

Try it in the Python shell:

>>> assert True
>>> assert False
Traceback (most recent call last):
  File "", line 1, in 
AssertionError

Assertions can include an optional message, and you can disable them when you're done debugging. See here for the relevant documentation.

What is a percolator in Elasticsearch?

What you usually do is index documents and get them back by querying. What the percolator allows you to do in a nutshell is index your queries and percolate documents against the indexed queries to know which queries they match. 

It's also called reversed search, as what you do is the opposite to what you are used to. 

 There are different use-cases for the percolator, the first one being any platform that stores users interests in order to send the right content to the right users as soon as it comes in. For instance a user subscribes to a specific topic, and as soon as a new article for that topic comes in, a notification will be sent to the interested users. 

You can express the users interests as an elasticsearch query, using the query DSL, and you can register it in elasticsearch as it was a document. Every time a new article is issued, without needing to index it, you can percolate it to know which users are interested in it. At this point in time you know who needs to receive a notification containing the article link (sending the notification is not done by elasticsearch though). An additional step would also be to index the content itself but that is not required.

How to set specific logging for tests in Play Framework 2 ?

Specifying a different logging configuration is very simple.

Play Framework 2's default logging is logback. To set specific logging configurations for tests follow the steps below:

1. Just create a logback configuration file (eg test-logger.xml):

<configuration>

 <conversionRule conversionWord="coloredLevel" converterClass="play.api.Logger$ColoredLevel" />

 <appender name="FILE" class="ch.qos.logback.core.FileAppender">
 <file>${application.home}/logs/application.log</file>
 <encoder>
 <pattern>%date - [%level] - from %logger in %thread %n%message%n%xException%n</pattern>
 </encoder>
 </appender>

 <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
 <encoder>
 <pattern>%coloredLevel %logger{15} - %message%n%xException{5}</pattern>
 </encoder>
 </appender>

 <logger name="play" level="INFO" />
 <logger name="application" level="DEBUG" />

 <!-- Off these ones as they are annoying, and anyway we manage configuration ourself -->
 <logger name="com.avaje.ebean.config.PropertyMapLoader" level="OFF" />
 <logger name="com.avaje.ebeaninternal.server.core.XmlConfigLoader" level="OFF" />
 <logger name="com.avaje.ebeaninternal.server.lib.BackgroundThread" level="OFF" />
 <logger name="com.gargoylesoftware.htmlunit.javascript" level="OFF" />

 <root level="ERROR">
 <appender-ref ref="STDOUT" />
 <appender-ref ref="FILE" />
 </root>

</configuration>

2. Go to root project folder, open

   build.sbt

   file and add:

   
   javaOptions in Test +="-Dlogger.resource=test-logger.xml"
   
   

   Now whenever you run your tests, the logging configuration written in

   test-logger.xml

   will be read.

Installing psycopg in ubuntu for python

You will need to install these packages libpq-dev python-dev using sudo apt-get install. and then easy_install psycopg2

Installing numpy and scipy inside a virtualenev

Prerequisites:

• sudo apt-get install git gfortran g++
• sudo apt-get install libatlas-base-dev liblapack-dev

And:

• pip install numpy scipy

How to install virtualenv, virtualenvwrapper in ubuntu

Follow below:

• sudo apt-get update

• sudo apt-get install python-setuptools python-dev build-essential git-core -y

• sudo easy_install pip

• sudo pip install virtualenv

• sudo pip install virtualenvwrapper

• mkdir ~/virtualenvs 

•  echo "export WORKON_HOME=~/virtualenvs" >> ~/.bashrc

•  echo "source /usr/local/bin/virtualenvwrapper.sh" >> ~/.bashrc 

•  echo "export PIP_VIRTUALENV_BASE=~/virtualenvs" >> ~/.bashrc 

•  source ~/.bashrc 

• mkvirtualenv blog

If you want to get out/off your virtualenv use this command:

• deactivate

If you want to jump back on the virtualenv we just created and installed django use this command:

• workon xxx

And finally if you want to remove the virtualenv altogether

• rmvirtualenv blog 

Setup Eclipse: interpreter
Create a new PyDev Project

File -> New -> PyDev Project

A window will popup asking about the project details. Alternatively if you have already created a project go to

Project -> Properties

Click on "Click here to configure an interpreter no listed"

Click the New button

A new window will popup

Interpreter name: VIRTUALENVNAME (or whatever you like)

Interpreter executable: ~.virtualenvs/VIRTUALENVNAME/bin/python (or your custom location to the virtualenv/bin/python)

Standard Directory Layout in Maven

Have you ever wondered like me, what is the standard folder structure in maven?
Look here: Standard Folder Structure in Maven

Which dependency in the hierarchy does Maven use when managing dependencies

A misconception about Maven's dependency management is that “Maven chooses the highest version” when two or more transitive dependencies disagree on the version of a given groupId and ArtifactId coordinate.

The truth is that it uses Maven resolves the version nearest to the top of the dependency tree in the end. To view this dependency tree type:

 mvn dependency:tree

resource: Maven dependency management

Setting up jdk path (JAVA_HOME) for Tomcat7 in ubuntu

If you are a newbie like me, you might have the same problem as me when you wanted to start the tomcat7 on ubuntu:

• no JDK found - please set JAVA_HOME

Make sure the JAVA_HOME is set properly: if issuing "echo $JAVA_HOME" does not show any paths, you should add the following lines to your ~./bashrc (if you want to set it locally ) or if you want to set it globally you should add these to /etc/bash.bashrc :

#Java Environment Variable
JAVA_HOME=/usr/lib/jvm/jdk1.7.0/
export JAVA_HOME
JRE_HOME=/usr/lib/jvm/jdk1.7.0/jre
export JRE_HOME
PATH=$PATH:$JAVA_HOME:$JRE_HOME
export PATH

Now, normally, after reopening the terminal and issuing "sudo service tomcat7 start" should start the tomcat. But if you see the error above again:

• no JDK found - please set JAVA_HOME

Just to this: "gksudo gedit /etc/default/tomcat7" and uncomment the line that sets the JAVA_HOME variable:

Now run the tomcat. This should do the trick.
If you are interested in seeing some examples in Java 8, checkout my new blog about Java 8 Examples click on this link: Java 8 Examples

Difference between "Provided" and "Compiled" scopes Maven?

Q: Maybe this question seems to be a cliché but it bothers me somehow. What it difference in using maven scope compile and provided when artifact is builded as a JAR? If it was WAR, then I understand - artifact would be attached or not to WEB-INF/lib. But in case of the JAR it doesn't matter - dependencies aren't attached. They have to be on classpath when their scope is compile or provided. I know that provided dependencies aren't transitive - but is it only one difference?

A:

From the Maven Doc:

• compile

This is the default scope, used if none is specified. Compile dependencies are available in all classpaths of a project. Furthermore, those dependencies are propagated to dependent projects.

• provided

This is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime. For example, when building a web application for the Java Enterprise Edition, you would set the dependency on the Servlet API and related Java EE APIs to scope provided because the web container provides those classes. This scope is only available on the compilation and test classpath, and is not transitive.

Recap:

• dependencies are not transitive (as you mentioned)
• provided scope is only available on the compilation and test classpath, whereas compile scope is available in all classpaths.
• provided dependencies are not packaged

Source: http://stackoverflow.com/questions/6646959/difference-between-maven-scope-compile-and-provided-for-jar-packaging