GarciaPL Notes - Java and Others

Some of you might be interested in presentation which I made recently for internal training purpose. Topic is "Packer by HashiCorp".

Some of you might know this unofficial Stack Careers Android app which allows you search job in IT sector. There is a link => Stack Careers on Google Play. I have been using it for a while, but some time ago it stopped working. Only what I got was : 'No Results'. So, I downloaded repository and found out that feed API of Stack Careers has been changed. I mean that application got HTTP 301 status which means Moved Permanently and no redirect has been performed using standard HttpConnection component of Android stack. More info about what I did you might find below and under pull request link.


In fact that I have been using you app occasionally, I found someday that it does not work now. I managed to figure out that guys from Stackoverflow changed feed API and moreover you app was not able to follow up redirect (HTTP 301 Moved Permanently).

So, according to this pull request what I did and what I did not :

• feed API has not been changed 
• added OkHttp library within required by it another library called Okio 
• replaced HttpURLConnection with client from OkHttp 
• added required rules for proguard to cover up OkHttp 

Some of you might be interested in presentation which I made recently for internal training purpose. Topic is "Consul and Consul Pusher".

Some of you might thinking how to create sequence for table which contains some records. You might always export all records from database, then eventually create sequence and after all import those records once again into database. Nevertheless there is a solution how to create this sequence using PL/SQL.

DECLARE
  seq_value_holder        NUMBER;
BEGIN
  -- create a sequence for YOUR_TABLE
  SELECT NVL(MAX(id), 0) + 1
  INTO seq_value_holder
  FROM YOUR_TABLE;
  EXECUTE immediate 'create sequence SEQ_YOUR_TABLE start with ' || seq_value_holder || ' increment by 1';
END;

A few days ago, I got an email with inquiry if I would like to participate in recruitment process to Google. I thought why not. It is always good to gain some experience around that. After a phone interview which was not successful for me, but I am not sad about that fact at all, I thought that I might give you some insight what areas you should refresh or just learn quickly. Of course your questions will be correlated with those areas which you picked up before phone interview, but I assume that some of them might be similar with those which I chose.

Some of you might be interested in presentation which I made recently for internal training purpose. Topic is "Mutation testing with Pitest".

If you are trying to speed up your Android phone, you should consider uninstalling Facebook! You can read more about that phenomenon for instance here : https://www.reddit.com/r/Android/comments/42kyph/uninstalling_facebook_speeds_up_your_android/. To be honest my phone is much faster after removing Facebook.

Have you ever wondered how to map enums from one to another ? Did you use switch statement to make it work ? Now you can use method immutableEnumMap from class Maps which is part of Guava. Below you can find an example.

public class EnumSourceMapper {

    static ImmutableMap<EnumSource, EnumDestination> mapper;

    static {
        mapper = Maps.immutableEnumMap(ImmutableMap.<EnumSource, EnumDestination>builder()
                .put(EnumSource.SUCCESS,                  EnumDestination.SUCCESS)
                .put(EnumSource.INCOMPLETE,               EnumDestination.ERROR)
                .put(EnumSource.FAIL,                     EnumDestination.ERROR)
                .build());
    }

    public EnumDestination getEnumDestination(EnumSource enumSource) {
        return mapper.get(enumSource);
    }
}

Recently I was trying to convert some cash in EUR currency, but I did not have time to watch currency graph all the time. So, I have created small tool which will let me know via email when currency will get more expensive above some concrete level. You can put below script in cron to execute it with some time interval. I used Sparkpost as a email provider.

import urllib2
import json
from sparkpost import SparkPost

sp = SparkPost('YOUR_API_KEY')

def currencyConverter(currency_from,currency_to):
    yql_base_url = "https://query.yahooapis.com/v1/public/yql"
    yql_query = 'select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20("'+currency_from+currency_to+'")'
    yql_query_url = yql_base_url + "?q=" + yql_query + "&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys"
    try:
        yql_response = urllib2.urlopen(yql_query_url)
        try:
            yql_json = json.loads(yql_response.read())
            currency_output = 1 * float(yql_json['query']['results']['rate']['Rate'])
            return currency_output
        except (ValueError, KeyError, TypeError):
            return "JSON format error"

    except IOError, e:
        if hasattr(e, 'code'):
            return e.code
        elif hasattr(e, 'reason'):
            return e.reason

currency_from = "EUR" # currency codes : http://en.wikipedia.org/wiki/ISO_4217
currency_to = "PLN"
direction_rate = 4.44

rate = currencyConverter(currency_from,currency_to)
print rate

if rate > direction_rate:
 response = sp.transmissions.send(
     recipients=['YOUR_EMAIL@gmail.com'],
     html='Rate of ' + currency_from + currency_to + ' equals ' + str(round(rate, 2)) + '

',
     from_email='test@sparkpostbox.com',
     subject='EuroMonitor'
 )

 print(response)
else:
   print "Rate too low"

I had a chance to work with Spring Test DBUnit [1] (integration between Spring testing framework and DBUnit) with few tests related with Spring Integration. Most of them use the same common text context which contains embedded database H2. Funny thing was that some tests failed, because of some tables already exist. The issue is that embedded database is not cleared between tests and it is reused within the same context. That's why you should use @DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_CLASS) with @TestExecutionListeners({DependencyInjectionTestExecutionListener.class, DirtiesContextTestExecutionListener.class}) like below :

@ContextConfiguration
@RunWith(SpringJUnit4ClassRunner.class)
@TestExecutionListeners({DependencyInjectionTestExecutionListener.class, DirtiesContextTestExecutionListener.class})
@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_CLASS)
public class YourTest {

}

I would like to announce that new Android app has been released recently times by me. This time application is called PerlJobs. This application helps you as a Perl developer to find new job opportunities across the globe. Job offers are divided into sections : Standard, Mod, Catalyst, Mason, Telecommute and By Country. The main source of all jobs is website : https://jobs.perl.org

Yes! I finally managed to create it. Obviously it is not so pretty as it might be, but.. never mind :) If you would like to create your own Google Play Developer Page where you can add some promotion text and graphics (icon and background), just go to your Developer Console and then click Settings and then Developer Page. If you are looking for let's say 'inspiration', you can have a look on my Developer Page which link you can find below :

This time I would like to share with small snippet of code written in Java and Spring MVC which might allow you to pack and download some files (in this case .csv file) in ZIP archive. So, if you will hit URL http://localhost:8090/yourApp/download/zip, Zip archive will be downloaded with name 'download.zip'.

    @ResponseBody
    @RequestMapping(value = {"/download/zip"}, method = RequestMethod.GET)
    public void downloadZipArchive(HttpServletResponse response) throws IOException {

        List<MyClass> list; //should contains some records!
        if (list != null && !list.isEmpty()) {
            if (list.size() > 200000) {

                response.setContentType("application/zip");
                response.addHeader("Content-Disposition", "attachment; filename=\"download.zip\"");
                response.addHeader("Content-Transfer-Encoding", "binary");

                OutputStream servletOutputStream = response.getOutputStream();
                ZipOutputStream zos = new ZipOutputStream(servletOutputStream);

                int counter = 0;
                List<List<MyClass>> dividedlist = Lists.partition(list, 200000);
                for (List<MyClass> partition : dividedlist) {
                    zos.putNextEntry(new ZipEntry("file_" + counter + ".csv"));
                    CSVWriter writer = new CSVWriter(new OutputStreamWriter(zos));
                    writer.writeNext(new String[]{"HEADER"});
                    for (MyClass item : partition) {
                        writer.writeNext(new String[]{item.getText()});
                    }
                    writer.flush();
                    zos.closeEntry();
                    counter++;
                }
                zos.close();
                response.getOutputStream().flush();
                response.getOutputStream().close();
            }
        }
    }

A few days ago I had issue, that I need to get first object from some list which meet my requirements. Of course I can create some loop, write some if statement. If I will find interesting me object, then I am gonna return it. If I will not find any useful in whole list, then I am will return null.

Above solution is done in quite old-style approach. Now it is time for functional programming! I found very useful a library called Guava and it's utility class called FluentIterable. It supports you to manipulate Iterable instances in a chained fashion. This class has a lot of functionalities, but I would like to focus only on one case - get first interesting object to my pattern or just return null.

MyClass interestingObjectOrNull = FluentIterable.from(myList)
    .firstMatch(new Predicate<MyClass>() {
      @Override
      public boolean apply(MyClass element) {
        return element.getId == 125L
      }
    })
    .orNull();

Recently I had an issue during installation of HipChat from Atlassian on my Ubuntu. I mean that installation went well, but I had issue with GPG keys which was :

"GPG error: http://downloads.hipchat.com stable InRelease: The following signatures couldn't be verified because the public key is not available"

So, I managed to find that WebUpd8Team provides tool called y-ppa-manager. All you have to do is install y-ppa-manager like below :

sudo add-apt-repository ppa:webupd8team/y-ppa-manager
sudo apt-get update
sudo apt-get install y-ppa-manager

In recent times I had issue with web application written in Spring. The problem was that some numbers stored in database as a BigDecimal's and Long's were not being stored/processed properly for different locales. On backend the numbers were processed of course using English locale, but when you have number saved with different locale the calculations might be different.

Saved BigDecimal's and Long's were processed against English locale, but presentation of numbers were based on appropriate locale of present user context.


Parse BigDecimal => 12,333,444
English => 12333444
Indonesian => 12333444

Print BigDecimal => 12345.50
English => 12345.50
Indonesian => 12345,50


Only difference for printed numbers for above locales was how decimal places is presented. For English we use dot. For Indonesian comma is used.


Parse Long => 12,333,444
English => 12333444
Indonesian => 12333444

Print Long => 12333444
English => 12333444
Indonesian => 12333444


For Long's the formatter we are going to just remove grouping commas.

So, below you can find CurrencyLocaleBigDecimalFormatter :

package pl.garciapl.test;

import org.springframework.format.Formatter;

import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.text.ParseException;
import java.util.Locale;

public class CurrencyLocaleBigDecimalFormatter implements Formatter<BigDecimal> {

    @Override
    public BigDecimal parse(String text, Locale locale) throws ParseException {
        DecimalFormat format = (DecimalFormat) NumberFormat.getNumberInstance(Locale.ENGLISH);
        format.applyPattern("#,##0.00");
        format.setParseBigDecimal(true);
        format.setGroupingUsed(true);
        return (BigDecimal) format.parse(text);
    }

    @Override
    public String print(BigDecimal object, Locale locale) {
        DecimalFormat format = (DecimalFormat) NumberFormat.getNumberInstance(locale);
        format.applyPattern("#,##0.00");
        format.setParseBigDecimal(true);
        format.setGroupingUsed(false);
        return format.format(object);
    }
}

package pl.garciapl.test;

import org.springframework.format.Formatter;

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.text.ParseException;
import java.util.Locale;

public class CurrencyLocaleLongFormatter implements Formatter<Long> {

    @Override
    public Long parse(String text, Locale locale) throws ParseException {
        DecimalFormat format = (DecimalFormat) NumberFormat.getNumberInstance(Locale.ENGLISH);
        format.applyPattern("#,##0.00");
        format.setParseBigDecimal(false);
        format.setGroupingUsed(true);
        return (Long) format.parse(text);
    }

    @Override
    public String print(Long object, Locale locale) {
        DecimalFormat format = (DecimalFormat) NumberFormat.getNumberInstance(locale);
        format.applyPattern("#,##0.00");
        format.setParseBigDecimal(false);
        format.setGroupingUsed(false);
        return format.format(object);
    }
}

package pl.garciapl.test;

import org.springframework.format.Formatter;
import org.springframework.format.FormatterRegistrar;
import org.springframework.format.FormatterRegistry;

import java.util.HashSet;
import java.util.Set;

public class CurrencyLocaleFormatterRegistrar implements FormatterRegistrar {

    private Set<Formatter> formatters = new HashSet<>();

    public CurrencyLocaleFormatterRegistrar(Set<Formatter> formatters) {
        this.formatters = formatters;
    }

    @Override
    public void registerFormatters(FormatterRegistry registry) {
        for (Formatter element : this.formatters) {
            registry.addFormatter(element);
        }
    }
}

    <bean id="currencyLocaleBigDecimalFormatter" class="ie.garciapl.test.CurrencyLocaleBigDecimalFormatter"/>
    <bean id="currencyLocaleLongFormatter" class="ie.garciapl.test.CurrencyLocaleLongFormatter"/>
    <bean id="currencyLocaleRegistrar" class="ie.garciapl.test.CurrencyLocaleFormatterRegistrar">
        <constructor-arg>
            <set>
                <ref bean="currencyLocaleBigDecimalFormatter"/>
                <ref bean="currencyLocaleLongFormatter"/>
            </set>
        </constructor-arg>
    </bean>

<mvc:annotation-driven conversion-service="conversionCurrencyService"/>

Below you can find GitHub Gist of User Agents in JSON based on massive list of user agents provided by Chris Pederik [1]. I provided the same list of user agents in more friendly form as a JSON because of this one provided in reference is nested multiple times, what obviously affects the use of content. Moreover I removed duplicates.

I just would like to show you how setup styles.xml and values-v21/styles.xml to use Material Design with AppCompat. First of all rename styles21.xml as styles.xml and place in your res/values-v21 folder (you may need to create a values-v21 folder if you don't already have one). Below you might found AndroidManifest.xml.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="uk.co.thewirelessguy.myappname" >

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="uk.co.thewirelessguy.myappname.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.1"

    defaultConfig {
        applicationId "uk.co.thewirelessguy.myappname"
        minSdkVersion 9
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            runProguard false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:21.0.0'
}

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="AppTheme.Base"/>

    <style name="AppTheme.Base" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->

        <!-- colorPrimary is used for the default action bar background -->
        <item name="colorPrimary">@color/colorPrimary</item>

        <!-- colorPrimaryDark is used for the status bar -->
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>

        <!-- colorAccent is used as the default value for colorControlActivated
             which is used to tint widgets -->
        <item name="colorAccent">@color/colorAccent</item>

        <!-- You can also set colorControlNormal, colorControlActivated
             colorControlHighlight & colorSwitchThumbNormal. -->
    </style>

</resources>

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <style name="AppTheme" parent="AppTheme.Base">
        <!-- Customize your theme using Material Design here. -->
    </style>
</resources>

In this post I would like to give you some introduction how to integrate Bower and Gulp into your Java project. On the beginning I just would like to explain briefly you what Bower and Gulp are.

Bower - package management system for client-side programming on the World Wide Web. It depends on Node.js and npm. It works with git and GitHub repositories. [Wikipedia]

Gulp - fast and intuitive streaming build tool built on Node.js.


First of all we are going to use very useful plugin called frontend-maven-plugin provided under groupId com.github.eirslett [3]. This plugin will allows us to download/install Node and NPM locally for your project, run NPM install, and then any combination of Bower, Grunt, Gulp, Jspm, Karma, or Webpack.

<plugin>
                <groupId>com.github.eirslett</groupId>
                <artifactId>frontend-maven-plugin</artifactId>
                <version>0.0.26</version>

                <executions>
                    <execution>
                        <id>install node and npm</id>
                        <goals>
                            <goal>install-node-and-npm</goal>
                        </goals>
                        <phase>generate-resources</phase>
                        <configuration>
                            <nodeVersion>v0.12.9</nodeVersion>
                            <npmVersion>2.14.14</npmVersion>
                        </configuration>
                    </execution>

                    <execution>
                        <id>npm install</id>
                        <goals>
                            <goal>npm</goal>
                        </goals>
                        <!-- Uses package.json -->
                        <configuration>
                            <arguments>install</arguments>
                        </configuration>
                    </execution>

                    <execution>
                        <id>bower install</id>
                        <goals>
                            <goal>bower</goal>
                        </goals>
                        <!-- Uses bower.json -->
                        <configuration>
                            <arguments>install</arguments>
                        </configuration>
                    </execution>

                    <execution>
                        <id>gulp build</id>
                        <goals>
                            <goal>gulp</goal>
                        </goals>
                        <!-- Uses gulpfile.js -->
                        <configuration>
                            <arguments>default --env ${gulp.task}</arguments>
                        </configuration>
                    </execution>

                </executions>
            </plugin>

{
  "name": "simple-web",
  "repository": "git@bitbucket.org:test/test.git",
  "version": "1.0.0",
  "private": true,
  "description": "Simple Web",
  "main": "index.js",
  "author": "GarciaPL",
  "dependencies": {
    "bower": "1.7.0",
    "gulp": "3.9.0",
    "gulp-concat": "2.6.0",
    "gulp-uglify": "1.5.1",
    "gulp-sourcemaps": "1.6.0",
    "gulp-less": "3.0.5",
    "gulp-minify-css": "1.2.2",
    "gulp-environments": "0.1.1"
  }
}

{
  "name": "Simple Web",
  "version": "1.0.0",
  "private": true,
  "ignore": [
    "**/.*",
    "node_modules",
    "bower_components",
    "test",
    "tests"
  ],
  "dependencies": {
    "jquery": "1.11.3",
    "underscore": "1.8.3",
    "autoNumeric": "1.9.25"
  }
}

var gulp = require('gulp');
var concat = require('gulp-concat');
var uglify = require('gulp-uglify');
var sourcemaps = require('gulp-sourcemaps');
var less = require('gulp-less');
var minifyCSS = require('gulp-minify-css');
var environments = require('gulp-environments');
var development = environments.development;
var production = environments.production;

gulp.task('default', function () {
    console.log('Preparing vendor.js for ' + (production() ? "production" : "development"));
    gulp.start('vendorJS');
    console.log('Preparing less for ' + (production() ? "production" : "development"));
    gulp.start('less');
});

gulp.task('vendorJS', function () {
    gulp.src(['bower_components/jquery/dist/jquery.min.js',
            'bower_components/underscore/underscore-min.js',
            'bower_components/autoNumeric/autoNumeric.js'])
        .pipe(development(sourcemaps.init()))
        .pipe(concat('vendor.js'))
        .pipe(production(uglify()))
        .pipe(development(sourcemaps.write('./')))
        .pipe(gulp.dest('./src/main/webapp/static/js/vendor'));
});

gulp.task('less', function () {
    return gulp.src('src/main/webapp/static/less/base.less')
        .pipe(less())
        .pipe(production(minifyCSS()))
        .pipe(gulp.dest('./src/main/webapp/static/css'));
});