Joni Karppinen jonikarppinen

Software developer & entrepreneur. Backend & Android mostly. Java, Scala & Kotlin.

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jonikarppinen / Question20442265.java

Last active December 30, 2015 17:39

Answer for this question about Gson: http://stackoverflow.com/questions/20442265/how-to-decode-json-with-unknown-field-using-gson. This demonstrates how to use custom deserialiser to parse a big list of properties of the same type but unknown/random/varying names. Besides JDK, depends on Guava library.

	import com.google.common.base.Charsets;
	import com.google.common.io.Files;
	import com.google.gson.*;

	import java.io.File;
	import java.io.IOException;
	import java.lang.reflect.Type;
	import java.util.ArrayList;
	import java.util.List;
	import java.util.Map;

jonikarppinen / markdown-comments.md

Last active June 25, 2025 10:31

How to comment out stuff in Markdown on GitHub?

Comments in GitHub flavour of Markdown

As answers to this Stack Overflow question reveal, using  or  works (view source by clicking "Raw"):

jonikarppinen / proguard-project.txt

Last active August 1, 2017 09:56

Example ProGuard config for a project using RxJava, Guava and Gson

	# Add project specific ProGuard rules here.
	# By default, the flags in this file are appended to flags specified
	# in ${sdk.dir}/tools/proguard/proguard-android.txt
	# You can edit the include path and order by changing the ProGuard
	# include property in project.properties.
	#
	# For more details, see
	# http://developer.android.com/guide/developing/tools/proguard.html

jonikarppinen / CustomErrorController.java

Last active June 16, 2021 02:19

Example of replacing Spring Boot "whitelabel" error page with custom error responses (with JSON response body)

	package com.company.project.controllers;

	import com.company.project.model.api.ErrorJson;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.beans.factory.annotation.Value;
	import org.springframework.boot.autoconfigure.web.ErrorAttributes;
	import org.springframework.boot.autoconfigure.web.ErrorController;
	import org.springframework.web.bind.annotation.RequestMapping;
	import org.springframework.web.bind.annotation.RestController;
	import org.springframework.web.context.request.RequestAttributes;

jonikarppinen / CustomObjectMapper.java

Last active June 28, 2018 21:28

Example of making Jackson behave more sensibly by default (also, more like Gson)

	import com.fasterxml.jackson.annotation.JsonInclude;
	import com.fasterxml.jackson.databind.DeserializationFeature;
	import com.fasterxml.jackson.databind.ObjectMapper;
	import com.fasterxml.jackson.databind.SerializationFeature;

	/**
	* ObjectMapper customised for my tastes and most typical needs
	*
	* @author Joni Karppinen
	*/

jonikarppinen / StringUtils.java

Last active July 2, 2024 05:30

StringUtils – common utility methods for Java

	import com.google.common.base.Charsets;
	import com.google.common.base.Joiner;
	import com.google.common.base.Splitter;
	import com.google.common.base.Strings;
	import com.google.common.collect.Lists;
	import com.google.common.collect.Maps;

	import java.io.UnsupportedEncodingException;
	import java.net.URLDecoder;
	import java.net.URLEncoder;

jonikarppinen / PdfOrErrorController.java

Last active November 17, 2021 11:49

Example of using ExceptionHandler in Spring Boot: a controller method that returns either binary data or error JSON

	package com.company.project.controllers;

	import org.springframework.http.HttpHeaders;
	import org.springframework.http.HttpStatus;
	import org.springframework.http.MediaType;
	import org.springframework.http.ResponseEntity;
	import org.springframework.web.bind.annotation.*;

	import java.util.Random;

jonikarppinen / Messages.java

Last active February 23, 2021 23:36

Example of using message resources in Spring Boot service layer code, in as simple way as possible (hopefully!). NOTE: this approach supports only a single locale, not dynamically changing it.

	package com.company.project.components;

	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.context.MessageSource;
	import org.springframework.context.support.MessageSourceAccessor;
	import org.springframework.stereotype.Component;

	import javax.annotation.PostConstruct;
	import java.util.Locale;

jonikarppinen / Specs2-output.txt

Last active December 8, 2015 20:34

Specs2 output when run in IntelliJ IDEA: "Test framework quit unexpectedly" (see http://stackoverflow.com/questions/34159857/specs2-how-to-test-a-class-with-more-than-one-injected-dependency)

	Testing started at 22:28 ...
	services.ReportServiceSpec$

	java.lang.ClassNotFoundException: services.ReportServiceSpec$


	STACKTRACE
	java.net.URLClassLoader.findClass(URLClassLoader.java:381)
	java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)

jonikarppinen / 1_RxJava-connectivity-status-example.md

Last active November 23, 2022 18:16

Example of listening to connectivity status in Android and reacting to going offline. (Subscription, Observable, Observer, PublishSubject are from RxJava.)

Example of using RxJava to listen to connectivity status in Android

You could use the same approach to listen to any status, but this example includes network connectivity specifics too (ConnectionChangeReceiver and AndroidUtils.isConnected).

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