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unit test June 7, 2016 3 min read by mkyong 9 comments

JUnit – How to test a List

First, exclude the JUnit bundled copy of hamcrest-core, and include the useful hamcrest-library, it contains many useful methods to test the List data type. pom.xml <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> <exclusions> <exclusion> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-core</artifactId> </exclusion> </exclusions> </dependency> <!– This will get hamcrest-core automatically –> <dependency> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-library</artifactId> <version>1.3</version> <scope>test</scope> </dependency> </dependencies> 1. Assert List […]

unit test June 6, 2016 1 min read by mkyong 1 comment

Hamcrest – How to assertThat check null value?

Try to check null value with the Hamcrest assertThat assertion, but no idea how? @Test public void testApp() { //ambiguous method call? assertThat(null, is(null)); } 1. Solution 1.1 To check null value, try is(nullValue), remember static import org.hamcrest.CoreMatchers.* //hello static import, nullValue here import static org.hamcrest.CoreMatchers.*; import org.junit.Test; //… @Test public void testApp() { //true, […]

unit test May 31, 2016 1 min read by mkyong 2 comments

Maven and JUnit example

In Maven, you can declare the JUnit dependency like this: pom.xml <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> </dependencies> But, it comes with a bundled copy of hamcrest-core library. $ mvn dependency:tree … [INFO] \- junit:junit:jar:4.12:test [INFO] \- org.hamcrest:hamcrest-core:jar:1.3:test … 1. Maven + JUnit + Hamcrest Note Not a good idea to use the default […]

swing May 29, 2016 8 min read by Marilena 11 comments

Java Swing – JOptionPane showInputDialog example

This is a review of the showInputDialog() method of JOptionPane Class. With this method we can prompt the user for input while customizing our dialog window. The showConfirmDialog returns either String or Object and can be called using the following combinations of parameters: Object (returns String) – Shows a question-message dialog requesting input from the […]

unit test May 29, 2016 1 min read by mkyong 1 comment

Gradle and JUnit example

In Gradle, you can declare the JUnit dependency like this: build.gradle apply plugin: ‘java’ dependencies { testCompile ‘junit:junit:4.12’ } By default, JUnit comes with a bundled copy of hamcrest-core $ gradle dependencies –configuration testCompile testCompile – Compile classpath for source set ‘test’. \— junit:junit:4.12 \— org.hamcrest:hamcrest-core:1.3 1. Gradle + JUnit + Hamcrest Normally, we need […]

logging May 7, 2016 3 min read by mkyong 4 comments

Logback – Set log file name programmatically

In Logback, it is easy to set a log file name programmatically : In logback.xml, declares a variable like ${log.name} In Java, set the variable via System.setProperty(“log.name”, “abc”) 1. Full example 1.1 A logback file, we will set the ${log.name} variable later. src/main/resources/logback.xml <?xml version="1.0" encoding="UTF-8"?> <configuration> <property name="PRO_HOME" value="/home/mkyong/ant/logs" /> <property name="USER_HOME" value="${PRO_HOME}" /> […]

mongodb May 3, 2016 2 min read by mkyong 6 comments

MongoDB – group, count and sort example

Some MongoDB examples to show you how to perform group by, count and sort query. 1. Test Data A whois_range collection, containing many records. > db.whois_range.find(); { "_id" : 1, "country" : "us", "source" : "ARIN", "status" : "NEW", "createdDate" : ISODate("2016-05-03T08:52:32.434Z") }, { "_id" : 2, "country" : "us", "source" : "ARIN", "status" : […]

java April 28, 2016 2 min read by mkyong 3 comments

Java – find class fields with specified data type

Some Java reflection API examples. 1. Display all fields and data type A Java reflection example to loop over all the fields declared by a class. 1.1 A POJO. CompanyA.java package com.mkyong.test; import java.util.List; import java.util.Map; import java.util.Set; public class CompanyA { String orgName; int count; List<String> comments; Set<String> branches; Map<String, String> extra; //… } […]

java8 April 14, 2016 9 min read by mkyong 10 comments

Java 8 flatMap example

This article explains the Java 8 Stream.flatMap and how to use it. Topic What is flatMap? Why flat a Stream? flatMap example – Find a set of books. flatMap example – Order and LineItems. flatMap example – Splits the line by spaces. flatMap and Primitive type 1. What is flatMap()? 1.1 Review the below structure. […]

java8 April 13, 2016 3 min read by mkyong 5 comments

Java – How to convert Array to Stream

In Java 8, you can either use Arrays.stream or Stream.of to convert an Array into a Stream. 1. Object Arrays For object arrays, both Arrays.stream and Stream.of returns the same output. TestJava8.java package com.mkyong.java8; import java.util.Arrays; import java.util.stream.Stream; public class TestJava8 { public static void main(String[] args) { String[] array = {"a", "b", "c", "d", […]

java8 April 12, 2016 2 min read by mkyong 9 comments

Java – Stream has already been operated upon or closed

In Java 8, Stream cannot be reused, once it is consumed or used, the stream will be closed. 1. Example – Stream is closed! Review the following example, it will throw an IllegalStateException, saying “stream is closed”. TestJava8.java package com.mkyong.java8; import java.util.Arrays; import java.util.stream.Stream; public class TestJava8 { public static void main(String[] args) { String[] […]

computer tips April 8, 2016 2 min read by mkyong 35 comments

Windows 10 – Can not create new folder

Suddenly, my Windows 10 is unable to create new folder: In desktop or C drive, right click, then “new” -> “folder” option is disappeared!? On C drive, the top “New folder” and “New Item” icons are malfunctioning, click on it, nothing will happen? In the command prompt, the mkdir command is working fine. 1. NewFolderFix.reg […]

java8 April 7, 2016 4 min read by mkyong 36 comments

Java 8 – Stream Collectors groupingBy examples

In this article, we will show you how to use Java 8 Stream Collectors to group by, count, sum and sort a List. 1. Group By, Count and Sort 1.1 Group by a List and display the total count of it. Java8Example1.java package com.mkyong.java8; import java.util.Arrays; import java.util.List; import java.util.Map; import java.util.function.Function; import java.util.stream.Collectors; public […]

computer tips April 6, 2016 1 min read by mkyong 2 comments

Windows 10 – Edit Hosts file

In this tutorial, we will show you how to add a mapping of IP addresses to host names in the Windows Hosts file. Windows Hosts file C:\Windows\System32\drivers\etc\hosts 1. Notepad – Run as Administrator In desktop, left-bottom search box, type notepad, right click on the notepad icon and select run as administrator. 2. Edit hosts 2.1 […]

java March 24, 2016 3 min read by mkyong 15 comments

Java – How to override equals and hashCode

Some Java examples to show you how to override equals and hashCode. 1. POJO To compare two Java objects, we need to override both equals and hashCode (Good practice). User.java public class User { private String name; private int age; private String passport; //getters and setters, constructor } User user1 = new User("mkyong", 35, "111222333"); […]

java8 March 19, 2016 3 min read by mkyong 20 comments

Java 8 – Convert List to Map

Few Java 8 examples to show you how to convert a List of objects into a Map, and how to handle the duplicated keys. Hosting.java package com.mkyong.java8 public class Hosting { private int Id; private String name; private long websites; public Hosting(int id, String name, long websites) { Id = id; this.name = name; this.websites […]

design pattern March 18, 2016 5 min read by mkyong 2 comments

Java Builder pattern examples

The Builder Pattern in Java is a creational design pattern that helps in constructing complex objects step by step. Here are three examples of the Builder pattern in Java: 1. Building a User Profile This example models a User with optional fields using the Builder Pattern. User.java package com.mkyong.builder; class User { private final String […]

java March 10, 2016 2 min read by mkyong 0 comments

Java – Compare Enum value

In Java, you can use == operator to compare Enum value. 1. Java Enum example Language.java package com.mkyong.java public enum Language { JAVA, PYTHON, NODE, NET, RUBY } 2. Compare with == Example to compare enum value with == operator. Test.java package com.mkyong.java public class Test { public static void main(String[] args) { // Covert […]

swing February 29, 2016 6 min read by Marilena 16 comments

Java Swing – JFileChooser example

JFileChooser is a quick and easy way to prompt the user to choose a file or a file saving location. Below are some simple examples of how to use this class. JFileChooser has 6 constructors: JFileChooser() – empty constructor that points to user’s default directory JFileChooser(String) – uses the given path JFileChooser(File) – uses the […]

java February 24, 2016 2 min read by Datsabk 17 comments

How to read and write Java object to a file

Java object Serialization is an API provided by Java Library stack as a means to serialize Java objects. Serialization is a process to convert objects into a writable byte stream. Once converted into a byte-stream, these objects can be written to a file. The reverse process of this is called de-serialization. A Java object is […]

java8 February 23, 2016 3 min read by mkyong 2 comments

Java 8 Map filter examples

This article shows a few examples of filtering a Map by its keys or values using the Java 8 stream APIs. Table of contents: 1. Java Map filter (Classic) 2. Java Map filter (Java 8) 3. Java Map filter (Java 8 Predicate) 4. References 1. Java Map filter (Classic) Before Java 8, we looped the […]

logging February 12, 2016 1 min read by mkyong 9 comments

Logback – Disable logging in Unit Test

While the unit test is running in the IDE, the Logback is showing a lot of configuration or status like this : 21:16:59,569 |-INFO in ch.qos.logback.classic.LoggerContext[default] – Could NOT find resource [logback.groovy] 21:16:59,569 |-INFO in ch.qos.logback.classic.LoggerContext[default] – Could NOT find resource [logback-test.xml] 21:16:59,569 |-INFO in ch.qos.logback.classic.LoggerContext[default] – Found resource [logback.xml] at … //… omitted for […]

java8 February 11, 2016 5 min read by mkyong 31 comments

Java 8 Streams filter examples

In this tutorial, we will show you few Java 8 examples to demonstrate the use of Streams filter(), collect(), findAny() and orElse() 1. Streams filter() and collect() 1.1 Before Java 8, filter a List like this : BeforeJava8.java package com.mkyong.java8; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class BeforeJava8 { public static void main(String[] args) […]

python February 10, 2016 1 min read by mkyong 0 comments

Python – How to join two list

In Python, you can simply join two list with a plus + symbol like this: list1 = [1,2,3] list2 = [4,5,6] list3 = list1 + list2 print list3 #[1, 2, 3, 4, 5, 6] Note Try to compare with this Java example – how to join arrays. Python really makes join list extremely easy.

java8 February 9, 2016 2 min read by mkyong 4 comments

Java 8 – StringJoiner example

In this article, we will show you a few StringJoiner examples to join String. 1. StringJoiner 1.1 Join String by a delimiter StringJoiner sj = new StringJoiner(","); sj.add("aaa"); sj.add("bbb"); sj.add("ccc"); String result = sj.toString(); //aaa,bbb,ccc 1.2 Join String by a delimiter and starting with a supplied prefix and ending with a supplied suffix. StringJoiner sj […]

java February 8, 2016 3 min read by mkyong 8 comments

Java – How to join Arrays

In this article, we will show you a few ways to join a Java Array. Apache Commons Lang – ArrayUtils Java API Java 8 Stream 1. Apache Commons Lang – ArrayUtils The simplest way is add the Apache Commons Lang library, and use ArrayUtils. addAll to join arrays. This method supports both primitive and object […]

gradle February 7, 2016 7 min read by mkyong 4 comments

Gradle – How to exclude some tests

There are two ways to exclude some unit tests in Gradle. Test filtering (preferred option) Include and exclude Topics. 1. Gradle Test filtering 1.1 Test classes 1.2 Exclude tests from a package 1.3 Exclude a single test using a class name 1.4 Exclude a single method of a test class 1.5 Exclude test methods contains […]

unix / linux February 6, 2016 1 min read by mkyong 0 comments

Debian – Show apt-get package version

On Debian, you can use apt-cache policy ‘package name’ to check the package version. 1.1 Display Tomcat7 version. $ sudo apt-cache policy tomcat7 tomcat7: Installed: (none) Candidate: 7.0.52-1ubuntu0.3 Version table: 7.0.52-1ubuntu0.3 0 500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages 500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages 7.0.52-1 0 500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages 1.2 Display OpenJDK-7 version. $ sudo […]

java February 5, 2016 2 min read by mkyong 6 comments

Java – Mutable and Immutable Objects

This article shows you the difference between Mutable and Immutable objects in Java 1. Mutable object – You can change the states and fields after the object is created. For examples: StringBuilder, java.util.Date and etc. 2. Immutable object – You cannot change anything after the object is created. For examples: String, boxed primitive objects like […]

gradle February 5, 2016 2 min read by mkyong 7 comments

Gradle – How to continue build if test is failed

By default, the Gradle build process will be stopped and failed if any unit test is failed. $ gradle build :clean :compileJava :processResources :classes :compileTestJava :processTestResources UP-TO-DATE :testClasses :test com.mkyong.example.TestExample > test_example FAILED java.lang.Exception at TestExample.java:9 //… 3 tests completed, 1 failed :test FAILED //… BUILD FAILED // <————– see status In this article, we […]

gradle February 4, 2016 3 min read by mkyong 1 comment

Gradle – How to display test result in the console

By default, gradle test displays only the test summary. Terminal % gradle test BUILD SUCCESSFUL in 4s 6 actionable tasks: 3 executed, 3 up-to-date P.S Gradle test generates the detailed tests’ result at the build/reports/tests/test/index.html page. P.S Tested with Gradle 6.7.1 1. Display test result in the console. 1.1 We add the testLogging events to […]

java February 3, 2016 5 min read by mkyong 5 comments

How to print an Array in Java

In this article, we will show you a few ways to print a Java Array. Table of contents. 1. JDK 1.5 Arrays.toString 2. Java 8 Stream APIs 3. Java 8 Stream APIs – Collectors.joining 4. Jackson APIs 5. References 1. JDK 1.5 Arrays.toString We can use Arrays.toString to print a simple array and Arrays.deepToString for […]

gradle February 2, 2016 1 min read by mkyong 2 comments

Gradle – Exclude commons-logging from Spring

Gradle example to exclude commons-logging from Spring frameworks. build.gradle compile(‘org.springframework:spring-webmvc:4.2.4.RELEASE’){ exclude group: ‘commons-logging’, module: ‘commons-logging’ } If you have multiple Spring dependencies, you have to exclude for each build.gradle compile(‘org.springframework:spring-webmvc:4.2.4.RELEASE’){ exclude group: ‘commons-logging’, module: ‘commons-logging’ } compile(‘org.springframework:spring-test:4.2.4.RELEASE’){ exclude group: ‘commons-logging’, module: ‘commons-logging’ } A better solution is excluding commons-logging at the project level. build.gradle configurations.all […]

gradle February 1, 2016 1 min read by mkyong 6 comments

Jenkins – Could not find GradleWrapperMain

Create a Gradle project in Jenkins CI, source management with Git, and build with Gradle Wrapper 1. Problem Jenkins console output, the build is failed – “Could not find org.gradle.wrapper.GradleWrapperMain” [Gradle] – Launching build. [workspace] $ /var/lib/jenkins/jobs/GradleTest/workspace/gradlew clean test Error: Could not find or load main class org.gradle.wrapper.GradleWrapperMain Build step ‘Invoke Gradle script’ changed build […]

gradle January 31, 2016 2 min read by mkyong 4 comments

How to use Gradle Wrapper

In this tutorial, we will show you how to create Gradle wrapper for your project and how to use it. What is Gradle wrapper? The Gradle wrapper allows you to run a Gradle task without requiring that Gradle is installed on your system. 1. Create a Gradle Wrapper 1.1 Declares a wrapper task. build.gradle task […]

gradle January 30, 2016 1 min read by mkyong 1 comment

Gradle JaCoCo – Incompatible version 1006

A Gradle build + JaCoCo coverage report. build.gradle apply plugin: ‘java’ apply plugin: ‘eclipse-wtp’ apply plugin: ‘jacoco’ //code coverage repositories { mavenLocal() mavenCentral() } jacoco { toolVersion = "0.7.5+" } jacocoTestReport { reports { html.enabled = true xml.enabled = true csv.enabled = false } } P.S Tested with Gradle 2.10 1. Problem 1.1 Run the […]

java January 30, 2016 4 min read by Marilena 23 comments

Java RMI Hello World example

RMI stands for Remote Method Invocation and it is the object-oriented equivalent of RPC (Remote Procedure Calls). RMI was designed to make the interaction between applications using the object-oriented model and run on different machines seem like that of stand-alone programs. The code below will give you the basis to Java RMI with a very […]

Intellij January 29, 2016 1 min read by mkyong 13 comments

Intellij IDEA – Auto reload a web application (hot deploy)

In this tutorial, we will show you how to ‘hot deploy’ or ‘hot swap’ a web application in IDEA. Note Tested with Intellij IDEA 14 and 15 1. Select exploded WAR Go Run –>> Edit Configurations –>> “Deployment” tab, clicks + icon –>> select an “exploded artifact” 2. Update classes and resources Select “Server” tab, […]

maven January 28, 2016 2 min read by mkyong 5 comments

Maven – Deploy web application to WildFly

In Maven, we can use the official JBoss WildFly Maven Plugin to deploy a web application (war file) to the WildFly application server. Technologies tested : Maven 3.3.9 WildFly 9.0.2.final WildFly Maven Plugin 1.1.0.Alpha5 P.S This Spring MVC web application will be used for this deployment test. 1. Deploy WAR To WildFly 1.1 Start WildFly […]

maven January 27, 2016 1 min read by mkyong 7 comments

Maven – webxml attribute is required

Maven package a web application and hits the following error message : $ mvn package //… [ERROR] Failed to execute goal org.apache.maven.plugins:maven-war-plugin:2.2:war (default-war) on project spring4-mvc-maven-ajax-example: Error assembling WAR: webxml attribute is required (or pre-existing WEB-INF/web.xml if executing in update mode) -> [Help 1] Solution 1. For servlet container < 3, make sure WEB-INF/web.xml file […]