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Logback – Set log file name programmatically

May 7, 2016 by mkyong

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 – group, count and sort example

May 3, 2016 by mkyong

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 – find class fields with specified data type

April 28, 2016 by mkyong

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; //… } …

Java 8 flatMap example

December 16, 2020April 14, 2016 by mkyong

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. …

Java – How to convert Array to Stream

April 13, 2016 by mkyong

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", …

Java – Stream has already been operated upon or closed

April 12, 2016 by mkyong

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[] …

Windows 10 – Can not create new folder

April 8, 2016 by mkyong

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 …

Java 8 – Stream Collectors groupingBy examples

August 10, 2016April 7, 2016 by mkyong

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 …

Windows 10 – Edit Hosts file

April 6, 2016 by mkyong

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 – How to override equals and hashCode

March 24, 2016 by mkyong

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"); …

Java 8 – Convert List to Map

May 26, 2017March 19, 2016 by mkyong

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 …

Java Builder pattern examples

February 28, 2025March 18, 2016 by mkyong

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 – Compare Enum value

March 24, 2016March 10, 2016 by mkyong

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 …

Java Swing – JFileChooser example

November 29, 2016February 29, 2016 by Marilena

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 …

How to read and write Java object to a file

November 24, 2016February 24, 2016 by Datsabk

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 …

Java 8 Map filter examples

March 13, 2024February 23, 2016 by mkyong

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 …

Logback – Disable logging in Unit Test

February 8, 2017February 12, 2016 by mkyong

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 …

Java 8 Streams filter examples

April 3, 2017February 11, 2016 by mkyong

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 – How to join two list

February 10, 2016 by mkyong

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.

Java 8 – StringJoiner example

February 9, 2016 by mkyong

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 – How to join Arrays

February 8, 2016 by mkyong

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 – How to exclude some tests

February 21, 2021February 7, 2016 by mkyong

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 …

Debian – Show apt-get package version

February 6, 2016 by mkyong

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 – Mutable and Immutable Objects

December 5, 2016February 5, 2016 by mkyong

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 – How to continue build if test is failed

February 5, 2016 by mkyong

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 – How to display test result in the console

February 4, 2021February 4, 2016 by mkyong

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 …

How to print an Array in Java

October 18, 2021February 3, 2016 by mkyong

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 – Exclude commons-logging from Spring

February 2, 2016 by mkyong

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 …

Jenkins – Could not find GradleWrapperMain

February 1, 2016 by mkyong

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 …

How to use Gradle Wrapper

January 31, 2016 by mkyong

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 JaCoCo – Incompatible version 1006

January 30, 2016 by mkyong

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 RMI Hello World example

November 30, 2016January 30, 2016 by Marilena

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 IDEA – Auto reload a web application (hot deploy)

January 14, 2017January 29, 2016 by mkyong

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 – Deploy web application to WildFly

January 28, 2016 by mkyong

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 – webxml attribute is required

January 27, 2016 by mkyong

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 ...

Spring MVC + Mustache JS template example

April 19, 2017January 26, 2016 by mkyong

In this tutorial, we will show you a Spring MVC + Mustache JS template web application example. Technologies used : Spring 4.2.4.RELEASE mustache.js JDK 1.8.0_66 Jackson 2.7 Eclipse 4.3 Tomcat 8 Maven 3 Bootstrap 3 Note This solution is still working, but recommend this simple Spring Boot + JMustache solution. In Spring, we can use …

Jetty – java.net.BindException: Address already in use

January 24, 2016January 24, 2016 by mkyong

Start a Java webapp with Maven Jetty plugin. $ mvn jetty:run 1. Problem But it hits the following error messages : [WARNING] FAILED org.eclipse.jetty.maven.plugin.JettyServer@1f53481b: java.net.BindException: Address already in use at sun.nio.ch.Net.bind0(Native Method) at sun.nio.ch.Net.bind(Net.java:433) at sun.nio.ch.Net.bind(Net.java:425) at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:223) at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:74) at org.eclipse.jetty.server.ServerConnector.open(ServerConnector.java:321) at org.eclipse.jetty.server.AbstractNetworkConnector.doStart(AbstractNetworkConnector.java:80) //… 2. Solution By default, the maven-jetty-plugin start Jetty on port …

Linux – Which application is using port 8080

January 24, 2016 by mkyong

Always, Java developers need to know which application is using the high demand 8080 port. In this tutorial, we will show you two ways to find out which application is using port 8080 on Linux. 1. lsof + ps command 1.1 Bring up the terminal, type lsof -i :8080 $ lsof -i :8080 COMMAND PID …

jQuery – Ajax request return 200 OK but error event is fired?

January 23, 2016 by mkyong

Review a jQuery Ajax form submit. $(document).ready(function () { $("#hostingForm").submit(function (e) { e.preventDefault(e); var data = {} data["id"] = $("#id").val(); data["domain"] = $("#domain").val(); data["name"] = $("#name").val(); //… $.ajax({ type: "POST", contentType: "application/json", url: "{{home}}/hosting/update", data: JSON.stringify(data), dataType: ‘json’, timeout: 600000, success: function (data) { console.log("SUCCESS: ", data); }, error: function (e) { console.log("ERROR: ", e); …

How to view HTTP headers in Google Chrome?

January 22, 2016 by mkyong

To view the request or response HTTP headers in Google Chrome, take the following steps : In Chrome, visit a URL, right click, select Inspect to open the developer tools. Select Network tab. Reload the page, select any HTTP request on the left panel, and the HTTP headers will be displayed on the right panel.