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eclipse January 25, 2017 by mkyong 1 comment

Eclipse – How to know this class belongs to which JAR

For example, I want to know this SpringBootApplication class belongs to which JAR or dependency : import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class SpringBootWebApplication { public static void main(String[] args) throws Exception { SpringApplication.run(SpringBootWebApplication.class, args); } } Solution In Eclipse IDE, double clicks on the class name, press CTRL + SHIFT + T (win/*nix) or […]

Intellij January 24, 2017 by mkyong 0 comments

IntelliJ IDEA – How to know this class belongs to which JAR

For example, how to find out this FileUploadBase class belongs to which JAR or dependency? //… import org.apache.tomcat.util.http.fileupload.FileUploadBase; @ExceptionHandler(FileUploadBase.FileSizeLimitExceededException.class) public String handleError3(Exception e, RedirectAttributes redirectAttributes) { redirectAttributes.addFlashAttribute("message", e.getCause().getMessage()); return "redirect:/uploadStatus"; } Solution In IntelliJ IDEA, double clicks on the class name and press CTRL + n (win/*nix) or CMD + n (mac) to prompt out […]

spring boot January 23, 2017 by mkyong 32 comments

Spring Boot file upload example

This article shows you how to upload a file in Spring Boot web application. Tools used : Spring Boot 1.4.3.RELEASE Spring 4.3.5.RELEASE Thymeleaf Maven Embedded Tomcat 8.5.6 1. Project Structure A standard project structure. 2. Project Dependency Spring boot dependencies, no need extra library for file upload. pom.xml <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.mkyong</groupId> […]

Intellij January 22, 2017 by mkyong 8 comments

Eclipse Ctrl + Shift + O in IntelliJ IDEA

In Eclipse, you press CTRL + SHIFT + O “Organize Imports” to import packages automatically. For IntelliJ IDEA, if you press CTRL + ALT + O “Optimize Imports”, it just removes some unused imports, never imports any package. And the worst is you need click on the class name and press ALT + ENTER keys […]

java January 20, 2017 by Marilena 1 comment

Java RMI – Distributed objects example

Image Source: Wikimedia.org In Java RMI Hello World example we introduced the Java Remote Method Invocation with a very basic String-based communication between Server-Client. In this example we will take it one small step further and introduce Server-Client communication using Distributed Objects. 1. The Remote Interface First we will develop the Remote Interface which contains […]

swing January 19, 2017 by Marilena 0 comments

Java Swing – Keep dialog window up

The most common (and simple) way to implement a dialog in our application is the JOptionPane class. In this article we will discuss how to “overwrite” the default behaviour of JOptionPane that closes the dialog window when the user clicks a JOptionPane-created button. What we need to know before we move on to the examples […]

swing January 18, 2017 by Marilena 1 comment

Java Swing – Draw shapes dynamically example

In this article we create an application that randomly puts shapes on a JPanel. The user can choose between the different shapes our application supports as well as the amount that will be drawn. As a design decision our application can make circles and stars. You can download the example at the end of the […]

java January 17, 2017 by Marilena 9 comments

jsoup – Basic web crawler example

A Web Crawler is a program that navigates the Web and finds new or updated pages for indexing. The Crawler starts with seed websites or a wide range of popular URLs (also known as the frontier) and searches in depth and width for hyperlinks to extract. A Web Crawler must be kind and robust. Kindness […]

javafx January 16, 2017 by Marilena 8 comments

JavaFX Animated Ball Example

The Bouncing Ball is the “Hello World” of animations in JavaFx. It’s simple to write, easy to understand and reveals the potential of JavaFx even from this primitive stage. We will start by creating a moving ball that will set the basis for the bouncing ball that will follow. 1. Moving Ball Example Apart from […]

Intellij January 15, 2017 by mkyong 32 comments

IntelliJ IDEA – Run / debug web application on Tomcat

This article shows you how to run or debug a web application on Tomcat server, using IntelliJ IDEA. Note Unlike Eclipse IDE, there is always a ‘server view’ to configure the add server, IntelliJ do things differently, you need to add an “artifact (war file)” first, then only the “server view” will be displayed at […]

spring January 14, 2017 by mkyong 6 comments

Spring MVC – How to handle max upload size exceeded exception

In Spring, you can declare a @ControllerAdvice to catch the ugly max upload size exceeded exception like this : Solution Depends the types of multipartResolver : StandardServletMultipartResolver – catch MultipartException, refer to this example. CommonsMultipartResolver – catch MaxUploadSizeExceededException – refer to this example. GlobalExceptionHandler.java package com.mkyong.exception; import org.springframework.web.bind.annotation.ControllerAdvice; import org.springframework.web.bind.annotation.ExceptionHandler; import org.springframework.web.multipart.MaxUploadSizeExceededException; import org.springframework.web.multipart.MultipartException; import […]

spring January 13, 2017 by mkyong 2 comments

Spring MVC file upload example – Commons FileUpload

This article will shows you how to use CommonsMultipartResolver to handle file upload in Spring MVC web application. Tools used : Spring 4.3.5.RELEASE commons-fileupload 1.3.2 Maven 3 Tomcat 7 or 8 and Jetty 8, 9 Note For StandardServletMultipartResolver – file upload using Servlet 3.0 multipart request parsing, please refer to this Spring MVC file upload […]

spring January 13, 2017 by mkyong 8 comments

Spring file upload and connection reset issue

A Spring servlet initializer to configure the file upload limit, 5mb per file and 10mb per request. MyWebInitializer.java public class MyWebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer { private int maxUploadSizeInMb = 5 * 1024 * 1024; // 5 MB //… @Override protected void customizeRegistration(ServletRegistration.Dynamic registration) { // upload temp file will put here File uploadDirectory = new File(System.getProperty("java.io.tmpdir")); […]

Intellij January 11, 2017 by mkyong 2 comments

Eclipse Ctrl + T in IntelliJ IDEA

CTRL + H is IDEA equivalent of Eclipse show class hierarchy. Clicks on a class and press CTRL + H, it will display the subtypes hierarchy of the class. 1. Windows or & *nix = CTRL + H 2. Mac OSX Control + H References Show class hierarchy in Eclipse IDE

spring boot January 10, 2017 by mkyong 33 comments

Spring Boot – Deploy WAR file to Tomcat

In this article, we will show you how to create a Spring Boot traditional WAR file and deploy to a Tomcat servlet container. In Spring Boot, to create a WAR for deployment, we need 3 steps: Extends SpringBootServletInitializer Marked the embedded servlet container as provided. Update packaging to war Tested with Spring Boot 2.1.2.RELEASE Tomcat […]

java January 9, 2017 by Marilena 12 comments

Java – Digital Signatures example

In Asymmetric Cryptography example we discussed the use of Public Key Pair in Cryptography. Another important use of the Public Key Infrastructure is in Digital Signatures. Digital Signatures are the digital equivalent of handwritten signatures with one important difference; they are not unique but come as a product of the message. A valid digital signature […]

java January 8, 2017 by Marilena 5 comments

How to copy an Array in Java

The methods described below are only applicable to one dimensional arrays. Before we talk about the different ways to copy an array in Java we will show you how NOT to copy an Array. How NOT to copy an Array in Java Arrays in Java are Objects. If you try to treat them as variables… […]

swing January 7, 2017 by Marilena 5 comments

Java Swing – JOptionPane showOptionDialog example

The showOptionDialog method of JOptionPane is the Grand Unification of showConfirmDialog, showInputDialog and showMessageDialog. The showOptionDialog returns an integer which represents the position of the user’s choice in the Object[]. Note If you want to read more about the different showXxxDialog methods, refer to Java Swing – JOptionPane showConfirmDialog example Java Swing – JOptionPane showInputDialog […]

java8 January 6, 2017 by Marilena 0 comments

Java 8 – Math Exact examples

Java 8 introduced new methods in the Math class that will throw an ArithmeticException to handle overflows. These methods consist of addExact, substractExact, multiplyExact, incrementExact, decrementExact and negateExact with int and long arguments. In addition, there’s a static toIntExact method to convert a long value to an int that also throws ArithmeticException. Before Java 8 […]

spring boot January 5, 2017 by mkyong 4 comments

Spring Boot @ConfigurationProperties example

Spring Boot @ConfigurationProperties lets developers map or bind the entire external configuration values in .properties or .yml files to Java objects. Table of contents: 1. Access a single value using @Value 2. @ConfigurationProperties 3. Add JSR303 Validation 3.1 Add JSR 303 dependencies 3.2 @ConfigurationProperties and @Validated 4. Testing @ConfigurationProperties 5. Download Source Code 6. References […]

spring boot January 4, 2017 by mkyong 0 comments

Spring Boot Logging Example

This article will demonstrate Spring Boot Logging using the Logback SLF4J implementation. Technologies used: Spring Boot 3.2.2 Java 17 Maven 3 Table of contents: 1. Project Directory 2. Spring Boot Logging Dependencies 3. Spring Boot Logging using Logback 3.1. Log Example 3.2 Log variables 4. Log to File 4.1 File Rotation 5. Log Levels 6. […]

mac January 4, 2017 by mkyong 5 comments

wget on Mac OS X

By default, there is no wget on Mac OS X. $ wget http://www-us.apache.org/dist/tomcat/tomcat-8/v8.5.9/bin/apache-tomcat-8.5.9.tar.gz -bash: wget: command not found On Mac OS X, the equivalent of Linux’s wget is curl -O $ curl -O http://www-us.apache.org/dist/tomcat/tomcat-8/v8.5.9/bin/apache-tomcat-8.5.9.tar.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 49 9112k 49 […]

java December 29, 2016 by Datsabk 35 comments

Apache POI – Reading and Writing Excel file in Java

In this article, we will discuss about how to read and write an excel file using Apache POI 1. Basic definitions for Apache POI library This section briefly describe about basic classes used during Excel Read and Write. HSSF is prefixed before the class name to indicate operations related to a Microsoft Excel 2003 file. […]

java December 28, 2016 by Datsabk 13 comments

iText – Read and Write PDF in Java

This article talks about reading and writing PDF using iText PDF library. pom.xml <dependency> <groupId>com.itextpdf</groupId> <artifactId>itextpdf</artifactId> <version>5.5.10</version> </dependency> P.S Tested with iTextPdf 5.5.10 1. iText – Write PDF iText PdfWriter example to write content to a PDF file. PdfWriteExample.java package com.mkyong; import com.itextpdf.text.*; import com.itextpdf.text.pdf.PdfWriter; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; public class […]

spring boot December 26, 2016 by mkyong 26 comments

Intellij IDEA – Spring boot reload static file is not working

In Eclipse, just include the Spring Boot Dev Tools dependency, then the hot swapping and static file reload will be enabled magically. For Intellij IDE, we need extra steps to enable it. 1. Spring Boot Dev Tools With Spring Boot Dev Tools enabled : Any changes to views or resources can be seen in the […]

spring boot December 23, 2016 by mkyong 8 comments

Spring Boot – Which main class to start

If Spring Boot project contains multiple main classes, Spring Boot will fail to start or packag for deployment. Terminal $ mvn package #or $ mvn spring-boot:run Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:1.4.2.RELEASE:run (default-cli) Execution default-cli of goal org.springframework.boot:spring-boot-maven-plugin:1.4.2.RELEASE:run failed: Unable to find a single main class from the following candidates [com.mkyong.Test, com.mkyong.SpringBootWebApplication] -> [Help 1] Maven […]

java December 15, 2016 by Datsabk 15 comments

JExcel API – Reading and Writing Excel file in Java

In this article, we will discuss about how to read and write an excel file using JExcel API, a simple library and widely used for simple operations which do not involve a high level of formatting and complex formulas based operations. P.S Tested with JExcel API – 2.6.12 1. Download JExcel Maven user. pom.xml <dependency> […]

spring boot December 6, 2016 by mkyong 5 comments

Spring Boot – Jetty as embedded server

By default, Spring Boot use Tomcat as the default embedded server, to change it to Jetty, just exclude Tomcat and include Jetty like this : 1. spring-boot-starter-web pom.xml <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <exclusions> <exclusion> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-tomcat</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jetty</artifactId> </dependency> 2. spring-boot-starter-thymeleaf pom.xml <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-thymeleaf</artifactId> <exclusions> <exclusion> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-tomcat</artifactId> </exclusion> </exclusions> </dependency> […]

spring boot December 5, 2016 by mkyong 3 comments

How to change the default port in Spring Boot

Default, Spring Boot web application starts embedded web server (Tomcat, Jetty, etc.) in port 8080. And we can configure or change the port using the server.port property. Table of contents 1. application.properties 2. application.yml 3. Command Line 4. Environment Variable 5. WebServerFactoryCustomizer 6. Download Source Code 7. References P.S Tested with Spring Boot 1, 2, […]

java December 4, 2016 by Datsabk 8 comments

Java Thread – Mutex and Semaphore example

Java multi threads example to show you how to use Semaphore and Mutex to limit the number of threads to access resources. Semaphores – Restrict the number of threads that can access a resource. Example, limit max 10 connections to access a file simultaneously. Mutex – Only one thread to access a resource at once. […]

spring boot December 4, 2016 by mkyong 6 comments

Spring Boot – How to change Context Path

In Spring Boot, to change the context path, update server.contextPath properties. The following examples update the context path from / to /mkyong or http://localhost:8080/mkyong Note By default, the context path is “/”. P.S Tested with Spring Boot 1.4.2.RELEASE 1. Properties & Yaml 1.1 Update via a properties file. /src/main/resources/application.properties server.port=8080 server.contextPath=/mkyong 1.2 Update via a […]

spring boot December 3, 2016 by mkyong 40 comments

Spring Boot Hello World Example – Thymeleaf

In this article, we will show you how to develop a Spring Boot web application, using Thymeleaf view, embedded Tomcat and package it as an executable JAR file. Technologies used : Spring Boot 2.1.2.RELEASE Spring 5.1.4.RELEASE Thymeleaf 3.0.11.RELEASE Tomcat embed 9.0.14 JUnit 4.12 Maven 3 Java 8 1. Project Directory 2. Maven Put spring-boot-starter-web and […]

jpa December 2, 2016 by Johnny Morgan 9 comments

JPA optimistic lock exception in Java Development

This post explains the JPA technology and its use in java development. Experts of java development India are explaining the use case of technologies- JPA and Hibernate, MySql database, Maven. Read this post and know what they want to say. Technology: JPA stands for the Java Persistence API which is the standard from Sun Micro […]

java November 30, 2016 by Marilena 1 comment

Java – Hybrid Cryptography example

Hybrid Cryptography is the silver lining between safe, but slow cryptography over big data (Asymmetric Cryptography) and unsafe but fast cryptography (Symmetric Cryptography). Hybrid Cryptography combines the speed of One-Key encryption and decryption along with the security that the Public-Private Key pair provides and thus considered a highly secure type of encryption. The most common […]

java November 29, 2016 by Marilena 24 comments

Java – Asymmetric Cryptography example

Asymmetric Cryptography, also known as Public Key Cryptography, is an encryption system in which two different but uniquely related cryptographic keys are used. The data encrypted using one key can be decrypted with the other. These keys are known as Public and Private Key Pair, and as the name implies the private key must remain […]

spring boot November 28, 2016 by mkyong 54 comments

Spring Boot Hello World Example – JSP

A Spring Boot web application example, using embedded Tomcat + JSP template, and package as an executable WAR file. Technologies used : Spring Boot 1.4.2.RELEASE Spring 4.3.4.RELEASE Tomcat Embed 8.5.6 Maven 3 Java 8 1. Project Directory Create the following folders manually : 2. Project Dependencies Maven example. Read comments for self-explanatory. pom.xml <?xml version="1.0" […]

swing November 27, 2016 by Marilena 8 comments

Java Swing – JOptionPane showConfirmDialog example

This is a review of the showConfirmDialog() method of JOptionPane Class. This method is a quick and easy way to get user input by asking a confirming question, like yes/no/cancel . The showConfirmDialog() can be called using the following combinations of parameters: Component, Object Component, Object, String, int Component, Object, String, int, int Component, Object, […]

swing November 26, 2016 by Marilena 8 comments

Java Swing – JOptionPane showMessageDialog example

This is a review of the showMessageDialog() method of JOptionPane Class. This method is a quick and easy way to tell the user about something that has happened . The showMessageDialog() can be called using the following combinations of parameters: Component, Object Component, Object, String, int Component, Object, String, int, Icon Component – The first […]

spring boot November 25, 2016 by mkyong 5 comments

Spring Boot web JSP – No Java compiler available

Spring boot web application with embeded Tomcat and JSP. Run and access the JSP page, but hits the following errors $ mvn spring-boot:run … java.lang.IllegalStateException: No Java compiler available at org.apache.jasper.JspCompilationContext.createCompiler(JspCompilationContext.java:235) ~[tomcat-embed-jasper-8.5.6.jar:8.5.6] at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:592) ~[tomcat-embed-jasper-8.5.6.jar:8.5.6] at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:368) ~[tomcat-embed-jasper-8.5.6.jar:8.5.6] at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385) ~[tomcat-embed-jasper-8.5.6.jar:8.5.6] at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329) ~[tomcat-embed-jasper-8.5.6.jar:8.5.6] at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) [tomcat-embed-core-8.5.6.jar:8.5.6] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) [tomcat-embed-core-8.5.6.jar:8.5.6] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.6.jar:8.5.6] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) […]

java November 23, 2016 by Marilena 2 comments

Java – Symmetric-Key Cryptography example

Symmetric-Key Cryptography is an encryption system in which the same key is used for the encoding and decoding of the data. The safe distribution of the key is one of the drawbacks of this method, but what it lacks in security it gains in time complexity. One should always assume that the encryption algorithms are […]