Tag: java

java July 26, 2012 by Rajiv Srivastava 2 comments

How to work with Java 6’s NavigableSet and NavigableMap

You can use latest Java 6’s Collection API to navigate a set and Map collections. These API gives a lot of flexibility to find out required result from the collection. 1. NavigableMap Example package com.example.collection; import java.util.NavigableMap; import java.util.TreeMap; public class NavigableMapDemo { public static void main(String[] args) { NavigableMap<String,Integer> navigableMap=new TreeMap<String, Integer>(); navigableMap.put("X", 500); […]

java July 24, 2012 by Rene Enriquez 11 comments

How to use reflection to copy properties from Pojo to other Java Beans

Sometimes we need copy properties from a Java class to other, we can do it this manually or with our own reflection implementation, but in this case use us reflection for automate it with a utility from apache Requirements commons-beanutils , you can download from here http://commons.apache.org/beanutils/ commons-loging , you can download from here http://commons.apache.org/logging/ […]

java July 23, 2012 by Dhina Prakash 17 comments

How to run a task periodically in Java

Some java application need to execute a method between a regular interval of time. For example GUI application should update some information from database. 1. Scheduler Task For this functionality, You should create a class extending TimerTask(available in java.util package). TimerTask is a abstract class. Write your code in public void run() method that you […]

java July 9, 2012 by mkyong 4 comments

Java and zip code example

Recently, answered an question about leading zero problem ZipCode, what is the most proper data type for country’s zip code? 1. ZipCode – int In Java, some claimed it should declare as “int”, and use DecimalFormat to format and display the leading zero. For example, package com.mkyong; import java.text.DecimalFormat; public class ZipCodeExample { public static […]

java July 4, 2012 by mkyong 37 comments

How to get URL content in Java

In this Java example, we show you how to get content of a page from URL “mkyong.com” and save it into local file drive, named “test.html”. package com.mkyong; import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.File; import java.io.FileWriter; import java.io.IOException; import java.io.InputStreamReader; import java.net.MalformedURLException; import java.net.URL; import java.net.URLConnection; public class GetURLContent { public static void main(String[] args) […]

java April 27, 2012 by mkyong 7 comments

Convert PNG to JPEG image in Java

This article shows how to convert an PNG image format to an JPEG image format in Java. 1. PNG Image Below is a PNG image with a transparent background. 2. Java Convert PNG to JPEG Since the JPEG image format doesn’t support the transparent background, we will create a white background as a replacement. Below […]

google app engine April 9, 2012 by mkyong 9 comments

GAE + Java – Integrating Google user account

For this tutorial, we will show you how to integrate Google user account in GAE + Java project, via Google Java SDK UserService class. Tools used : JDK 1.6 Eclipse 3.7 + Google Plugin for Eclipse Google App Engine Java SDK 1.6.3.1 1. GAE User service example If user login by using their Google account, […]

google app engine March 31, 2012 by mkyong 27 comments

Google app engine Java hello world example using Eclipse

In this tutorial, we will show you how to use Eclipse to create a Google App Engine (GAE) Java project (hello world example), run it locally, and deploy it to Google App Engine account. Tools used : JDK 1.6 Eclipse 3.7 + Google Plugin for Eclipse Google App Engine Java SDK 1.6.3.1 Note GAE supports […]

java February 20, 2012 by mkyong 6 comments

How to check if Date is within a certain range in Java?

A Java example to check if a provided date is within a range of 3 momths before and after current date. The idea is quite simple, just use Calendar class to roll the month back and forward to create a “date range”, and use the Date.before() and Date.after() to check if the Date is within […]

java February 3, 2012 by mkyong 10 comments

Java try-with-resources example

This article shows you how to use try-with-resources in Java. Table of contents: 1 Java try-with-resources before and after 2. try-with-resources with single resource 3. try-with-resources with multiple resources 3.1 JDBC example. 4. Custom resource with AutoCloseable interface 5. Resource open and closing order 6. Java 9 – final or effectively final variables Download Source […]

java January 20, 2012 by mkyong 7 comments

How to read file in Java – FileInputStream

In Java, we use FileInputStream to read bytes from a file, such as an image file or binary file. Topics FileInputStream – Read a file FileInputStream – Remaining bytes FileInputStream – Better performance FileInputStream vs BufferedInputStream InputStreamReader – Convert FileInputStream to Reader FileInputStream – Read a Unicode file Note However, all the below examples use […]

javaee November 13, 2011 by mkyong 4 comments

The method getRealPath(String) from the type ServletRequest is deprecated

See following example to get the real server file path via servletRequest.getRealPath(“/”). However, warning is prompt and complained that this method is deprecated. import javax.servlet.http.HttpServletRequest; public class DisplayAction { private HttpServletRequest servletRequest; public String execute() { //The method getRealPath(String) from the type ServletRequest is deprecated String filePath = servletRequest.getRealPath("/"); } @Override public void setServletRequest(HttpServletRequest arg0) […]

java August 11, 2011 by mkyong 16 comments

How to loop ArrayList in Java

No nonsense, four ways to loop ArrayList in Java For loop For loop (Advance) While loop Iterator loop package com.mkyong.core; import java.util.ArrayList; import java.util.Iterator; import java.util.List; public class ArrayListLoopingExample { public static void main(String[] args) { List<String> list = new ArrayList<String>(); list.add("Text 1"); list.add("Text 2"); list.add("Text 3"); System.out.println("#1 normal for loop"); for (int i = […]

java August 4, 2011 by mkyong 11 comments

JAXB hello world example

Jakarta XML Binding (JAXB; formerly Java Architecture for XML Binding) is an XML binding framework to convert Java objects to and from XML. XML Marshalling – Convert Java objects into XML. XML Unmarshalling – Convert XML back into Java Objects. Note This article will focus on Java 11, JAXB 3 and EclipseLink MOXy JAXB RI. […]

mongodb May 2, 2011 by mkyong 48 comments

Java + MongoDB hello world example

A simple Java + MongoDB hello world example – how to connect, create database, collection and document, save, update, remove, get and display document (data). Tools and technologies used : MongoDB 2.2.3 MongoDB-Java-Driver 2.10.1 JDK 1.6 Maven 3.0.3 Eclipse 4.2 P.S Maven and Eclipse are both optional, just my personal favorite development tool. 1. Create […]

java May 1, 2011 by mkyong 2 comments

Java – How to convert Char[] to String

In Java, we can use String.valueOf() to convert a char array to a String. JavaSample1.java package com.mkyong.markdown; public class JavaSample1 { public static void main(String[] args) { char[] charArrays = new char[]{‘1’, ‘2’, ‘3’, ‘A’, ‘B’, ‘C’}; String str = new String(charArrays); System.out.println(str); // 123ABC String str2 = String.valueOf(charArrays); System.out.println(str2); // 123ABC } } Output […]

java May 1, 2011 by mkyong 8 comments

Java – How to convert String to Char Array

In Java, you can use String.toCharArray() to convert a String into a char array. StringToCharArray.java package com.mkyong.utils; public class StringToCharArray { public static void main(String[] args) { String password = "password123"; char[] passwordInCharArray = password.toCharArray(); for (char temp : passwordInCharArray) { System.out.println(temp); } } } Output p a s s w o r d 1 […]

jax-ws March 14, 2011 by mkyong 30 comments

JAX-WS + Java Web Application Integration Example

Often times, JAX-WS always be part of your Java web application. Here we show you how to integrate JAX-WS into Java web application easily. 1. Project Folder First, review this project folder structure. 2. Web Service A super simple web service. Code is self-explanatory. File : HelloWorld.java package com.mkyong.ws; import javax.jws.WebMethod; import javax.jws.WebService; @WebService public […]

unix / linux February 26, 2011 by mkyong 8 comments

How to unzip a WAR file in Java

In J2EE web development, Web Application Archive(WAR) file is just a normal JAR file, which consists all of your web application components like, servlets, Java classes, libraries, resources and etc. Read Wiki for detail. Problem Current web application WAR file is generated via Ant or Maven tool, copy to *nix environment for deployment, but no […]

java February 26, 2011 by mkyong 5 comments

java.lang.ClassNotFoundException: com.sun.mail.util.MessageRemovedIOException

Problem Use JavaMail API to send Email via GMail smtp server, but hit the following error message : Caused by: java.lang.ClassNotFoundException: com.sun.mail.util.MessageRemovedIOException at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) … 1 more P.S The javaee.jar library is included. Solution To solve it, you need to include the […]

java December 30, 2010 by mkyong 49 comments

How to get MAC address in Java

Since JDK 1.6, Java developers are able to access network card detail via NetworkInterface class. In this example, we show you how to get the localhost MAC address in Java. App.java – Get MAC Address via NetworkInterface.getByInetAddress() package com.mkyong; import java.net.InetAddress; import java.net.NetworkInterface; import java.net.SocketException; import java.net.UnknownHostException; public class App{ public static void main(String[] args){ […]

java December 30, 2010 by mkyong 20 comments

How to get Server IP address in Java

In Java, you can use InetAddress.getLocalHost() to get the Ip Address of the current Server running the Java app. package com.mkyong; import java.net.InetAddress; import java.net.UnknownHostException; public class Test { public static void main(String[] args) { InetAddress ip; try { ip = InetAddress.getLocalHost(); System.out.println("Current IP address : " + ip.getHostAddress()); } catch (UnknownHostException e) { e.e.printStackTrace(); […]

java December 30, 2010 by mkyong 5 comments

How to convert negative number to positive in Java

To convert negative number to positive number (this is called absolute value), uses Math.abs(). This Math.abs() method is work like this “number = (number < 0 ? -number : number);". See a complete example : package com.mkyong; public class app{ public static void main(String[] args) { int total = 1 + 1 + 1 + […]

java November 28, 2010 by mkyong 43 comments

Java HttpsURLConnection example

Here’s a simple Java HTTPS client to demonstrate the use of HttpsURLConnection class to send a HTTP GET request yo get the https URL content and certificate detail. P.S You may interest at this example – automate login a website with HttpsURLConnection. HttpsClient.java package com.mkyong.client; import java.net.MalformedURLException; import java.net.URL; import java.security.cert.Certificate; import java.io.*; import javax.net.ssl.HttpsURLConnection; […]

java November 1, 2010 by mkyong 13 comments

How to validate URL in Java

A short example to show the use of apache.commons.validator.UrlValidator class to validate an URL in Java. import org.apache.commons.validator.UrlValidator; public class ValidateUrlExample{ public static void main(String[] args) { UrlValidator urlValidator = new UrlValidator(); //valid URL if (urlValidator.isValid("https://mkyong.com")) { System.out.println("url is valid"); } else { System.out.println("url is invalid"); } //invalid URL if (urlValidator.isValid("http://invalidURL^$&%$&^")) { System.out.println("url is valid"); […]

java November 1, 2010 by mkyong 5 comments

java.lang.NoClassDefFoundError: org/apache/oro/text/perl/Perl5Util

Problem Validate an URL with Apache common URLValidator to validate an URL, but it hits following error message ? java.lang.NoClassDefFoundError: org/apache/oro/text/perl/Perl5Util at org.apache.commons.validator.UrlValidator.isValid(UrlValidator.java:242) … Caused by: java.lang.ClassNotFoundException: org.apache.oro.text.perl.Perl5Util at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1516) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1361) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) … 28 more Solution The URLValidator class is required Jakarta-ORO library, make sure you include the oro-xxx.jar into your project class […]

java August 23, 2010 by mkyong 1 comment

Java – Convert XML to a properties file

This article shows how to convert an XML file to a properties file. Table of contents 1. Properties – Convert XML file to a properties file 2. DOM – Convert XML file to a properties file 3. Download Source Code 4. References P.S Tested with Java 11. 1. Properties – Convert XML file to a […]

java August 23, 2010 by mkyong 16 comments

How to get free disk space in Java

In Java old days, it lacks of method to determine the free disk space on a partition. But this is changed since JDK 1.6 released, a few new methods – getTotalSpace(), getUsableSpace() and getFreeSpace(), are bundled with java.io.File to retrieve the partition or disk space detail. Example package com.mkyong; import java.io.File; public class DiskSpaceDetail { […]

java August 23, 2010 by mkyong 1 comment

How to make a file read only in Java

A Java program to demonstrate the use of java.io.File setReadOnly() method to make a file read only. Since JDK 1.6, a new setWritable() method is provided to make a file to be writable again. Example package com.mkyong; import java.io.File; import java.io.IOException; public class FileReadAttribute { public static void main(String[] args) throws IOException { File file […]

java August 23, 2010 by mkyong 3 comments

How to check if a file is hidden in Java

A Java program to demonstrate the use of java.io.File isHidden() to check if a file is hidden. package com.mkyong; import java.io.File; import java.io.IOException; public class FileHidden { public static void main(String[] args) throws IOException { File file = new File("c:/hidden-file.txt"); if(file.isHidden()){ System.out.println("This file is hidden"); }else{ System.out.println("This file is not hidden"); } } } Note […]

java August 23, 2010 by mkyong 6 comments

Java – Convert File to Hex

This article shows how to convert a file into a hexadecimal (hex) representative format. for example, below is a text file. /path/to/text.txt ABCDEFG 12345678 !@#$%^&*() Testing only And we will convert the above file into the following hex format. 41 42 43 44 45 46 47 0D 0A 31 32 33 34 35 36 | […]

java July 7, 2010 by mkyong 113 comments

Java object sorting example (Comparable and Comparator)

In this tutorial, it shows the use of java.lang.Comparable and java.util.Comparator to sort a Java object based on its property value. 1. Sort an Array To sort an Array, use the Arrays.sort(). String[] fruits = new String[] {"Pineapple","Apple", "Orange", "Banana"}; Arrays.sort(fruits); int i=0; for(String temp: fruits){ System.out.println("fruits " + ++i + " : " + […]

java July 7, 2010 by mkyong 1 comment

How to sort an Array in java

Java example to show the use of Arrays.sort() to sort an Array. The code should be self-explanatory. import java.util.Arrays; import java.util.Collections; public class ArraySorting{ public static void main(String args[]){ String[] unsortStringArray = new String[] {"c", "b", "a", "3", "2", "1"}; int[] unsortIntArray = new int[] {7,5,4,6,1,2,3}; System.out.println("Before sort"); System.out.println("— unsortStringArray —"); for(String temp: unsortStringArray){ System.out.println(temp); […]

java July 7, 2010 by mkyong 19 comments

How to sort an ArrayList in java

By default, the ArrayList’s elements are display according to the sequence it is put inside. Often times, you may need to sort the ArrayList to make it alphabetically order. In this example, it shows the use of Collections.sort(‘List’) to sort an ArrayList. import java.util.ArrayList; import java.util.Collections; import java.util.List; public class SortArrayList{ public static void main(String […]

java July 7, 2010 by mkyong 50 comments

How to sort a Map in Java

Few Java examples to sort a Map by its keys or values. Note If you are using Java 8, refer to this article – How to use Stream APIs to sort a Map 1. Sort by Key 1.1 Uses java.util.TreeMap, it will sort the Map by keys automatically. SortByKeyExample1.java package com.mkyong.test; import java.util.HashMap; import java.util.Map; […]

java June 25, 2010 by mkyong 7 comments

How to initialize an ArrayList in one line

Here’s a few ways to initialize an java.util.ArrayList, see the following full example: InitArrayList.java package com.mkyong.examples; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class InitArrayList { public static void main(String[] args) { //1. Normal way List<String> list = new ArrayList<String>(); list.add("String A"); list.add("String B"); list.add("String C"); System.out.println("List 1……"); for (String temp : list) { System.out.println(temp); […]

java June 5, 2010 by mkyong 5 comments

How to check if directory is empty in Java

Here’s an example to check if a directory is empty. Example package com.mkyong.file; import java.io.File; public class CheckEmptyDirectoryExample { public static void main(String[] args) { File file = new File("C:\\folder"); if(file.isDirectory()){ if(file.list().length>0){ System.out.println("Directory is not empty!"); }else{ System.out.println("Directory is empty!"); } }else{ System.out.println("This is not a directory"); } } }

java June 5, 2010 by mkyong 15 comments

How to delete directory in Java

If we use the NIO Files.delete to delete a non-empty directory in Java, it throws DirectoryNotEmptyException; for legacy IO File.delete to delete a non-empty directory, it returns a false. The standard solution is to loop the directory recursively, and delete all its children’s contents first (sub-files or sub-directories), and delete the parent later. This example […]

java June 5, 2010 by mkyong 25 comments

How to create directory in Java

In Java, we can use the NIO Files.createDirectory to create a directory or Files.createDirectories to create a directory including all nonexistent parent directories. try { Path path = Paths.get("/home/mkyong/a/b/c/"); //java.nio.file.Files; Files.createDirectories(path); System.out.println("Directory is created!"); } catch (IOException e) { System.err.println("Failed to create directory!" + e.getMessage()); } 1. Create Directory – Java NIO 1.1 We can […]

java June 4, 2010 by mkyong 53 comments

How to move file to another directory in Java

This article shows how to move a file to another directory in the same file drive or remote server. Files.move – Move file in local system. JSch – Move file to remove server (SFTP) 1. Move file to another directory This Java example uses NIO Files.move to move a file from to another directory in […]