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 …
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 …
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 …
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 …
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) …
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 = …
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. …
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 …
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 …
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 …
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 …
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 …
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 …
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){ …
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(); …
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 + ...
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; …
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"); …
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 …
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 …
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 { …
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 …
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 …
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 | …
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 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); …
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 …
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; …
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); …
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"); } } }
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 …
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 …
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 …
In Java, we can use the following two Files.createTempFile() methods to create a temporary file in the default temporary-file directory. Path createTempFile(Path dir, String prefix, String suffix, FileAttribute<?>… attrs) throws IOException Path createTempFile(String prefix, String suffix, FileAttribute<?>… attrs) throws IOException The default temporary file folder is vary on operating system. Windows – %USER%\AppData\Local\Temp Linux – …
Java I/O tutorial with full example, including file , temporary file and directory manipulation, file serialization and compression with Zip or GZip.
In Java (@since 1.7), we can use the NIO Files.readAttributes to get all the file metadata, including the file creation date. Path file = Paths.get(fileName); BasicFileAttributes attr = Files.readAttributes(file, BasicFileAttributes.class); System.out.println("creationTime: " + attr.creationTime()); // creationTime: 2020-07-20T09:29:54.627222Z 1. Files.readAttributes (NIO) This example uses Files.readAttributes to print the file creation date. GetCreationDate1.java package com.mkyong.io.howto; import java.io.IOException; …
This article shows four ways to copy a file in Java. Files.copy (NIO) Apache Commons IO Guava Plain Java In Java 7+, the NIO Files.copy is the simplest way to copy a file, because it is a built-in API. Before Java 7, the Apache Commons IO FileUtils.copyFile is a preferable solution because the legacy IO …
In Java, we can use the NIO Files.delete() or Files.deleteIfExists() to delete a temporary file, it works the same like delete a regular text file. // create a temporary file Path path = Files.createTempFile(null, ".log"); // delete Files.delete(path); // or if(Files.deleteIfExists(path)){ // success }else{ // file does not exist } 1. Delete Temporary File – …
In Java, we can use BufferedWriter to write content into a file. // jdk 7 try (FileWriter writer = new FileWriter("app.log"); BufferedWriter bw = new BufferedWriter(writer)) { bw.write(content); } catch (IOException e) { System.err.format("IOException: %s%n", e); } Note If possible, uses Files.write instead, one line, simple and nice. List<String> list = Arrays.asList("Line 1", "Line 2"); …
The temporary file is just a regular file created on a predefined directory. In Java, we can use the NIO Files.write() to write data to a temporary file. // create a temporary file Path tempFile = Files.createTempFile(null, null); // Writes a string to the above temporary file Files.write(tempFile, "Hello World\n".getBytes(StandardCharsets.UTF_8)); // Append List<String> content = …