If a web request is coming from Google crawler or Google bot, the requested “user agent” should look similar like this : Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html) or (rarely used): Googlebot/2.1 (+http://www.google.com/bot.html) Source : Google crawlers 1. Java Example In Java, you can get the “user agent” from HttpServletRequest. Example : Service hosted at abcdefg.com @Autowired […]
This example shows you how to get the HTTP request headers in Java. To get the HTTP request headers, you need this class HttpServletRequest : 1. HttpServletRequest Examples 1.1 Loop over the request header’s name and print out its value. WebUtils.java package com.mkyong.web.utils; import javax.servlet.http.HttpServletRequest; import java.util.Enumeration; import java.util.HashMap; import java.util.Map; public class WebUtils { […]
You have been told a lot that you can’t manage memory in Java. Well, it has changed since HotSpot release of the Java VM. There is a way to directly allocate and deallocate memory as well as write and read it… Of course we are talking about the JVM memory where the Java program runs. […]
In this tutorial, we will show you how to create two custom annotations – @Test and @TestInfo, to simulate a simple unit test framework. P.S This unit test example is inspired by this official Java annotation article. 1. @Test Annotation This @interface tells Java this is a custom annotation. Later, you can annotate it on […]
This article shows the difference in time taken for similar operations on a String object and StringBuffer object. String being an immutable class, it instantiates a new object each time an operation is performed on it StringBuffer being a mutable class, the overhead of object instantiation during operations is removed. Hence, the time taken for […]
In this tutorial, we show you how to convert an IP address to its decimal equivalent in Java, and vice versa. For examples : 255.255.255.255 <-> 4294967295 192.168.1.2 <-> 3232235778 1. IP Address to Decimal We show you two ways to convert an IP address to a decimal number Normal power of 256 Bit shifting […]
Before you understand what is & 0xFF, make sure you know following stuffs : Bitwise AND operator, link. Converts hex to/from binary, and decimal to/from binary. In short, & 0xFF is used to make sure you always get the last 8 bits. Let’s see an example to convert an IP address to/from decimal number. 1. […]
This tutorial shows you how to work with java.util.Date and java.util.Calendar. 1. Java Date Examples Few examples to work with Date APIs. Example 1.1 – Convert Date to String. SimpleDateFormat sdf = new SimpleDateFormat("dd/M/yyyy"); String date = sdf.format(new Date()); System.out.println(date); //15/10/2013 Example 1.2 – Convert String to Date. SimpleDateFormat sdf = new SimpleDateFormat("dd-M-yyyy hh:mm:ss"); String […]
The JDK source code is inside the src.zip, this article shows you how to get it on Windows, Ubuntu (Linux) and Mac OSX. 1. Windows In Windows, visit the Oracle website and download the JDK (not JRE). Install the JDK and the src.zip is inside the JDK installed folder, for example : C:\Program Files\Java\jdk1.7.0_40\src.zip 2. […]
A leap year is a year containing one additional day (366 days a year). Review the leap year algorithm : if year is divisible by 400 then is_leap_year else if year is divisible by 100 then not_leap_year else if year is divisible by 4 then is_leap_year else not_leap_year P.S Algorithm from wikipedia leap year. 1. […]
Two Java examples show you how to print the elapsed time in days, hours, minutes and seconds format. 1. Standard JDK Date APIs You need to calculate the elapsed time manually. DateTimeUtils.java package com.mkyong.dateUtils; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; public class DateTimeUtils { public static void main(String[] args) { DateTimeUtils obj = new DateTimeUtils(); […]
In this example, we show you how to find a location (country, city, latitude, longitude) using an IP address. 1. GeoLite Database The MaxMind provides a free GeoLite database (IP Address to Location). Get a free GeoLite free Databases – here Get a GeoIP client Java APIs – here Start code it. 2. GeoLite Java […]
There are many ways the favicon can be recognized by the web browser : Example 1 <head> <link rel="icon" href="http://example.com/image.ico" /> </head> Example 2 <head> <link rel="icon" href="http://example.com/image.png" /> </head> Example 3 – weird, but Google use it. <head> <meta content="/images/google_favicon_128.png" itemprop="image" /> </head> 1. Jsoup Example Code snippets to get above favicon with Jsoup. […]
In this article, we show you 2 examples to join two lists in Java. JDK – List.addAll() Apache Common – ListUtils.union() 1. List.addAll() example Just combine two lists with List.addAll(). JoinListsExample.java package com.mkyong.example; import java.util.ArrayList; import java.util.List; public class JoinListsExample { public static void main(String[] args) { List<String> listA = new ArrayList<String>(); listA.add("A"); List<String> listB […]
A simple example to use Jackson to convert a JSON string to a Map. String json = "{name:\"mkyong\"}"; Map<String,String> map = new HashMap<String,String>(); ObjectMapper mapper = new ObjectMapper(); map = mapper.readValue(json, new TypeReference<HashMap<String,String>>(){}); Problem When the program is executed, it hits following error message org.codehaus.jackson.JsonParseException: Unexpected character (‘n’ (code 110)): was expecting double-quote to start […]
In this tutorial, we will show you how to convert a String to java.util.Date. Many Java beginners are stuck in the Date conversion, hope this summary guide will helps you in some ways. // String -> Date SimpleDateFormat.parse(String); // Date -> String SimpleDateFormat.format(date); Refer to table below for some of the common date and time […]
A short guide to show you how to convert a String with commas to a long type. 1. For a normal String, you can use Long.valueOf to convert it directly. String bigNumber = "1234567899"; long result = Long.valueOf(bigNumber); 2. For a String with commas, you can use java.text.NumberFormat to convert it. String bigNumber = "1,234,567,899"; […]
In this tutorial, we will show you how to use Java library – “Apache Commons Net” to get WHOIS data of a domain. 1. Simple Java Whois Example For domain registered under internic.net, you can get the whois data directly. WhoisTest.java package com.mkyong.whois.bo; import java.io.IOException; import java.net.SocketException; import org.apache.commons.net.whois.WhoisClient; public class WhoisTest { public static […]
This example shows how to generate a simple report using DynamicReports and JasperReports. DynamicReports is a Java reporting library that allows you to produce report documents that can be exported into many popular formats. It is based on the well-known JasperReports library. Tools used in this article : DynamicReports 3.1.3 JasperReports 5.0.4 MySQL 5.5 Maven […]
In this article, we will show you a few examples to make HTTP GET/POST requests via the following APIs Apache HttpClient 4.5.10 OkHttp 4.2.2 Java 11 HttpClient Java 1.1 HttpURLConnection (Not recommend) 1. Apache HttpClient In the old days, this Apache HttpClient is the de facto standard to send an HTTP GET/POST request in Java. […]
This article shows you how to use Apache HttpClient to send an HTTP GET/POST requests, JSON, authentication, timeout, redirection and some frequent used examples. P.S Tested with HttpClient 4.5.10 pom.xml <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version>4.5.10</version> </dependency> 1. Send GET Request 1.1 Close manually. HttpClientExample1_1.java package com.mkyong.http; import org.apache.http.HttpEntity; import org.apache.http.HttpHeaders; import org.apache.http.client.methods.CloseableHttpResponse; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.CloseableHttpClient; […]
In this example, we will show you how to login a website via standard Java HttpsURLConnection. This technique should be working in most of the login form. Tools & Java Library used in this example Google Chrome Browser – Network tab to analyze HTTP request and response header fields. jsoup library – Extracts HTML form […]
A funny Java example to create an ASCII art graphic. The concept is simple, get the image’s rgb color in “integer mode”, later, replace the color’s integer with ascii text. P.S This example is credited for this post ASCIIArtService.java package com.mkyong.service; import java.awt.*; import java.awt.image.BufferedImage; import java.io.IOException; public class ASCIIArtService { public static void main(String[] […]
In the DOM parser, we can use a recursive loop of the child nodes to find or count the depth of the XML document. Table of contents 1. An XML file 2. DOM Parser + Recursive Loop 3. DOM Parser + Tree Walker 4. Download Source Code 5. References P.S Tested with Java 11. Note […]
This article shows how to read and parse a comma-separated values (CSV) file. Topics: CSV file and RFC 4180 OpenCSV – Read and Parse CSV file OpenCSV – Convert CSV file to Object Parse CSV file Challenges – Embedded commas, double quotes, and line breaks Single class to read and parse a CSV file String#split […]
In this article, we show you how to use the Locale class to play around the list of countries. P.S Tested with JDK 1.6 1. List of Countries The Locale.getISOCountries() will return a list of all 2-letter country codes defined in ISO 3166. ListCountry.java package com.webmitta.model; import java.util.Locale; public class ListCountry { public static void […]
The HttpURLConnection‘s follow redirect is just an indicator, in fact it won’t help you to do the “real” http redirection, you still need to handle it manually. URL obj = new URL(url); HttpURLConnection conn = (HttpURLConnection) obj.openConnection(); conn.setInstanceFollowRedirects(true); //you still need to handle redirect manully. HttpURLConnection.setFollowRedirects(true); 1. Java Http Redirect Example If a server is […]
This example shows you how to get the Http response header values in Java. 1. Standard JDK example. URL obj = new URL("https://mkyong.com"); URLConnection conn = obj.openConnection(); //get all headers Map<String, List<String>> map = conn.getHeaderFields(); for (Map.Entry<String, List<String>> entry : map.entrySet()) { System.out.println("Key : " + entry.getKey() + " ,Value : " + entry.getValue()); } […]
This article shows how to fix the Maven error JAVA_HOME is not defined correctly. Terminal $ mvn -version Error: JAVA_HOME is not defined correctly. We cannot execute /usr/libexec/java_home/bin/java Further Reading How to set $JAVA_HOME environment variable on macOS 1. $JAVA_HOME and macOS 10.15 Catalina, macOS 11 Big Sur On macOS 10.15 Catalina and later, the […]
Problem Using Spring data and Mongodb, below is a function to find data within a date range. public List<RequestAudit> findByIpAndDate(String ip, Date startDate, Date endDate) { Query query = new Query( Criteria.where("ip").is(ip) .andOperator(Criteria.where("createdDate").gte(startDate)) .andOperator(Criteria.where("createdDate").lt(endDate)) ); return mongoOperation.find(query, RequestAudit.class); } It hits following error message : org.springframework.data.mongodb.InvalidMongoDbApiUsageException: Due to limitations of the com.mongodb.BasicDBObject, you can’t add […]
This article shows how to set the $JAVA_HOME environment variable on older Mac OS X and the latest macOS 11. Topics macOS release history What is /usr/libexec/java_home $JAVA_HOME and macOS 11 Big Sur $JAVA_HOME and Mac OS X 10.5 Leopard $JAVA_HOME and older Mac OS X Switch between different JDK versions Solution Steps to set […]
In Java, you can use HttpServletRequest.getRemoteAddr() to get the client’s IP address that’s accessing your Java web application. import javax.servlet.http.HttpServletRequest; String ipAddress = request.getRemoteAddr(); 1. Proxy Server or Cloudflare For web application which is behind a proxy server, load balancer or the popular Cloudflare solution, you should get the client IP address via the HTTP […]
Problem Downloaded a Java sample from Alexa API on Amazon service, imports it into Eclipse, but unable to compile and hits following “Access restriction” errors : Access restriction: The type BASE64Encoder is not accessible due to restriction on required library /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/classes.jar P.S Using JDK 1.6 and Eclipse IDE 4.2 import sun.misc.BASE64Encoder; // Access restriction error […]
In this tutorial, we show you 2 examples to calculate date / time difference in Java : Manual time calculation. Joda time library. 1. Manual time calculation Converts Date in milliseconds (ms) and calculate the differences between two dates, with following rules : 1000 milliseconds = 1 second 60 seconds = 1 minute 60 minutes […]
In this example, we show you how to use Java and DOM XML parser to get the Alexa ranking from below the undocumented API : http://data.alexa.com/data?cli=10&url=domainName 1. Alexa API For example, type following URL in your browser : http://data.alexa.com/data?cli=10&url=mkyong.com Alexa will return back following XML result : <ALEXA VER="0.9" URL="mkyong.com/" HOME="0" AID="="> <DMOZ> <SITE BASE="mkyong.com/" […]
In this example, we will show you how to get Google PageRank (PR) in Java. To request a PageRank for “mkyong.com”, you just need to send following HTTP request : http://toolbarqueries.google.com/tbr?client=navclient-auto&hl=en&ch=6236440745 &ie=UTF-8&oe=UTF-8&features=Rank&q=info:mkyong.com P.S Above URL is used by Google toolbar plugin. The tricky part is following hashing value : ch=6236440745 Google is using Bob Jenkins […]
Jsoup, a HTML parser, its “jquery-like” and “regex” selector syntax is very easy to use and flexible enough to get whatever you want. Below are three examples to show you how to use Jsoup to get links, images, page title and “div” element content from a HTML page. Download jsoup The jsoup is available in […]
This tutorial shows you how to convert a Java project to Java web application project in Eclipse 4.2, it should work in older version as well. 1. Java Project A simple Java project. 2. Project Facets Right click on the project properties. Select “Project Facets“, and click “convert to faceted form…” Check “Dynamic Web Module” […]
Here’s an example to show you how to search a file named “post.php” from directory “/Users/mkyong/websites” and all its subdirectories recursively. FileSearch.java package com.mkyong; import java.io.File; import java.util.ArrayList; import java.util.List; public class FileSearch { private String fileNameToSearch; private List<String> result = new ArrayList<String>(); public String getFileNameToSearch() { return fileNameToSearch; } public void setFileNameToSearch(String fileNameToSearch) { […]
In Java, we can use ProcessBuilder or Runtime.getRuntime().exec to execute external shell command : 1. ProcessBuilder ProcessBuilder processBuilder = new ProcessBuilder(); // — Linux — // Run a shell command processBuilder.command("bash", "-c", "ls /home/mkyong/"); // Run a shell script //processBuilder.command("path/to/hello.sh"); // — Windows — // Run a command //processBuilder.command("cmd.exe", "/c", "dir C:\\Users\\mkyong"); // Run a […]
