In Python, you can use time.sleep(seconds) to make the current executing Python program to sleep or delay a few seconds. import time time.sleep(1) # delays for 1 seconds time.sleep(10) # delays for 10 seconds time.sleep(60) # delays for 1 minute time.sleep(3600) # delays for 1 hour Full example. test_delay.py import time def main(): while True: […]
In this tutorial, we will show you how to loop a dictionary in Python. 1. for key in dict: 1.1 To loop all the keys from a dictionary – for k in dict: for k in dict: print(k) 1.2 To loop every key and value from a dictionary – for k, v in dict.items(): for […]
In Java, you can use Map.containsKey() to check if a key exists in a Map. TestMap.java package com.mkyong.examples; import java.util.HashMap; import java.util.Map; public class TestMap { public static void main(String[] args) { Map<String, Integer> fruits = new HashMap<>(); fruits.put("apple", 1); fruits.put("orange", 2); fruits.put("banana", 3); fruits.put("watermelon", null); System.out.println("1. Is key ‘apple’ exists?"); if (fruits.containsKey("apple")) { //key […]
In this article, we will show you how to create a simple Whois client both in Python 2 and Python 3. Tested Python 2.7.10 Python 3.4.3 1. Python 3 Whois example In Python 3, the socket accepts bytes, so you need to encode() and decode() manually. whois3.py import sys import socket s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) […]
On Debian, type cat /etc/debian_version to display the Debian version. Terminal $ cat /etc/debian_version 9.5 Alternatively, cat /etc/issue Terminal $ cat /etc/issue Debian GNU/Linux 9 \n \l The last one, lsb-release -a, it will display the Debian detail. Terminal $ lsb-release -a -bash: lsb-release: command not found $ sudo apt-get install lsb-release $ lsb_release -a […]
In Python, you can use the in operator to check if a key exists in a dictionary. test.py def main(): fruits = { ‘apple’:1, ‘orange’:2, ‘banana’:3 } #if key ‘apple’ exists in fruits? if ‘apple’ in fruits: print(fruits[‘apple’]) if __name__ == ‘__main__’: main() Output 1 P.S Tested with Python 3.4.3 Note has_key() is deprecated in […]
Learn how to set the JAVA_HOME environment variable on Windows 10 or 11 with easy-to-follow steps and screenshots.
In Java 8, we can use the new forEach to loop or iterate a Map, List, Set, or Stream. Topics Loop a Map Loop a List forEach and Consumer forEach and Exception handling forEach vs forEachOrdered 1. Loop a Map 1.1 Below is a normal way to loop a Map. public static void loopMapClassic() { […]
In this article, we will show you three ways to generate random integers in a range. java.util.Random.nextInt Math.random java.util.Random.ints (Java 8) 1. java.util.Random This Random().nextInt(int bound) generates a random integer from 0 (inclusive) to bound (exclusive). 1.1 Code snippet. For getRandomNumberInRange(5, 10), this will generates a random integer between 5 (inclusive) and 10 (inclusive). private […]
In this example, we will show you how to use Java 8 Lambda expression to write a Comparator to sort a List. 1. Classic Comparator example. Comparator<Developer> byName = new Comparator<Developer>() { @Override public int compare(Developer o1, Developer o2) { return o1.getName().compareTo(o2.getName()); } }; 2. Lambda expression equivalent. Comparator<Developer> byName = (Developer o1, Developer o2)->o1.getName().compareTo(o2.getName()); […]
Just upgraded to Java 8, and the Tomcat 7 keeps prompting the following exceptions: Jul 20, 2015 4:06:36 PM org.apache.catalina.startup.ContextConfig processAnnotationsJar SEVERE: Unable to process Jar entry [jdk/nashorn/internal/objects/NativeURIError.class] from Jar [jar:file:/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre/lib/ext/nashorn.jar!/] for annotations org.apache.tomcat.util.bcel.classfile.ClassFormatException: Invalid byte tag in constant pool: 15 at org.apache.tomcat.util.bcel.classfile.Constant.readConstant(Constant.java:131) at org.apache.tomcat.util.bcel.classfile.ConstantPool.<init>(ConstantPool.java:60) at org.apache.tomcat.util.bcel.classfile.ClassParser.readConstantPool(ClassParser.java:209) at org.apache.tomcat.util.bcel.classfile.ClassParser.parse(ClassParser.java:119) at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2066) at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:1942) at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1908) […]
Review a Python 2 socket example whois.py import sys import socket s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(("whois.arin.net", 43)) s.send(sys.argv[1] + "\r\n") #Python 2.7 send signature #socket.send(string[, flags]) If compile with Python 3, it prompts the following error? Traceback (most recent call last): File "C:\repos\hc\whois\python\whois.py", line 6, in <module> s.send(sys.argv[1] + "\r\n") TypeError: ‘str’ does not support […]
In HSQLDB you can use IDENTITY keyword to define an auto-increment column, normally, this is the primary key. Review below examples : 1. IDENTITY – Default By default, the IDENTITY value is start with zero. CREATE TABLE users ( id INTEGER IDENTITY PRIMARY KEY, name VARCHAR(30), email VARCHAR(50) ); INSERT INTO users (name, email) VALUES […]
Here’s the scenario, the controller returns a ModelAndView, and an exception is thrown while rendering the JSP view page, reason behind is one of message code is not found. org.apache.jasper.JasperException: org.springframework.context.NoSuchMessageException: No message found under code ‘Diff.userform.password’ for locale ‘en_US’. org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) An exception is thrown and render an HTTP 500 error […]
In a nutshell, a servlet filter lets you intercepts requests and responses on your web application. This article shows you how to register a servlet filter in Spring XML and JavaConfig. 1. Servlet Filter Review the following custom filter, it will catch any exceptions and redirect to an error page. package com.mkyong.form.web; import java.io.IOException; import […]
Spring examples to show you how to mix both Spring XML and JavaConfig together. 1. Load JavaConfig From Spring XML A Spring MVC example, uses @Configuration to load everything, and you want integrate with web.xml SpringWebConfig.java package com.mkyong.form.config; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.config.annotation.EnableWebMvc; import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter; import org.springframework.web.servlet.view.InternalResourceViewResolver; import org.springframework.web.servlet.view.JstlView; @EnableWebMvc […]
In this article, we will show you how to validate the submitted form values with Spring validator and Hibernate Validator (bean validation). Technologies used : Spring 4.1.6.RELEASE Hibernate Validator 5.1.3.Final 1. Hibernate Validator The Hibernate validator will be fired if @Valid is provided. import org.hibernate.validator.constraints.NotEmpty; public class User { @NotEmpty String name; //… } @RequestMapping(value […]
In this article, we will show you few Spring form tag examples to check if a field has an error message. Review the following Spring MVC bean validation example : Technologies used : Spring 4 JSTL 1.2 //Bean validation import org.hibernate.validator.constraints.NotEmpty; public class User { @NotEmpty String name; //… } //Controller class @RequestMapping(value = "/users", […]
Converting a Python 2 socket example to Python 3 whois.py import sys import socket s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(("whois.arin.net", 43)) s.send((sys.argv[1] + "\r\n").encode()) response = "" while True: data = s.recv(4096) response += data if not data: break s.close() print(response) If compile with Python 3, it prompts the following error? Traceback (most recent call last): […]
In this tutorial, we will show you a few examples to configure the embedded database engines like HSQL, H2 and Derby in Spring framework. Technologies used : Spring 4.1.6.RELEASE jUnit 4.1.2 Maven 3 Embedded databases tested : HSQLDB 2.3.2 H2 1.4.187 Derby 10.11.1.1 The embedded database concept is very helpful during the development phase, because […]
In Spring, you can use MethodInvokingFactoryBean to run a method, get the result and inject the result into another bean. This method invoker is very useful in XML configuration, but less use now in favor of annotation and Spring expression. 1. MethodInvokingFactoryBean 1.1 Example to get the current Java version. Spring XML Configuration <!– 1. […]
In this example, we will show you how to set active @Profile in a Spring MVC web application. @Profile Examples @Configuration public class AppConfig { @Profile("dev") @Bean public CacheManager cacheManager() { //… } @Profile("live") @Bean public EhCacheManagerFactoryBean ehCacheCacheManager() { //… } @Profile("testdb") @Bean public DataSource dataSource() { //… } } To set active @Profile in […]
A Spring @Configuration example to start an HSQLDB embedded database or in-memory database. DataSourceConfig.java package com.mkyong.config.db; import javax.sql.DataSource; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.jdbc.datasource.embedded.EmbeddedDatabase; import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder; import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType; @Configuration public class DataSourceConfig { @Bean public DataSource dataSource(){ //jdbc:hsqldb:mem:testdb EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder(); EmbeddedDatabase db = builder.setType(EmbeddedDatabaseType.HSQL) .addScript("db/hsqldb/db.sql") .build(); return db; } } Review the […]
In this tutorial, we will show you how to setup slf4j and logback in a Spring MVC web application. Technologies used : Spring 4.1.6.RELEASE Logback 1.1.3 Maven 3 or Gradle 2.0 Tomcat 7 Eclipse 4.4 Note By default, Spring is using the Jakarta Commons Logging API (JCL), read this. To setup logback framework you need […]
The source code is attached to the JAR, but Eclipse is keep showing “Source not found” while I jumped to the source via “F3 – Open Declaration”. Tools tested : Gradle 2.4 Eclipse 4.4 1. Gradle Eclipse Project 1.1 A web project build with Gradle and development in Eclipse IDE. build.gradle apply plugin: ‘java’ apply […]
In this tutorial, we will show you how to display project dependencies with the Gradle build tool. Review a simple Spring MVC project dependencies. build.gradle dependencies { compile ‘org.slf4j:jcl-over-slf4j:1.7.12’ compile ‘ch.qos.logback:logback-classic:1.1.3’ compile(‘org.springframework:spring-webmvc:4.1.6.RELEASE’){ exclude group: ‘commons-logging’, module: ‘commons-logging’ } compile ‘org.hsqldb:hsqldb:2.3.2’ providedCompile ‘javax.servlet:servlet-api:2.5’ } P.S Tested with Gradle 2.4 1. gradle dependencies Display project dependencies (direct […]
If you run or debug a web project in Eclipse, the project name will be the default context root. For example, a project named “springmvc”, the default context root will be http://localhost:8080/springmvc Technologies tested : Eclipse 4.4 Eclipse Tomcat server plugin Maven 3 Gradle 2.0 Note The context root tell you the URL of a […]
Few Maven Jetty 8.x and 9.x plugin examples, just for quick reference. 1. Maven Jetty Plugin 9.x Note You need to use Maven 3 and Java 1.7 for Maven Jetty 9.x plugin. 1.1 The ‘groupId’ is org.eclipse.jetty, by default, it runs on port 8080, in root context ‘/’. pom.xml <plugin> <groupId>org.eclipse.jetty</groupId> <artifactId>jetty-maven-plugin</artifactId> <version>9.2.11.v20150529</version> </plugin> To […]
Code snippets to show you how to convert string to bytes and vice versa. 1. To convert a string to bytes. data = "" #string data = "".encode() #bytes data = b"" #bytes 2. To convert bytes to a String. data = b"" #bytes data = b"".decode() #string data = str(b"") #string P.S Tested with […]
In Java, we can use Integer.parseInt(String) to convert a String to an int; For unparsable String, it throws NumberFormatException. Integer.parseInt("1"); // ok Integer.parseInt("+1"); // ok, result = 1 Integer.parseInt("-1"); // ok, result = -1 Integer.parseInt("100"); // ok Integer.parseInt(" 1"); // NumberFormatException (contains space) Integer.parseInt("1 "); // NumberFormatException (contains space) Integer.parseInt("2147483648"); // NumberFormatException (Integer max 2,147,483,647) […]
In Maven, you can use mvn dependency:tree to display the project dependencies in tree format. 1. Maven Project Review a simple Maven project, declared Spring and logback dependencies. pom.xml <properties> <spring.version>4.1.6.RELEASE</spring.version> <logback.version>1.1.3</logback.version> <jcl.slf4j.version>1.7.12</jcl.slf4j.version> </properties> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>${spring.version}</version> <exclusions> <exclusion> <groupId>commons-logging</groupId> <artifactId>commons-logging</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>${spring.version}</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>jcl-over-slf4j</artifactId> <version>${jcl.slf4j.version}</version> […]
In this tutorial, we will show you how to associate a NameCheap domain name to an Amazon EC2 instance. In AWS Create an Elastic IP and point to the Amazon EC2 instance. Go to service Route 53, create a ‘A’ record and point to the Elastic IP. In Route 53, copy the Amazon NS (name […]
In Java, there are few ways to display double in 2 decimal places. Table of contents. 1. DecimalFormat("0.00") 2. String.format("%.2f") 3. BigDecimal 4. References Possible Duplicate How to round double / float value to 2 decimal places 1. DecimalFormat(“0.00”) We can use DecimalFormat("0.00") to ensure the number is round to 2 decimal places. DecimalExample.java package […]
A simple Math.pow example, display 2 to the power of 8. In Math 2^8 = 2x2x2x2x2x2x2x2 =256 In Java Math.pow(2, 8) Note In Java, the symbol ^ is a XOR operator, DON’T use this for the power calculation. TestPower.java package com.mkyong.test; import java.text.DecimalFormat; public class TestPower { static DecimalFormat df = new DecimalFormat(".00"); public static […]
To quick start a new Gradle Java project, type gradle init –type java-library $ gradle init –type java-library :wrapper :init BUILD SUCCESSFUL Total time: 4.866 secs The following files and folders will be created automatically. P.S Tested with Gradle 2.0 1. Java Project Structure Both src/main/java and src/test/java folders are created. The Library*.java is a […]
In this tutorial, we will show you how to do the data grouping with Spring Data + MongoDB aggregation framework. 1. Test Data domain.json { "_id" : 1, "domainName" : "test1.com", "hosting" : "hostgator.com" } { "_id" : 2, "domainName" : "test2.com", "hosting" : "aws.amazon.com"} { "_id" : 3, "domainName" : "test3.com", "hosting" : "aws.amazon.com" […]
In Gardle, the application plugin, you can pass the system properties via applicationDefaultJvmArgs : gradle.build apply plugin:’application’ mainClassName = "com.mkyong.analyzer.engine.hydra.entryPointForJar" applicationName = ‘analyzer’ distZip { archiveName ‘analyzer-‘ + version + ‘.zip’ } applicationDefaultJvmArgs = ["-Dlogback.configurationFile=logback.xml"] The problem is how to get the APP_HOME for logback.xml? gradle.build applicationDefaultJvmArgs = ["-Dlogback.configurationFile=APP_HOME/logback.xml"] You can hard code the APP_HOME, […]
A Spring MVC web application, noticed all the Spring’s beans are loaded twice!? package com.mkyong.config.db; @Configuration public class MongoDevConfig { private final static Logger logger = LoggerFactory.getLogger(MongoDevConfig.class); @Bean MongoDbFactory mongoDbFactory() throws Exception { logger.debug("Init…… MongoDbFactory() in production mode!"); //… return new new SimpleMongoDbFactory(mongo, "db");; } } During Application startup : 2015-03-05 17:52:32 DEBUG c.m.config.MongoLiveConfig – […]
In MongoDB console, you can use field:1 to select the fields to return from a query : > db.hosting.find({},{domain:1, count:1}); In Spring Data for MongoDB, you use query.fields().include : HostingDaoImpl.java package com.mkyong.core.hosting.dao; import java.util.List; import org.springframework.data.domain.Sort; import org.springframework.data.mongodb.core.query.Criteria; import org.springframework.data.mongodb.core.query.Query; import org.springframework.data.mongodb.core.query.Update; import org.springframework.stereotype.Repository; import com.hostingcompass.core.db.dao.MongoDaoImpl; @Repository public class HostingDaoImpl extends MongoDaoImpl<Hosting> implements HostingDao { […]
In Gradle, the WAR plugin will generate the final WAR file with the following pattern: ${baseName}-${appendix}-${version}-${classifier}.${extension} Example : hello.1.0.war To change the default WAR filename, update war.archiveName. For example : build.gradle project(‘:web’) { apply plugin: ‘war’ war { archiveName ‘hello-gradle.war’ } dependencies { compile project(‘:core’) providedCompile ‘javax.servlet:servlet-api:2.5’ providedCompile ‘org.apache.tomcat:tomcat-jsp-api:7.0.55’ //… } } Build it… $ […]
