mkyong

java January 16, 2010 2 min read by mkyong 2 comments

The Java Archive Tool (JAR) Examples

Here’s the project structure. /workspace/test/classes/com/mkyong/awt/AwtExample.class /workspace/test/classes/com/mkyong/awt/AwtExample2.class /workspace/test/classes/com/mkyong/awt/AwtExample3.class /workspace/test/classes/manifest.txt P.S Assume you are in “/workspace/test/classes/“ 1. Create a jar file -c create new archive -v generate verbose output on standard output -f specify archive file name 1.1 Create a Jar file which include AwtExample.class only. jar -cvf test.jar com/mkyong/awt/AwtExample.class 1.2 Create a Jar file which include […]

java January 16, 2010 1 min read by mkyong 1 comment

How to list out all system drives in your system

File.listRoots() will list out all the available file system roots / drives in your current system. Example package com.mkyong.io; import java.io.File; public class App{ public static void main (String args[]) { File[] rootDrive = File.listRoots(); for(File sysDrive : rootDrive){ System.out.println("Drive : " + sysDrive); } } } Output Drive : A:\ Drive : C:\ Drive […]

java best practices January 15, 2010 4 min read by mkyong 35 comments

Java – What is serialVersionUID

In Java, serialVersionUID is something like version control, assure both serialized and deserialized objects are using the compatible class. For example, if an object saved into a file (Serialization) with serialVersionUID=1L, when we convert the file back to an object (Derialization), we must use the same serialVersionUID=1L, otherwise an InvalidClassException is thrown. Terminal Exception in […]

java January 15, 2010 1 min read by mkyong 11 comments

Java – How to generate serialVersionUID

This article shows you a few ways to generate the serialVersionUID for serialization class. 1. serialver JDK has a built-in command serialver to generate a serialVersionUID automatically. In this example, we use serialver to generate a serialVersionUID for an Address class. Terminal $ serialver Address Address: static final long serialVersionUID = -687991492884005033L; 2. Eclispe IDE […]

java January 14, 2010 1 min read by mkyong 3 comments

How to load classes which are not in your classpath

In certain scenario, you may need to load some classes which are not in your classpath. Java Example Assume folder “c:\\other_classes\\” is not in your project classpath, here’s an example to show how to load a Java class from this folder. The code and comments are self-explanatory. import java.io.File; import java.net.URL; import java.net.URLClassLoader; import java.security.CodeSource; […]

java January 14, 2010 1 min read by mkyong 5 comments

How to add a manifest into a Jar file

In Java, you can use manifest file to define application’s entry point, adding classpath or package version for a JAR file. In this short tutorial , we will show you how to add a custom manifest file into a Jar file. 1. Project Structure Assume this is your project folder structure /workspace/test/classes/com/mkyong/awt/AwtExample.class /workspace/test/classes/manifest.txt 2. Jar […]

java best practices January 14, 2010 1 min read by mkyong 3 comments

Constant value should always come first in comparison

Normal practice Constant value comes second in comparison. private static final String COMPARE_VALUE = "VALUE123"; public boolean compareIt(String input){ if(input.equals(COMPARE_VALUE)){ return true; }else{ return false; } } Problem This is fine to compare a constant value with the above method, however it will potentially causing a NullPointerException, if user pass a “null” value for the […]

java January 13, 2010 1 min read by mkyong 3 comments

How to run a Java application with no main method

Java application usually required a main() method as entry point to run it. Here’s an example by using static initializer to run a Java application even without the main() method. P.S The static initializer is called while the Java class is loaded. This is for fun only, do not use this example in real environment […]

java January 13, 2010 1 min read by mkyong 17 comments

How to print out the current project classpath

Java’s “SystemClassLoader” can use to pint out the current project classpath , indirectly display the library dependency as well. Example package com.mkyong.io; import java.net.URL; import java.net.URLClassLoader; public class App{ public static void main (String args[]) { ClassLoader cl = ClassLoader.getSystemClassLoader(); URL[] urls = ((URLClassLoader)cl).getURLs(); for(URL url: urls){ System.out.println(url.getFile()); } } } Output /E:/workspace/HibernateExample/target/test-classes/ /E:/workspace/HibernateExample/target/classes/ /D:/maven/repo/antlr/antlr/2.7.7/antlr-2.7.7.jar […]

java January 13, 2010 1 min read by mkyong 5 comments

How to get the standard input in Java

Note This post is duplicated, please refer to this – 3 ways to read input from console in Java. A quick example to show you how to read the standard input in Java. package com.mkyong.pageview; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class Test { public static void main(String[] args) { BufferedReader br = null; […]

java January 12, 2010 1 min read by mkyong 8 comments

How to assign file content into a variable in Java

Most people will read the file content and assign to StringBuffer or String line by line. Here’s another trick that may interest you – how to assign whole file content into a variable with one Java’s statement, try it 🙂 Example In this example, you will use DataInputStreamto convert all the content into bytes, and […]

java January 12, 2010 1 min read by mkyong 10 comments

How to traverse a directory structure in Java

In this example, the program will traverse the given directory and print out all the directories and files absolute path and name one by one. Example package com.mkyong.io; import java.io.File; public class DisplayDirectoryAndFile{ public static void main (String args[]) { displayIt(new File("C:\\Downloads")); } public static void displayIt(File node){ System.out.println(node.getAbsoluteFile()); if(node.isDirectory()){ String[] subNote = node.list(); for(String […]

java January 12, 2010 1 min read by mkyong 66 comments

How to open a PDF file in Java

In this article, we show you two ways to open a PDF file with Java. 1. rundll32 – Windows Platform Solution In Windows, you can use “rundll32” command to launch a PDF file, see example : package com.mkyong.jdbc; import java.io.File; //Windows solution to view a PDF file public class WindowsPlatformAppPDF { public static void main(String[] […]

java January 11, 2010 1 min read by mkyong 6 comments

How to clear / delete the content of StringBuffer()

The StringBuffer is always been using for the String concatenation. However this class didn’t provide a method to clear the existing content. Why there are no clear() function? You can use the delete(int start, int end) as dirty trick : sb.delete(0, sb.length()); 1 . Example package com.mkyong.io; public class App{ public static void main (String […]

java January 11, 2010 1 min read by mkyong 2 comments

How to convert HTML to Javascript (.js) in Java

For some security reasons, you may need to convert your HTML file into Javascript (js) file, and display the JS file instead of the HTML file directly. The concept is quite simple – using the document.write HTML <h1>Convert HTML to Javascript file</h1> Javascript (js) document.write(‘<h1>Convert HTML to Javascript file</h1>’); 1. Test.html Create a simple HTML […]

java January 10, 2010 2 min read by mkyong 5 comments

How to get file last modified date in Java

In Java, we can use Files.readAttributes() to get the file metadata or attribute, and then lastModifiedTime() to display the last modified date of a file. Path file = Paths.get("/home/mkyong/file.txt"); BasicFileAttributes attr = Files.readAttributes(file, BasicFileAttributes.class); System.out.println("lastModifiedTime: " + attr.lastModifiedTime()); 1. BasicFileAttributes (NIO) This example uses the java.nio.* to display the file attributes or metadata – creation […]

java January 10, 2010 2 min read by mkyong 13 comments

How to get the current working directory in Java

In Java, we can use System.getProperty("user.dir") to get the current working directory, the directory from where your program was launched. String dir = System.getProperty("user.dir"); // directory from where the program was launched // e.g /home/mkyong/projects/core-java/java-io System.out.println(dir); One of the good things about this system property user.dir is we can easily override the system property via […]

java January 10, 2010 4 min read by mkyong 8 comments

How to read an object from file in Java (ObjectInputStream)

This example shows how to use ObjectInputStream to read a serialized object from a file in Java, aka Deserialization. public static Object readObjectFromFile(File file) throws IOException, ClassNotFoundException { Object result = null; try (FileInputStream fis = new FileInputStream(file); ObjectInputStream ois = new ObjectInputStream(fis)) { result = ois.readObject(); } return result; } // Convert byte[] to […]

java January 9, 2010 3 min read by mkyong 13 comments

How to write an object to file in Java (ObjectOutputStream)

This example shows how to use ObjectOutputStream to write objects to a file in Java, aka Serialization. public static void writeObjectToFile(Person obj, File file) throws IOException { try (FileOutputStream fos = new FileOutputStream(file); ObjectOutputStream oos = new ObjectOutputStream(fos)) { oos.writeObject(obj); oos.flush(); } } Note More Java Serialization and Deserialization examples 1. Java object We can […]

java January 9, 2010 1 min read by mkyong 5 comments

How to delete files with certain extension only

In Java, you can implements the FilenameFilter, override the accept(File dir, String name) method, to perform the file filtering function. In this example, we show you how to use FilenameFilter to list out all files that are end with “.txt” extension in folder “c:\\folder“, and then delete it. package com.mkyong.io; import java.io.*; public class FileChecker […]

java January 8, 2010 2 min read by mkyong 18 comments

How to check if a file exists in Java

In Java, we can use Files.exists(path) to test whether a file exists. The path can be a file or a directory. It is better to combine with !Files.isDirectory(path) to ensure the existing file is not a directory. Path path = Paths.get("/home/mkyong/test/test.log"); // file exists and it is not a directory if(Files.exists(path) && !Files.isDirectory(path)) { System.out.println("File […]

applet January 8, 2010 1 min read by mkyong 2 comments

JMF – Unable to handle format: mpeglayer3

Problem You may encounter the following error while using Java media framework (JMF) to play a mp3 file. Unable to handle format: mpeglayer3, 44100.0 Hz, 16-bit, Stereo, LittleEndian, Signed, 16000.0 frame rate, FrameSize=32768 bits Failed to realize: com.sun.media.PlaybackEngine@19ec4ed Error: Unable to realize com.sun.media.PlaybackEngine@19ec4ed server running at port: 4264 Solution This is because Java took out […]

hibernate January 1, 2010 1 min read by mkyong 21 comments

How to display hibernate sql parameter values – Log4j

Problem Hibernate has basic logging feature to display the SQL generated statement with show_sql configuration property. Hibernate: INSERT INTO mkyong.stock_transaction (CHANGE, CLOSE, DATE, OPEN, STOCK_ID, VOLUME) VALUES (?, ?, ?, ?, ?, ?) However , it just isn’t enough for debugging, the Hibernate SQL parameter values are missing. Solution – Log4j Log4J is required to […]

logging December 31, 2009 1 min read by mkyong 70 comments

log4j.properties example

I can’t find many log4j.properties examples, here are a few log4j.properties examples that are used in my project, just for sharing. 1. Output to Console All logging will be redirected to your console. log4j.properties # Root logger option log4j.rootLogger=INFO, stdout # Direct log messages to stdout log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.Target=System.out log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L – %m%n […]

hibernate December 31, 2009 2 min read by mkyong 7 comments

Display Hibernate SQL to console – show_sql , format_sql and use_sql_comments

Hibernate has build-in a function to enable the logging of all the generated SQL statements to the console. You can enable it by add a “show_sql” property in the Hibernate configuration file “hibernate.cfg.xml“. This function is good for basic troubleshooting, and to see what’s Hibernate is doing behind. 1. show_sql Enable the logging of all […]

unix / linux December 30, 2009 1 min read by mkyong 9 comments

How to access Windows shares in Ubuntu

Problem Ubuntu doesn’t has build-in tool for browsing or accessing the Windows share in network. Is there any ways to access the Windows share in Ubuntu? Solution Ubuntu has smb installed by default, you can use smb to access the Windows shares. 1. File Browser Open “Computer – File Browser”, Click on “Go” –> “Location…” […]

hibernate December 30, 2009 5 min read by mkyong 44 comments

Maven 2 + Hibernate 3.2 + MySQL Example (Annotation)

Note This article is outdated, and some information is no longer valid in latest Hibernate development. You should refer to this latest – Maven 3 + Hibernate 3.6.3 + Oracle 11g Example (Annotation) tutorial. This tutorial will modify the previous Maven 2 + Hibernate 3.2 + MySQL Example (XML mapping), and replace the Hibernate XML […]

hibernate December 30, 2009 2 min read by mkyong 27 comments

How to configure logging in Hibernate – SLF4j + Log4j

Try logback Try logback logging framework, read this article for the “reasons to prefer logback over log4j. To integrate logback with Hibernate, refer this – How to configure logging in Hibernate – Logback Hibernate uses Simple Logging Facade for Java (SLF4J) to redirect the logging output to your perfer logging frameworkis (log4j, JCL, JDK logging, […]

hibernate December 29, 2009 1 min read by mkyong 9 comments

Hibernate Error – Exception in thread “main” java.lang.NoClassDefFoundError: antlr/ANTLRException

This is caused by missing of the antlr library. It’s usually happened when you did invoke Hibernate’s query statement. Exception in thread "main" java.lang.NoClassDefFoundError: antlr/ANTLRException at org.hibernate.hql.ast.ASTQueryTranslatorFactory.createQueryTranslator(ASTQueryTranslatorFactory.java:35) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:74) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:56) at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:72) at org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:133) at org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:112) at org.hibernate.impl.SessionImpl.createQuery(SessionImpl.java:1623) at com.mkyong.common.App.main(App.java:23) Caused by: java.lang.ClassNotFoundException: antlr.ANTLRException 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 […]

hibernate December 29, 2009 1 min read by mkyong 4 comments

Hibernate Error – Initial SessionFactory creation failed.java.lang.NoClassDefFoundError: org/hibernate/annotations/common/reflection/ReflectionManager

This is caused by missing of the Hibernate commons annotations library. Initial SessionFactory creation failed.java.lang.NoClassDefFoundError: org/hibernate/annotations/common/reflection/ReflectionManager Exception in thread "main" java.lang.ExceptionInInitializerError at com.mkyong.persistence.HibernateUtil.buildSessionFactory(HibernateUtil.java:19) at com.mkyong.persistence.HibernateUtil.<clinit>(HibernateUtil.java:8) at com.mkyong.common.App.main(App.java:11) Caused by: java.lang.NoClassDefFoundError: org/hibernate/annotations/common/reflection/ReflectionManager at com.mkyong.persistence.HibernateUtil.buildSessionFactory(HibernateUtil.java:13) … 2 more Caused by: java.lang.ClassNotFoundException: org.hibernate.annotations.common.reflection.ReflectionManager 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) […]

hibernate December 28, 2009 2 min read by mkyong 26 comments

Hibernate Error – An AnnotationConfiguration instance is required to use

The Hibernate annotation is required “AnnotationConfiguration” instead of normal “Configuration()” to build the session factory. INFO: Configuration resource: /hibernate.cfg.xml Initial SessionFactory creation failed.org.hibernate.MappingException: An AnnotationConfiguration instance is required to use <mapping class="com.mkyong.common.Stock"/> Exception in thread "main" java.lang.ExceptionInInitializerError at com.mkyong.persistence.HibernateUtil.buildSessionFactory(HibernateUtil.java:19) at com.mkyong.persistence.HibernateUtil.<clinit>(HibernateUtil.java:8) at com.mkyong.common.App.main(App.java:11) Caused by: org.hibernate.MappingException: An AnnotationConfiguration instance is required to use <mapping class="com.mkyong.common.Stock"/> […]

hibernate December 28, 2009 1 min read by mkyong 10 comments

Hibernate SQL Dialects Collection

Hibernate SQL Dialect is telling your Hibernate application which SQL language should be use to talk with your database. 1. DB2 org.hibernate.dialect.DB2Dialect 2. DB2 AS/400 org.hibernate.dialect.DB2400Dialect 3. DB2 OS390 org.hibernate.dialect.DB2390Dialect 4. PostgreSQL org.hibernate.dialect.PostgreSQLDialect 5. MySQL org.hibernate.dialect.MySQLDialect 6. MySQL with InnoDB org.hibernate.dialect.MySQLInnoDBDialect 7. MySQL with MyISAM org.hibernate.dialect.MySQLMyISAMDialect 8. Oracle 8 org.hibernate.dialect.OracleDialect 9. Oracle 9i/10g org.hibernate.dialect.Oracle9Dialect 10. […]

hibernate December 26, 2009 1 min read by mkyong 3 comments

Hibernate Error – Initial SessionFactory creation failed.java.lang.NoClassDefFoundError: com/mchange/v2/c3p0/DataSources

Hibernate’s “C3P0” connection pool error, this is caused by the missing dependency library – C3P0. Initial SessionFactory creation failed.java.lang.NoClassDefFoundError: com/mchange/v2/c3p0/DataSources Exception in thread "main" java.lang.ExceptionInInitializerError at com.mkyong.persistence.HibernateUtil.buildSessionFactory(HibernateUtil.java:19) at com.mkyong.persistence.HibernateUtil.<clinit>(HibernateUtil.java:8) at com.mkyong.common.App.main(App.java:11) Caused by: java.lang.NoClassDefFoundError: com/mchange/v2/c3p0/DataSources at org.hibernate.connection.C3P0ConnectionProvider.configure(C3P0ConnectionProvider.java:154) at org.hibernate.connection.ConnectionProviderFactory.newConnectionProvider(ConnectionProviderFactory.java:124) at org.hibernate.connection.ConnectionProviderFactory.newConnectionProvider(ConnectionProviderFactory.java:56) at org.hibernate.cfg.SettingsFactory.createConnectionProvider(SettingsFactory.java:410) at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:62) at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:2009) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1292) at com.mkyong.persistence.HibernateUtil.buildSessionFactory(HibernateUtil.java:13) … 2 more Caused […]

hibernate December 25, 2009 2 min read by mkyong 5 comments

How to add Hibernate XML mapping file (hbm.xml) programmatically

Hibernate XML mapping file contains the mapping relationship between Java class and database table. This is always named as “xx.hbm.xml” and declared in the Hibernate configuration file “hibernate.cfg.xml”. For example, the mapping file (hbm.xml) is declared in the “mapping” tag <?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <property name="hibernate.bytecode.use_reflection_optimizer">false</property> […]

java December 24, 2009 6 min read by mkyong 14 comments

Java – How to get current date time

In this tutorial, we will show you how to get the current date time from the new Java 8 java.time.* like Localdate, LocalTime, LocalDateTime, ZonedDateTime, Instant and also the legacy date time APIs like Date and Calendar. Table of contents 1. Get current date time in Java 2. java.time.LocalDate 3. java.time.LocalTime 4. java.time.LocalDateTime 5. java.time.ZonedDateTime […]

hibernate December 24, 2009 2 min read by mkyong 16 comments

How to configure the C3P0 connection pool in Hibernate

Connection Pool Connection pool is good for performance, as it prevents Java application create a connection each time when interact with database and minimizes the cost of opening and closing connections. See wiki connection pool explanation Hibernate comes with internal connection pool, but not suitable for production use. In this tutorial, we show you how […]

hibernate December 23, 2009 1 min read by mkyong 20 comments

How to load hibernate.cfg.xml from different directory

Hibernate XML configuration file “hibernate.cfg.xml” is always put at the root of your project classpath, outside of any package. If you place this configuration file into a different directory, you may encounter the following error : Initial SessionFactory creation failed.org.hibernate.HibernateException: /hibernate.cfg.xml not found Exception in thread "main" java.lang.ExceptionInInitializerError at com.mkyong.persistence.HibernateUtil.buildSessionFactory(HibernateUtil.java:25) at com.mkyong.persistence.HibernateUtil.<clinit>(HibernateUtil.java:8) at com.mkyong.common.App.main(App.java:11) Caused […]

java December 21, 2009 5 min read by mkyong 5 comments

How to read XML file in Java – (JDOM Parser)

JDOM is open-source Java-based XML parser framework built on top of DOM and SAX, also a document object model(DOM) in-memory representation of an XML document. JDOM makes navigating XML documents easier by providing more straightforward APIs and a standard Java-based collection interface. If you don’t mind downloading a small library to parse an XML file, […]

java December 20, 2009 3 min read by mkyong 4 comments

How to convert InputStream to File in Java

Below are some Java examples of converting InputStream to a File. Plain Java – FileOutputStream Apache Commons IO – FileUtils.copyInputStreamToFile Java 7 – Files.copy Java 9 – InputStream.transferTo 1. Plain Java – FileOutputStream This example downloads the google.com HTML page and returns it as an InputStream. And we use FileOutputStream to copy the InputStream into […]

hibernate December 19, 2009 1 min read by mkyong 2 comments

Hibernate Error – Initial SessionFactory creation failed.java.lang.NoClassDefFoundError: net/sf/cglib/proxy/CallbackFilter

A common Hibernate’s error, this is caused by the missing dependency library – cglib. Initial SessionFactory creation failed.java.lang.NoClassDefFoundError: net/sf/cglib/proxy/CallbackFilter Exception in thread "main" java.lang.ExceptionInInitializerError at com.mkyong.persistence.HibernateUtil.buildSessionFactory(HibernateUtil.java:18) at com.mkyong.persistence.HibernateUtil.<clinit>(HibernateUtil.java:8) at com.mkyong.common.App.main(App.java:17) Caused by: java.lang.NoClassDefFoundError: net/sf/cglib/proxy/CallbackFilter at org.hibernate.bytecode.cglib.BytecodeProviderImpl.getProxyFactoryFactory(BytecodeProviderImpl.java:33) at org.hibernate.tuple.entity.PojoEntityTuplizer.buildProxyFactoryInternal(PojoEntityTuplizer.java:182) at org.hibernate.tuple.entity.PojoEntityTuplizer.buildProxyFactory(PojoEntityTuplizer.java:160) at org.hibernate.tuple.entity.AbstractEntityTuplizer.<init>(AbstractEntityTuplizer.java:135) at org.hibernate.tuple.entity.PojoEntityTuplizer.<init>(PojoEntityTuplizer.java:55) at org.hibernate.tuple.entity.EntityEntityModeToTuplizerMapping.<init>(EntityEntityModeToTuplizerMapping.java:56) at org.hibernate.tuple.entity.EntityMetamodel.<init>(EntityMetamodel.java:295) at org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:434) at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:109) at org.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:55) at […]

Posts by mkyong