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 […]
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 […]
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 […]
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; […]
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 […]
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 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’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 […]
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; […]
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 […]
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 […]
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[] […]
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 […]
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 […]
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 […]
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 […]
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 […]
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 […]
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 […]
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 […]
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 […]
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 […]
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 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 […]
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…” […]
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 […]
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, […]
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 […]
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) […]
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 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’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 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> […]
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 […]
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 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 […]
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, […]
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 […]
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 […]
A common Hibernate’s error, this is caused by the missing dependency library – Apache Common Collection. Initial SessionFactory creation failed.java.lang.NoClassDefFoundError: org/apache/commons/collections/SequencedHashMap 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: org/apache/commons/collections/SequencedHashMap at org.hibernate.mapping.Table.<init>(Table.java:33) at org.hibernate.cfg.Mappings.addTable(Mappings.java:165) at org.hibernate.cfg.HbmBinder.bindRootPersistentClassCommonValues(HbmBinder.java:290) at org.hibernate.cfg.HbmBinder.bindRootClass(HbmBinder.java:273) at org.hibernate.cfg.HbmBinder.bindRoot(HbmBinder.java:144) at org.hibernate.cfg.Configuration.add(Configuration.java:669) at org.hibernate.cfg.Configuration.addInputStream(Configuration.java:504) at org.hibernate.cfg.Configuration.addResource(Configuration.java:566) at org.hibernate.cfg.Configuration.parseMappingElement(Configuration.java:1587) at […]
