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Use Multiple JVM versions on Mac OS and Linux

Linux Download multiple Java versions and put them into /opt/ If you already have some JDK from ubuntu repo or etc not a big deal, just fix the paths bellow Register them as alternatives sudo update-alternatives --install /usr/bin/java java /opt/java-8-oracle/bin/java 1081 sudo update-alternatives --install /usr/bin/java java /opt/sap-machine-jdk-11.0.3/bin/java 1080 Edit your ~/.bashrc file alias java11='sudo update-alternatives --set java /opt/sapmachine-jdk-11.0.3/bin/java;export JAVA_HOME=/opt/sapmachine-jdk-11.0.3/' alias java8='sudo update-alternatives --set java /opt/java-8-oracle/bin/java;export JAVA_HOME=/usr/lib/java-8-oracle/' SAVE and start a new bash terminal execute java8 to use java8 java11 to use java11 the latest version you have set stays as system wide, but the JAVA_HOME is not :( you can put java8 or java11 as a last line in the bashrc but since it is sudo it will always require password when start and is not gr...
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Hibernate Generic DAO.

When you use Hibernate and DAO pattern it is a good idea to use a Generic Base Dao. The fallowing code snippet contains GenericDAO that is a base class for all my DAO classes. This GenericDAO uses HibernateDaoSupport from Spring for its implementation if you want you can use JpaDaoSupport or JdbcDaoSupport in your projects. My Generic DAO interface looks like this : package org.joke.myproject.dao.base; import java.io.Serializable; import java.util.List; /** * @author Naiden Gochev * @param <E> * @param <PK> */ public interface GenericDao<E,PK  extends Serializable> {     PK save(E newInstance);     void update(E transientObject);     void saveOrUpdate(E transientObject);     void delete(E persistentObject);     E findById(PK id);     List<E> findAll();     List<E> f...
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Patching a Maven library with your custom class.

Sometimes you use a library that has a bug. Or maybe it doesn’t has a bug but you want to change something. Of course if it is an open source you can get the sources… build them … with your change and so on. However this first takes a lot of time and second you need the sources. What you usually want .. is to just replace one class.. or few classes with something custom… maybe add a line .. or remove a line and so on. Yesterday… I had an issue with jboss-logging. The version I was using was 3.2.0Beta1 and it turns out that using this version and log4j2 2.0 final basically meant that no log is send to log4j2. The reason was a null pointer exception that was catched in jboss logging class called Log4j2Logger. The bug I submitted is here https://issues.jboss.org/browse/JBLOGGING-107 and it was fixed at the same day. However I will use it as an example since I didn’t knew when this will be fixed.. and I didn’t want to wait till it is fixed. So I was thinking what I want.. to take the j...
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