Tech Trek: A Software Engineer's Guide to Code and Beyond

What is Liquibase ?

1. Liquibase is an open source database-independent library for tracking, managing and applying database changes.
2. All changes to the database are stored in XML files and identified by a combination of an "id" and "author" tag as well as the name of the file itself.
3. A list of all applied changes is stored in each database which is consulted on all database updates to determine what new changes need to be applied.
4. Liquibase executes changes based on this XML file to handle different revisions of database structures and data.
5. When you first run a changelog, LiquiBase manages those changelogs by adding two tables into your database.
databasechangelog: maintains the database changes that were run.
databasechangeloglock: ensures that two machines don't attempt to modify the database at one time.
6. Limitations do exist such that it will not export triggers, stored procedures, functions and packages.

Sample changeLog file:

The above is an example of creating table EMPLOYEE and adding columns into it.

<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-2.0.xsd">

    <changeSet author="waheed" id="123456789-1">
       <createTable tableName="EMPLOYEE">
           <column autoIncrement="true" name="EMPLOYEE_ID" type="BIGINT">
               <constraints nullable="false" primaryKey="true" />
           </column>
           <column name="NAME" type="VARCHAR(255)" />
           <column name="GENDER" type="VARCHAR(2)" />
           <column name="COUNTRY" type="VARCHAR(255)" />
           <column name="ABOUT_YOU" type="VARCHAR(255)" />
       </createTable>
    </changeSet>
</databaseChangeLog>

How to integrate Liquibase with Spring and Hibernate ?

A sample tutorial on how to integrate Liquibase with Spring and Hibernate.

While writing this tutorial, I have added javadoc in the code for better understanding and I believe You already have good knowledge on Spring and Hibernate. The main motto of this tutorial is to give an idea on how you can integrate Liquibase with Spring and Hibernate.

If you are new to Liquibase : Click Here

To integrate liquibase into your project, you need liquibase jars, So download it before starting the project.

I have created an application named "SHLIntegration". The Structure of the project is as follows :

The dependencies are also listed here:

Lets start with Employee class :

1. Create Employee class having getter/setter and add proper JPA annotation to each variable as below.

public class Employee {

    @Id
    @GeneratedValue
    @Column(name="EMPLOYEE_ID")
    private long id;

    @Column(name="NAME")
    private String name;

    @Column(name="GENDER")
    private String gender;

    @Column(name="COUNTRY")
    private String country;

    @Column(name="ABOUT_YOU")
    private String aboutYou;
.....
....
.... // getter setter of each object

}

2. Create liquibase file i,e db-changelog.xml file

<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-2.0.xsd">

    <changeSet author="waheed" id="123456789-1">
        <createTable tableName="EMPLOYEE">
            <column autoIncrement="true" name="EMPLOYEE_ID" type="BIGINT">
                <constraints nullable="false" primaryKey="true" />
            </column>
            <column name="NAME" type="VARCHAR(255)" />
            <column name="GENDER" type="VARCHAR(2)" />
            <column name="COUNTRY" type="VARCHAR(255)" />
            <column name="ABOUT_YOU" type="VARCHAR(255)" />
        </createTable>
    </changeSet>
</databaseChangeLog>

3. Add liquibase bean in your bean :

    <bean id="LiquibaseUpdater" class="liquibase.integration.spring.SpringLiquibase">
        <property name="dataSource" ref="dataSource" />
        <property name="changeLog" value="classpath:db-changelog.xml" />
    </bean>

and others beans which are required for Spring/Hibernate. Check bean file

The complete tutorial :
https://github.com/abdulwaheed18/SHLIntegration

Please feel free to do comment or drop me a mail regarding any suggestion/Feedback.
Email : waheedtechblog@gmail.com

Some ANT task

1. How to build project from another build.

<target name="project2"
            description="Builds project2 project, required depedency">
        

        <subant target="dist" verbose="yes" inheritall="false">
            <filelist dir="../com.waheed.project2"
                      files="build.xml" />
        </subant>
    </target>

2. How to read SVN revision and write into some file

<loadfile property="revision" srcFile="./.svn/entries">
       <filterchain>
            <headfilter skip="3" lines="1"/>
                 </filterchain>
        </loadfile>
            <tstamp>
               <format property="date" pattern="dd/MM/yyyy hh:mm:ss" />
            </tstamp>
           <echo append="true" file="<FILE_NAME>" >revision=${revision}${line.separator}</echo>

3. How to generate Keystore

4. How to get current time

<target name="time">
        <tstamp>
            <format property="build-time" pattern="yyyy-MM-dd-HH-mm" />
        </tstamp>
        <echo>${build-start-time}</echo>
    </target>

5 . How to create jar with manifest

6. How to compile source



        <javac destdir="bin" debug="true">
            <src path="src" />
            <classpath>
                <pathelement location="../dependency/bin" />
                <fileset dir="../lib">
                    <include name="*.jar" />
                </fileset>
            </classpath>
        </javac>

7. How to compile source with dependency class path

8. How to build Zip file

9. How to build tar file

10 . How to check OS

11. How to set permission to file

12 .How to read property file

Suppose I have following data in my filename1.properties file and want to read it and write it to another file lets say name filename2.properties.

filename1.properties

REVISION 777

<property file="${dist}/filename1.properties" prefix="version"/>
<echo file="${dist}/filename2.properties" append="true">revision ${version.REVISION}${line.separator}</echo>