Older Newer

Create an XSD from XML using Trang

13 Oct 2012

I recently needed to create an XML Schema XSD file from an existing XML file. A short research pointed me to Trang. Description from their website:

Trang, a program for converting between different schema languages, focused on RELAX NG; in particular, it can convert between the compact and XML syntaxes, it can convert between RELAX NG and DTDs, and it can convert from RELAX NG to W3C XML Schema

But beside the convertion between different schema languages, Trang is also able to create schemas based on XML files.

The creation of an XSD is done as follows for UTF-8 encoding using a JRE 1.5 or above:

 
java -jar trang.jar -i encoding=UTF-8 message.xml message.xsd

Or, with explicit input and output format if the former command does not work as expected:

java -jar trang.jar -I xml -O xsd -i encoding=UTF-8 message.xml message.xsd

Easy.

Original post: http://peter-on-java.blogspot.com/2012/10/create-xsd-from-xml-using-trang.html

Tags xml

Short novice guide for importing a project to Subversion

28 Aug 2012

My new employer uses Subversion as the central version control system, so I'm trying to take the first steps as my former employer still used the good old CVS. (This also means that you don't find advanced infos here but only novice infos.)

So, how to import an existing project to Subversion? I don't mind loosing the history of the project, of course this makes the whole migration process a lot easier.

1. Create a Subversion repository

First, a central Subversion repository has to be created if it does not exist already:

 
$ svnadmin create /svn/repos

2. Import an existing project to the trunk

So, let's import the project directory myproject to Subversion. I already learned that the recommended structure should be as follows:

 
myproject/
 trunk/
 tags/
 branches/

As in a non-Subversion project, the trunk, tags and branches directories usually do not exist yet, they have to be created first. The import sequence for the project directory myproject becomes as follows:

 
$ cd <parent directory of the project directory myproject>
$ mkdir myproject_svn myproject_svn/tags myproject_svn/branches
$ mv myproject myproject_svn/trunk
$ svn import myproject_svn file:///svn/repos/myproject

As the Subversion repository is locally visible, I use the file:// schema.

Don't forget to add myproject to the last command or all files in svn_myproject will be imported directly into the root directory of the repository.

You cannot work directly with the created myproject_svn directory above, you first have to checkout it again:

 
$ svn checkout file:///svn/repos/myproject/trunk -d myproject

3. Create a branch

Creating a branch is just a Subversion copy:

 
$ cd myproject
$ svn copy trunk/ branches/myproject-branch
$ svn status
A + branches/myproject-branch

Here, the trunk/ directory is copied recursively in the working directory brances/myproject-branch. The output of the command svn status indicates that the directory is ready to be added to the repository. The + says that branches/myproject-branch is just a copy and nothing new.

When commiting, Subversion creates the directory in the repository:

 
$ svn commit -m"creating new branch"
Adding     branches/myproject-branch
Committed revision 987.

Subversion does not really copy all files, but just creates a new repository entry pointing to the original tree, so this is also called a “cheap copy”. Please refer to the Subversion documentation for more detailed infos.

The one step method without the need of a temporary directory is as follows:

 
$ svn copy file:///svn/repos/myproject-trunk \
 file:///svn/repos/myproject/branches/myproject-branch \
 -m"creating new branch"

Original post: http://peter-on-java.blogspot.com/2012/08/short-novice-guide-for-importing.html

Tags vcs

How to set up Eclipse template for inserting Log4j Logger

18 Jun 2012

Tired adding private static final Logger logger = Logger.getLogger(XXX.class); by hand to your Java classes?

Use Eclipse templates instead. Navigate to Windows -> Preferences -> Java -> Editor -> Templates. And add following new template to the Java context:

 
private static final Logger logger = Logger.getLogger(${enclosing_type}.class);
${:import(org.apache.log4j.Logger)}

Finally, this should look as follows:

Now, if you are in the Java context, then type "logger" followed by "Ctrl+space". You are invited to choose from different templates including your template entered above:

After choosing the template, you ending up with an added logger plus the corresponding Java import:

Original post: http://peter-on-java.blogspot.com/2012/06/eclipse-template-for-inserting-log4j.html

Tags ide

Reading and Writing UTC Timestamps to DB with Hibernate

22 Apr 2012

Reading and writing UTC timestamps to a database when the default timezone may change. E.g., this might happen in an application server if an application running in the same JRE changes the default timezone as follows:

 
TimeZone.setDefault(TimeZone.getTimeZone("Europe/Zurich"));

The easiest solution to solve this problem I know is to create an own mapping type extending the standard Hibernate timestamp type org.hibernate.type.TimestampType:

 
package ch.meteoswiss.commons.hibernate;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;
import java.util.Calendar;
import java.util.SimpleTimeZone;

/**
 * <tt>Timestamp</tt>: A type that maps an SQL TIMESTAMP to a Java
 * java.util.Date or java.sql.Timestamp using UTC time zone.
 */
public class UTCTimestampType extends org.hibernate.type.TimestampType {
     
    @Override
    public Object get(ResultSet rs, String name) throws SQLException {
        return rs.getTimestamp(name, createUTCCalendar());
    } 

   /**
    * Creates UTC calendar. DO NOT USE a static calendar instance.
    * This may lead to concurrency problems with (at least) the Oracle DB
    * driver!
    * @return Calendar with UTC time zone.
    */
    private static Calendar createUTCCalendar() {
        final Calendar c = Calendar.getInstance();
        c.setTimeZone(new SimpleTimeZone(0, "UTC"));
        return c;
    }

    @Override
    public void set(PreparedStatement st, Object value, int index) 
        throws SQLException {
            
        Timestamp ts;
        if (value instanceof Timestamp) {
            ts = (Timestamp) value;
        } else {
            ts = new Timestamp(((java.util.Date)value).getTime());
        }
        st.setTimestamp(index, ts, createUTCCalendar());
    }

}

Use it as follows with Java annotations (you could use the type class also in a XML configuration file):

 
import java.util.Date;

import org.hibernate.annotations.Type;
@Entity
@Table(name="...")
public class Data {
   
    private Date receptionTimeDt;

    @Type(type="ch.meteoswiss.commons.hibernate.UTCTimestampType")
    @Column(name="RECEPTION_TIME_DT", nullable=false)
    public Date getReceptionTimeDt() {
            return receptionTimeDt;
    }
}

Of course, this mapping class only works with Hibernate and is not standard JPA.

Original post: http://peter-on-java.blogspot.com/2012/04/reading-and-writing-utc-timestamps-to.html

Tags orm

Hibernate returning NULL entities?

10 Apr 2012

Ever got NULL entity entries from Hibernate? I did.

Having a table V_MEAS_SITE with following attributes:

 
MEAS_SITE_ID:     NUMBER(8
INSTALLATION_ID   NUMBER(8
NAME_TX           VARCHAR2(10
...

The V_ in the table name indicates that this is a Oracle view and not a table. This name follows our naming conventions. As the name of the view indicates, the view is holding all information about measurement sites (I actually work for the national weather service). This table is mapped to the following Java class:

 
@Entity(table="V_MEAS_SITE")
public class MeasurementSite {

    @Id
    @Column(name="MEAS_SITE_ID")
    private int measurementSiteId;
    
    @Column(name="INSTALLATION_ID")
    private int installationId;

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

    // getter/setter are ommited for brevit
    
    @Overrid
    public int hashCode() { 
        final int prime = 31;
        int result = 1;
        return = prime * result + ((getMeasurementSiteId() == null) ? 0 : getMeasurementSiteId().hashCode());
    }

    @Overrid
    public boolean equals(Object obj) { 
        if (this == obj) { 
            return true;
        }
        if (obj == null) { 
            return false;
        }
        if (!(obj instanceof MeasurementSite)) { 
            return false;
        }
        MeasurementSite other = (MeasurementSite)obj;
        if (installationId == null) {
            if (other.getInstallationId() != null) { 
                return false;
            }
        } else if (!getMeasurementSiteId().equals(other.getMeasurementSiteId())) { 
            return false;
        }
        return true;
    }
}

Let's write an EJB session bean reading some data:

 
@Session
public class MeasurementSiteService implements MeasurementSiteLocal {

    @PersistenceContext(unitName="DefaultEntityManager")
    private EntityManager em;

    public List<MeasurementSite> findByName(String name) {
        String sql = "select m from MeasurementSite where m.name like :name";
        return em.createQuery(sql)
            .setParameter("name", name)
            .list();
    }

    // used for testing
    public void setEntityManager(EntityManager em) { 
        this.em = em;
    }

}

That's easy. OK, let's test this mapping with a JUnit test class:

 
public class MeasurementSiteServiceTest {

    private EntityManager em = ....; // set up the entity manager  

    @Test
    public void findByName() 
         MeasurementSiteService s = new MeasurementSiteService();
         s.setEntityManager(em);
         List<MeasurementSite> list = s.findByName("Z%");
         for (MeasurementSite m: list) {
             Assert.notNull(m);
         }
    }
}

However, this test fails. There are indeed some NULL entity entries in the list. Hibernate must be broken! Of course, Hibernate is not broken. Do you see what went wrong?

I did after some time of debugging. The view catches content of different tables and is therefore de-normalized. The primary key of the V_MEAS_SITE view is not MEAS_SITE_ID but INSTALLATION_ID!

As a view has no explicit contraints there is no primary key constraint neither and therefore you have no explicit indications about the "logic" in the data. In this case it means that there are more than one entry for a given measurement site ID. And that's why Hibernate returned the NULL values.

Of course it would be nice, if Hibernate had thrown some Exceptions to help a careless Java developer...

By the way, Oracle DB allows to query the DLL statement:

 
select dbms_metadata.get_ddl('VIEW', 'V_MEAS_SITE') as dll from dua

Original post: http://peter-on-java.blogspot.com/2012/04/hibernate-returning-null-entities.html

Tags orm

Older Newer