Armin Widegreen

Bash script template with parameter evaluation

Armin Widegreen — Mon, 14 Nov 2011 22:59:53 +0000

just a handy bash script template:

#!/bin/bash

scriptname="script_template"

### functions
function usage
{
echo -e "usage: $scriptname MANDATORY [OPTION]\n"
echo -e "MANDATORY mandatory parameter:"
echo -e " -m, --mandatory VAL The desc of the mandatory parameter\n"
echo -e "OPTION optional parameter:\n"
echo -e " -h, --help Prints this help"
echo -e " -o1, --optional1 The optional1 parameter"
echo -e " -o2, --optional2 VAL The optional2 parameter\n"
echo -e "EXAMPLE:"
echo -e " $scriptname -m mandatory -o1 opt1"
}

# more...
#####

### Main

if [ $# == 0 ]; then
echo "Called with no parameter!"
usage
exit 1
fi

mand=
opt1="false" # or use 1 and 0, with default 0
opt2="defaultValue"

# parameter while-loop
while [ "$1" != "" ];
do
case $1 in
-m | --mandatory ) shift
mand=$1
;;
-o1 | --optional1 ) opt1="true"
;;
-o2 | --optional2 ) shift
opt2=$1
;;
-h | --help ) usage
exit
;;
*) usage
echo "The parameter $1 is not allowed"
exit 1 # error
;;
esac
shift
done

if [ "$mand" == "" ]; then
echo "mandatroy parameter is missing"
usage

exit 1 # error
fi

echo "params: $mand, $opt1, $opt2"
#####

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Comparing JPQL, Criteria string-based and typesafe queries

Armin Widegreen — Fri, 07 May 2010 22:13:16 +0000

The last two evenings I stucked in searching for more or less complex examples of different JPA 2 queries. By complex I mean, constructing constructor queries with multiple joins, group by and an average function (avg). The JPQL solution (using a normal query defined as string) wasn't to hard to find, compared to the Criteria API version (introduced in the JPA 2 specification).

In the following article I'm going to describe three semantically identical queries using:

JPQL query
Criteria API string based Query
Criteria API dynamic, typesafe Query (using a canonical Metamodel)

I don't want to go to much in details by explaining Criteria API here, because there are obviously enough resources on the net (see references). To construct a complex query, I use three Entity Beans: Car, CarModel, CarManufacturer. The dependencies between the classes are straightforward: a car has a reference to a model and the model refer to a car manufacturer. The car also has a property mileage (Double), consider a used car. Furthermore, both, car model and manufacturer, also have a name property (String). Here is the graphical representation of this class structure.

All subsequent queries correspond to the following SQL-Statement:

SELECT cmf.name, AVG(c.mileage)
FROM Car c
INNER JOIN CarModel cm
ON c.carModel = cm.uuid
INNER JOIN CarManufacturer cmf
ON cm.manufacturer = cmf.uuid
GROUP BY cmf.name

meaning: Get all car manufacturer name and the belonging average mileage for all cars of the manufacturer.

Before getting started with the interesting stuff, I must introduce an additional class that is essential for this examples. The problem is, if you want to compound your Query result, you have to construct a value object class like CompoudElement I use. It is important that you have a constructor that explicitly matches your Query Selection-clause. So, I want to receive a String (name) and a Double (avg value) for my query, so the class looks something like this:

public class CompoundElement {
private String name;
private Double dValue;

public CompoundElement(String name, Double value) {
this.name = name;
this.dValue = value;
}

/* needed for Criteria query */
public CompoundElement(String name, Object num) {
this.name = name;
this.dbValue = (Double)num;
}

/* getter an setter */
}

The JPQL query isn't so far away from the SQL one. This query is also called constructor query, because of the previous mentioned CompoundElement class you need.

public class SomeClassJPQL {
@PersistenceContext
private EntityManager em;

public List<CompoundElement> findAvgMileageForManufacturer() {
Query query = em.createQuery(
"SELECT NEW aw.queries.api.vo.CompoundElement(cmfJoin.name, AVG(c.mileage)) " +
"FROM Car c " +
"JOIN c.carModel cm " +
"JOIN cm.manufacturer cmfJoin " +
"GROUP BY cmfJoin.name"
);

return (List<CompoundElement>)query.getResultList();
}
}

While the query is executed, the JPA creates a List of CompoundElements, adds a new CompoundElement for every result tuple and returns the constructed result list (see getResultList).

Now lets view the Criteria API code for that string based query. In contrast to the JPQL code, the query here uses the

CompoundElement(String, Object)

constructor. So we have to cast the Object to Double inside the constructor (see CompoundElement definition).

public class SomeClassStrings {
@PersistenceContext
private EntityManager em;

public List<CompoundElement> findAvgMileageForManufacturer() {
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<CompoundElement> q = cb.createQuery(CompoundElement.class);

Root<Car> c = q.from(Car.class);
Join<Car, CarModel> cmJoin = c.join("carModel");
Join<CarModel, CarManufacturer> cmfJoin = cmJoin.join("manufacturer");

Expression<Double> mileage = c.get("mileage");

CompoundSelection<CompoundElement> cSelect = cb.construct(CompoundElement.class, cmfJoin.get("name"), cb.avg(mileage));
q.select(cSelect);
Expression<String> manuName = cmfJoin.get("name");
q.groupBy(manuName);

TypedQuery<CompoundElement> query = em.createQuery(q);

return (List<CompoundElement>)query.getResultList();
}
}

The last example uses the Criteria API typesafe query based on a metamodel which you have to define [JavaEE6Tut]. This is obviously a very annoying task, thats why eclipseLink provides you a metamodel generator [genCanonicalModel]. I had some strange experiences with this generation process using maven and NetBeans 6.8.

Using the standard canonical classes definition results in: Car_, CarModel_ and CarManufacturer_. The query for the typesafe version looks like this:

public class SomeClassDynamic {
@PersistenceContext
private EntityManager em;

public List<CompoundElement> findAvgMileageForManufacturer() {
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<CompoundElement> q = cb.createQuery(CompoundElement.class);

Root<Car> c = q.from(Car.class);
Join<Car, CarModel> cmJoin = c.join(Car_.carModel);
Join<CarModel, CarManufacturer> cmfJoin = cmJoin.join(CarModel_.manufacturer);

CompoundSelection<CompoundElement> cSelect =
cb.construct(CompoundElement.class, cmfJoin.get(CarManufacturer_.name), cb.avg(c.get(Car_.mileage)));
q.select(cSelect);
q.groupBy(cmfJoin.get(CarManufacturer_.name));

TypedQuery<CompoundElement> query = em.createQuery(q);

return (List<CompoundElement>)query.getResultList();
}
}

References:

[1] IBM developer works - Dynamic, typesafe queries in JPA 2.0
[2] Oracle (Sun) - The Java EE 6 Tutorial Part I
[3] In Relation to ... - A typesafe criteria query API for JPA
[4] The little island of excitement - Generating JPA 2.0 Criteria canonical metamodels ...
[5] Sirius ICT - A Look at JPA 2.0 Criteria API

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Short node on (B)Lobs in Entity Beans

Armin Widegreen — Mon, 03 May 2010 21:08:33 +0000

Have you ever thought about storing files in an Entity-Table, using the JPA? Well here is the solution:

@Entity
@Table(name = "histories")
@NamedQueries({
@NamedQuery(name = History.FIND_ALL, query = "SELECT his FROM History his")
})
public class History extends EntityBase {
public static final String FIND_ALL = "findAllHistories";
@Temporal(TemporalType.TIMESTAMP)
@Column(name="import_date")
private Calendar importDate;
...
/* BEGIN here */
@Column(name="excel_file", length=20000000, columnDefinition="longblob")
@Lob
private byte[] excelFile;
/* END here */
}

As usual the name in the Column annotation specifies the corresponding Column-name in the destination table. The length property specifies the length of the Column. Actually, this is important, because the default length, provided by the JPA, is 4096, I think. Obviously, the columnDefinition defines the datatype, which should be created from the JPA. At least add the @Lob annotation.

The resulting column in the database table should look smth like:

name: excel_file
nulls allowed: no
data type: LONGVARBINARY
column size: 2147483647
...

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A paper made tux

Armin Widegreen — Sun, 10 Jan 2010 19:29:34 +0000

Actually, I really have to learn for my exam ... but then I found this:

But I think 15 minutes are indeed very optimistic - I took an hour or so. Here is my result of tux:

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Happy New Year 2010!

Armin Widegreen — Sun, 03 Jan 2010 13:03:06 +0000

Binz / Rügen - 01.01.2010:

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Winter impressions from Rügen

Armin Widegreen — Sun, 20 Dec 2009 17:10:41 +0000

20th Dec. 2009: Garz/Rügen, -12°C and Snow - so I went out and took some photos (Glewitz and Puddemin):

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executebin-servicemenu-kde

Armin Widegreen — Thu, 26 Nov 2009 17:25:57 +0000

The executebin-servicemenu-kde is an KDE service menu for setting a file (e.g. the google-earth install file *.bin) as executable (chmod +x) and executing the file from your favorite filesystem-browser (e.g. Dolphin).

I've published the service menu on kde-apps.org: http://kde-apps.org/content/show.php?content=116129

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PathFinder on OpenDesktop.org

Armin Widegreen — Tue, 24 Nov 2009 22:20:57 +0000

We also published PathFinder on OpenDesktop.org: http://opendesktop.org/content/show.php/PathFinder?content=115719

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PathFinder goes SourceForge

Armin Widegreen — Wed, 18 Nov 2009 16:32:56 +0000

Today, we hosted our project PathFinder on SourceForge.net. So, if you're interested, visit the project homepage: https://sourceforge.net/projects/jpathfinder/.

Feel free to contribute some comments or enhancements here or on the projectpage.

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A fuzzyclock for the bash (german)

Armin Widegreen — Wed, 11 Nov 2009 22:11:42 +0000

Last weekend I've got some time to do some funny stuff. A friend of mine asked me if I know a script which displays a fuzzyclock in the bash. To refresh my bash skills, I took the time and "hacked" (a bit dirty) this for him. The script displays the current time as written german words ... see the following screenshot:
If you are interested, here is the script: fuzzyclock_v0.1.tar.gz
For feedback or improvements, please leave a comment.

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