Feeds

Groovy: XML without the bloat

Flexible strings

Internet Security Threat Report 2014

Groovy also includes a very handy feature for handling tree structures: builders. In the same way that Groovy has excellent built-in support for collections - lists and maps - it also comes with support for trees. Builders are perfect for all kinds of tree structures, from HTML to GUI elements to XML.

For a real-world example let’s say we have a nested structure that we want to export to XML. It could be the results of a query to a MySQL database, the data from a class hierarchy or some other source. In our example the data relates to a simple personnel database, with a record for each person. We store this as follows:

pers=["john":[surname:"smith",age:37,gender:'m',children:2],
      "jill":[surname:"jones",age:28,gender:'f',children:0]
      ]

Before we dive into the builder, let’s remind ourselves of what we can do with Groovy’s iterators and closures:

pers.each {name, data ->
  println name + ' ' + data['surname'] + ' is ' + data['age'] + ' years old'
}

That single line of code iterates through each person’s record, mapping the key value to the name variable, and the map of data to the variable we’ve cleverly labeled data. We can then address the contents of the data map directly by name. Running that line of code gives the following on the command line:

john smith is 37 years old
jill jones is 28 years old

We’re going to do something similar using a groovy.xml.MarkupBuilder object, as shown below:

s_xml=new StringWriter()
builder=new groovy.xml.MarkupBuilder(s_xml)
people=builder.people{
  pers.each{ name, data ->
    person(first_name:name, surname:data['surname']){
      age(data['age']){}
      gender(data['gender']){}
      children('count':data['children']){}
    }
  }
}

println s_xml

This clever little bit of code creates a builder object that writes its data to the StringWriter variable called s_xml. The builder uses a closure that contains our data source called pers, which uses the "each" iterator as in the previous example. The magic is in the pers.each closure. Here we use a set of pseudo-methods called person, age, gender and children. These are all turned into XML elements, and the arguments to these pseudo-methods are the values of the elements. If we run the above code we can see the results clearly enough:

<people>
  <person first_name='john' surname='smith'>
    <age>37</age>
    <gender>m</gender>
    <children count='2' />
  </person>
  <person first_name='jill' surname='jones'>
    <age>28</age>
    <gender>f</gender>
    <children count='0' />
  </person>
</people>

No wonder the language is called Groovy! We can even spool that out to file in a few lines of code as well:

str=s_xml.toString()
def fw= new FileWriter('pers.xml')
'<?xml version="1.0"?>\n'.each{fw.write(it)}
s_xml.toString().each{fw.write(it)}
fw.close()

Anyone who’s ever had to write code to get complex, hierarchical data out into XML will recognize that this is a very easy and natural way to go about navigating through the data and organizing it into the required format.

In second part of this series, I shall turn to the other side of this programming equation - reading in XML and querying or transforming it.®

Internet Security Threat Report 2014

More from The Register

next story
New 'Cosmos' browser surfs the net by TXT alone
No data plan? No WiFi? No worries ... except sluggish download speed
iOS 8 release: WebGL now runs everywhere. Hurrah for 3D graphics!
HTML 5's pretty neat ... when your browser supports it
Mathematica hits the Web
Wolfram embraces the cloud, promies private cloud cut of its number-cruncher
Mozilla shutters Labs, tells nobody it's been dead for five months
Staffer's blog reveals all as projects languish on GitHub
'People have forgotten just how late the first iPhone arrived ...'
Plus: 'Google's IDEALISM is an injudicious justification for inappropriate biz practices'
SUSE Linux owner Attachmate gobbled by Micro Focus for $2.3bn
Merger will lead to mainframe and COBOL powerhouse
iOS 8 Healthkit gets a bug SO Apple KILLS it. That's real healthcare!
Not fit for purpose on day of launch, says Cupertino
prev story

Whitepapers

Secure remote control for conventional and virtual desktops
Balancing user privacy and privileged access, in accordance with compliance frameworks and legislation. Evaluating any potential remote control choice.
Intelligent flash storage arrays
Tegile Intelligent Storage Arrays with IntelliFlash helps IT boost storage utilization and effciency while delivering unmatched storage savings and performance.
WIN a very cool portable ZX Spectrum
Win a one-off portable Spectrum built by legendary hardware hacker Ben Heck
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Beginner's guide to SSL certificates
De-mystify the technology involved and give you the information you need to make the best decision when considering your online security options.