Java 8 Friday Goodies: Lambdas and XML

At Data Geekery, we love Java. And as we’re really into jOOQ’s fluent API and query DSL, we’re absolutely thrilled about what Java 8 will bring to our ecosystem. We have blogged a couple of times about some nice Java 8 goodies, and now we feel it’s time to start a new blog series, the…

Java 8 Friday

Every Friday, we’re showing you a couple of nice new tutorial-style Java 8 features, which take advantage of lambda expressions, extension methods, and other great stuff. You’ll find the source code on GitHub. tweet this

Java 8 Goodie: Lambdas and XML

There isn’t too much that Java 8 can do to the existing SAX and DOM APIs. The SAX ContentHandler has too many abstract methods to qualify as a @FunctionalInterface, and DOM is a huge, verbose API specified by w3c, with little chance of adding new extension methods.

Luckily there is a small Open Source library called jOOX that allows for processing the w3c standard DOM API through a wrapper API that mimicks the popular jQuery library. jQuery leverages JavaScript’s language features by allowing users to pass functions to the API for DOM traversal. The same is the case with jOOX. Let’s have a closer look:

Assume that we’re using the following pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.jooq</groupId>
  <artifactId>java8-goodies</artifactId>
  <version>1.0-SNAPSHOT</version>

  <dependencies>
    <dependency>
      <groupId>org.jooq</groupId>
      <artifactId>joox</artifactId>
      <version>1.2.0</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.3.2</version>
        <configuration>
          <fork>true</fork>
          <maxmem>512m</maxmem>
          <meminitial>256m</meminitial>
          <encoding>UTF-8</encoding>
          <source>1.8</source>
          <target>1.8</target>
          <debug>true</debug>
          <debuglevel>lines,vars,source</debuglevel>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Let’s assume we wanted to know all the involved artifacts in Maven’s groupId:artifactId:version notation. Here’s how we can do that with jOOX and lambda expressions:

$(new File("./pom.xml")).find("groupId")
                        .each(ctx -> {
    System.out.println(
        $(ctx).text() + ":" +
        $(ctx).siblings("artifactId").text() + ":" +
        $(ctx).siblings("version").text()
    );
});

Executing the above yields:

org.jooq:java8-goodies:1.0-SNAPSHOT
org.jooq:joox:1.2.0
org.apache.maven.plugins:maven-compiler-plugin:2.3.2

Let’s assume we only wanted to display those artifacts that don’t have SNAPSHOT in their version numbers. Simply add a filter:

$(new File("./pom.xml"))
    .find("groupId")
    .filter(ctx -> $(ctx).siblings("version")
                         .matchText(".*-SNAPSHOT")
                         .isEmpty())
    .each(ctx -> {
        System.out.println(
        $(ctx).text() + ":" +
        $(ctx).siblings("artifactId").text() + ":" +
        $(ctx).siblings("version").text());
    });

This will now yield

org.jooq:joox:1.2.0
org.apache.maven.plugins:maven-compiler-plugin:2.3.2

We can also transform the XML content. For instance, if the target document doesn’t need to be a POM, we could replace the matched groupId elements by an artifical artifact element that contains the artifact name in Maven notation. Here’s how to do this:

$(new File("./pom.xml"))
    .find("groupId")
    .filter(ctx -> $(ctx).siblings("version")
                         .matchText(".*-SNAPSHOT")
                         .isEmpty())
    .content(ctx ->
        $(ctx).text() + ":" +
        $(ctx).siblings("artifactId").text() + ":" +
        $(ctx).siblings("version").text()
    )
    .rename("artifact")
    .each(ctx -> System.out.println(ctx));

The above puts new content in place of the previous one through .content(), and then renames the groupId elements to artifact, before printing out the element. The result is:

<artifact>org.jooq:joox:1.2.0</artifact>
<artifact>org.apache.maven.plugins:maven-compiler-plugin:2.3.2</artifact>

More goodies next week

What becomes immediately obvious is the fact that the lambda expert group’s choice of making all SAMs (Single Abstract Method interfaces) eligible for use with lambda expressions adds great value to pre-existing APIs. Quite a clever move.

But there are also new APIs. Last week, we have discussed how the existing JDK 1.2 File API can be improved through the use of lambdas. Some of our readers have expressed their concerns that the java.io API has been largely replaced by java.nio (nio as in New I/O). Next week, we’ll have a look at Java 8’s java.nnio API (for new-new I/O ;-) ) and how it relates to the Java 8 Streams API.

More on Java 8

In the mean time, have a look at Eugen Paraschiv’s awesome Java 8 resources page

A jOOX First-Time Experience Article

Here’s some nice first-time user experience about jOOX, my lesser-known product:
http://www.kubrynski.com/2013/03/as-developer-i-want-to-use-xml.html

As a reminder, here’s what jOOX is all about:

jOOX stands for Java Object Oriented XML. It is a simple wrapper for the org.w3c.dom package, to allow for fluent XML document creation and manipulation where DOM is required but too verbose. jOOX only wraps the underlying document and can be used to enhance DOM, not as an alternative.

Unlike other, similar tools that mimick jQuery (e.g. jsoup, jerry, gwtquery), jOOX really aims to leverage standard w3c DOM usage, which isn’t such a bad thing after all, with its performant, standard Xerces implementation.

Some simple example code:

// Find the order at index 4 and 
// add an element "paid"
$(document).find("orders")
           .children().eq(4)
           .append("<paid>true</paid>");

// Find those orders that are paid 
// and flag them as "settled"
$(document).find("orders")
           .children().find("paid")
           .after("<settled>true</settled>");

FluentDOM, another mimick of jQuery DOM manipulation, in PHP

The triumph of jQuery over any other XML API seems prominent, in many languages. Here is another example of a nice jQuery-port to PHP: FluentDOM.

http://fluentdom.github.com/

Similar to jOOX, FluentDOM aims to combine a jQuery-like fluent API with XPath and general DOM XML manipulation. Here are some simple examples taken from the FluentDOM documentation:

// read a file and set the message tag's content
echo FluentDOM($xmlFile)
  ->find('/message')
  ->text('Hello World!');

// Find the <root> first then the second element in it
var_dump($fd->find('/root')->find('*[2]')->item(0)->textContent);

// Append elements to an object
$menu
  ->append('<li/>')
  ->append('<a/>')
  ->attr('href', '/sample.php')
  ->text('Sample');

I’m in contact with the developers of FluentDOM. As always with OSS, there is great potential for synergy, which in the end will make both products better. For jOOX, this means that loading of files/streams is going to be a nice plus. XPath is already implemented in the upcoming release 0.9.2. On the other hand, maybe FluentDOM can get inspiration from jOOQ’s document creation syntax (which isn’t part of jQuery):

$("root",
  $("element",
    $("child", "text"),
    $("child", "more text")));

… which will create

<root>
  <element>
    <child>text</child>
    <child>more text</child>
  </element>
</root>

Excited as always, let’s get back to hacking! :-)

See the latest progress here: http://code.google.com/p/joox/

Another Fluent API: jOOX. Porting jQuery to Java

Recently, in my every day programming madness, I really felt the urge to kill someone involved with the formal specification of DOM. The beloved Document Object Model. While everyone understands that this API is complete in functionality and scope and it’s a standard, and it’s almost the same in every language…. well it’s incredibly verbose. Manipulating XML is about as fun and exciting as cleaning the dishes of a 2000-people Indian wedding.

And then, suddenly, I remembered that this is how I felt with Java’s support for advanced SQL and how JPA/CriteriaQuery made me feel like that poor dishwasher, before. And I wondered whether someone had felt like me before. So I asked this question on Stack Overflow:

http://stackoverflow.com/questions/6996013/a-nice-java-xml-dom-utility

And I got the expected answers about JDOM and dom4j. Two dinosaur projects that are neither sexier nor more efficient than the standard itself (e.g. Xerces). See this answer about performance:

http://stackoverflow.com/questions/6996013/a-nice-java-xml-dom-utility#6998870

I had also found one project, that has a somewhat fluent approach:

http://code.google.com/p/xmltool/

It looks quite nice, actually, although it is a bit biased towards DOM creation, not navigation. And then, it struck me like lightning: “Why hasn’t anyone ported jQuery” to Java, yet?? jQuery is exactly how an XML API should be: Awesome. Fluent. Fun, and efficient to use. So I tried to hack something together that looks like jQuery and that’s the beginning of another product in the “jOO-Star suite”: jOOX with X for XML! I wanted this to be fluent, and fun and efficient to use. Like jOOQ. So jOOX will be an attempt for doing precisely that. Here’s an example of what jOOX code looks like:

// Find the order at index for and add an element "paid"
joox(document).find("orders")
              .children()
              .eq(4)
              .append("<paid>true</paid>");

// Find those orders that are paid and flag them as "settled"
joox(document).find("orders")
              .children()
              .find("paid")
              .after("<settled>true</settled>");

This rapid prototype of a jQuery port looks very promising to me, even if the most important features aren’t there yet (e.g. navigation with expression languages, selectors, etc). With Java’s static typing and without all the browser-related issues and JavaScript event handling and CSS and all that, pure DOM navigation and manipulation is actually not that hard to wrap. In any case, I have now even more respect for the jQuery guys, as I’m just touching the tip of the iceberg.

So in the future, I will also post one or two entries about jOOX on this blog. Looking forward to feedback!

Download jOOX from Google Code:

http://code.google.com/p/joox/