Parsing with JDOM

[Mike London]

Hi,

If you have an XML structure like this:

<?Xml version="1.0" encoding="utf-8"?>
<ROOT>
  <ERRORCODE>0</ERRORCODE>
  <RESULT>
    <X>
      <Y>
        <DATA>2017-11-011</DATA>
      </Y>
    </X>
    <X>
      <Y>
        <DATA>2018-01-01</DATA>
      </Y>
    </X>
  </RESULT>
</ROOT>

how do you visit all the DATA nodes using JDOM (to get the dates)? I've tried to write code, but I just end up visiting the parent nodes.

There can be multiple DATA nodes; we would not know how many of these ahead of time.

Thanks much in advance,

- mike

[Paul Clapham]

It's a very long time since I used JDOM but I'm sure it had methods which allowed you to navigate through the children of a node. But I expect you're already trying to use those methods; if so then perhaps you could post the code which isn't acting the way you would like?

[Mike London]

Paul Clapham wrote:It's a very long time since I used JDOM but I'm sure it had methods which allowed you to navigate through the children of a node. But I expect you're already trying to use those methods; if so then perhaps you could post the code which isn't acting the way you would like?

If you have a better suggestion for XML parsing, that would be welcome as well.

The problem I have is that all the examples online are simple with a simple structure. A real XML document with multiple elements and some of those elements being nested doesn't seem to be simple to parse. So far, I have not found a single example.

Thanks,

- mike

[Liutauras Vilda]

The problem I have is that all the examples online are simple with a simple structure. A real XML document with multiple elements and some of those elements being nested doesn't seem to be simple to parse. So far, I have not found a single example.

Nesting shouldn't over-complicate things that much. Root node has children. Those children are possibly root nodes to their children. Those children are possibly...

As mentioned, post the actual XML file structure you have and post the code you wrote.

[Mike London]

Here's the code that works. It's tied to the specific XML file, but I guess all XML Parsing code is. The code below specifically, not generically, knows the structure of the XML document and has nested blocks to handle it.

(Note: I changed the element name from Data to Date).

I'm assuming if you wanted to, say, change the value of a date in an XML file, it might be easier to just use a regex search and replace rather than trying to parse the XML document like this.

- mike

 Element rootNode = document.getRootElement();
            
            List colList = rootNode.getChildren("RESULT");
            StringBuffer text = new StringBuffer();

            for (int i = 0 ; i < colList.size(); i++)
            {
                List contents = ((Element) colList.get(i)).getChildren();

                for (Object obj : contents)
                {
                    if (obj instanceof Element)
                    {
                        Element e = (Element) obj;
                        List xNodes = e.getChildren();

                        for (Object element : xNodes)
                        {
                            text.append(((Element) xNodes.get(0)).getChild("DATE").getValue() +"\n");
                        }
                    }
                }

[Liutauras Vilda]

I just pulled that jdom (actually jdom2) library and gave a try, that is a quick solution against your file:

new SAXBuilder().build(inputFile)
				.getRootElement()
				.getChild("RESULT")
				.getChildren("X")
				.forEach(x -> x.getChild("Y")
							   .getChildren("DATA")
							   .forEach(e -> System.out.println(e.getValue())));

However, if you know little to nothing about the the file structure beforehand, that might be a bit more complicated by having few more checks, but that shouldn't be much more complicated. Recursion might be helpful, but dangerous though and probably used as a last resort.

Don't know whether Regex is a right way to go if there is a talk about the XML parsing, modifying it. That is why this library has been created for.

Let's see what others think.

[Tim Moores]

I strongly advise against using regexps for XML manipulation. Given that XML can contain all kinds of stuff in CDATA sections, it's a brittle approach compared to using one of the available libraries (XOM and dom4j are others).

[Mike London]

Tim Moores wrote:I strongly advise against using regexps for XML manipulation. Given that XML can contain all kinds of stuff in CDATA sections, it's a brittle approach compared to using one of the available libraries (XOM and dom4j are others).

Thanks, but ...

 try
        {
            new SAXBuilder().build(new StringReader(xml))
                    .getRootElement()
                    .getChild("RESULT")
                    .getChildren("X")
                    .forEach(x -> x.getChild("Y")
                            .getChildren("DATA")
                            .forEach(e -> System.out.println(e.getValue())));
        }
        catch (JDOMException e)
        {
            e.printStackTrace();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }

Didn't find anything.

[Liutauras Vilda]

Mike London wrote:Didn't find anything.

For me it did and it still does.

[Mike London]

Liutauras Vilda wrote:

Mike London wrote:Didn't find anything.

For me it did and it still does.

My bad. Sorry. I had changed DATA to DATE. Yep, it works.

Very nice, thanks very much.

- mike

[Liutauras Vilda]

Yeah, but what's next? Did we have any problem to solve? Or that was the problem...

[g tsuji]

I notice this <?Xml ...>. The prolog is written <?xml ...>, uppercase X will not do.

jdom2 with all its nice or less nice constructions has its convenience methods trying to make it stand out in competition.

First you define an element filter

ElementFilter efilter=new ElementFilter("DATA");

or pack it into the one-liner if you like.

Then you use getDescendants() to get to your target elements DATA (or DATE if that's a typo).

new SAXBuilder().build(new StringReader(xml))
    .getRootElement()
    .getDescendants(efilter)
    .forEach(e -> System.out.println(e.getText().trim()));

[Liutauras Vilda]

g tsuji, have a cow.

Certainly more elegant way to do that in this particular case.

[Mike London]

Liutauras Vilda wrote:g tsuji, have a cow.

Certainly more elegant way to do that in this particular case.

Man, that's amazing!  I wasn't even aware you could chain methods like that off the SAXBUilder().

JDOM is an odd beast in that it's such a sweet API on the one hand, but, on the other hand, it's nearly impossible to find through documentation with plentiful examples.

Regardless, seems like how ever much I "think" I know, there's still so much more to learn (since starting Java in 2002). The Java 8 syntax still eludes me sometimes. I like its declarativeness, but often, what I want to do is complicated and raises the question whether it's the best way to go vs. the formerly-traditional coding methods. In my case, I make small (meant to be searched) example programs for future reference.

Thanks again..Oh, I did find that capitalization problem and fixed it.

--

The actual problem was that the XML file had one or more incorrectly formatted dates that would not import into the third-party application. So, in the end, rather than using JDOM at all, I just read the XML file line by line and searched for the incorrect formatted date. Then if found, fixed it, and wrote the fixed date and the rest of the XML file to a new file.

You guys are amazing!

Best,

- mike