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I've read several questions and tutorials over the internet such as

But since this is the very first time I have to manipulate XML documents in Java I'm still a little bit confused. The XML content is written with String concatenation and that seems to me wrong. It is the same to concatenate Strings to produce a JSON object instead of using a JSONObject class. That's the way the code is written right now:

"<msg:restenv xmlns:msg=\"http://www.b2wdigital.com/umb/NEXM_processa_nf_xml_req\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xsi:schemaLocation=\"http://www.b2wdigital.com/umb/NEXM_processa_nf_xml_req req.xsd\"><autenticacao><usuario>"
            + usuario + "</usuario><senha>" + StringUtils.defaultIfBlank(UmbrellaRestClient.PARAMETROS_INFRA_UMBRELLA.get("SENHA_UMBRELLA"), "WS.INTEGRADOR")
            + "</senha></autenticacao><parametros><parametro><p_vl_gnre>" + valorGNRE + "</p_vl_gnre><p_cnpj_destinatario>" + cnpjFilial + "</p_cnpj_destinatario><p_num_ped_compra>" + idPedido
            + "</p_num_ped_compra><p_xml_sefaz><![CDATA[" + arquivoNfe + "]]></p_xml_sefaz></parametro></parametros></msg:restenv>"

In my research I think that almost everything I've read pointed to SAX as the best solution but I never really found something really useful to read about it, almost everything states that we have to create a handler and override startElement, endElement and characters methods.

I don't have to serialize the XML file in hard disk or database or anything else, I just need to pass its content to a webservice.

So my question really is, which is the right way to do it?

  • Concatenate Strings the way things are done right now?
  • Write the XML file using a Java API like Xerces? I have no clue on how that can be done.

  • Read the XML file with streams and just change node texts? My XML without the files would be like that:

    <msg:restenv xmlns:msg="{url}"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="{schemaLocation}">
    <autenticacao>
        <usuario></usuario>
        <senha></senha>
    </autenticacao>
    <parametros>
        <parametro>
            <p_vl_gnre></p_vl_gnre>
            <p_cnpj_destinatario></p_cnpj_destinatario>
            <p_num_ped_compra></p_num_ped_compra>
            <p_xml_sefaz><![CDATA[]]></p_xml_sefaz>
        </parametro>
    </parametros>
</msg:restenv>

  • I've also read something about using Apache Velocity as a template Engine since I don't actually have to serialize the XML and that's a approach that I really like because I've already worked with this framework and it's a really simple framework.

Again, I'm not looking for the best way, but the right one with tutorials and examples, if possible, on how to get things done.

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Philippe Gioseffi
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    If you need to send data to a web service then check whether your platform supports generating a proxy class or object based on the web service description/spec, then probably you don't need to work with XML directly, instead, you deal with Java objects and the serialization to XML is done by the platform/framework infrastructure to communicate with a web service. Your XML sample indicates a schema is available, so data binding like JAXB is probably also an option. – Martin Honnen Jan 25 '16 at 16:52
  • I'm afraid that's not up to my team, that's the way the government requires us to do things. The CDATA inside the node, for example, is a XML file. – Philippe Gioseffi Jan 25 '16 at 16:55
  • I think string concatenation is so dangerous. I once spent a week hunting down a comma. I like data binding for this with JAXB. Sometimes I have also seen people use a template (e.g. velocity). Spring has its own mapping approach. I guess the big question is whether you can do data binding and whether to use streaming or document based approach? I would recommend abstracting this nicely (domain model + destination = XML) and giving whichever approach seems easiest a try. – Keefe Roedersheimer Jan 25 '16 at 17:04
  • I don't like String concatenation either. I think I'll use velocity option. – Philippe Gioseffi Jan 25 '16 at 17:11

3 Answers3

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It all depends on context. There is no single "right way".

The biggest issues with concatenation is the combination of escaping the XML in to a String constant (which is fiddly), but also escaping the values that you can using so that they're correct for an XML document.

For small XMLs, that's fine.

But for larger ones, it can be a pain.

If most of your XML is boilerplate with just a few values inserted, you may find that templates using something like Velocity or any of the other several libraries may be quite effective. It helps keep the template "native" (you don't have to wrap it in "'s and escape it), plus it keeps the XML out of your code, but easily lets you stamp in the parts that you need to do.

Will Hartung
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I agree that there's not just one way to do it, but I would advise you to take a look at JAXB. You can easily consume and produce XML without any of that pesky String manipulation. Look here for a simple intro: https://docs.oracle.com/javase/tutorial/jaxb/index.html

Michael Peacock
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The Answer by Will Hartung is correct. There is not one right way as it depends on your situation.

For a beginner programmer, I suggest writing the strings manually so you get to understand XML in general and your content in particular. As for the mechanics of String concatenation, you would generally be using StringBuilder rather than String for better performance. Where thread-safety is needed, use StringBuffer.

The major issue is memory.

  • Abundant Memory
    If you have lots of memory and small XML documents, you can load the entire document into memory. This way you can traverse a document forwards, backwards, and jump around arbitrarily. This approach is know as Document Object Model (DOM). One better-known implementation of this approach is Apache Xerces. There are other good implementations as well.
  • Scarce Memory
    If you have little memory and large XML documents, then you need to plow through the document from start to finish, biting off small chunks at a time for lower memory usage. This approach is known as SAX. You can find multiple good implementations.

Another issue is validation. Do you want to validate the XML documents against a DTD or Schema? Some tools do this and some do not.

When all you need is to serialize the content of a Java object and read it back, I recommend the Simple XML Serialization library. Much simpler with a quicker learning-curve than the other tools.

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Basil Bourque
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