How can I parse XML using Java?

Question

<?xml version="1.0" ?> 
<input>
    <sys>
      <protocol>TL1</protocol> 
      <ipAddress>10.05.2.3</ipAddress>
      <port>2001</port>
      <prompt>agent</prompt>       
       <TL1Command>
           <type>get</type>
           <command_code>...........</command_code>
           <staging_block>      
                <tid>...........</tid>
                <aid>...........</aid>
                <ctag>..........</ctag>
                <gen_block>.....</gen_block>
           </staging_block>
           <payload_block>
                <data_block>.......</data_block>
           </payload_block>
    </TL1Command>
    </sys>
    <sys>
      <protocol>TL1</protocol> 
      <ipAddress>10.5.2.98</ipAddress>
      <port>2001</port>
      <prompt>agent</prompt>       
       <TL1Command>
           <type>get</type>
           <command_code>...........</command_code>
           <staging_block>      
                <tid>...........</tid>
                <aid>...........</aid>
                <ctag>..........</ctag>
                <gen_block>.....</gen_block>
           </staging_block>
           <payload_block>
                <data_block>.......</data_block>
                <data_block>.......</data_block>
                <data_block>.......</data_block>
           </payload_block>
    </TL1Command>
    </sys>
</input>

I want to know how to parse this XML using Java. Such that I can use that data as it is in the same given way for my program. I know of how to parse it but the problem is for each command there might be different number of data blocks. So after parsing I need to use respective datablocks for respective commands. I mean for first command while retriving I should get only one data block value and for 2nd command 3 data blocks and so on. Please let me know any sample code for solving this issue.

Answer 1

There are two basic approaches to parsing XML.

1. A cursor (StAX) or event (SAX) based approach. Much more lightweight but often more verbose. This is particularly good when you only want to grab out small parts or the processing is easy; and
2. Tree-based approaches (DOM). Typically DOM parsers are built on top of SAX/StAX parsers anyway. They require more processing and typically require you to have an entire document in memory before you can do anything (whereas SAX/StAX can be much more efficient and quicker to respond). But this is useful for "random" access to document parts.

Pick whichever is most appropriate for your circumstances.

Answer 2

Simplest way would be to load the document as a DOM Document

Then get what you need using XPath

Document document =  DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(inputStream);

NodeList nodeList = XPathAPI.selectNodeList(document, "/sys");
for (int i = 0; i < nodeList.getLength(); i++) {
    Node node = nodeList.item(i);
    System.out.println(node.getTextContent());
}

Check out an xpath tutorial here.