如何使用Java在xml中的特定标签内获取子节点？

Question

Below is an xml File that i have to parse..

<dataroot>
 <PARM>
   <P1>123</P1>
   <P2>abc</P2>
 </PARM>
 <PARM>
   <P1>456</P1>
   <P2>def</P2>
 </PARM>
 <PARM>
   <P1>789</P1>
   <P2>ghi</P2>
 </PARM>
.......(15times)
</dataroot>

my goal is to get the child nodes (ie p1,p2 not the values inside) and compare those names with a template.

say if p2 is not present i have to append that particular tag to that particular position in the xml file. The problem is when i use getElementsByTagNames() and store that in an array and then compare it with the template it includes dataroot and PARM as well which i don't want.

so how can i get just p1 and p2 (for upto 15times) only.

Answer 1

For me, the simplest approach would be to use JAXB to unmarshal and marshal, thus adding the missing elements of PARM. You need to add a few annotations in the classes for dataroot and PARM if the XML element names require different case, but then it's a matter of a few lines of code for unmarshalling and marshalling.

@XmlRootElement(name="dataroot")
@XmlType(propOrder = {"parm"})
public class Data {
    @XmlElement(name="PARM")
    private List<Parm> parm = new ArrayList<>();
    public List<Parm> getParm(){ return parm; }
}

@XmlRootElement(name="PARM")
public class Parm {
    private String p1="";
    @XmlElement(name="P1")
    public String getP1(){ return p1; }
    public void setP1( String v ){ p1 = v; }
}

In the same package, add a file jaxb.index containing a single line:

Data

The main program:

JAXBContext jc = JAXBContext.newInstance( PACKAGE ); // dir path
Unmarshaller u = jc.createUnmarshaller();
Data data = (Data)u.unmarshal( new File( XMLIN ) );  // file path
Marshaller m = jc.createMarshaller();
Writer sw = ...;                  // whatever you need
m.marshal( data, sw );

Note the initialisation for field p1 . This ensures that the element will show up with an empty string. A null results in omitting the element.