将XML文件导入到Processing，Java时发生NullPointerException

Question

I'm trying to get data from an XML-file and use this data in processing. When doing so I get a NPE, and I can't quite figure out where I'm wrong. The XML got several layers and I have to get data from this "child":

http://i62.tinypic.com/2mb90g.png

My code looks like this:

XML xml;

void setup(){

xml = loadXML("parker.xml");

XML[] children = xml.getChildren("kml");

XML[] Folder=children[0].getChildren("Folder");

XML[] Placemark=Folder[1].getChildren("Placemark");

XML[] Polygon=Placemark[2].getChildren("Polygon");

XML[] outerBoundaryIs=Polygon[3].getChildren("outerBoundaryIs");

XML[] LinearRing=outerBoundaryIs[4].getChildren("LinearRing");

  for (int i = 0; i < LinearRing.length; i++) {
    float coordinates = children[i].getFloat("coordinates");
    println(coordinates);

  }
}

Best Chris

Stack trace:

[Fatal Error] :1:1: Content is not allowed in prolog. org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog. at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:257) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:347) at processing.data.XML.(XML.java:187) at processing.core.PApplet.loadXML(PApplet.java:6310) at processing.core.PApplet.loadXML(PApplet.java:6300) at XMLtryout.setup(XMLtryout.java:21) at processing.core.PApplet.handleDraw(PApplet.java:2359) at processing.core.PGraphicsJava2D.requestDraw(PGraphicsJava2D.java:240) at processing.core.PApplet.run(PApplet.java:2254) at java.lang.Thread.run(Thread.java:744)

XML file:

https://www.dropbox.com/s/xn3thjskhlf2wai/parker.xml

Answer 1

This error maybe caused because missing this at the top of your xml file

<?xml version="1.0" encoding="utf-8"?>

or there's some non-printable garbage at the start of your file.

Answer 2

The ' Content is not allowed in prolog ' error indicates that you have some content between the XML declaration and the appearance of the document element, for example

<?xml version="1.0" encoding="utf-8"?>
content here is not allowed
<kml xmlns="http://earth.google.com/kml/2.1">
...
</kml>

The XML file you linked is ok though, so it seems you're

• reading the XML binary incorrectly before passing it to the XML parser,
• or (more likely) you're not reading the XML at all (can happen when you read from a web URL and getting an error response). I assume you get a HTTP 40x error which you don't recognize, and read the response (usually HTML) as XML, which causes the error. Remember that applets usually can only read resources from the same server (that's what might cause the error).

To verify this, attempt to read the URL content and output it as text, and check if it looks ok.

Answer 3

Make it more easy

try like this

public static void setUp(){
    try {
  File file = new File("parker.xml");
  DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
  DocumentBuilder db = dbf.newDocumentBuilder();
  Document doc = db.parse(file);
  doc.getDocumentElement().normalize();
  System.out.println("Root element " + doc.getDocumentElement().getNodeName());
  NodeList nodeLst = doc.getElementsByTagName("LinearRing");
  System.out.println("Information");

  for (int s = 0; s < nodeLst.getLength(); s++) {

    Node fstNode = nodeLst.item(s);

    if (fstNode.getNodeType() == Node.ELEMENT_NODE) {

           Element fstElmnt = (Element) fstNode;
      NodeList fstNmElmntLst = fstElmnt.getElementsByTagName("coordinates");
      Element fstNmElmnt = (Element) fstNmElmntLst.item(0);
      NodeList fstNm = fstNmElmnt.getChildNodes();
      System.out.println("coordinates : "  + ((Node) fstNm.item(0)).getNodeValue());

      //

      //
    }

  }
  } catch (Exception e) {
    e.printStackTrace();
  }
}

that should display :

Root element kml
Information
coordinates : 
              10.088512,56.154109,0
              10.088512,56.154109,0
              10.088512,56.154109,0
              10.088511,56.15411,0
              10.088511,56.15411,0
              10.08851,56.15411,0
              10.08851,56.154111,0
              10.088509,56.154111,0
              10.088508,56.154111,0
              10.088508,56.154111,0
              10.088507,56.154111,0
              10.088506,56.154111,0
              10.088506,56.154111,0
              10.088505,56.154111,0
              10.088504,56.154111,0
              10.088504,56.154111,0
              10.088503,56.15411,0
              10.088503,56.15411,0
              10.088502,56.15411,0
              10.088502,56.154109,0
              10.088502,56.154109,0
              10.088501,56.154109,0
              10.088501,56.154108,0
              10.088501,56.154108,0
              10.088501,56.154108,0
              10.088501,56.154107,0
              10.088285,56.154094,0
              10.088104,56.154372,0
              10.088061,56.154401,0
              10.087988,56.15445,0
              10.087915,56.154611,0
              10.08791,56.154613,0
              10.087912,56.154613,0
              10.087877,56.1548,0
              10.08772,56.15482,0
              10.087558,56.154911,0
              10.087421,56.155111,0
              10.087316,56.155308,0
              10.087328,56.15538,0
              10.087372,56.155413,0
              10.087446,56.155453,0
              10.087484,56.155487,0
              10.08747,56.155601,0
              10.08772,56.155616,0
              10.087719,56.155618,0
              10.088618,56.155671,0
              10.089096,56.1557,0
              10.089096,56.155699,0
              10.089138,56.155701,0
              10.089127,56.155706,0
              10.089004,56.155787,0
              10.08888,56.155853,0
              10.088799,56.155806,0
              10.088571,56.155914,0
              10.088455,56.155946,0
              10.088112,56.156081,0
              10.088184,56.156138,0
              10.087733,56.156353,0
              10.087489,56.156421,0
              10.087288,56.156341,0
              10.087268,56.156333,0
              10.086893,56.156182,0
              10.08684,56.156271,0
              10.087049,56.156373,0
              10.086893,56.156455,0
              10.086664,56.156575,0
              10.086443,56.156698,0
              10.086425,56.156708,0
              10.085983,56.156955,0
              10.085655,56.157139,0
              10.085462,56.157276,0
              10.085272,56.157233,0
              10.085176,56.157328,0
              10.084917,56.157393,0
              10.084883,56.157458,0
              10.08495,56.157513,0
              10.084947,56.157524,0
              10.084943,56.157539,0
              10.084855,56.15787,0
              10.084855,56.15787,0
              10.084321,56.157317,0
              10.085553,56.156195,0
              10.085555,56.156194,0
              10.085553,56.156194,0
              10.085734,56.156035,0
              10.085821,56.155977,0
              10.085937,56.155932,0
              10.085993,56.155942,0
              10.086031,56.155959,0
              10.086171,56.15592,0
              10.086227,56.155901,0
              10.086392,56.155841,0
              10.086513,56.155786,0
              10.08664,56.155699,0
              10.086686,56.155657,0
              10.086727,56.155605,0
              10.086777,56.155486,0
              10.086861,56.155289,0
              10.086916,56.155134,0
              10.087006,56.154899,0
              10.087075,56.154706,0
              10.087094,56.154649,0
              10.0871,56.154574,0
              10.087112,56.154464,0
              10.087111,56.154362,0
              10.087112,56.154279,0
              10.087112,56.154279,0
              10.087113,56.15427,0
              10.087114,56.154198,0
              10.087108,56.15413,0
              10.087091,56.154054,0
              10.086992,56.153698,0
              10.087,56.153678,0
              10.087031,56.153647,0
              10.087036,56.153648,0
              10.087046,56.153652,0
              10.087035,56.153647,0
              10.087039,56.153645,0
              10.087072,56.153612,0
              10.087367,56.153308,0
              10.087371,56.153303,0
              10.08742,56.15323,0
              10.087568,56.152963,0
              10.087568,56.152962,0
              10.087569,56.152962,0
              10.08757,56.152961,0
              10.087571,56.15296,0
              10.087573,56.152959,0
              10.087574,56.152959,0
              10.087575,56.152958,0
              10.087577,56.152958,0
              10.087579,56.152958,0
              10.087581,56.152957,0
              10.087582,56.152957,0
              10.087584,56.152957,0
              10.087586,56.152958,0
              10.087588,56.152958,0
              10.087589,56.152958,0
              10.087591,56.152959,0
              10.087592,56.152959,0
              10.087593,56.15296,0
              10.087594,56.152961,0
              10.087595,56.152962,0
              10.087596,56.152963,0
              10.087596,56.152964,0
              10.087596,56.152965,0
              10.087596,56.152965,0
              10.087614,56.152967,0
              10.087921,56.152988,0
              10.088134,56.153019,0
              10.088311,56.15304,0
              10.088454,56.153052,0
              10.088469,56.153378,0
              10.08847,56.153445,0
              10.088473,56.153597,0
              10.088473,56.153597,0
              10.088473,56.153597,0
              10.088703,56.153614,0
              10.088703,56.153614,0
              10.088703,56.153614,0
              10.088704,56.153614,0
              10.088705,56.153614,0
              10.088705,56.153615,0
              10.088706,56.153615,0
              10.088706,56.153615,0
              10.088707,56.153616,0
              10.088707,56.153616,0
              10.088707,56.153616,0
              10.088707,56.153617,0
              10.088707,56.153617,0
              10.088707,56.153617,0
              10.088707,56.153618,0
              10.088512,56.154108,0
              10.088512,56.154109,0

coordinates : 
              10.086779,56.155487,0
              10.086778,56.155488,0
              10.086779,56.155487,0
              10.086779,56.155487,0

coordinates : 
              10.08847,56.153602,0
              10.088469,56.153602,0
              10.088469,56.153602,0
              10.08847,56.153602,0

PS : kml is the root element