Develop Reference

Java DOM: getElementsByTagName is returning no elements?

I am trying to parse the XML document at http://web.mta.info/status/ServiceStatusSubway.xml and extract all the PtSituationElement elements with the following code:
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document subwayStatusDoc = builder.parse(new URL("http://web.mta.info/status/ServiceStatusSubway.xml").openStream());
NodeList situationList = subwayStatusDoc.getDocumentElement().getElementsByTagName("PtSituationElement");
System.out.println(situationList.item(0)); //prints null
What am I doing wrong here ?

The PtSituationElement tags contain child tags, so you need to go into those. Just printing .item(0) relies on the toString() method, and apparently it does not do a great job of explaining your nodes.
So add this to see some of the data in the child nodes:
Node item = situationList.item(0);
NodeList childNodes = item.getChildNodes();
for (int j = 0; j < childNodes.getLength(); j++) {
System.out.println(childNodes.item(j).getTextContent());
}
(I'm not sure what you want to do with the data in the xml structure, but this example shows how you can proceed with your work.)
Also, I noted that the LongDescription tags contain HTML that is not correct XML (<br clear=left> should be <br clear=left> etc). The parser could have a problem with that. It would be better if the HTML was escaped (see How to escape "&" in XML?).

Getting null values from XPath query

I have this xml file:
<?xml version="1.0" encoding="UTF-8"?>
<iet:aw-data xmlns:iet="http://care.aw.com/IET/2007/12" class="com.aw.care.bean.resource.MessageResource">
<iet:metadata filter=""/>
<iet:message-resource>
<iet:message>some message 1</iet:message>
<iet:customer id="1"/>
<iet:code>edi.claimfilingindicator.11</iet:code>
<iet:locale>iw_IL</iet:locale>
</iet:message-resource>
<iet:message-resource>
<iet:message>some message 2</iet:message>
<iet:customer id="1"/>
<iet:code>edi.claimfilingindicator.12</iet:code>
<iet:locale>iw_IL</iet:locale>
</iet:message-resource>
.
.
.
.
</iet:aw-data>
Using this code below i'm getting over the data and finding what I need.
try {
FileInputStream fileIS = new FileInputStream(new File("resources\\bootstrap\\content\\MessageResources_iw_IL\\MessageResource_iw_IL.ctdata.xml"));
DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
builderFactory.setNamespaceAware(true); // never forget this!
DocumentBuilder builder = builderFactory.newDocumentBuilder();
Document xmlDocument = builder.parse(fileIS);
XPath xPath = XPathFactory.newInstance().newXPath();
String query = "//*[local-name()='message-resource']//*[local-name()='code'][contains(text(), 'account')]";
NodeList nodeList = (NodeList) xPath.compile(query).evaluate(xmlDocument, XPathConstants.NODESET);
System.out.println("size= " + nodeList.getLength());
for (int i = 0; i < nodeList.getLength(); i++) {
System.out.println(nodeList.item(i).getNodeValue());
}
}
catch (Exception e){
e.printStackTrace();
}
The issue is that i'm getting only null values while printing in the for loop, any idea why it's happened?
The code needs to return a list of nodes which have a code and message fields that contains a given parameters (same as like SQL query with two parameters with operator of AND between them)

Check the documentation:
https://docs.oracle.com/javase/7/docs/api/org/w3c/dom/Node.html
getNodeValue() applied to an element node returns null.
Use getTextContent().
Alternatively, if you find DOM too frustrating, switch to one of the better tree models like JDOM2 or XOM.
Also, if you used an XPath 2.0 engine like Saxon, it would (a) simplify your expression to
//*:message-resource//*:code][contains(text(), 'account')]
and (b) allow you to return a sequence of strings from the XPath expression, rather than a sequence of nodes, so you wouldn't have to mess around with nodelists.
Another point: I suspect that the predicate [contains(text(), 'account')] should really be [.='account']. I'm not sure of that, but using text() instead of ".", and using contains() instead of "=", are both common mistakes.

Namespace aware document returning empty NodeList

I am trying to parse general XML containing namespace elements. However, getElementsByTagNameNS() always returns an empty NodeList. For example, the following code, in which I've hard-coded some SAML text, (because it has namespaces and was available) returns an empty NodeList:
NodeList test() {
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
documentBuilderFactory.setValidating(false);
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
Document document = documentBuilder.parse(new StringInputStream(
"<samlp:Response xmlns:samlp=\"urn:oasis:names:tc:SAML:2.0:protocol\" xmlns:saml=\"urn:oasis:names:tc:SAML:2.0:assertion\">\n" +
" <saml:Assertion>\n" +
" </saml:Assertion>\n" +
"</samlp:Response>"
));
return document.getElementsByTagNameNS("saml", "Assertion");
}
The thing is, I've set it as namespace aware. As near as I can tell, this should return a NodeList with one result.
EDIT
There are numerous similar questions, but they are all asked by people who had forgotten to enable namespace awareness.
EDIT
For precision's sake, I ran this code using open JDK 1.8.0.151.

The first parameter to getElementsByTagNameNS() is the namespace URI, not the prefix. So it should be
return document.getElementsByTagNameNS("urn:oasis:names:tc:SAML:2.0:assertion", "Assertion");

Access data in xml as string

I am receiving a xml in string format. Is there any library to search for elements in the string?
<Version value="0"/>
<IssueDate>2017-12-15</IssueDate>
<Locale>en_US</Locale>
<RecipientAddress>
<Category>Primary</Category>
<SubCategory>0</SubCategory>
<Name>Vitsi</Name>
<Attention>Stowell Group Llc.</Attention>
<AddressLine1>511 6th St</AddressLine1>
<City>Lake Oswego</City>
<Country>United States</Country>
<PresentationValue>Lake Oswego OR 97034-2903</PresentationValue>
<State>OR</State>
<ZIPCode>97034</ZIPCode>
<ZIP4>2903</ZIP4>
</RecipientAddress>
<RecipientAddress>
<Category>Additional</Category>
<SubCategory>1</SubCategory>
<Name>Vitsi</Name>
<AddressLine1>Po Box 957</AddressLine1>
<City>Lake Oswego</City>
<Country>United States</Country>
<PresentationValue>Lake Oswego OR 97034-0104</PresentationValue>
<State>OR</State>
<ZIPCode>97034</ZIPCode>
<ZIP4>0104</ZIP4>
</RecipientAddress>
<SenderName>TMO</SenderName>
<SenderId>IL</SenderId>
<SenderAddress>
<Name>T-mobile</Name>
<AddressLine1>Po Box 790047</AddressLine1>
<City>St. Louis</City>
<PresentationValue>ST. LOUIS MO 63179-0047</PresentationValue>
<State>MO</State>
<ZIPCode>63179</ZIPCode>
.
.
.
.
I want to access the element RecipientAddress, which is a list. Is there any library to do that? Please note that what I receive is a string. It is an invoice and there will be many to process, so performance is important

Following options are available:
Convert xml string to java objects using JAXB.
Use .indexOf() in string method to retrieve specific parts of xml.
Use regular expression to retrieve specific parts of xml.
SAX/DOM/STAX parser for parsing and extraction from xml.
Xpath for fetching the specific values from xml.

You could use XPATH. Java has inbuilt support for XML querying without any thirdparty library,
Code piece would be,
String xmlInputStr = "<YOUR_XML_STRING_INPUT>"
String xpathExpressionStr = "<XPATH_EXPRESSION_STRING>"
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(xmlInputStr);
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile(xpathExpressionStr);
You can write your own expression string for querying. Typical example
"/RecipientAddress/Category"
Evaluate your xml against expression to retrieve list of nodes.
NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
And iterate over nodes,
for (int i = 0; i < nodes.getLength(); i++) {
Node nNode = nodes.item(i);
...
}

There lot of pre-implemented api is available to convert xml to java object.
please look at that the xerces from Apache.
If you want extract only specified value the put whole in to string and use indexOf("string")

XPath select element with an attribute

I have a xml file which looks like:
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<alarm-response-list xmlns="http://www.ca.com/spectrum/restful/schema/response"
error="EndOfResults" throttle="277" total-alarms="288">
<alarm-responses>
<alarm id="53689bf8-6cc8-1003-0060-008010186429">
<attribute id="0x11f4a" error="NoSuchAttribute" />
<attribute id="0x12b4c">UPS DIAGNOSTIC TEST FAILED</attribute>
<attribute id="0x10b5a">IDG860237, SL3-PL4, US, SapNr=70195637,</attribute>
</alarm>
<alarm id="536b8c9a-28b3-1008-0060-008010186429">
<attribute id="0x11f4a" error="NoSuchAttribute" />
<attribute id="0x12b4c">DEVICE IN MAINTENANCE MODE</attribute>
<attribute id="0x10b5a">IDG860237, SL3-PL4, US, SapNr=70195637,</attribute>
</alarm>
</alarm-responses>
</alarm-response-list>
There a lot of these alarms. Now I want save for every alarm tag the attribute with the id = 0x10b5a in a String. But I haven't a great clue. In my way it doesn't do it. I get only showed the expression.
My idea:
FileInputStream file = new FileInputStream(
new File(
"alarms.xml"));
DocumentBuilderFactory builderFactory = DocumentBuilderFactory
.newInstance();
DocumentBuilder builder = builderFactory.newDocumentBuilder();
Document xmlDocument = builder.parse(file);
XPath xPath = XPathFactory.newInstance().newXPath();
System.out.println("*************************");
String expression = "/alarm-responses/alarm/attribute[#id='0x10b5a'] ";
System.out.println(expression);
NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(
xmlDocument, XPathConstants.NODESET);
for (int i = 0; i < nodeList.getLength(); i++) {
System.out.println(nodeList.item(i).getFirstChild()
.getNodeValue());
}

There are several different problems here that are interacting to mean that your XPath expression doesn't match anything. Firstly the alarm-responses element isn't the root of the document - you need an extra step on the front of the path to select the alarm-response-list element. But more importantly you have namespace issues.
XPath only works when the XML has been parsed with namespaces enabled, which for some reason is not the default for DocumentBuilderFactory. You need to enable namespaces before you do newDocumentBuilder.
Now your XML document has xmlns="http://www.ca.com/spectrum/restful/schema/response", which puts all the elements in this namespace, but unprefixed node names in an XPath expression always refer to nodes that are not in a namespace. In order to match namespaced nodes you need to bind a prefix to the namespace URI and then use prefixed names in the path.
For javax.xml.xpath this is done using a NamespaceContext, but annoyingly there is no default implementation of this interface available by default in the Java core library. There is a SimpleNamespaceContext implementation available as part of Spring, or it's fairly simple to write your own. Using the Spring class:
DocumentBuilderFactory builderFactory = DocumentBuilderFactory
.newInstance();
// enable namespaces
builderFactory.setNamespaceAware(true);
DocumentBuilder builder = builderFactory.newDocumentBuilder();
Document xmlDocument = builder.parse(file);
XPath xPath = XPathFactory.newInstance().newXPath();
// Set up the namespace context
SimpleNamespaceContext ctx = new SimpleNamespaceContext();
ctx.bindNamespaceUri("ca", "http://www.ca.com/spectrum/restful/schema/response");
xPath.setNamespaceContext(ctx);
System.out.println("*************************");
// corrected expression
String expression = "/ca:alarm-response-list/ca:alarm-responses/ca:alarm/ca:attribute[#id='0x10b5a']";
System.out.println(expression);
NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(
xmlDocument, XPathConstants.NODESET);
for (int i = 0; i < nodeList.getLength(); i++) {
System.out.println(nodeList.item(i).getTextContent());
}
Note also how I'm using getTextContent() to get the text under each matched element. The getNodeValue() method always returns null for element nodes.