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I am getting NullPointerException in the following code:
String str = SOME_HTML_STRING;
Node node = convertStrIntoNodeUsingJTidy();
domToString(node);
//converts node to string
public static String domToString(org.w3c.dom.Node node)throws Exception {
try {
StringWriter sw = new StringWriter();
TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
// NullPointerException at this line, although node is not null
transformer.transform(new DOMSource(node), new StreamResult(sw));
return sw.toString();
} catch (Exception ex) {
throw new Exception("Error converting to String", ex);
}
}
The stacktrace is:
Caused by: javax.xml.transform.TransformerException: java.lang.NullPointerException
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
at com.example.Util.domToString(Util.java:3179)
... 128 more
Caused by: java.lang.NullPointerException
at com.sun.org.apache.xml.internal.serializer.ToXMLStream.processingInstruction(Unknown Source)
at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.processingInstruction(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(Unknown Source)
... 131 more
I have already checked the following link: http://geekymeeky.blogspot.in/2008/10/javaxxmltransform-transformerexception.html
The above post says, if a text node is null then this exception occurs.
I want to know, what value of variable str caused the text node value to null and lead to this exception.
369
NullPointerException is thrown when a reference variable is accessed (or de-referenced) and is not pointing to any object. This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.
The NullPointerException occurs due to a situation in application code where an uninitialized object is attempted to be accessed or modified. Essentially, this means the object reference does not point anywhere and has a null value.
Answer: Some of the best practices to avoid NullPointerException are: Use equals() and equalsIgnoreCase() method with String literal instead of using it on the unknown object that can be null. Use valueOf() instead of toString() ; and both return the same result. Use Java annotation @NotNull and @Nullable.
A null pointer exception is thrown when an application attempts to use null in a case where an object is required. These include: Calling the instance method of a null object. Accessing or modifying the field of a null object.
As you can see in stack trace, Exception was throws when parser trying to parse some incorrect processing instruction.
You can easily reproduce it with code below:
Document d = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
Node n = d.createProcessingInstruction("test", null);
System.out.println(domToString(n));
what raises exception almost like your.
Caused by: javax.xml.transform.TransformerException: java.lang.NullPointerException
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:732)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:336)
at TestNode.domToString(TestNode.java:63)
... 31 more
Caused by: java.lang.NullPointerException
at com.sun.org.apache.xml.internal.serializer.ToXMLStream.processingInstruction(ToXMLStream.java:281)
at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.processingInstruction(ToUnknownStream.java:886)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:235)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:90)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(TransformerImpl.java:679)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:723)
... 33 more
EDIT:
Similar exception happen when you get empty comments or textNodes, for example:
Node n = d.createComment("test");
n.setTextContent(null); // throws exception on parse
Node n = d.createTextNode(null); // throws exception on parse
It is not common situation, and possible only if incorrect/corrupted xml was passes as input source.
103
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