java 将 Dom 元素转换为字符串时获取 NullPointerException
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Getting NullPointerException while transforming Dom element to string
提问by Dheeraj Kumar Aggarwal
I am getting NullPointerException in the following code:
我在以下代码中收到 NullPointerException：
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:
堆栈跟踪是：
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
我已经检查了以下链接：http: //geekymeeky.blogspot.in/2008/10/javaxxmltransform-transformerexception.html
The above post says, if a text node is null then this exception occurs.
上面的帖子说，如果文本节点为空，则会发生此异常。
I want to know, what value of variable strcaused the text node value to null and lead to this exception.
我想知道，变量str 的什么值导致文本节点值为空并导致此异常。
回答by user1516873
As you can see in stack trace, Exception was throws when parser trying to parse some incorrect processing instruction.
正如您在堆栈跟踪中看到的那样，当解析器尝试解析一些不正确的处理指令时会抛出异常。
You can easily reproduce it with code below:
您可以使用以下代码轻松重现它：
Document d = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
Node n = d.createProcessingInstruction("test", null);
System.out.println(domToString(n));
what raises exception almost like your.
什么引发异常几乎像你一样。
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:
编辑：
Similar exception happen when you get empty comments or textNodes, for example:
当您获得空评论或 textNodes 时，会发生类似的异常，例如：
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.
这不是常见的情况，只有当不正确/损坏的 xml 作为输入源传递时才有可能。
