java 解析xml时如何检查空标签？
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How do I check for empty tags while parsing xml?
提问by roymustang86
I am using the Document object to extract all the tags from an xml. If the xml has an empty tag, I get a null pointer exception. How do I guard against this? How do I check for an empty tag?
我正在使用 Document 对象从 xml 中提取所有标签。如果 xml 有一个空标签，我会得到一个空指针异常。我该如何防范？如何检查空标签？
<USTrade>
<CreditorId>
<CustomerNumber>xxxx</CustomerNumber>
<Name></Name>
<Industry code="FY" description="Factor"/>
</CreditorId>
<DateReported format="MM/CCYY">02/2012</DateReported>
<AccountNumber>54000</AccountNumber>
<HighCreditAmount>0000299</HighCreditAmount>
<BalanceAmount>0000069</BalanceAmount>
<PastDueAmount>0000069</PastDueAmount>
<PortfolioType code="O" description="Open Account (30, 60, or 90 day account)"/>
<Status code="5" description="120 Dys or More PDue"/>
<Narratives>
<Narrative code="GS" description="Medical"/>
<Narrative code="CZ" description="Collection Account"/>
</Narratives>
</USTrade>
<USTrade>
So, when I use:
所以，当我使用：
NodeList nm = docElement.getElementsByTagName("Name");
if (nm.getLength() > 0)
name = nullIfBlank(((Element) nm.item(0))
.getFirstChild().getTextContent());
Nodelist gives a length of 1, because there is a tag, but when I do getTextContent(), it hits the null pointer because FirstChild() doesn't return anything for tag = Name
Nodelist 给出的长度为 1，因为有一个标签，但是当我执行 getTextContent() 时，它会命中空指针，因为 FirstChild() 没有为 tag = Name 返回任何内容
And, I have done this for each xml tag. Is there a simple check I can do before every tag extraction?
而且，我为每个 xml 标签都做了这个。在每次提取标签之前，我可以做一个简单的检查吗？
回答by Colin D
The first thing I would do would be to unchain your calls. This will give you the chance to determine exactly which reference is null and which reference you need to do a null check for:
我要做的第一件事就是解开你的电话。这将使您有机会准确确定哪个引用为空以及您需要对哪个引用进行空检查：
NodeList nm = docElement.getElementsByTagName("Name");
if (nm.getLength() > 0) {
Node n = nm.item(0);
Node child = n.getFirstChild();
if(child == null) {
// null handling
name = null;
}
else {
name = nullIfBlank(child.getTextContent());
}
}
Also, check out the hasChildNodes()method on Node! http://docs.oracle.com/javase/1.4.2/docs/api/org/w3c/dom/Node.html#hasChildNodes%28%29
另外，请查看hasChildNodes()Node 上的方法！http://docs.oracle.com/javase/1.4.2/docs/api/org/w3c/dom/Node.html#hasChildNodes%28%29
回答by Chad
while(current != null){
if(current.getNodeType() == Node.ELEMENT_NODE){
String nodeName = current.getNodeName();
System.out.println("\tNode: "+nodeName);
NamedNodeMap attributes = current.getAttributes();
System.out.println("\t\tNumber of Attributes: "+attributes.getLength());
for(int i=0; i<attributes.getLength(); i++){
Node attr = attributes.item(i);
String attName = attr.getNodeName();
String attValue= attr.getNodeValue();
System.out.println("\t\tAttribute Name: "+ attName+ "\tAttribute Value:"+ attValue);
}
}
Are you also wanting to print out the value of the node? If so, it's one line of code in my example you would have to add, and I can share that as well.
您是否还想打印出节点的值？如果是这样，您必须在我的示例中添加一行代码，我也可以分享它。
回答by DonCallisto
Did you tried something like that?
你有没有尝试过这样的事情？
NodeList nm = docElement.getElementsByTagName("Name");
if ((Element) nm.item(0))
name = nullIfBlank(((Element) nm.item(0)).getFirstChild().getTextContent());
