使用 DOMParser 和 selectSingleNode 的 NullPointerException

发布于 2024-10-11 04:58:33 字数 710 浏览 6 评论 0原文

String url = "http://www.amazon.com/Classic-Starts-Great-Expectations/dp/1402766459/ref=sr_1_1?s=books&ie=UTF8&qid=1294405505&sr=1-1";

DOMParser parser = new DOMParser();
parser.parse(url);

Document document = parser.getDocument();
DOMReader reader = new DOMReader();
org.dom4j.Document nhddoc = reader.read(document);

//book price
Node price = nhddoc.selectSingleNode("/HTML/BODY/DIV[2]/FORM/TABLE[3]/TBODY/TR/TD/DIV/TABLE/TBODY/TR/TD[2]/B");
System.out.println(price.getText().toString().trim());

我得到的错误是：

Exception in thread "main" java.lang.NullPointerException
        at nekodom4j.Main.main(Main.java:44)

空指针异常是否意味着没有选择节点？

原文

String url = "http://www.amazon.com/Classic-Starts-Great-Expectations/dp/1402766459/ref=sr_1_1?s=books&ie=UTF8&qid=1294405505&sr=1-1";

DOMParser parser = new DOMParser();
parser.parse(url);

Document document = parser.getDocument();
DOMReader reader = new DOMReader();
org.dom4j.Document nhddoc = reader.read(document);

//book price
Node price = nhddoc.selectSingleNode("/HTML/BODY/DIV[2]/FORM/TABLE[3]/TBODY/TR/TD/DIV/TABLE/TBODY/TR/TD[2]/B");
System.out.println(price.getText().toString().trim());

the error i get is :

Exception in thread "main" java.lang.NullPointerException
        at nekodom4j.Main.main(Main.java:44)

does the null pointer exception means no node was selected ?

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有深☉意 2024-10-18 04:58:33

我不太清楚问题的原因可能是什么，但调试它时我要做的第一件事就是一次走一层路径，看看它在哪里无法返回您期望的结果。

Node html = nhddoc.selectSingleNode("/HTML");
/* maybe print out some information about the Node just acquired */
Node body = html.selectSingleNode("/BODY");

ETC...

I have no particular idea what the cause of the problem might be, but the first thing I would do to debug it would be to walk the path one level at a time and see where it fails to return what you expect.

Node html = nhddoc.selectSingleNode("/HTML");
/* maybe print out some information about the Node just acquired */
Node body = html.selectSingleNode("/BODY");

etc...

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