Question

我为我的xml页面编写了一个解析器，我得到一个奇怪的错误，我完全不明白为什么。首先，我想向您展示我的xml页面：

<?xml version="1.0" encoding="UTF-8"?>
<drugs xmlns:xs="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://drugbank.ca" xs:schemaLocation="http://www.drugbank.ca/docs/drugbank.xsd" schemaVersion="1.4">
<drug type="biotech" created="2005-06-13 07:24:05 -0600" updated="2012-02-13 17:42:20 -0700" version="3.0">
<drugbank-id>DB00001</drugbank-id>
<name>Lepirudin</name>
<drug-interactions>
  <drug-interaction>
    <drug>DB01381</drug>
    <name>Ginkgo biloba</name>
    <description>Additive anticoagulant/antiplatelet effects may increase bleed risk. Concomitant therapy should be avoided.</description>
  </drug-interaction>
  <drug-interaction>
    <drug>DB00374</drug>
    <name>Treprostinil</name>
    <description>The prostacyclin analogue, Treprostinil, increases the risk of bleeding when combined with the anticoagulant, Lepirudin. Monitor for increased bleeding during concomitant thearpy. </description>
  </drug-interaction>
</drug-interactions>
<targets>
  <target partner="54">
    <actions>
      <action>inhibitor</action>
    </actions>
  </target>
</targets>
  </drug>
<partners>
<partner id="54">
  <name>Prothrombin</name>
  <general-function>Involved in blood clotting cascade</general-function>
</partner>
  </partners>

在这里，您可以看到药物相互作用标签，其中有关于相互作用药物的信息。因此，当我删除药物相互作用标签时，我的解析器工作得很好，但是使用药物交互标签，我得到了NullPointerException。

错误行：

if(nameElement.getChildNodes().item(0).getNodeValue().equals(str))

我在这里放了整个解析器代码。你也可以自己尝试一下。为什么我会收到此错误，如何解决？抱歉很长的帖子。感谢

import java.io.File;
import java.util.ArrayList;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class xmlParser {

public static void main(String argv[]) {
    getDrug("Lepirudin");
}


public static void getDrug(String str){
    ArrayList<String> arr = new ArrayList();
    String trgts = "";
    try {
        File file = new File("test.xml");
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse(file);
        doc.getDocumentElement().normalize();
        System.out.println("Root element " + doc.getDocumentElement().getNodeName());

        NodeList drugList = doc.getElementsByTagName("drug");

        for (int s = 0; s < drugList.getLength(); s++) {

            Node drugNode = drugList.item(s);

            if (drugNode.getNodeType() == Node.ELEMENT_NODE) {

                Element drugElement = (Element) drugNode;

                Element nameElement = (Element) drugElement.getElementsByTagName("name").item(0);

                if(nameElement.getChildNodes().item(0).getNodeValue().equals(str)){
                    System.out.println("Name : " + nameElement.getChildNodes().item(0).getNodeValue());


                    Element drugNodeElement = (Element) drugElement.getElementsByTagName("drugbank-id").item(0);
                    System.out.println("ID : "  + drugNodeElement.getChildNodes().item(0).getNodeValue());

                    /////////////////////////////////////////////////
                    NodeList targetList = (NodeList) drugElement.getElementsByTagName("target");
                    for(int t=0; t<targetList.getLength(); t++)     
                    {
                        Node targetNode = targetList.item(t);
                        if(targetNode.getNodeType() == Node.ELEMENT_NODE)
                        {
                            Element targetElement = (Element) targetNode;


                            if(targetElement.getAttribute("position").equals(""))
                            {
                                System.out.println("target partner: " + targetElement.getAttribute("partner"));
                            }
                            else
                            {
                                System.out.println("target position: "+ targetElement.getAttribute("position")+ "target partner: "+ targetElement.getAttribute("partner"));

                            }
                            arr.add(targetElement.getAttribute("partner"));

                        }
                    }

                    System.out.println("-------------------------");

                }
            }

        }
        NodeList partnersList = doc.getElementsByTagName("partners");

        for (int q = 0; q < partnersList.getLength(); q++)
        {

            Node partnersNode = partnersList.item(q);
            if (partnersNode.getNodeType() == Node.ELEMENT_NODE) {
                Element partnersElement = (Element) partnersNode;
                NodeList partnerList = (NodeList) partnersElement.getElementsByTagName("partner");


                for(int w=0; w<partnerList.getLength(); w++)        
                {

                    Node partnerNode = partnerList.item(w);
                    if(partnerNode.getNodeType() == Node.ELEMENT_NODE)
                    {
                        Element partnerElement = (Element) partnerNode;

                        if(arr.contains(partnerElement.getAttribute("id"))){
                            Element partnernameElement = (Element) partnerElement.getElementsByTagName("name").item(0);
                            trgts += partnernameElement.getChildNodes().item(0).getNodeValue() + "," ;
                        }
                    }
                }
            }

        }

        trgts = trgts.substring(0, trgts.length()-1);
        System.out.println(trgts);

    } catch (Exception e) {
        e.printStackTrace();
    }
}


}

Answer 1

Null Pointer Exception意味着您尝试在空指针上执行函数。我建议你做的是弄清楚你得到的音符有多远。一次删除一个函数调用，直到找出null的发生位置，并查看是否可以找出该值返回null的原因。

nameElement.getChildNodes().item(0).getNodeValue().equals(str)

尝试使用dom解析xml页面时获取空指针异常

1 个答案: