我正在尝试编写一个读取XML文件的java程序，并返回用户感兴趣的各种元素。我有一些问题需要编译，我已经创建了一个测试类，以便正确显示它。这是我迄今为止所拥有的。
编辑：测试课中的粗线让我有问题。该错误无法从String转换为Resources。public class T_Resources {
public static void main(String[] args) {
Resources resources = ResourceImporter.importResourcesFromXML("http://free1.ed.gov/xml/gemexport.xml");
displayResources(resources);
}
private static void displayResources(Resources resources) {
Subject[] subjects;
**Resources resource = resources.getTitle();**
System.out.println(resource.getTitle());
System.out.println(resource.getDescription());
System.out.println(resource.getIdentifier());
subjects = resource.getSubjects();
for (int i=0; i < subjects.length; ++i) {
System.out.println(subjects[i].getCategory() + " :: " + subjects[i].getSubcategory());
}
System.out.println();
}
}
import java.io.File;
import java.io.IOException;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
public class ResourceImporter {
// This operation loads the XML document specified by the document location, which can a file or a URL,
// and returns a reference to the document. If the operation cannot successfully load the document
// the operation returns the null reference.
//
private static Document loadXMLDocument(String documentLocation) {
// The XML document.
//
Document documentIn = null;
// The parser that reads in an XML files.
//
DocumentBuilder parser = null;
// Pull the document
//
try {
// Obtain a document parser.
//
DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
builderFactory.setNamespaceAware(true);
parser = builderFactory.newDocumentBuilder();
documentIn = parser.parse(documentLocation);
} catch (ParserConfigurationException p) {
System.out.println("Error creating parser.");
System.out.println(" " + p.getMessage());
} catch (SAXException s) {
System.out.println("Document is not well formed.");
System.out.println(" " + s.getMessage());
} catch (IOException i) {
System.out.println("Error accessing the file.");
System.out.println(" " + i.getMessage());
} catch (Exception e) {
System.out.println("Unknown error occurred.");
System.out.println(" " + e.getMessage());
}
return documentIn;
}
public static Resources importResourcesFromXML(String documentLocation) {
Resources resource = new Resources();
Document doc;
Element resourceElement;
Element titleElement;
String title;
Element descriptionElement;
String description;
Element identifierElement;
String identifiers;
Element urlElement;
String url;
NodeList subjectList;
Element subjectElement;
String subjects;
Element categoryElement;
String category;
Element subcategoryElement;
String subcategory;
doc = loadXMLDocument(documentLocation);
resourceElement = (Element)doc.getElementsByTagName("resource").item(0);
if (resourceElement != null) {
titleElement = (Element)resourceElement.getElementsByTagName("title").item(0);
resource.setTitle( titleElement == null ? "unknown" : titleElement.getTextContent() );
descriptionElement = (Element)resourceElement.getElementsByTagName("description").item(0);
resource.setDescription( descriptionElement == null ? "unknown" : descriptionElement.getTextContent() );
identifierElement = (Element)resourceElement.getElementsByTagName("identifier").item(0);
if (identifierElement != null) {
Identifier identifier = new Identifier();
urlElement = (Element)identifierElement.getElementsByTagName("url").item(0);
identifier.setURL( urlElement == null ? "unknown" : urlElement.getTextContent() );
subjectElement = (Element)resourceElement.getElementsByTagName("subjects").item(0);
if (subjectElement != null) {
subjectList = subjectElement.getElementsByTagName("subject");
for (int i=0; i < subjectList.getLength(); ++i) {
Subject subject = new Subject();
subjectElement = (Element)subjectList.item(i);
categoryElement = (Element)subjectElement.getElementsByTagName("category").item(0);
subject.setCategory( categoryElement == null ? "unknown" : categoryElement.getTextContent() );
subcategoryElement = (Element)subjectElement.getElementsByTagName("subcategory").item(0);
subject.setSubcategory( subcategoryElement == null ? "unknown" :subcategoryElement.getTextContent() );
resource.addSubject(subject);
}
}
}
}
return resource;
}
}
public class Resources {
private static final int MAX_SUBJECTS = 20;
private String title;
private String description;
private Identifier identifier;
private Subject[] subjects;
private int subjectCount;
public Resources() {
title = "unknown title";
description = "unknown description";
identifier = null;
subjects = new Subject[MAX_SUBJECTS];
subjectCount = 0;
}
public void setTitle(String newTitle) {
title = newTitle;
}
public String getTitle() {
return title;
}
public void setDescription(String newDescription) {
description = newDescription;
}
public String getDescription() {
return description;
}
public void setIdentifier(Identifier newIdentifier) {
identifier = newIdentifier;
}
public Identifier getIdentifier() {
return identifier;
}
public void addSubject(Subject newSubject) {
subjects[subjectCount++] = newSubject;
}
public Subject[] getSubjects() {
Subject[] result = new Subject[subjectCount];
System.arraycopy(subjects, 0, result, 0, subjectCount);
return result;
}
}
public class Subject {
private String category;
private String subcategory;
public Subject() {
String category = "unknown";
String subcategory = "unknown";
}
public Subject(Subject subject) {
category = subject.category;
subcategory = subject.subcategory;
}
public void setCategory(String newCategory) {
category = (newCategory == null) ? "unknown" : newCategory;
}
public String getCategory() {
return category;
}
public void setSubcategory(String newSubcategory) {
subcategory = newSubcategory;
}
public String getSubcategory() {
return subcategory;
}
}
public class Identifier {
private String url;
public Identifier() {
url = "unknown";
}
public void setURL(String newURL) {
url = newURL;
}
public String getURL() {
return url;
}
}
答案 0 :(得分：1)
private static void displayResources(Resources resources) {
Subject[] subjects;
// DELETE THIS
// **Resources resource = resources.getTitle();**
// RENAME 'resource' to 'resources', or just change the method parameter above...
System.out.println(resources.getTitle());
//System.out.println(resource.getTitle());
System.out.println(resources.getDescription());
//System.out.println(resource.getDescription());
System.out.println(resources.getIdentifier());
//System.out.println(resource.getIdentifier());
....
您传递了一个资源对象，通常您希望直接使用它？
目前这看起来似乎只是在这里，所有其他代码都可以工作，我测试并获得了奇特的控制台输出。
在以下评论后的ResourceImporter.java添加行中：
if (resourceElement != null) {
titleElement = (Element)resourceElement.getElementsByTagName("title").item(0);
resource.setTitle( titleElement == null ? "unknown" : titleElement.getTextContent() );
descriptionElement = (Element)resourceElement.getElementsByTagName("description").item(0);
resource.setDescription( descriptionElement == null ? "unknown" : descriptionElement.getTextContent() );
identifierElement = (Element)resourceElement.getElementsByTagName("identifier").item(0);
if (identifierElement != null) {
Identifier identifier = new Identifier();
urlElement = (Element)identifierElement.getElementsByTagName("url").item(0);
identifier.setURL( urlElement == null ? "unknown" : urlElement.getTextContent() );
// ADDED THIS LINE HERE
resource.setIdentifier(identifier);
subjectElement = (Element)resourceElement.getElementsByTagName("subjects").item(0);
if (subjectElement != null) {
subjectList = subjectElement.getElementsByTagName("subject");
....
您可能还希望在主方法中使用的辅助方法中使用此行作为syso：System.out.println(resources.getIdentifier().getURL());，否则您将获得无法解释的信息。
答案 1 :(得分：1)
我要改变
private static void displayResources(Resources resources)
到
private static void displayResources(Resources resource)
（注意我删除了's'），并删除粗线。
如JB Nizet所述，当您需要传递给静态方法的资源时，您的方法返回一个String。
答案 2 :(得分：0)
getTitle（）方法声明为
public String getTitle()
但是您将其结果分配给类型为Resources的变量：
Resources resource = resources.getTitle();
这显然不起作用，因此错误，这是非常不言自明的：
无法从String转换为资源
你可能想要
String title = resources.getTitle();
代替。