java - 如何在 startElement 中使用 SAX 解析器从 XML 中获取元素的值？

Question

是否可以在 startElement 函数(SAX 处理程序的覆盖函数)中从 XML 文件中获取元素的内容？

下面是规范。

1) XML文件

<employees>
   <employee id="111">
      <firstName>Rakesh</firstName>
      <lastName>Mishra</lastName>
      <location>Bangalore</location>
   </employee>
   <employee id="112">
      <firstName>John</firstName>
      <lastName>Davis</lastName>
      <location>Chennai</location>
   </employee>
   <employee id="113">
      <firstName>Rajesh</firstName>
      <lastName>Sharma</lastName>
      <location>Pune</location>
   </employee>
</employees>

2) startElement 函数

@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
    .......code in here..........
}

3)预期结果

element name   : employee
attribute name : id
attribute value: 111
firstName      : Rakesh
lastName       : Mishra
location       : Bangalore

element name   : employee
attribute name : id
attribute value: 112
firstName      : John
lastName       : Davis
location       : Chennai

element name   : employee
attribute name : id
attribute value: 113
firstName      : Rajesh
lastName       : Sharma
location       : Pune

Answer 1

您可以在 startElement 中获取元素的名称和 endElement .您还可以在 startElement 中获取属性.您应该在 characters 中获得的值.

这是一个关于如何使用 ContentHandler 获取元素值的非常基本的示例 :

public class YourHandler extends DefaultHandler {

    boolean inFirstNameElement = false;

    public class startElement(....) {
        if(qName.equals("firstName") {
            inFirstNameElement = true;
        }
    }

    public class endElement(....) {
        if(qName.equals("firstName") {
            inFirstNameElement = false;
        }
    }

    public class characters(....) {
        if(inFirstNameElement) {
            // do something with the characters in the <firstName> element
        }
    }
}

如果你有一个简单的例子，为每个标签设置 boolean 标志是可以的。如果您有更复杂的场景，您可能更喜欢使用元素名称作为键将标志存储在 map 中，甚至创建一个或多个 Employee映射到您的 XML 的类，每次都实例化它们 <employee>在 startElement 中找到，填充其属性，并将其添加到 endElement 中的集合中.

这是一个完整的 ContentHandler适用于您的示例文件的示例。我希望它能帮助您入门:

public class SimpleHandler extends DefaultHandler {

    class Employee {
        public String firstName;
        public String lastName;
        public String location;
        public Map<String, String> attributes = new HashMap<>();
    }
    boolean isFirstName, isLastName, isLocation;
    Employee currentEmployee;
    List<Employee> employees = new ArrayList<>();

    @Override
    public void startElement(String uri, String localName, String qName,
            Attributes atts) throws SAXException {
        if(qName.equals("employee")) {
            currentEmployee = new Employee();
            for(int i = 0; i < atts.getLength(); i++) {
                currentEmployee.attributes.put(atts.getQName(i),atts.getValue(i));
            }
        }
        if(qName.equals("firstName")) { isFirstName = true; }
        if(qName.equals("lastName"))  { isLastName = true;  }
        if(qName.equals("location"))  { isLocation = true;  }
    }

    @Override
    public void endElement(String uri, String localName, String qName)
            throws SAXException {
        if(qName.equals("employee")) {
            employees.add(currentEmployee);
            currentEmployee = null;
        }
        if(qName.equals("firstName")) { isFirstName = false; }
        if(qName.equals("lastName"))  { isLastName = false;  }
        if(qName.equals("location"))  { isLocation = false;  }
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        if (isFirstName) {
            currentEmployee.firstName = new String(ch, start, length);
        }
        if (isLastName) {
            currentEmployee.lastName = new String(ch, start, length);
        }
        if (isLocation) {
            currentEmployee.location = new String(ch, start, length);
        }
    }

    @Override
    public void endDocument() throws SAXException {
        for(Employee e: employees) {
            System.out.println("Employee ID: " + e.attributes.get("id"));
            System.out.println("  First Name: " + e.firstName);
            System.out.println("  Last Name: " + e.lastName);
            System.out.println("  Location: " + e.location);
        }
    }
}