如何在startElement中使用SAX解析器从XML获取元素的值？ [英] How to get element's value from XML using SAX parser in startElement?

问题描述

是否可以从 startElement 函数中的XML文件中获取元素的内容，该函数是SAX处理程序的覆盖函数？

Is it possible to get the content of an element from a XML file in startElement function that is the override function of the SAX handler?

以下是规范。

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 function

2) startElement function

@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

推荐答案

你可以得到元素的名称在 startElement 和 endElement 中。您还可以在 startElement 中获取属性。你应该用字符获得的值。

You can get the element's name in startElement and endElement. You can also get attributes in startElement. Values you should get in characters.

以下是关于如何使用 ContentHandler 非常基本的示例 $ c>：

Here is a very basic example on how to get the value of an element using a ContentHandler:

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，设置布尔值每个标记的标记都可以。如果你有一个更复杂的场景，你可能更喜欢使用元素名称作为键将标记存储在地图中，或者甚至创建一个或多个 Employee 映射到XML的类，每次在 startElement 中找到< employee> 时，实例化它们，填充其属性，以及将其添加到 endElement 。

If you have a simple example, setting boolean flags for each tag is OK. If you have a more complex scenario, you might prefer store the flags in a map using element names as keys, or even create one or more Employee classes mapped to your XML, instantiate them every time <employee> is found in startElement, populate its properties, and add it to a Collection in endElement.

这是一个完整的 ContentHandler 示例，它适用于您的示例文件。我希望它可以帮助您入门：

Here is a complete ContentHandler example that works with your example file. I hope it helps you get started:

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);
        }
    }
}

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