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

How to get element's value from XML using SAX parser in startElement?

提问by sakura

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

是否可以从作为startElementSAX 处理程序的覆盖函数的函数中的XML 文件中获取元素的内容？

Below is the specification.

下面是规格。

1) XML file

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) startElementfunction

2)startElement功能

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

3) Expected result

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

回答by helderdarocha

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

您可以在和 中获取元素的名称。您还可以在. 你应该得到的价值观。startElementendElementstartElementcharacters

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

这是一个非常基本的示例，说明如何使用 a 获取元素的值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
        }
    }
}

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 Employeeclasses mapped to your XML, instantiate them every time <employee>is found in startElement, populate its properties, and add it to a Collection in endElement.

如果你有一个简单的例子，为每个标签设置布尔标志就可以了。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映射中，甚至创建一个或多个Employee映射到您的 XML 的类，每次<employee>在 中找到时实例化它们startElement，填充其属性，然后添加它到endElement.

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

这是一个ContentHandler适用于您的示例文件的完整示例。我希望它可以帮助您入门：

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);
        }
    }
}