When dealing with XML, first make sure that the XML is well-formed, and then consider validation. 1. well-formed means that XML must follow XML syntax rules, such as tag closure. 2. validation refers to checking whether XML complies with a specific schema, such as DTD or XSD. Make sure these two steps make the XML document syntax correct and comply with business rules.

When dealing with XML, first make sure that the XML is well-formed, and then consider validation. Let's dive into these two concepts and share some practical experiences.

When processing XML, make sure that the XML is well-formed, which means that the XML document must follow XML syntax rules. Without well-formed XML documentation, any further processing or verification is meaningless. For example, if your XML document has an unclosed tag, it is not well-formed and any XML parser will refuse to process it.

 <!-- This is a well-formed XML document -->
<root>
    <child>Content</child>
</root>

<!-- This is not well-formed, because the <child> tag is not closed-->
<root>
    <child>Content
</root>

After ensuring that the XML is well-formed, you can consider validation next. Validation refers to checking whether an XML document complies with a specific schema (such as DTD, XSD, etc.). It's like checking whether your XML document complies with a specific "contract" or "rule set". For example, if you have an XSD file that defines the structure of an XML document, you can use this XSD file to verify that your XML complies with these rules.

 <!-- This is a simple XSD file -->
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="root">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="child" type="xs:string"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

<!-- This is an XML document that complies with the above XSD-->
<root>
    <child>Content</child>
</root>

In actual projects, I found that making sure XML is well-formed is usually automated, because most modern programming languages ??and tools have built-in XML parsers that automatically check if XML is well-formed. If the XML is not well-formed, the parser throws an exception, which makes the problem easy to detect and fix.

However, validation usually requires more configuration and manual work. For example, in Java, you can use JAXB (Java Architecture for XML Binding) to verify that the XML document complies with an XSD file. Here is a simple example:

 import javax.xml.XMLConstants;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.util.JAXBSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;

public class XMLValidator {
    public static void main(String[] args) {
        try {
            // Create JAXB context JAXBContext jc = JAXBContext.newInstance(Root.class);

            // Create JAXB source JAXBSource source = new JAXBSource(jc, new Root());

            // Create schema factory SchemaFactory sf = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);

            // Load the XSD file Schema schema = sf.newSchema(XMLValidator.class.getResource("schema.xsd"));

            // Create a validator Validator validator = schema.newValidator();

            // Verify XML
            validator.validate(source);
            System.out.println("XML is valid");
        } catch (Exception e) {
            System.out.println("XML is not valid: " e.getMessage());
        }
    }
}

When using validation, I find a common challenge to make sure that XSD files and XML documents are kept in sync. If the XSD file is modified but the XML document is not updated accordingly, the verification may fail. This requires good communication and version control between teams.

Another thing to note is that excessive dependence on validation can lead to insufficient flexibility. In some cases, you may want XML documents to be flexible rather than strictly abide by a certain pattern. In this case, consider using a looser pattern, or providing more friendly error messages when verification fails, rather than simply rejecting processing.

Overall, making sure XML is well-formed, this is the first step in dealing with XML, and then consider validation. Through these two steps, you can ensure that your XML document is not only syntax correct, but also complies with specific business rules.

The above is the detailed content of XML: well formed and validation , what is first?. For more information, please follow other related articles on the PHP Chinese website!