In Java, you can use the DOM API to validate an XML document against an XML schema. XML schema is a way to describe the structure and content of an XML document, and it can be used to validate the document against a set of rules defined in the schema.

Here's an example of how to use the DOM API to validate an XML document against an XML schema:

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true);
factory.setNamespaceAware(true);
factory.setAttribute(JAXP_SCHEMA_LANGUAGE, W3C_XML_SCHEMA);

SchemaFactory schemaFactory = SchemaFactory.newInstance(W3C_XML_SCHEMA);
Schema schema = schemaFactory.newSchema(new File("schema.xsd"));

DocumentBuilder builder = factory.newDocumentBuilder();
builder.setErrorHandler(new MyErrorHandler());
builder.setSchema(schema);

Document document = builder.parse(new File("document.xml"));

In this example, a DocumentBuilderFactory is created with validation and namespace awareness enabled. The JAXP_SCHEMA_LANGUAGE attribute is set to W3C_XML_SCHEMA, which specifies that the XML schema should be used for validation. A SchemaFactory is then created, and a Schema object is obtained from the factory by parsing the XML schema file.

A DocumentBuilder is then created from the DocumentBuilderFactory, and its error handler and schema are set. The MyErrorHandler class is a custom implementation of the org.xml.sax.ErrorHandler interface, which can be used to handle validation errors that occur during parsing.

Finally, the XML document is parsed using the DocumentBuilder and the resulting Document object can be used for further processing. If the document fails to validate against the schema, an exception will be thrown.

Using the DOM API for XML schema validation is a powerful way to ensure that your XML documents conform to a specific structure and set of rules. However, it can be relatively complex and memory-intensive for large documents. If you are working with very large XML documents, you may want to consider using a different API such as StAX or SAX, which provide a more streaming-based approach to parsing and processing XML.