Exemplo de validação de Schema XML usando api padrão do Java. Se o XML estiver OK, nada ocorre. Se estiver errado, será lançada uma org.xml.sax.SAXParseException.

pedido.xml

<?xml version="1.0" encoding="UTF-8"?>

<pedido id="1"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="pedido.xsd">
  <cliente>João</cliente>
  <destino>
    <nomekkk>Maria</nomekkk>
    <endereco>SCS 1</endereco>
    <cidade>Brasília</cidade>
  </destino>
  <item>
    <produto>Apostila Java</produto>
    <quantidade>1</quantidade>
    <preco>10.90</preco>
  </item>
  <item>
    <produto>Apostila Javascript</produto>
    <quantidade>1</quantidade>
    <preco>9.90</preco>
  </item>
</pedido>

pedido.xsd

<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xs:element name="pedido">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="cliente" type="xs:string"/>
      <xs:element name="destino">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="nome" type="xs:string"/>
            <xs:element name="endereco" type="xs:string"/>
            <xs:element name="cidade" type="xs:string"/>
          </xs:sequence>
        </xs:complexType>
      </xs:element>
      <xs:element name="item" maxOccurs="unbounded">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="produto" type="xs:string"/>
            <xs:element name="quantidade" type="xs:positiveInteger"/>
            <xs:element name="preco" type="xs:decimal"/>
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
    <xs:attribute name="id" type="xs:string" use="required"/>
  </xs:complexType>
</xs:element>

</xs:schema>

Teste.java

package validador;

import java.io.File;

public class Teste {

	public static void main(String[] args) throws Exception {
		Validador validador = new Validador();
		validador.valida(new File("pedido.xml"), new File("pedido.xsd"));
	}
}

Validador.java

package validador;

import java.io.File;

import javax.xml.XMLConstants;
import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;

public class Validador {
	
	public void valida(File xml, File xsd) throws Exception{
		Source schemaFile = new StreamSource(xsd);
		Source xmlFile = new StreamSource(xml);
		SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
		Schema schema = schemaFactory.newSchema(schemaFile);
		Validator validator = schema.newValidator();
		validator.validate(xmlFile);
	}

}