Java XML校验API可以通过XSD（XML Schema Definition）校验XML文件内容的合法性。

在以下的案例中使用javax.xml.validation.Validator 类通过一个xsd文件来鉴定XML内容合法性。

以下是我们将要用于校验的xsd文件和xml文件的内容。

Employee.xsd

<?

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

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://www.journaldev.com/Employee"

xmlns:empns="http://www.journaldev.com/Employee" elementFormDefault="qualified">

    <element name="empRequest" type="empns:empRequest"></element>

    <element name="empResponse" type="empns:empResponse"></element>

    <complexType name="empRequest">

        <sequence>

            <element name="id" type="int"></element>

        </sequence>

    </complexType>

    <complexType name="empResponse">

        <sequence>

            <element name="id" type="int"></element>

            <element name="role" type="string"></element>

            <element name="fullName" type="string"></element>

        </sequence>

    </complexType>

</schema>

须要注意的是上面的XSD包括两种根元素。同一时候具有命名空间，以下两种xml文件内容都是合法的：

EmployeeRequest.xml

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

<empns:empRequest xmlns:empns="http://www.journaldev.com/Employee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.journaldev.com/Employee Employee.xsd ">

  <empns:id>5</empns:id>

</empns:empRequest>

EmployeeResponse.xml

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

<empns:empResponse xmlns:empns="http://www.journaldev.com/Employee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.journaldev.com/Employee Employee.xsd ">

  <empns:id>1</empns:id>

  <empns:role>Developer</empns:role>

  <empns:fullName>Pankaj Kumar</empns:fullName>

</empns:empResponse>

以下的一个xml文件内容是不满足XSD约束的：

employee.xml

<?xml version="1.0"?

>

<Employee>

    <name>Pankaj</name>

    <age>29</age>

    <role>Java Developer</role>

    <gender>Male</gender>

</Employee>

接下来看怎样通过程序来校验这三个xml文件内容是否满足XSD的约束，validateXMLSchema方法接受两个參数，各自是xsd和xml文件的路径，假设xml文件内容是合法的，该方法返回true，否则返回false。

XMLValidation.java

package com.journaldev.xml;

import java.io.File;

import java.io.IOException;

import javax.xml.XMLConstants;

import javax.xml.transform.stream.StreamSource;

import javax.xml.validation.Schema;

import javax.xml.validation.SchemaFactory;

import javax.xml.validation.Validator;

import org.xml.sax.SAXException;

public class XMLValidation {

    public static void main(String[] args) {

      System.out.println("EmployeeRequest.xml validates against Employee.xsd?

"+validateXMLSchema("Employee.xsd", "EmployeeRequest.xml"));

      System.out.println("EmployeeResponse.xml validates against Employee.xsd?

"+validateXMLSchema("Employee.xsd", "EmployeeResponse.xml"));

      System.out.println("employee.xml validates against Employee.xsd?

"+validateXMLSchema("Employee.xsd", "employee.xml"));

      }

    public static boolean validateXMLSchema(String xsdPath, String xmlPath){

        try {

            SchemaFactory factory =

                    SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);

            Schema schema = factory.newSchema(new File(xsdPath));

            Validator validator = schema.newValidator();

            validator.validate(new StreamSource(new File(xmlPath)));

        } catch (IOException | SAXException e) {

            System.out.println("Exception: "+e.getMessage());

            return false;

        }

        return true;

    }

}

执行上面程序。控制台输出：

EmployeeRequest.xml validates against Employee.xsd?

true

EmployeeResponse.xml validates against Employee.xsd?

true

Exception: cvc-elt.1: Cannot find the declaration of element 'Employee'.

employee.xml validates against Employee.xsd? false