How to generate XML data from XSD using Java?

Question

In an application I'm working on I need to generate sample data (XML instance) from XSD. I have XSD in the form of a String and need to generate respective XML as String again.

For example consider the below XSD

<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Employee">
    <xs:complexType>
      <xs:sequence>
        <xs:element type="xs:string" name="name"/>
        <xs:element type="xs:byte" name="age"/>
        <xs:element type="xs:string" name="role"/>
        <xs:element type="xs:string" name="gender"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

I want to generate

<Employee>
  <name>string</name>
  <age>2</age>
  <role>string</role>
  <gender>string</gender>
</Employee>

After searching for a while came across various online tools which does this, but I want to be able to achieve it using Java . Also there are IDEs like Eclipse, Netbeans, IntelliJ which are able to achieve the desired functionality, except that they rely on XSD to be given as a File.

After bit of searching around seems like most of these use Apache XMLBeans .

I tried following the installation guide and setup all the environment variables mentioned like below

export XMLBEANS_HOME=/home/user/Programs/xmlbeans-3.1.0
PATH=$PATH:$XMLBEANS_HOME/bin
export CLASSPATH=$XMLBEANS_HOME/lib/xmlbeans-3.1.0.jar:$CLASSPATH
export XMLBEANS_LIB=/home/user/Programs/xmlbeans-3.1.0/lib/xmlbeans-3.1.0.jar

After all this if I run the command given below

./xsd2inst ../../Schema.xsd

I get error

Error: Could not find or load main class org.apache.xmlbeans.impl.xsd2inst.SchemaInstanceGenerator

Questions:

1. What can I do to fix this error?
2. If I get this working I can probably invoke the this command from a java process after writing XSD string in to a file and pass that as an argument to the command just like I have shown above. But I don't think this is an elegant solution, Is there any other way to accomplish what I have mentioned?

Note:

1. I cannot make use of any commercial products/libraries.
2. I'm aware of using JAXB, but that will require me to create a POJO for the types that I want to generate data for which isn't something that I can do since XSD data is dynamic and I cannot reuse those POJOs even if I create it.

Answer 1

After digging in a little bit, realised the environment variable value for XMLBEANS_LIB is wrongly set. The XMLBEANS_LIB expects to be pointed to the lib directory of the XML Beans distribution not to xmlbeans-3.1.0.jar . So the correct value for that is

 export XMLBEANS_LIB=/home/user/Programs/xmlbeans-3.1.0/lib

I was able to generate the XMLInstance (as a String) using XSD ( given as String) using the below code.

import org.apache.xmlbeans.SchemaType;
import org.apache.xmlbeans.SchemaTypeSystem;
import org.apache.xmlbeans.XmlBeans;
import org.apache.xmlbeans.XmlException;
import org.apache.xmlbeans.XmlObject;
import org.apache.xmlbeans.XmlOptions;
import org.apache.xmlbeans.impl.xsd2inst.SampleXmlUtil;
import org.apache.xmlbeans.impl.xsd2inst.SchemaInstanceGenerator;

import java.util.ArrayList;
import java.util.List;

public class XmlInstanceGeneratorImpl {
  private static final Logger logger = LogManager.getLogger(XmlInstanceGeneratorImpl.class);

  /**
   * Specifies if network downloads are enabled for imports and includes.
   * Default value is {@code false}
   */
  private static final boolean ENABLE_NETWORK_DOWNLOADS = false;

  /**
   * disable particle valid (restriction) rule
   * Default value is {@code false}
   */
  private static final boolean NO_PVR = false;

  /**
   * disable unique particle attribution rule.
   * Default value is {@code false}
   */
  private static final boolean NO_UPA = false;


  public String generateXmlInstance(String xsdAsString, String elementToGenerate){
    return generateXmlInstance(xsdAsString, elementToGenerate, ENABLE_NETWORK_DOWNLOADS, NO_PVR, NO_UPA);
  }


  public String generateXmlInstance(String xsAsString, String elementToGenerate, boolean enableDownloads,
                                    boolean noPvr, boolean noUpa){
    List<XmlObject> schemaXmlObjects = new ArrayList<>();
    try {
      schemaXmlObjects.add(XmlObject.Factory.parse(xsAsString));
    } catch (XmlException e) {
      logger.error("Error Occured while Parsing Schema",e);
    }
    XmlObject[] xmlObjects = schemaXmlObjects.toArray(new XmlObject[1]);
    SchemaInstanceGenerator.Xsd2InstOptions options = new SchemaInstanceGenerator.Xsd2InstOptions();
    options.setNetworkDownloads(enableDownloads);
    options.setNopvr(noPvr);
    options.setNoupa(noUpa);
    return xsd2inst(xmlObjects, elementToGenerate, options);
  }

  private String xsd2inst(XmlObject[] schemas, String rootName, SchemaInstanceGenerator.Xsd2InstOptions options){
    SchemaTypeSystem schemaTypeSystem = null;
    if (schemas.length > 0) {
      XmlOptions compileOptions = new XmlOptions();
      if (options.isNetworkDownloads())
        compileOptions.setCompileDownloadUrls();
      if (options.isNopvr())
        compileOptions.setCompileNoPvrRule();
      if (options.isNoupa())
        compileOptions.setCompileNoUpaRule();
      try {
        schemaTypeSystem = XmlBeans.compileXsd(schemas, XmlBeans.getBuiltinTypeSystem(), compileOptions);
      } catch (XmlException e) {
        logger.error("Error occurred while compiling XSD",e);
      }
    }
    if (schemaTypeSystem == null) {
      throw new RuntimeException("No Schemas to process.");
    }

    SchemaType[] globalElements = schemaTypeSystem.documentTypes();
    SchemaType elem = null;
    for (SchemaType globalElement : globalElements) {
      if (rootName.equals(globalElement.getDocumentElementName().getLocalPart())) {
        elem = globalElement;
        break;
      }
    }
    if (elem == null) {
      throw new RuntimeException("Could not find a global element with name \"" + rootName + "\"");
    }
    // Now generate it and return the result
    return SampleXmlUtil.createSampleForType(elem);
  }
}