Convert Java Objects to XML and XML to Java Objects with XStream

Once I got to deal with an incident where I had to load a lot of data (20 MB+) from the DB and populate it as java object (the java object is of many nested / referenced classes), and I needed to load that every time I started my server. Though we have a distributed cache in place, subsequent loads would be very fast. However, the first time load was taking more than 9 minutes...

I was thinking that rather than loading from the DB on server restart, I could load from the local file!! (as the data in the db updates less often) that's where I got to learn about the XStream Library, and it's so simple that I could convert any java object to XML and back.

Here I will show you how easy it is to use the XStream library

First let's create a Sample Object (you can use any existing class as well) as follows

SampleObject.java

public class SampleObject { 
 private String name="Test"; 
 private int testInt ; 
 public String getName() { 
 return name; 
 } 
 public void setName(String name) { 
 this.name = name; 
 } 
 public int getTestInt() { 
 return testInt; 
 } 
 public void setTestInt(int testInt) { 
 this.testInt = testInt; 
 } 
 } 

and a helper class for conversion XStreamTranslator.java

 import java.io.File; 
 import java.io.FileReader; 
 import java.io.FileWriter; 
 import java.io.IOException; 
 import java.util.Iterator; 
 import java.util.List; 
 import com.thoughtworks.xstream.XStream; 

 public final class XStreamTranslator { 
 private XStream xstream = null; 
 private XStreamTranslator(){ 
 xstream = new XStream(); 
 xstream.ignoreUnknownElements(); 
} 
 /** 
 * Convert a any given Object to a XML String 
 * @param object 
 * @return 
 */ 
 public String toXMLString(Object object) { 
 return xstream.toXML(object); 
 } 
 /** 
 * Convert given XML to an Object 
 * @param xml 
 * @return 
 */ 
 public Object toObject(String xml) { 
 return (Object) xstream.fromXML(xml); 
 } 
 /** 
 * return this class instance 
 * @return 
 */ 
 public static XStreamTranslator getInstance(){ 
 return new XStreamTranslator(); 
 } 
 /** 
 * convert to Object from given File 
 * @param xmlFile 
 * @return 
 * @throws IOException 
 */ 
 public Object toObject(File xmlFile) throws IOException { 
 return xstream.fromXML(new FileReader(xmlFile)); 
 } 
 /** 
 * create XML file from the given object with custom file name 
 * @param fileName 
 * @param file 
 * @throws IOException 
 */ 
 public void toXMLFile(Object objTobeXMLTranslated, String fileName ) throws IOException { 
 FileWriter writer = new FileWriter(fileName); 
 xstream.toXML(objTobeXMLTranslated, writer); 
 writer.close(); 
 } 
 public void toXMLFile(Object objTobeXMLTranslated, String fileName, List omitFieldsRegXList) throws IOException { 
 xstreamInitializeSettings(objTobeXMLTranslated, omitFieldsRegXList); 
 toXMLFile(objTobeXMLTranslated, fileName); 
 } 
 /** 
 * @ 
 * @param objTobeXMLTranslated 
 */ 
 public void xstreamInitializeSettings(Object objTobeXMLTranslated, List omitFieldsRegXList) { 
 if(omitFieldsRegXList != null && omitFieldsRegXList.size() > 0){ 
 Iterator itr = omitFieldsRegXList.iterator(); 
 while(itr.hasNext()){ 
 String omitEx = itr.next(); 
 xstream.omitField(objTobeXMLTranslated.getClass(), omitEx); 
 } 
 } 
 } 
 /** 
 * create XML file from the given object, file name is generated automatically (class name) 
 * @param objTobeXMLTranslated 
 * @throws IOException 
 * @throws XStreamTranslateException 
 */ 
 public void toXMLFile(Object objTobeXMLTranslated) throws IOException { 
 toXMLFile(objTobeXMLTranslated,objTobeXMLTranslated.getClass().getName()+".xml"); 
 } 
 }

few Test cases to verify

import static org.junit.Assert.assertEquals; 
 import static org.junit.Assert.assertNotNull; 
 import static org.junit.Assert.assertTrue; 
 import java.io.File; 
 import java.io.IOException; 
 import java.util.ArrayList; 
 import java.util.List; 
 import org.apache.commons.io.FileUtils; 
 import org.junit.After; 
 import org.junit.Before; 
 import org.junit.Test; 

 public class XStreamTranslatorTest { 
 SampleObject sampleObj; 
 XStreamTranslator xStreamTranslatorInst; 
 /** 
 * @throws java.lang.Exception 
 */ 
 @Before 
 public void setUp() throws Exception { 
 sampleObj = new SampleObject(); 
 xStreamTranslatorInst = XStreamTranslator.getInstance(); 
 } 
 /** 
 * @throws java.lang.Exception 
 */ 
 @After 
 public void tearDown() throws Exception { 
 } 
 @Test 
 public void simpleObjectToXMLStringNotNullTest() { 
 String xml = xStreamTranslatorInst.toXMLString(sampleObj); 
 assertNotNull(xml); 
 } 
 @Test 
 public void simpleObjectToXMLStringVerifyTest() { 
 sampleObj.setName("Test"); 
 assertEquals("Test",sampleObj.getName()); 
 sampleObj.setTestInt(9); 
 assertEquals(9,sampleObj.getTestInt()); 
 String xml = xStreamTranslatorInst.toXMLString(sampleObj); 
 String expected = getExpectedStringOutOfSampleObject(); 
 assertEquals(expected, xml.replaceAll("[\\n\\s\\t]+", "")); 
 } 
 @Test 
 public void xmlToObjectVerifyTest(){ 
 String xml = getExpectedStringOutOfSampleObject(); 
 SampleObject sampleObj = (SampleObject) xStreamTranslatorInst.toObject(xml); 
 assertNotNull(sampleObj); 
 } 
 @Test (expected=IOException.class) 
 public void xmlToAnyObjectFromFileThatNotExists() throws IOException{ 
 SampleObject sampleObj = (SampleObject) xStreamTranslatorInst.toObject(new File("C:\\MyHome\\mySampleCodes\\xstream-samples\\src\\test\\resources\\testNoFile.xml")); 
 assertNotNull(sampleObj); 
 assertEquals("somename",sampleObj.getName()); 
 } 
 @Test 
 public void xmlToAnyObjectFromFile() throws IOException{ 
 SampleObject sampleObj = (SampleObject) xStreamTranslatorInst.toObject(new File("C:\\MyHome\\mySampleCodes\\xstream-samples\\src\\test\\resources\\testSampleObject.xml")); 
 assertNotNull(sampleObj); 
 assertEquals("Test",sampleObj.getName()); 
 } 
 @Test 
 public void objToXmlFileTestForNotNull() throws IOException { 
 SampleObject sampleObj = new SampleObject(); 
 sampleObj.setName("Test2"); 
 assertEquals("Test2",sampleObj.getName()); 
 sampleObj.setTestInt(99); 
 assertEquals(99,sampleObj.getTestInt()); 
 xStreamTranslatorInst.toXMLFile(sampleObj); 
 File file = new File(sampleObj.getClass().getName()+".xml"); 
 assertTrue(file.exists()); 
 String sample = FileUtils.readFileToString(file); 
 assertNotNull(sample); 
 } 
 @Test 
 public void objToXmlFileCreate() throws IOException { 
 SampleObject sampleObj = new SampleObject(); 
 sampleObj.setName("Test2"); 
 assertEquals("Test2",sampleObj.getName()); 
 sampleObj.setTestInt(99); 
 assertEquals(99,sampleObj.getTestInt()); 
 xStreamTranslatorInst.toXMLFile(sampleObj); 
 File file = new File(sampleObj.getClass().getName()+".xml"); 
 assertTrue(file.exists()); 
 String sample = FileUtils.readFileToString(file); 
 assertNotNull(sample); 
 assertEquals(getExpectedStringOutOfSampleObject2(),sample.replaceAll("[\\n\\s\\t]+", "")); 
 } 
 private String getExpectedStringOutOfSampleObject() { 
 return "<com.mysamples.thoughtworks.xstream.SampleObject><name>Test</name><testInt>9</testInt></com.mysamples.thoughtworks.xstream.SampleObject>"; 
 } 
 private String getExpectedStringOutOfSampleObject2() { 
 return "<com.mysamples.thoughtworks.xstream.SampleObject><name>Test2</name><testInt>99</testInt></com.mysamples.thoughtworks.xstream.SampleObject>"; 
 } 
 } 

Add the following dependency in your pom.xml (dependencies section)

<dependency> 
 <groupId>com.thoughtworks.xstream</groupId> 
 <artifactId>xstream</artifactId> 
 <version>1.4.5</version> 
</dependency> 

Run your test cases and see for yourself how the xml got generated from the sample object and back to SampleObject.

following is the sample xml that I have..

<com.mysamples.thoughtworks.xstream.SampleObject> 
 <name>Test2</name> 
 <testInt>99</testInt> 
</com.mysamples.thoughtworks.xstream.SampleObject>