HTML 5 validation in Java (based on the Nu HTML Checker)

pom.xml

<!-- Add this in your POM -->
<dependency>
	<groupId>nu.validator</groupId>
	<artifactId>validator</artifactId>
	<version>15.3.14</version>
	<scope>test</scope>
	<exclusions>
		<exclusion>
			<groupId>org.eclipse.jetty</groupId>
			<artifactId>*</artifactId>
		</exclusion>
	</exclusions>
</dependency>

Validator.java

/**
 * Verifies that a HTML content is valid.
 * @param htmlContent the HTML content
 * @return true if it is valid, false otherwise
 * @throws Exception
 */
public boolean validateHtml( String htmlContent ) throws Exception {

	InputStream in = new ByteArrayInputStream( htmlContent.getBytes( "UTF-8" ));
	ByteArrayOutputStream out = new ByteArrayOutputStream();

	SourceCode sourceCode = new SourceCode();
	ImageCollector imageCollector = new ImageCollector(sourceCode);
	boolean showSource = false;
	MessageEmitter emitter = new TextMessageEmitter( out, false );
	MessageEmitterAdapter errorHandler = new MessageEmitterAdapter( sourceCode, showSource, imageCollector, 0, false, emitter );
	errorHandler.setErrorsOnly( true );

	SimpleDocumentValidator validator = new SimpleDocumentValidator();
	validator.setUpMainSchema( "http://s.validator.nu/html5-rdfalite.rnc", new SystemErrErrorHandler());
	validator.setUpValidatorAndParsers( errorHandler, true, false );
	validator.checkHtmlInputSource( new InputSource( in ));

	return 0 == errorHandler.getErrors();
}

The errors flow from SimpleDocumentValidator into the MessageEmitterAdapter into the TextMessageEmitter into the ByteArrayOutputStream.

To actually see them you'll have to call errorHandler.end(...) before reading out.

I agree a nicer way to 'programmatically' collect the errors would be great, but I didn't see anything particulary nice yet.