Simple Maven plugin example

BeautifyEclipsePlugin.java

package at.molindo.maven.plugin.beautifyeclipse;

import java.io.File;
import java.util.Collections;
import java.util.LinkedList;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugin.MojoFailureException;
import org.apache.maven.project.MavenProject;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.w3c.dom.Text;

/**
 * @goal beautify
 */
public class BeautifyEclipsePlugin extends AbstractMojo {

	public static class ClassPathEntry implements Comparable<ClassPathEntry> {

		private enum Kind {
			src, lib, output, con, var;
		}
		
		private final Kind _kind;
		private final String _name;
		private final Node _node;

		ClassPathEntry(final String kind, final String path, final Node node) {
			if (kind == null || path == null || node == null) {
				throw new NullPointerException("all arguments must be != null");
			}

			_kind = Kind.valueOf(kind);
			if (_kind == null) {
				throw new IllegalArgumentException("unknown kind: " + kind);
			}

			_name = path.substring(path.lastIndexOf("/") + 1);
			_node = node;
		}

		public int compareTo(final ClassPathEntry o) {
			if (o == null) {
				return -1;
			}

			final int val = _kind.compareTo(o._kind);
			if (val != 0) {
				return val;
			}
			return _name.compareToIgnoreCase(o._name);
		}

		@Override
		public boolean equals(final Object obj) {
			if (obj instanceof ClassPathEntry) {
				return compareTo((ClassPathEntry) obj) == 0;
			}
			return false;
		}

		@Override
		public int hashCode() {
			// better weak than wrong
			return _name.hashCode();
		}

		@Override
		public String toString() {
			return "kind=" + _kind + ", name=" + _name;
		}

		public Node getNode() {
			return _node;
		}

	}

	/**
	 * The project whose project files to create.
	 * 
	 * @parameter expression="${project}"
	 * @required
	 * @readonly
	 */
	protected MavenProject project;

	// /**
	// * The currently executed project (can be a reactor project).
	// *
	// * @parameter expression="${executedProject}"
	// * @readonly
	// */
	// protected MavenProject executedProject;

	@SuppressWarnings("unchecked")
	public void execute() throws MojoExecutionException, MojoFailureException {
		getLog().info("hey ho, let's go: " + project.getName());

		final File directory = project.getBasedir();

		beautify(new File(directory, ".classpath"));
	}

	void beautify(final File classpathFile) {
		if (!classpathFile.exists()) {
			getLog().info(".classpath file does not exist: " + classpathFile.getAbsolutePath());
			return;
		}

		final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

		try {
			final DocumentBuilder builder = factory.newDocumentBuilder();
			final Document dotClasspath = builder.parse(classpathFile);
			final NodeList entries = dotClasspath.getElementsByTagName("classpathentry");

			getLog().debug("found " + entries.getLength() + " classpath entries");

			final LinkedList<ClassPathEntry> list = new LinkedList<ClassPathEntry>();
			// read entries
			while (entries.getLength() > 0) {
				Node node = entries.item(0);
				node = node.getParentNode().removeChild(node);

				final Node kindAttr = node.getAttributes().getNamedItem("kind");
				final Node pathAttr = node.getAttributes().getNamedItem("path");
				final String kind = kindAttr.getNodeValue();
				final String path = pathAttr.getNodeValue();

				getLog().debug("kind=" + kind + ", path=" + path);

				final ClassPathEntry entry = new ClassPathEntry(kind, path, node);
				list.add(entry);
			}
			Collections.sort(list);

			getLog().debug(list.toString());
			//
			// final Document out = builder.newDocument();
			// final Node root = out.createElement("classpath");
			// out.appendChild(root);
			final Node root = dotClasspath.getFirstChild();

			// remove empty nodes
			int i = 0;
			final NodeList nodes = root.getChildNodes();
			while (i < nodes.getLength()) {
				final Node n = nodes.item(i);
				if (n instanceof Text) {
					final Text t = (Text) n;
					final String val = t.getNodeValue().trim();
					if ("".equals(val)) {
						root.removeChild(n);
						continue;
					}
				}
				// keep
				i++;
			}

			for (final ClassPathEntry e : list) {
				root.appendChild(e.getNode());
			}

			writeXmlFile(dotClasspath, classpathFile);

		} catch (final Exception e) {
			getLog().warn(e);
		}
	}

	public void writeXmlFile(final Document doc, final File file) throws Exception {
		// Prepare the DOM document for writing
		final Source source = new DOMSource(doc);
		final Result result = new StreamResult(file);

		// Write the DOM document to the file
		final Transformer xformer = TransformerFactory.newInstance().newTransformer();
		xformer.setOutputProperty(OutputKeys.INDENT, "yes");
		xformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
		xformer.transform(source, result);
	}
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-beautifyeclipse-plugin</artifactId>
	<packaging>maven-plugin</packaging>
	<version>1.0</version>
	<name>
		Beautify the Eclipse .project file of a multimodule project
	</name>

	<dependencies>
		<dependency>
			<groupId>org.apache.maven</groupId>
			<artifactId>maven-plugin-api</artifactId>
			<version>2.0</version>
		</dependency>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.4</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.apache.maven</groupId>
			<artifactId>maven-project</artifactId>
			<version>2.0</version>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<configuration>
					<source>1.5</source>
					<target>1.5</target>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>