Resource access in Maven projects.

AccessFileOnClasspath

/**
 * <p>Shows how files in the class path can be accessed when using the standard
 * Maven directory layout.</p>
 * 
 * <p>The test file is "src/test/resources/accessFileOnClasspath/test.txt".
 * It is accessed using either {@link ClassLoader#getResource(String)} or
 * {@link ClassLoader#getResourceAsStream(String)}. Note that the file's
 * path is always relative to the class path's root. Thus the test file is
 * accessed using "accessFileOnClasspath/test.txt".</p>
 * 
 * <p>When using the {@link Class#getResource(String)} and 
 * {@link Class#getResourceAsStream(String)} methods, the file's paths are
 * always relative to the package folder of the accessing class (
 * see {@link AccessFileOnClasspath#accessThisNoClassLoader()}.</p> 
 * 
 */
public class AccessFileOnClasspath {

	public static final String FILE = "accessFileOnClasspath/test.txt";
	public static final String FILE_CONTENT = "Test";
	public static final String CLASS_FILE = AccessFileOnClasspath.class.getSimpleName() + ".class";
	
	/**
	 * When not using {@link Class#getResource(String)} to access a file
	 * the directory of the given path is relative to the package folder
	 * of that class.
	 */
	@Test
	public void accessThisNoClassLoader() {
		
		/* 
		 * The class file is not found because the base directory is not set to
		 * the root of the class path, but ...
		 */
		URL testFile = this.getClass().getResource(FILE);
		Assert.assertNull(testFile);
		
		/* 
		 * ... the class file is found because the base directory is set to 
		 * the package folder of the class.
		 */
		URL classFile = this.getClass().getResource(CLASS_FILE);
		Assert.assertNotNull(classFile);
	}
	
	@Test
	public void accessThis() throws IOException {
		
		InputStream inputStream = 
				this.getClass().getClassLoader().getResourceAsStream(FILE);
		
		Assert.assertNotNull(inputStream);
		
		testFileContent(inputStream);
		
	}
	
	@Test
	public void accessStatic() throws IOException {
		
		InputStream inputStream = 
				AccessFileOnClasspath.class
				.getClassLoader().getResourceAsStream(FILE);
		
		Assert.assertNotNull(inputStream);
		
		testFileContent(inputStream);
		
	}
	
	
	@Test
	public void accessThisUrl() 
	throws URISyntaxException, IOException {
		
		URL url = 
				this.getClass().getClassLoader().getResource(FILE);
		
		Assert.assertNotNull(url);
		
		testFileContent(url);
	}
	
	@Test
	public void accessStaticUrl() 
	throws URISyntaxException, IOException {
		
		URL url = 
				AccessFileOnClasspath.class
				.getClassLoader().getResource(FILE);
		
		Assert.assertNotNull(url);
		
		testFileContent(url);
	}
	
	/**
	 * Generates an {@link InputStream} from the given {@link URL} and passes
	 * it to {@link AccessFileOnClasspath#testFileContent(InputStream)}.
	 * 
	 * @param url
	 * @throws IOException
	 * @throws URISyntaxException
	 */
	public void testFileContent(URL url) 
	throws IOException, URISyntaxException {
		
		File file = new File(url.toURI());
		InputStream inputStream = new FileInputStream(file);
		
		testFileContent(inputStream);
	}
	
	/**
	 * Checks the first line of the given {@link InputStream} and closes it.
	 *
	 * @param inputStream
	 * @throws IOException
	 */
	public void testFileContent(InputStream inputStream) throws IOException {
		
		BufferedReader reader = 
				new BufferedReader(new InputStreamReader(inputStream));
		
		String line = reader.readLine();
		
		Assert.assertEquals(FILE_CONTENT, line);
		
		reader.close();
	}
}