File utility for creating a new empty file

The java.io.File.createNewFile() method for creating new empty files
reports failure by returning false. To ease proper checking of return
values provide a utility method wrapping createNewFile() throwing
IOException on failure.

Change-Id: I42a3dc9d8ff70af62e84de396e6a740050afa896
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FileUtilTest.java

@@ -175,4 +175,19 @@ public void testMkdirs() throws IOException {
 		assertTrue(f.delete());
 	}
 
+	public void testCreateNewFile() throws IOException {
+		File f = new File(trash, "x");
+		FileUtils.createNewFile(f);
+		assertTrue(f.exists());
+
+		try {
+			FileUtils.createNewFile(f);
+			fail("creation of already existing file must fail");
+		} catch (IOException e) {
+			// expected
+		}
+
+		FileUtils.delete(f);
+	}
+
 }

org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties

@@ -130,6 +130,7 @@ couldNotWriteFile=Could not write file {0}
 countingObjects=Counting objects
 createBranchFailedUnknownReason=Create branch failed for unknown reason
 createBranchUnexpectedResult=Create branch returned unexpected result {0}
+createNewFileFailed=Could not create new file {0}
 credentialPassword=Password
 credentialUsername=Username
 daemonAlreadyRunning=Daemon already running

org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java

@@ -190,6 +190,7 @@ public static JGitText get() {
 	/***/ public String countingObjects;
 	/***/ public String createBranchFailedUnknownReason;
 	/***/ public String createBranchUnexpectedResult;
+	/***/ public String createNewFileFailed;
 	/***/ public String credentialPassword;
 	/***/ public String credentialUsername;
 	/***/ public String daemonAlreadyRunning;

org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java

@@ -47,6 +47,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.nio.channels.FileLock;
 import java.text.MessageFormat;
 
 import org.eclipse.jgit.JGitText;
@@ -219,4 +220,26 @@ public static void mkdirs(final File d, boolean skipExisting)
 					JGitText.get().mkDirsFailed, d.getAbsolutePath()));
 		}
 	}
+
+	/**
+	 * Atomically creates a new, empty file named by this abstract pathname if
+	 * and only if a file with this name does not yet exist. The check for the
+	 * existence of the file and the creation of the file if it does not exist
+	 * are a single operation that is atomic with respect to all other
+	 * filesystem activities that might affect the file.
+	 * <p>
+	 * Note: this method should not be used for file-locking, as the resulting
+	 * protocol cannot be made to work reliably. The {@link FileLock} facility
+	 * should be used instead.
+	 *
+	 * @param f
+	 *            the file to be created
+	 * @throws IOException
+	 *             if the named file already exists or if an I/O error occurred
+	 */
+	public static void createNewFile(File f) throws IOException {
+		if (!f.createNewFile())
+			throw new IOException(MessageFormat.format(
+					JGitText.get().createNewFileFailed, f));
+	}
 }