JavaEngine: split Builder initialization logic

Rather than doing all the work in the constructor, and throwing a
bunch of exceptions, let's keep construction as simple as possible,
then do all that initialization in its own method. This will make
error handling more robust in that we will be able to attempt calls to
builder.cleanup() even if something went wrong during initialization.

Author: ctrueden

src/main/java/org/scijava/plugins/scripting/java/JavaEngine.java

@@ -188,21 +188,19 @@ public Class<?> compile(String script) throws ScriptException {
 		File file = path == null ? null : new File(path);
 
 		final Writer writer = getContext().getErrorWriter();
+		final Builder builder = new Builder();
 		try {
-
-			final Builder builder;
-
 			if (file != null && file.exists()) {
 				// if the filename set in engine scope bindings is valid,
 				// ignore the given script and use that file instead.
-				builder = new Builder(file, writer);
+				builder.initialize(file, writer);
 			}
 			else {
 				// script may be null, but then we cannot create a StringReader for it,
 				// therefore null is passed if script is null.
 				final Reader reader =
 					(script == null) ? null : new StringReader(script);
-				builder = new Builder(reader, writer);
+				builder.initialize(reader, writer);
 			}
 			final MavenProject project = builder.project;
 			String mainClass = builder.mainClass;
@@ -292,10 +290,11 @@ public void compile(final File file) {
 	 * @see #compile(String)
 	 */
 	public void compile(final File file, final Writer errorWriter) {
+		final Writer writer =
+			(errorWriter == null) ? getContext().getErrorWriter() : errorWriter;
+		final Builder builder = new Builder();
 		try {
-			final Writer writer =
-				(errorWriter == null) ? getContext().getErrorWriter() : errorWriter;
-			final Builder builder = new Builder(file, writer);
+			builder.initialize(file, writer);
 			try {
 				builder.project.build();
 			}
@@ -319,8 +318,9 @@ public void compile(final File file, final Writer errorWriter) {
 	public void makeJar(final File file, final boolean includeSources,
 		final File output, final Writer errorWriter)
 	{
+		final Builder builder = new Builder();
 		try {
-			final Builder builder = new Builder(file, errorWriter);
+			builder.initialize(file, errorWriter);
 			try {
 				builder.project.build(true, true, includeSources);
 				final File target = builder.project.getTarget();
@@ -368,14 +368,17 @@ private void printOrThrow(Throwable t, Writer errorWriter) {
 	 */
 	private class Builder {
 
-		private final PrintStream err;
-		private final File temporaryDirectory;
+		private PrintStream err;
+		private File temporaryDirectory;
 		private String mainClass;
 		private MavenProject project;
 
 		/**
 		 * Constructs a wrapper around a possibly project for a source or maven
 		 * project file.
+		 * <p>
+		 * This method is intended to be called only once.
+		 * </p>
 		 * 
 		 * @param file the {@code .java} file to build (or null, if {@code reader}
 		 *          is set).
@@ -388,7 +391,7 @@ private class Builder {
 		 * @throws TransformerException
 		 * @throws TransformerFactoryConfigurationError
 		 */
-		private Builder(final File file, final Writer errorWriter)
+		private void initialize(final File file, final Writer errorWriter)
 			throws ScriptException, IOException, ParserConfigurationException,
 			SAXException, TransformerConfigurationException, TransformerException,
 			TransformerFactoryConfigurationError
@@ -411,6 +414,9 @@ private Builder(final File file, final Writer errorWriter)
 		/**
 		 * Constructs a wrapper around a possibly temporary project for source code
 		 * generated by a Reader.
+		 * <p>
+		 * This method is intended to be called only once.
+		 * </p>
 		 * 
 		 * @param reader provides the Java source if {@code file} is {@code null}
 		 * @param errorWriter where to write the error output.
@@ -422,7 +428,7 @@ private Builder(final File file, final Writer errorWriter)
 		 * @throws TransformerException
 		 * @throws TransformerFactoryConfigurationError
 		 */
-		private Builder(final Reader reader, final Writer errorWriter)
+		private void initialize(final Reader reader, final Writer errorWriter)
 			throws ScriptException, IOException, ParserConfigurationException,
 			SAXException, TransformerConfigurationException, TransformerException,
 			TransformerFactoryConfigurationError