If we have an error writer, let's print errors there

... even if those errors are actually Java exceptions.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

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

@@ -39,6 +39,7 @@
 import java.io.FileWriter;
 import java.io.IOException;
 import java.io.PrintStream;
+import java.io.PrintWriter;
 import java.io.Reader;
 import java.io.StringReader;
 import java.io.Writer;
@@ -110,8 +111,8 @@ public Object eval(Reader reader) throws ScriptException {
 		final String path = (String)get(FILENAME);
 		File file = path == null ? null : new File(path);
 
+		final Writer writer = getContext().getErrorWriter();
 		try {
-			final Writer writer = getContext().getErrorWriter();
 			final Builder builder = new Builder(file, reader, writer);
 			final MavenProject project = builder.project;
 			String mainClass = builder.mainClass;
@@ -162,9 +163,15 @@ public Class<? extends Command> loadClass() {
 				builder.cleanup();
 			}
 		} catch (Exception e) {
-			if (e instanceof ScriptException)
-				throw (ScriptException) e;
-			throw new ScriptException(e);
+			if (writer != null) {
+				final PrintWriter err = new PrintWriter(writer);
+				e.printStackTrace(err);
+				err.flush();
+			} else {
+				if (e instanceof ScriptException)
+					throw (ScriptException) e;
+				throw new ScriptException(e);
+			}
 		}
 		return null;
 	}

src/test/java/org/scijava/plugins/scripting/java/JavaEngineTest.java

@@ -183,7 +183,6 @@ private ScriptEngine evalJava(final File file) throws ScriptException {
 		miniMaven.put(ScriptEngine.FILENAME, file.getPath());
 		final ScriptContext context = miniMaven.getContext();
 		context.setWriter(new OutputStreamWriter(System.out));
-		context.setErrorWriter(new OutputStreamWriter(System.err));
 		miniMaven.eval((Reader) null);
 		return miniMaven;
 	}