java: make ContextIsolator throw exceptions when arguments are invalid

Currently the error is just printed on the console. Throwing exception
allows API user to react on this situation in the most appropriate
way. For example if new application is started using a web interface
printing on console is useless.

java/runjava/src/main/java/io/osv/ContextIsolator.java

@@ -87,9 +87,6 @@ public class ContextIsolator {
 
     public void runSync(String[] args) throws Throwable {
         Context context = run(args);
-        if (context == null) {
-            return;
-        }
 
         while (true) {
             try {
@@ -106,14 +103,12 @@ public class ContextIsolator {
         for (int i = 0; i < args.length; i++) {
             if (args[i].equals("-jar")) {
                 if (i + 1 >= args.length) {
-                    System.err.println("RunJava: Missing jar name after '-jar'.");
-                    return null;
+                    throw new IllegalArgumentException("Missing jar name after '-jar'.");
                 }
                 return runJar(args[i + 1], java.util.Arrays.copyOfRange(args, i + 2, args.length), classpath);
             } else if (args[i].equals("-classpath") || args[i].equals("-cp")) {
                 if (i + 1 >= args.length) {
-                    System.err.println("RunJava: Missing parameter after '" + args[i] + "'");
-                    return null;
+                    throw new IllegalArgumentException("Missing parameter after '" + args[i] + "'");
                 }
                 for (String c : expandClassPath(args[i + 1])) {
                     classpath.add(c);
@@ -122,8 +117,7 @@ public class ContextIsolator {
             } else if (args[i].startsWith("-D")) {
                 int eq = args[i].indexOf('=');
                 if (eq < 0) {
-                    System.err.println("RunJava: Missing '=' in parameter '" + args[i] + "'");
-                    return null;
+                    throw new IllegalArgumentException("Missing '=' in parameter '" + args[i] + "'");
                 }
                 String key = args[i].substring(2, eq);
                 String value = args[i].substring(eq + 1, args[i].length());
@@ -131,20 +125,17 @@ public class ContextIsolator {
             } else if (args[i].equals("-Xclassloader")) {
                 // Non-standard try - use a different class loader.
                 if (i + 1 >= args.length) {
-                    System.err.println("RunJava: Missing parameter after '" + args[i] + "'");
-                    return null;
+                    throw new IllegalArgumentException("Missing parameter after '" + args[i] + "'");
                 }
                 Xclassloader = args[i + 1];
                 i++;
             } else if (!args[i].startsWith("-")) {
                 return runClass(args[i], java.util.Arrays.copyOfRange(args, i + 1, args.length), classpath);
             } else {
-                System.err.println("RunJava: Unknown parameter '" + args[i] + "'");
-                return null;
+                throw new IllegalArgumentException("Unknown parameter '" + args[i] + "'");
             }
         }
-        System.err.println("RunJava: No jar or class specified to run.");
-        return null;
+        throw new IllegalArgumentException("No jar or class specified to run.");
     }
 
     private Context runJar(String jarname, String[] args, ArrayList<String> classpath) throws Throwable {
@@ -155,19 +146,15 @@ public class ContextIsolator {
             jar.close();
             String mainClass = mf.getMainAttributes().getValue("Main-Class");
             if (mainClass == null) {
-                System.err.println(
-                        "RunJava: No 'Main-Class' attribute in manifest of " +
-                                jarname);
-                return null;
+                throw new IllegalArgumentException("No 'Main-Class' attribute in manifest of " + jarname);
             }
             classpath.add(jarname);
             return runClass(mainClass, args, classpath);
         } catch (FileNotFoundException e) {
-            System.err.println("RunJava: File not found: " + jarname);
+            throw new IllegalArgumentException("File not found: " + jarname);
         } catch (ZipException e) {
-            System.err.println("RunJava: File is not a jar: " + jarname);
+            throw new IllegalArgumentException("File is not a jar: " + jarname);
         }
-        return null;
     }
 
     private Context runClass(final String mainClass, final String[] args, final Iterable<String> classpath) throws Throwable {

java/runjava/src/main/java/io/osv/RunJava.java

@@ -24,6 +24,8 @@ public class RunJava {
 
         try {
             ContextIsolator.getInstance().runSync(args);
+        } catch (IllegalArgumentException ex) {
+            System.err.println("RunJava: " + ex.getMessage());
         } catch (Throwable ex) {
             ex.printStackTrace();
         }