Add a feature to blacklist certain plugins

Right now, it must be done using the scijava.plugin.blacklist system
property, a colon-separated list of regexes defining plugins to ignore.

If this idea works out well, we can expose the API such that the
blacklist can be specified per context instead of globally.

Author: ctrueden

src/main/java/org/scijava/plugin/DefaultPluginFinder.java

@@ -31,8 +31,11 @@
 
 package org.scijava.plugin;
 
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
+import java.util.regex.Pattern;
+import java.util.regex.PatternSyntaxException;
 
 import org.scijava.annotations.Index;
 import org.scijava.annotations.IndexItem;
@@ -51,6 +54,8 @@ public class DefaultPluginFinder implements PluginFinder {
 	/** Class loader to use when querying the annotation indexes. */
 	private final ClassLoader customClassLoader;
 
+	private final PluginBlacklist blacklist;
+
 	// -- Constructors --
 
 	public DefaultPluginFinder() {
@@ -59,6 +64,7 @@ public DefaultPluginFinder() {
 
 	public DefaultPluginFinder(final ClassLoader classLoader) {
 		customClassLoader = classLoader;
+		blacklist = new SysPropBlacklist();
 	}
 
 	// -- PluginFinder methods --
@@ -77,6 +83,7 @@ public HashMap<String, Throwable> findPlugins(
 
 		// create a PluginInfo object for each item in the index
 		for (final IndexItem<Plugin> item : annotationIndex) {
+			if (blacklist.contains(item.className())) continue;
 			try {
 				final PluginInfo<?> info = createInfo(item, classLoader);
 				plugins.add(info);
@@ -109,4 +116,47 @@ private ClassLoader getClassLoader() {
 		return Thread.currentThread().getContextClassLoader();
 	}
 
+	// -- Helper classes --
+
+	private interface PluginBlacklist {
+		boolean contains(String className);
+	}
+
+	/**
+	 * A blacklist defined by the {@code scijava.plugin.blacklist} system
+	 * property, formatted as a colon-separated list of regexes.
+	 * <p>
+	 * If a plugin class matches any of the regexes, it is excluded from the
+	 * plugin index.
+	 * </p>
+	 */
+	private class SysPropBlacklist implements PluginBlacklist {
+		private final List<Pattern> patterns;
+
+		public SysPropBlacklist() {
+			final String sysProp = System.getProperty("scijava.plugin.blacklist");
+			final String[] regexes = //
+				sysProp == null ? new String[0] : sysProp.split(":");
+			patterns = new ArrayList<Pattern>(regexes.length);
+			for (final String regex : regexes) {
+				try {
+					patterns.add(Pattern.compile(regex));
+				}
+				catch (final PatternSyntaxException exc) {
+					// NB: Ignore this malformed pattern.
+				}
+			}
+		}
+
+		// -- PluginBlacklist methods --
+
+		@Override
+		public boolean contains(final String className) {
+			for (final Pattern pattern : patterns) {
+				if (pattern.matcher(className).matches()) return true;
+			}
+			return false;
+		}
+	}
+
 }