scan classpath for format handlers

docs-core/src/main/java/com/sismics/docs/core/util/format/FormatHandlerUtil.java

@@ -1,6 +1,7 @@
 package com.sismics.docs.core.util.format;
 
 import com.google.common.collect.Lists;
+import com.sismics.util.ClasspathScanner;
 
 import java.util.List;
 
@@ -11,17 +12,10 @@ import java.util.List;
  */
 public class FormatHandlerUtil {
     /**
-     * List of format handlers.
+     * List of format handlers scanned in the classpath.
      */
     private static final List<Class<? extends FormatHandler>> FORMAT_HANDLERS = Lists.newArrayList(
-            DocxFormatHandler.class,
+            new ClasspathScanner<FormatHandler>().findClasses(FormatHandler.class, "com.sismics.docs.core.util.format"));
-            PptxFormatHandler.class,
-            OdtFormatHandler.class,
-            VideoFormatHandler.class,
-            PdfFormatHandler.class,
-            TextPlainFormatHandler.class,
-            ImageFormatHandler.class
-    );
 
     /**
      * Find a suitable format handler for this MIME type.

docs-core/src/main/java/com/sismics/util/ClasspathScanner.java

@@ -0,0 +1,44 @@
+package com.sismics.util;
+
+import com.google.common.collect.Sets;
+import com.google.common.reflect.ClassPath;
+import com.sismics.docs.core.util.format.PdfFormatHandler;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.lang.reflect.Modifier;
+import java.util.Set;
+
+/**
+ * Classes scanner.
+ */
+public class ClasspathScanner<T> {
+    /**
+     * Logger.
+     */
+    private static final Logger log = LoggerFactory.getLogger(PdfFormatHandler.class);
+
+    /**
+     * Find classes assignable from another.
+     *
+     * @param topClass Top class or interface
+     * @param pkg In this package
+     * @return Set of classes
+     */
+    @SuppressWarnings("unchecked")
+    public Set<Class<T>> findClasses(Class<T> topClass, String pkg) {
+        Set<Class<T>> classes = Sets.newHashSet();
+        try {
+        for (ClassPath.ClassInfo classInfo : ClassPath.from(topClass.getClassLoader()).getTopLevelClasses(pkg)) {
+            Class<?> clazz = classInfo.load();
+            if (topClass.isAssignableFrom(clazz) && !Modifier.isAbstract(clazz.getModifiers()) && !clazz.isInterface()) {
+                classes.add((Class<T>) clazz);
+            }
+        }
+        } catch (Exception e) {
+            log.error("Error loading format handlers", e);
+        }
+        log.info("Found " + classes.size() + " classes for " + topClass.getSimpleName());
+        return classes;
+    }
+}