new: PackageScanner: error handling

new: CQueryBuilder#optional

assira/src/main/java/net/ranides/assira/collection/query/CQueryBuilder.java

@@ -96,6 +96,10 @@ public class CQueryBuilder<T> {
     public static <T> CQuery<T> empty() {
         return EMPTY;
     }
+
+    public static <T> CQuery<T> optional(T source) {
+        return source == null ? empty() : of(source);
+    }
     
     @SafeVarargs
     public static <T> CQuery<T> of(T... source) {

assira/src/main/java/net/ranides/assira/reflection/util/PackageScanner.java

@@ -16,6 +16,7 @@ import net.ranides.assira.io.ZipReader;
 import net.ranides.assira.io.uri.URIUtils;
 import net.ranides.assira.text.StringUtils;
 import net.ranides.assira.trace.ExceptionUtils;
+import org.slf4j.Logger;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -26,6 +27,8 @@ import java.nio.charset.Charset;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.*;
+import java.util.function.BiConsumer;
+import java.util.function.BiFunction;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.jar.JarEntry;
@@ -34,6 +37,8 @@ import java.util.jar.JarInputStream;
 
 public final class PackageScanner {
 
+    private BiFunction<String, Throwable, Class<?>> handler;
+
     private String root;
 
     private ClassLoader loader;
@@ -61,12 +66,27 @@ public final class PackageScanner {
         return this;
     }
 
+    public PackageScanner resolver(BiFunction<String, Throwable, Class<?>> handler) {
+        this.handler = handler;
+        return this;
+    }
+
+    public PackageScanner logger(BiConsumer<String, Throwable> handler) {
+        this.handler = (name,error) -> { handler.accept(name, error); return null; };
+        return this;
+    }
+
+    public PackageScanner logger(Logger logger) {
+        this.handler = (name,error) -> { logger.error("Can't load class: " + name, error); return null; };
+        return this;
+    }
+
     public CQuery<Class<?>> types() throws IOException {
         return names().map(toClass(cloader())).filter(Objects::nonNull);
     }
 
     public CQuery<String> names() throws IOException {
-        return files().filter(PackageScanner::isClass).map(PackageScanner::toClassName);
+        return files().filter(this::isClass).map(PackageScanner::toClassName);
     }
 
     public CQuery<String> files() throws IOException {
@@ -180,15 +200,18 @@ public final class PackageScanner {
 
     }
 
-    private static boolean isClass(String path) {
+    private boolean isClass(String path) {
         return path.endsWith(".class");
     }
     
-    private static Function<String, Class<?>> toClass(ClassLoader loader) {
+    private Function<String, Class<?>> toClass(ClassLoader loader) {
         return name -> {
             try {
                 return Class.forName(name, false, loader);
             } catch(ClassNotFoundException | NoClassDefFoundError cause) {
+                if(handler != null) {
+                    return handler.apply(name, cause);
+                }
                 return null;
             }
         };