[core] Improve classloaders

- Avoid a race condition that could produce multiple threads loading
   the same class at the same time.
 - Fixed a broken check on PMDASMClassLoader that would always return
   false.

pmd-core/src/main/java/net/sourceforge/pmd/util/ClasspathClassLoader.java

@@ -17,7 +17,6 @@ import java.util.StringTokenizer;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
-import org.apache.commons.io.IOUtils;
 import org.apache.commons.lang3.StringUtils;
 
 /**
@@ -30,7 +29,7 @@ import org.apache.commons.lang3.StringUtils;
 public class ClasspathClassLoader extends URLClassLoader {
 
     private static final Logger LOG = Logger.getLogger(ClasspathClassLoader.class.getName());
-
+    
     static {
         registerAsParallelCapable();
     }
@@ -64,9 +63,7 @@ public class ClasspathClassLoader extends URLClassLoader {
     }
 
     private static void addFileURLs(List<URL> urls, URL fileURL) throws IOException {
-        BufferedReader in = null;
-        try {
-            in = new BufferedReader(new InputStreamReader(fileURL.openStream()));
+        try (BufferedReader in = new BufferedReader(new InputStreamReader(fileURL.openStream()))) {
             String line;
             while ((line = in.readLine()) != null) {
                 LOG.log(Level.FINE, "Read classpath entry line: <{0}>", line);
@@ -76,8 +73,6 @@ public class ClasspathClassLoader extends URLClassLoader {
                     urls.add(createURLFromPath(line));
                 }
             }
-        } finally {
-            IOUtils.closeQuietly(in);
         }
     }
 
@@ -99,22 +94,24 @@ public class ClasspathClassLoader extends URLClassLoader {
     
     @Override
     protected Class<?> loadClass(final String name, final boolean resolve) throws ClassNotFoundException {
-        // First, check if the class has already been loaded
-        Class<?> c = findLoadedClass(name);
-        if (c == null) {
-            try {
-                // checking local
-                c = findClass(name);
-            } catch (final ClassNotFoundException | SecurityException e) {
-                // checking parent
-                // This call to loadClass may eventually call findClass again, in case the parent doesn't find anything.
-                c = super.loadClass(name, resolve);
+        synchronized (getClassLoadingLock(name)) {
+            // First, check if the class has already been loaded
+            Class<?> c = findLoadedClass(name);
+            if (c == null) {
+                try {
+                    // checking local
+                    c = findClass(name);
+                } catch (final ClassNotFoundException | SecurityException e) {
+                    // checking parent
+                    // This call to loadClass may eventually call findClass again, in case the parent doesn't find anything.
+                    c = super.loadClass(name, resolve);
+                }
             }
+    
+            if (resolve) {
+                resolveClass(c);
+            }
+            return c;
         }
-
-        if (resolve) {
-            resolveClass(c);
-        }
-        return c;
     }
 }

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/typeresolution/PMDASMClassLoader.java

@@ -100,7 +100,7 @@ public final class PMDASMClassLoader extends ClassLoader {
     }
 
     public synchronized Map<String, String> getImportedClasses(String name) throws ClassNotFoundException {
-        if (dontBother.containsValue(name)) {
+        if (dontBother.containsKey(name)) {
             throw new ClassNotFoundException(name);
         }
         try (InputStream classResource = getResourceAsStream(name.replace('.', '/') + ".class")) {