Fix issues #40 and #41: Code quality improvements

Issue #40: Extract hardcoded buffer size 8192 to shared constant
- Created ClassLoaderConstants utility class with DEFAULT_BUFFER_SIZE = 8192
- Replaced hardcoded values in 6 files: MavenNexusClassSource, NexusClassSource (2 locations), RestApiClassSource, MinioClassSource, HdfsClassSource
- Replaced local constants in 3 files: MavenRepositoryClassSource, RemoteClassSource, JarRemoteClassSource

Issue #41: Fix thread-safety in HashMap caches
- Replaced HashMap with ConcurrentHashMap in MavenRepositoryClassSource, MavenNexusClassSource, NexusClassSource
- Added thread-safety documentation to class Javadocs
- Ensures safe concurrent class loading operations

All 287 tests pass

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Flossy

src/main/java/org/flossware/jclassloader/JarRemoteClassSource.java

@@ -2,6 +2,8 @@
 
 import org.flossware.jclassloader.util.ClassNameUtil;
 import org.slf4j.Logger;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import org.slf4j.LoggerFactory;
 
 import java.io.ByteArrayOutputStream;
@@ -28,7 +30,6 @@ public class JarRemoteClassSource implements ClassSource, AutoCloseable {
     private static final Logger logger = LoggerFactory.getLogger(JarRemoteClassSource.class);
     private static final int DEFAULT_CONNECT_TIMEOUT_MS = 10000;
     private static final int DEFAULT_READ_TIMEOUT_MS = 30000;
-    private static final int DEFAULT_BUFFER_SIZE = 8192;
 
     private final String jarUrl;
     private final AuthConfig authConfig;

src/main/java/org/flossware/jclassloader/MavenNexusClassSource.java

@@ -3,23 +3,28 @@
 import org.flossware.jclassloader.util.ClassNameUtil;
 
 import java.io.ByteArrayOutputStream;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Base64;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.jar.JarEntry;
 import java.util.jar.JarInputStream;
 
 /**
  * ClassSource implementation for loading classes from Maven artifacts stored in Nexus.
  * Downloads JARs from Nexus and extracts class files from them.
  * Includes in-memory caching of loaded classes for performance.
+ *
+ * <p><b>Thread Safety:</b> This class is thread-safe. The internal class cache uses
+ * ConcurrentHashMap to support concurrent class loading operations.</p>
  */
 public class MavenNexusClassSource implements ClassSource {
     private final String nexusUrl;
@@ -50,7 +55,7 @@ public MavenNexusClassSource(String nexusUrl, String repository, List<MavenArtif
         this.repository = Objects.requireNonNull(repository, "repository cannot be null");
         this.artifacts = new ArrayList<>(artifacts);
         this.authConfig = authConfig != null ? authConfig : AuthConfig.none();
-        this.classCache = new HashMap<>();
+        this.classCache = new ConcurrentHashMap<>();
     }
 
     /**
@@ -124,7 +129,7 @@ private byte[] extractClassFromJar(String jarUrl, String classFileName) throws I
             while ((entry = jarIn.getNextJarEntry()) != null) {
                 if (entry.getName().equals(classFileName) && !entry.isDirectory()) {
                     ByteArrayOutputStream out = new ByteArrayOutputStream();
-                    byte[] buffer = new byte[8192];
+                    byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
                     int bytesRead;
                     while ((bytesRead = jarIn.read(buffer)) != -1) {
                         out.write(buffer, 0, bytesRead);

src/main/java/org/flossware/jclassloader/MavenRepositoryClassSource.java

@@ -3,26 +3,29 @@
 import org.flossware.jclassloader.util.ClassNameUtil;
 
 import java.io.ByteArrayOutputStream;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.jar.JarEntry;
 import java.util.jar.JarInputStream;
 
 /**
  * ClassSource implementation for loading classes from Maven repositories (Maven Central, custom repos).
  * Downloads JARs from the repository and extracts class files from them.
  * Includes in-memory caching of loaded classes for performance.
+ *
+ * <p><b>Thread Safety:</b> This class is thread-safe. The internal class cache uses
+ * ConcurrentHashMap to support concurrent class loading operations.</p>
  */
 public class MavenRepositoryClassSource implements ClassSource {
-    private static final int DEFAULT_BUFFER_SIZE = 8192;
-
     private final String repositoryUrl;
     private final List<MavenArtifact> artifacts;
     private final AuthConfig authConfig;
@@ -48,7 +51,7 @@ public MavenRepositoryClassSource(String repositoryUrl, List<MavenArtifact> arti
         this.repositoryUrl = repositoryUrl.endsWith("/") ? repositoryUrl : repositoryUrl + "/";
         this.artifacts = new ArrayList<>(artifacts);
         this.authConfig = authConfig != null ? authConfig : AuthConfig.none();
-        this.classCache = new HashMap<>();
+        this.classCache = new ConcurrentHashMap<>();
     }
 
     /**

src/main/java/org/flossware/jclassloader/NexusClassSource.java

@@ -3,20 +3,25 @@
 import org.flossware.jclassloader.util.ClassNameUtil;
 
 import java.io.ByteArrayOutputStream;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.Base64;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.jar.JarEntry;
 import java.util.jar.JarInputStream;
 
 /**
  * ClassSource implementation for loading classes from Sonatype Nexus repositories.
  * Supports both RAW repositories (direct .class files) and MAVEN repositories (classes from JARs).
+ *
+ * <p><b>Thread Safety:</b> This class is thread-safe. The internal JAR cache uses
+ * ConcurrentHashMap to support concurrent class loading operations.</p>
  */
 public class NexusClassSource implements ClassSource {
     private final String nexusUrl;
@@ -50,7 +55,7 @@ public NexusClassSource(String nexusUrl, String repository, NexusMode mode, Auth
         this.repository = Objects.requireNonNull(repository, "repository cannot be null");
         this.mode = mode != null ? mode : NexusMode.MAVEN;
         this.authConfig = authConfig != null ? authConfig : AuthConfig.none();
-        this.jarCache = new HashMap<>();
+        this.jarCache = new ConcurrentHashMap<>();
     }
 
     /**
@@ -159,7 +164,7 @@ private byte[] fetchUrl(String urlString) throws IOException {
         try (InputStream in = connection.getInputStream();
              ByteArrayOutputStream out = new ByteArrayOutputStream()) {
 
-            byte[] buffer = new byte[8192];
+            byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
             int bytesRead;
             while ((bytesRead = in.read(buffer)) != -1) {
                 out.write(buffer, 0, bytesRead);
@@ -186,7 +191,7 @@ protected byte[] loadClassFromJar(String jarUrl, String classFileName) throws IO
             while ((entry = jarIn.getNextJarEntry()) != null) {
                 if (entry.getName().equals(classFileName)) {
                     ByteArrayOutputStream out = new ByteArrayOutputStream();
-                    byte[] buffer = new byte[8192];
+                    byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
                     int bytesRead;
                     while ((bytesRead = jarIn.read(buffer)) != -1) {
                         out.write(buffer, 0, bytesRead);

src/main/java/org/flossware/jclassloader/RemoteClassSource.java

@@ -3,6 +3,8 @@
 import org.flossware.jclassloader.util.ClassNameUtil;
 
 import java.io.ByteArrayOutputStream;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
@@ -16,8 +18,6 @@
  * Supports optional authentication (Basic or Bearer token), configurable timeouts, and retry logic.
  */
 public class RemoteClassSource implements ClassSource {
-    private static final int DEFAULT_BUFFER_SIZE = 8192;
-
     /** Default connection timeout in milliseconds (10 seconds) */
     private static final int DEFAULT_CONNECT_TIMEOUT_MS = 10000;
 

src/main/java/org/flossware/jclassloader/RestApiClassSource.java

@@ -1,6 +1,8 @@
 package org.flossware.jclassloader;
 
 import java.io.ByteArrayOutputStream;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
@@ -66,7 +68,7 @@ public byte[] loadClassData(String className) throws IOException {
             try (InputStream in = connection.getInputStream();
                  ByteArrayOutputStream out = new ByteArrayOutputStream()) {
 
-                byte[] buffer = new byte[8192];
+                byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
                 int bytesRead;
                 while ((bytesRead = in.read(buffer)) != -1) {
                     out.write(buffer, 0, bytesRead);

src/main/java/org/flossware/jclassloader/filesystem/HdfsClassSource.java

@@ -1,6 +1,8 @@
 package org.flossware.jclassloader.filesystem;
 
 import org.apache.hadoop.conf.Configuration;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.flossware.jclassloader.ClassSource;
@@ -32,7 +34,7 @@ public byte[] loadClassData(String className) throws IOException {
         try (InputStream in = hdfs.open(classPath);
              ByteArrayOutputStream out = new ByteArrayOutputStream()) {
 
-            byte[] buffer = new byte[8192];
+            byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
             int bytesRead;
             while ((bytesRead = in.read(buffer)) != -1) {
                 out.write(buffer, 0, bytesRead);

src/main/java/org/flossware/jclassloader/objectstore/MinioClassSource.java

@@ -1,6 +1,8 @@
 package org.flossware.jclassloader.objectstore;
 
 import io.minio.GetObjectArgs;
+
+import static org.flossware.jclassloader.util.ClassLoaderConstants.DEFAULT_BUFFER_SIZE;
 import io.minio.MinioClient;
 import io.minio.StatObjectArgs;
 import org.flossware.jclassloader.ClassSource;
@@ -44,7 +46,7 @@ public byte[] loadClassData(String className) throws IOException {
                     .build());
              ByteArrayOutputStream out = new ByteArrayOutputStream()) {
 
-            byte[] buffer = new byte[8192];
+            byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
             int bytesRead;
             while ((bytesRead = stream.read(buffer)) != -1) {
                 out.write(buffer, 0, bytesRead);

src/main/java/org/flossware/jclassloader/util/ClassLoaderConstants.java

@@ -0,0 +1,26 @@
+package org.flossware.jclassloader.util;
+
+/**
+ * Common constants used throughout the JClassLoader library.
+ *
+ * <p>This class provides shared constant values for buffer sizes, timeouts,
+ * and other configuration parameters used across multiple ClassSource implementations.</p>
+ */
+public final class ClassLoaderConstants {
+
+    private ClassLoaderConstants() {
+        throw new AssertionError("Utility class - do not instantiate");
+    }
+
+    /**
+     * Default buffer size for reading class data (8KB).
+     *
+     * <p>This is a common default for I/O operations because:</p>
+     * <ul>
+     *   <li>Matches most filesystem block sizes</li>
+     *   <li>Good balance between memory usage and I/O performance</li>
+     *   <li>Standard in many Java libraries (BufferedInputStream default is 8192)</li>
+     * </ul>
+     */
+    public static final int DEFAULT_BUFFER_SIZE = 8192;
+}