Fixed multiple clients parallel access issue, created separate packag…

…e for exceptions

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>tk.pratanumandal</groupId>
 	<artifactId>unique4j</artifactId>
-	<version>1.0</version>
+	<version>1.1</version>
 	<packaging>jar</packaging>
 
 	<name>Unique4j</name>

src/main/java/tk/pratanumandal/unique4j/Unique.java

@@ -38,6 +38,8 @@
 import java.nio.channels.FileChannel;
 import java.nio.channels.FileLock;
 
+import tk.pratanumandal.unique4j.exception.Unique4jException;
+
 /**
  * The <code>Unique</code> class is the logical entry point to the library.<br>
  * It allows to create an application lock or free it and send and receive messages between first and subsequent instances.<br><br>
@@ -92,10 +94,10 @@ public abstract class Unique {
 	private static final String TEMP_DIR = System.getProperty("java.io.tmpdir");
 
 	/**
-	 * Unique string representing the application ID.
+	 * Unique string representing the application ID.<br><br>
 	 * 
 	 * The APP_ID must be as unique as possible.
-	 * Avoid generic names like "my_app_id" or "hello_world".
+	 * Avoid generic names like "my_app_id" or "hello_world".<br>
 	 * A good strategy is to use the entire package name (group ID + artifact ID) along with some random characters.
 	 */
 	public final String APP_ID;
@@ -113,10 +115,10 @@ public abstract class Unique {
 	private FileLock fileLock;
 
 	/**
-	 * Parameterized constructor.
+	 * Parameterized constructor.<br><br>
 	 * 
 	 * The APP_ID must be as unique as possible.
-	 * Avoid generic names like "my_app_id" or "hello_world".
+	 * Avoid generic names like "my_app_id" or "hello_world".<br>
 	 * A good strategy is to use the entire package name (group ID + artifact ID) along with some random characters.
 	 * 
 	 * @param APP_ID Unique string representing the application ID
@@ -170,34 +172,47 @@ public void run() {
 				while (!server.isClosed()) {
 					try {
 						// establish connection
-						Socket socket = server.accept();
-
-						// open writer
-						OutputStream os = socket.getOutputStream();
-						PrintWriter pw = new PrintWriter(os, true);
-
-						// open reader
-						InputStream is = socket.getInputStream();
-			            InputStreamReader isr = new InputStreamReader(is);
-			            BufferedReader br = new BufferedReader(isr);
-
-			            // read message from client
-			            String message = br.readLine();
-			            if (message == null) message = new String();
-
-			            // write response to client
-			            pw.write(APP_ID + "\r\n");
-			            pw.flush();
-
-			            // close writer and reader
-			            pw.close();
-				        br.close();
+						final Socket socket = server.accept();
 
-			            // perform user action on message
-						receiveMessage(message);
+						// handle socket on a different thread to allow parallel connections
+						Thread thread = new Thread() {
+							@Override
+							public void run() {
+								try {
+									// open writer
+									OutputStream os = socket.getOutputStream();
+									PrintWriter pw = new PrintWriter(os, true);
+
+									// open reader
+									InputStream is = socket.getInputStream();
+						            InputStreamReader isr = new InputStreamReader(is);
+						            BufferedReader br = new BufferedReader(isr);
+
+						            // read message from client
+						            String message = br.readLine();
+						            if (message == null) message = new String();
+
+						            // write response to client
+						            pw.write(APP_ID + "\r\n");
+						            pw.flush();
+
+						            // close writer and reader
+						            pw.close();
+							        br.close();
+
+						            // perform user action on message
+									receiveMessage(message);
+
+									// close socket
+									socket.close();
+								} catch (IOException e) {
+									handleException(new Unique4jException(e));
+								}
+							}
+						};
 
-						// close socket
-						socket.close();
+						// start socket thread
+						thread.start();
 					} catch (SocketException e) {
 						if (!server.isClosed()) {
 							handleException(new Unique4jException(e));
@@ -331,7 +346,10 @@ private void lockFile(int port) throws Unique4jException {
 		try {
 			lockRAF = new RandomAccessFile(file, "rw");
 			FileChannel fc = lockRAF.getChannel();
-			fileLock = fc.lock(0, Long.MAX_VALUE, true);
+			fileLock = fc.tryLock(0, Long.MAX_VALUE, true);
+			if (fileLock == null) {
+				throw new Unique4jException("Failed to obtain file lock");
+			}
 		} catch (FileNotFoundException e) {
 			throw new Unique4jException(e);
 		} catch (IOException e) {
@@ -375,23 +393,25 @@ public void free() throws Unique4jException {
 	}
 
 	/**
-	 * Method used in first instance to receive messages from subsequent instances.
+	 * Method used in first instance to receive messages from subsequent instances.<br>
+	 * This method is not synchronized.
 	 * 
 	 * @param message message received by first instance from subsequent instances
 	 */
 	public abstract void receiveMessage(String message);
 
 	/**
-	 * Method used in subsequent instances to send message to first instance.
+	 * Method used in subsequent instances to send message to first instance.<br>
+	 * This method is not synchronized.
 	 * 
 	 * @return message sent from subsequent instances
 	 */
 	public abstract String sendMessage();
 
 	/**
-	 * Method to receive and handle exceptions occurring while first instance is listening for subsequent instances.
-	 * 
-	 * By default prints stack trace of all exceptions. Override this method to change handle explicitly.
+	 * Method to receive and handle exceptions occurring while first instance is listening for subsequent instances.<br>
+	 * By default prints stack trace of all exceptions. Override this method to change handle explicitly.<br>
+	 * This method is not synchronized.
 	 * 
 	 * @param exception exception occurring while first instance is listening for subsequent instances
 	 */

src/main/java/tk/pratanumandal/unique4j/Unique4jException.java → src/main/java/tk/pratanumandal/unique4j/exception/Unique4jException.java

@@ -15,13 +15,13 @@
  * 
  */
 
-package tk.pratanumandal.unique4j;
+package tk.pratanumandal.unique4j.exception;
 
 /**
  * The <code>Unique4jException</code> class is a wrapper for all exceptions thrown from Unique4j.
  * 
  * @author Pratanu Mandal
- * @since 1.0
+ * @since 1.1
  *
  */
 public class Unique4jException extends Exception {

src/main/java/tk/pratanumandal/unique4j/exception/package-info.java

@@ -0,0 +1,25 @@
+/**
+ * Copyright 2019 Pratanu Mandal
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * 
+ */
+
+/**
+ * The <code>tk.pratanumandal.unique4j.exception</code> package contains exception classes of Unique4j library.
+ * 
+ * @author Pratanu Mandal
+ * @since 1.1
+ *
+ */
+package tk.pratanumandal.unique4j.exception;

src/main/java/tk/pratanumandal/unique4j/package-info.java

@@ -16,7 +16,7 @@
  */
 
 /**
- * The <code>tk.pratanumandal.unique4j</code> package is the root package of unique4j library.
+ * The <code>tk.pratanumandal.unique4j</code> package is the root package of Unique4j library.
  * 
  * @author Pratanu Mandal
  * @since 1.0

src/test/java/tk/pratanumandal/unique4j/Unique4jTest.java

@@ -19,6 +19,8 @@
 
 import org.junit.Test;
 
+import tk.pratanumandal.unique4j.exception.Unique4jException;
+
 public class Unique4jTest {
 
     @Test