Implemented file locking strategy

.gitignore

@@ -1,6 +1,7 @@
 # Created by https://www.gitignore.io/api/maven
 # Edit at https://www.gitignore.io/?templates=maven
 
+.idea/
 ### Maven ###
 target/
 pom.xml.tag
@@ -90,3 +91,6 @@ local.properties
 .sts4-cache/
 
 # End of https://www.gitignore.io/api/eclipse
+
+### VS Code ###
+.history/

pom.xml

@@ -1,15 +1,14 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0"
-	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>nf.fr.k49</groupId>
 	<artifactId>shielddb-parent</artifactId>
 	<version>0.1.4-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
 	<name>shieldb</name>
- 	<description>ShieldDB is a simple embedded database with JSON file backend with optional in-memory read cache.</description>
+	<description>ShieldDB is a simple embedded database with JSON file backend with optional in-memory read cache.</description>
 	<url>https://github.com/kuroidoruido/ShieldDB</url>
+
 	<licenses>
 		<license>
 			<name>MIT License</name>
@@ -37,13 +36,17 @@
 		<junit-jupiter-api.version>5.7.0</junit-jupiter-api.version>
 		<hamcrest.version>2.2</hamcrest.version>
 		<mockito.version>3.5.13</mockito.version>
+		<guava.version>30.1.1-jre</guava.version>
+		<commons-lang.version>3.12.0</commons-lang.version>
 	</properties>
+
 	<modules>
 		<module>shielddb-core</module>
 		<module>shielddb-demo-app</module>
 		<module>shielddb-gson-backend</module>
 	</modules>
-  <dependencyManagement>
+
+	<dependencyManagement>
 		<dependencies>
 			<dependency>
 				<groupId>org.junit.jupiter</groupId>
@@ -67,8 +70,31 @@
 				<version>${mockito.version}</version>
 				<scope>test</scope>
 			</dependency>
+			<dependency>
+				<groupId>com.google.guava</groupId>
+				<artifactId>guava</artifactId>
+				<version>${guava.version}</version>
+			</dependency>
+			<dependency>
+				<groupId>org.apache.commons</groupId>
+				<artifactId>commons-lang3</artifactId>
+				<version>${commons-lang.version}</version>
+			</dependency>
 		</dependencies>
 	</dependencyManagement>
+
+	<!-- Commons utils dependencies -->
+	<dependencies>
+		<dependency>
+			<groupId>com.google.guava</groupId>
+			<artifactId>guava</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.commons</groupId>
+			<artifactId>commons-lang3</artifactId>
+		</dependency>
+	</dependencies>
+
 	<distributionManagement>
 		<snapshotRepository>
 			<id>ossrh</id>
@@ -79,6 +105,7 @@
 			<url>https://oss.sonatype.org/service/local/staging/deploy/maven2/</url>
 		</repository>
 	</distributionManagement>
+
 	<build>
 		<plugins>
 			<plugin>
@@ -92,10 +119,10 @@
 				<version>3.2.1</version>
 				<executions>
 					<execution>
-					<id>attach-sources</id>
-					<goals>
-						<goal>jar-no-fork</goal>
-					</goals>
+						<id>attach-sources</id>
+						<goals>
+							<goal>jar-no-fork</goal>
+						</goals>
 					</execution>
 				</executions>
 			</plugin>
@@ -105,10 +132,10 @@
 				<version>3.2.0</version>
 				<executions>
 					<execution>
-					<id>attach-javadocs</id>
-					<goals>
-						<goal>jar</goal>
-					</goals>
+						<id>attach-javadocs</id>
+						<goals>
+							<goal>jar</goal>
+						</goals>
 					</execution>
 				</executions>
 			</plugin>
@@ -141,11 +168,11 @@
 					<autoReleaseAfterClose>true</autoReleaseAfterClose>
 				</configuration>
 			</plugin>
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-surefire-plugin</artifactId>
-        <version>3.0.0-M5</version>
-      </plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<version>3.0.0-M5</version>
+			</plugin>
 		</plugins>
 	</build>
 </project>

shielddb-core/pom.xml

@@ -1,6 +1,4 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0"
-	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 	<modelVersion>4.0.0</modelVersion>
 	<parent>
 		<groupId>nf.fr.k49</groupId>

shielddb-core/src/main/java/nf/fr/k49/shielddb/core/storage/FileStorage.java

@@ -1,5 +1,6 @@
 package nf.fr.k49.shielddb.core.storage;
 
+import java.io.File;
 import java.io.IOException;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
@@ -8,13 +9,21 @@
 import java.nio.file.Paths;
 import java.nio.file.StandardCopyOption;
 import java.util.stream.Collectors;
+import java.util.Objects;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.commons.lang3.StringUtils.isNotBlank;
 
 public class FileStorage implements ShieldDBStorage {
 
-	private Path parentDir;
-	private Path path;
-	private Path backupPath;
-	private Charset charset;
+	private final ReadWriteLock readWriteLock;
+
+	private final Path parentDir;
+	private final Path path;
+	private final Path backupPath;
+	private final Charset charset;
 
 	/**
 	 * Same as #FileStorage(String, Charset) with a default Charset set to
@@ -32,29 +41,43 @@ public FileStorage(final String path) throws IOException {
 	}
 
 	public FileStorage(final String path, final Charset charset) throws IOException {
+		checkArgument(isNotBlank(path), "Path cannot be null or empty");
+		checkArgument(Objects.nonNull(charset), "Charset cannot be null");
 		this.path = Paths.get(path).toAbsolutePath();
 		this.parentDir = this.path.getParent();
 		this.backupPath = Paths.get(path + ".backup").toAbsolutePath();
 		this.charset = charset;
+		this.readWriteLock = new ReentrantReadWriteLock();
 
-		if (path.contains("/") || path.contains("\\")) {
+		if (path.contains(File.separator)) {
 			this.parentDir.toFile().mkdirs();
 		}
 	}
 
 	@Override
-	public synchronized String read() throws IOException {
-		return Files.readAllLines(path, charset).stream().collect(Collectors.joining(""));
+	public String read() throws IOException {
+		try {
+			readWriteLock.readLock().lock();
+			return Files.readAllLines(path, charset).stream().collect(Collectors.joining(""));
+		} finally {
+			readWriteLock.readLock().unlock();
+		}
 	}
 
 	@Override
-	public synchronized void write(String json) throws IOException {
-		final Path tmp = Files.createTempFile(this.parentDir, "ShieldDB_", ".temp");
-		Files.write(tmp, json.getBytes());
-		Files.move(path, backupPath, StandardCopyOption.ATOMIC_MOVE);
-		Files.move(tmp, path, StandardCopyOption.ATOMIC_MOVE);
-		Files.deleteIfExists(tmp);
-		Files.deleteIfExists(backupPath);
+	public void write(String json) throws IOException {
+		try {
+			readWriteLock.writeLock().lock();
+			checkArgument(isNotBlank(json), "JSON cannot be null or empty");
+			final Path tmp = Files.createTempFile(this.parentDir, "ShieldDB_", ".temp");
+			Files.write(tmp, json.getBytes());			
+			Files.move(path, backupPath, StandardCopyOption.ATOMIC_MOVE);
+			Files.move(tmp, path, StandardCopyOption.ATOMIC_MOVE);
+			Files.deleteIfExists(tmp);
+			Files.deleteIfExists(backupPath);
+		} finally {
+			readWriteLock.writeLock().unlock();
+		}
 	}
 
 	@Override

shielddb-core/src/test/java/nf/fr/k49/shielddb/core/storage/FileStorageTest.java

@@ -1,20 +1,17 @@
 package nf.fr.k49.shielddb.core.storage;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
-import static org.junit.jupiter.api.Assertions.fail;
 import static org.hamcrest.MatcherAssert.*;
 import static org.hamcrest.CoreMatchers.*;
 
 import java.io.File;
 import java.io.IOException;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
-import java.nio.file.FileVisitOption;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.UUID;
-import java.util.stream.Collector;
 import java.util.stream.Collectors;
 
 import org.junit.jupiter.api.AfterAll;

shielddb-core/src/test/java/nf/fr/k49/shielddb/core/storage/FileStorageThreadTest.java

@@ -0,0 +1,9 @@
+package nf.fr.k49.shielddb.core.storage;
+
+import org.junit.jupiter.api.MethodOrderer;
+import org.junit.jupiter.api.TestMethodOrder;
+
+@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
+class FileStorageThreadTest {
+
+}

shielddb-gson-backend/src/main/java/nf/fr/k49/shielddb/gson/ShieldDBGson.java

@@ -6,6 +6,8 @@
 
 import com.google.gson.Gson;
 
+import org.apache.commons.lang3.StringUtils;
+
 import nf.fr.k49.shielddb.core.json.ShieldDBJsonMapper;
 
 public class ShieldDBGson<T> implements ShieldDBJsonMapper<T> {
@@ -28,7 +30,7 @@ public ShieldDBGson(final Gson gson, final Type collectionType) {
 
 	@Override
 	public List<T> toList(String json) {
-		if (json == null || json.length() == 0) {
+		if (StringUtils.isBlank(json)) {
 			return new ArrayList<>();
 		}
 		return new ArrayList<>(gson.fromJson(json, collectionType));