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version 3.0 [rewritten]
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‎CloremDB/build.gradle‎

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plugins {
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id 'java-library'
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}
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java {
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sourceCompatibility = JavaVersion.VERSION_16
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targetCompatibility = JavaVersion.VERSION_16
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}
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dependencies {
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implementation 'androidx.annotation:annotation:1.3.0'
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}

‎CloremDB/src/main/java/db/clorabase/clorem/Clorem.java‎

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package db.clorabase.clorem;
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import androidx.annotation.NonNull;
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import java.io.File;
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import java.lang.management.ThreadInfo;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.concurrent.Callable;
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import java.util.function.Consumer;
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import java.util.function.Predicate;
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import javax.naming.NoPermissionException;
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/**
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* Clorem is a simple, easy to use, and fast database engine for java applications.
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* It is a no-sql database which can save POJO's directly. You can organise your data
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* in volumes. Each volume is like a SQL table which contains the objects as rows. You can create
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* as many volumes as you want. You can also create as many objects as you want in
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* each volume. The only limitation is that the objects implement the {@link CloremObject}
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*
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* All the methods are thread safe. You can use the database in a multi-threaded environment.
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*
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* @author author Rahil khan
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* @version 1.0
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* @since 1.0
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*/
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public class Clorem {
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private static Clorem INSTANCE;
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private static File databaseDir;
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/**
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* This method returns the singleton instance of the Clorem database.
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* @param databaseDir The directory where the database will be stored on the disk. This directory must be writable.
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* @return The singleton instance of the Clorem database
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*/
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public static Clorem getInstance(File databaseDir) {
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if (INSTANCE == null){
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INSTANCE = new Clorem();
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if (databaseDir.canRead() && databaseDir.canWrite())
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Clorem.databaseDir = databaseDir;
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else
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throw new RuntimeException(new NoPermissionException("You do not have permission to read/write on this directory"));
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}
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return INSTANCE;
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}
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/**
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* This method creates a new volume in the database.
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* @param name The name of the volume
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*/
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public void createVolume(@NonNull String name){
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new File(databaseDir,name).mkdir();
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}
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/**
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* This method deletes a volume from the database. All the objects in the volume will be deleted.
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* @param name The name of the volume
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*/
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public void deleteVolume(@NonNull String name){
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var volume = new File(databaseDir,name);
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var files = volume.listFiles();
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for (File file : files) {
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file.delete();
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}
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volume.delete();
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}
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/**
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* Put an object in the database. The object must implement the {@link CloremObject} interface.
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* @param object The object to be saved
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* @param <T> The type of the object
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*/
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public synchronized <T extends CloremObject> void put(@NonNull T object){
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var volume = new File(databaseDir,object.getVolume());
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if (!volume.exists() && !volume.mkdir())
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throw new RuntimeException("The volume could not be created. You might not have permission to create a directory");
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else
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CloremUtils.writeObject(object,new File(volume,object.getKey()));
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}
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/**
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* Get an object from the database.
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* @param key The key of the object
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* @param volume The volume in which the object is stored
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* @return The object
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*/
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public synchronized Object get(@NonNull String key,@NonNull String volume){
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var volumeDir = new File(databaseDir,volume);
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var obj = new File(volumeDir,key);
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if (volumeDir.isDirectory() && obj.exists())
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return CloremUtils.readObject(obj);
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else
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throw new IllegalArgumentException("The volume or the object does not exist");
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}
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/**
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* Update an object in the database. Only use this method when you want to update whole object.
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* If you want to update only a few fields of the object, use the {@link #update(String, String, Class, Consumer)} method.
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* The object id must be the same as the object id of the object in the database.
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* @param object The object to be updated
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* @param <T> The type of the object
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*/
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public synchronized <T extends CloremObject> void update(@NonNull T object){
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var volume = new File(databaseDir,object.getVolume());
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var file = new File(volume,object.getKey());
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if (volume.isDirectory() && file.exists()){
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CloremUtils.writeObject(object,file);
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} else
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throw new IllegalArgumentException("The volume or the object does not exist");
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}
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/**
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* Update an object in the database. This method is used to update only required fields of the object.
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* @param key The key of the object
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* @param volume The volume in which the object is stored
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* @param clazz The class of the object
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* @param transition The transition function which will be used to update the object
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* @param <T> The type of the object
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*/
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public synchronized <T extends CloremObject> void update(@NonNull String key, @NonNull String volume,@NonNull Class<T> clazz,@NonNull Consumer<T> transition){
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var obj = clazz.cast(get(key,volume));
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transition.accept(obj);
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if (key.equals(obj.getKey()) && volume.equals(obj.getVolume()))
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update(obj);
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else {
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delete(key,volume);
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put(obj);
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}
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}
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/**
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* Delete an object from the database.
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* @param key The key of the object
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* @param volume The volume in which the object is stored
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*/
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public synchronized void delete(@NonNull String key,@NonNull String volume){
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var volumeDir = new File(databaseDir,volume);
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var obj = new File(volumeDir,key);
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if (volumeDir.isDirectory() && obj.exists())
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obj.delete();
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else
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throw new IllegalArgumentException("The volume or the object does not exist");
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}
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/**
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* Query the database. This method returns a list of objects which satisfy the condition.
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* @param volume The volume in which the objects are stored
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* @param clazz The class of the objects
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* @param condition The condition which the objects must satisfy. Returns true if the object is to be included in the list.
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* @param <T> The type of the objects
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* @return A list of objects which satisfy the condition
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*/
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public <T extends CloremObject> List<T> query(@NonNull String volume,@NonNull Class<T> clazz, @NonNull Predicate<T> condition){
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var files = new File(databaseDir,volume).listFiles();
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if (files == null)
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throw new RuntimeException("The volume does not exist");
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else {
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var list = new ArrayList<T>();
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for (File file : files) {
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var obj = get(file.getName(),volume);
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try {
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if (condition.test(clazz.cast(obj)))
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list.add(clazz.cast(obj));
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} catch (ClassCastException ignored){}
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}
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return list;
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}
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}
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/**
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* List all the objects in a volume.
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* @param volume The volume in which the objects are stored
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* @return A list of objects
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*/
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public List<Object> listObjects(@NonNull String volume){
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return CloremUtils.listObjects(new File(databaseDir,volume));
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}
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}

‎CloremDB/src/main/java/db/clorabase/clorem/CloremObject.java‎

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package db.clorabase.clorem;
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import java.io.Serializable;
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/**
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* This interface is implemented by all the objects which are to be saved in the database.
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* The objects must implement this interface to be saved in the database.
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*
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* @author author Rahil khan
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* @version 1.0
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* @since 1.0
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*/
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public interface CloremObject extends Serializable {
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String getKey();
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String getVolume();
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}

‎CloremDB/src/main/java/db/clorabase/clorem/CloremUtils.java‎

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package db.clorabase.clorem;
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import java.io.File;
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import java.io.FileInputStream;
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import java.io.FileNotFoundException;
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import java.io.FileOutputStream;
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import java.io.IOException;
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import java.io.ObjectInputStream;
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import java.io.ObjectOutputStream;
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import java.io.UncheckedIOException;
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import java.util.Arrays;
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import java.util.List;
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public class CloremUtils {
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protected static void writeObject(Object object, File file){
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try {
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var os = new ObjectOutputStream(new FileOutputStream(file));
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os.writeObject(object);
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os.close();
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} catch (IOException e) {
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throw new UncheckedIOException(e);
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}
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}
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protected static Object readObject(File file){
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try {
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var in = new ObjectInputStream(new FileInputStream(file));
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var object = in.readObject();
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in.close();
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return object;
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} catch (IOException | ClassNotFoundException e) {
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throw new RuntimeException(e);
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}
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}
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protected static List<Object> listObjects(File volume){
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var files = volume.listFiles();
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if (files == null)
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throw new RuntimeException("The volume does not exist");
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else {
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var objects = new Object[files.length];
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for (int i = 0; i < files.length; i++) {
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objects[i] = readObject(files[i]);
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}
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return Arrays.asList(objects);
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}
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}
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}

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