public final class Util

// File: Main.java
public class Main {
  public void init(Object o) {
    theme = UIManager.initFirstTheme("/theme");

    // IMPORTANT: Notice we don't use MyClass.class.getName()! This won't work due to obfuscation!
    Util.register("MyClass", MyClass.class);
  }

  public void start() {
    //...
  }

  public void stop() {
    //...
  }

  public void destroy() {
    //...
  }
}

// File: MyClass.java
public class MyClass implements Externalizable {
  // allows us to manipulate the version, in this case we are demonstrating a data change between the initial release
  // and the current state of object data
  private static final int VERSION = 2;

  private String name;
  private Map data;

  // this field was added after version 1
  private Date startedAt;

  public int getVersion() {
    return VERSION;
  }

  public void externalize(DataOutputStream out) throws IOException {
    Util.writeUTF(name, out);
    Util.writeObject(data, out);
    if(startedAt != null) {
        out.writeBoolean(true);
        out.writeLong(startedAt.getTime());
    } else {
        out.writeBoolean(false);
    }
  }
  public void internalize(int version, DataInputStream in) throws IOException {
    name = Util.readUTF(in);
    data = (Map)Util.readObject(in);
    if(version > 1) {
        boolean hasDate = in.readBoolean();
        if(hasDate) {
            startedAt = new Date(in.readLong());
        }
    }
  }
  public String getObjectId() {
    // IMPORTANT: Notice we don't use getClass().getName()! This won't work due to obfuscation!
    return "MyClass";
  }
}

// File: ReadAndWrite.java
// will read the file or return null if failed
MyClass object = (MyClass)Storage.getInstance().readObject("NameOfFile");

// write the object back to storage
Storage.getInstance().writeObject("NameOfFile", object);

// File: Main.java
public class Main {
  public void init(Object o) {
    theme = UIManager.initFirstTheme("/theme");

    // IMPORTANT: Notice we don't use MyClass.class.getName()! This won't work due to obfuscation!
    Util.register("MyClass", MyClass.class);
  }

  public void start() {
    //...
  }

  public void stop() {
    //...
  }

  public void destroy() {
    //...
  }
}

// File: MyClass.java
public class MyClass implements Externalizable {
  // allows us to manipulate the version, in this case we are demonstrating a data change between the initial release
  // and the current state of object data
  private static final int VERSION = 2;

  private String name;
  private Map data;

  // this field was added after version 1
  private Date startedAt;

  public int getVersion() {
    return VERSION;
  }

  public void externalize(DataOutputStream out) throws IOException {
    Util.writeUTF(name, out);
    Util.writeObject(data, out);
    if(startedAt != null) {
        out.writeBoolean(true);
        out.writeLong(startedAt.getTime());
    } else {
        out.writeBoolean(false);
    }
  }
  public void internalize(int version, DataInputStream in) throws IOException {
    name = Util.readUTF(in);
    data = (Map)Util.readObject(in);
    if(version > 1) {
        boolean hasDate = in.readBoolean();
        if(hasDate) {
            startedAt = new Date(in.readLong());
        }
    }
  }
  public String getObjectId() {
    // IMPORTANT: Notice we don't use getClass().getName()! This won't work due to obfuscation!
    return "MyClass";
  }
}

// File: ReadAndWrite.java
// will read the file or return null if failed
MyClass object = (MyClass)Storage.getInstance().readObject("NameOfFile");

// write the object back to storage
Storage.getInstance().writeObject("NameOfFile", object);

// File: Main.java
public class Main {
  public void init(Object o) {
    theme = UIManager.initFirstTheme("/theme");

    // IMPORTANT: Notice we don't use MyClass.class.getName()! This won't work due to obfuscation!
    Util.register("MyClass", MyClass.class);
  }

  public void start() {
    //...
  }

  public void stop() {
    //...
  }

  public void destroy() {
    //...
  }
}

// File: MyClass.java
public class MyClass implements Externalizable {
  // allows us to manipulate the version, in this case we are demonstrating a data change between the initial release
  // and the current state of object data
  private static final int VERSION = 2;

  private String name;
  private Map data;

  // this field was added after version 1
  private Date startedAt;

  public int getVersion() {
    return VERSION;
  }

  public void externalize(DataOutputStream out) throws IOException {
    Util.writeUTF(name, out);
    Util.writeObject(data, out);
    if(startedAt != null) {
        out.writeBoolean(true);
        out.writeLong(startedAt.getTime());
    } else {
        out.writeBoolean(false);
    }
  }
  public void internalize(int version, DataInputStream in) throws IOException {
    name = Util.readUTF(in);
    data = (Map)Util.readObject(in);
    if(version > 1) {
        boolean hasDate = in.readBoolean();
        if(hasDate) {
            startedAt = new Date(in.readLong());
        }
    }
  }
  public String getObjectId() {
    // IMPORTANT: Notice we don't use getClass().getName()! This won't work due to obfuscation!
    return "MyClass";
  }
}

// File: ReadAndWrite.java
// will read the file or return null if failed
MyClass object = (MyClass)Storage.getInstance().readObject("NameOfFile");

// write the object back to storage
Storage.getInstance().writeObject("NameOfFile", object);

// File: Main.java
public class Main {
  public void init(Object o) {
    theme = UIManager.initFirstTheme("/theme");

    // IMPORTANT: Notice we don't use MyClass.class.getName()! This won't work due to obfuscation!
    Util.register("MyClass", MyClass.class);
  }

  public void start() {
    //...
  }

  public void stop() {
    //...
  }

  public void destroy() {
    //...
  }
}

// File: MyClass.java
public class MyClass implements Externalizable {
  // allows us to manipulate the version, in this case we are demonstrating a data change between the initial release
  // and the current state of object data
  private static final int VERSION = 2;

  private String name;
  private Map data;

  // this field was added after version 1
  private Date startedAt;

  public int getVersion() {
    return VERSION;
  }

  public void externalize(DataOutputStream out) throws IOException {
    Util.writeUTF(name, out);
    Util.writeObject(data, out);
    if(startedAt != null) {
        out.writeBoolean(true);
        out.writeLong(startedAt.getTime());
    } else {
        out.writeBoolean(false);
    }
  }
  public void internalize(int version, DataInputStream in) throws IOException {
    name = Util.readUTF(in);
    data = (Map)Util.readObject(in);
    if(version > 1) {
        boolean hasDate = in.readBoolean();
        if(hasDate) {
            startedAt = new Date(in.readLong());
        }
    }
  }
  public String getObjectId() {
    // IMPORTANT: Notice we don't use getClass().getName()! This won't work due to obfuscation!
    return "MyClass";
  }
}

// File: ReadAndWrite.java
// will read the file or return null if failed
MyClass object = (MyClass)Storage.getInstance().readObject("NameOfFile");

// write the object back to storage
Storage.getInstance().writeObject("NameOfFile", object);

Form hi = new Form("ImageViewer", new BorderLayout());
final EncodedImage placeholder = EncodedImage.createFromImage(
        FontImage.createMaterial(FontImage.MATERIAL_SYNC, s).
                scaled(300, 300), false);

class ImageList implements ListModel {
    private int selection;
    private String[] imageURLs = {
        "http://awoiaf.westeros.org/images/thumb/9/93/AGameOfThrones.jpg/300px-AGameOfThrones.jpg",
        "http://awoiaf.westeros.org/images/thumb/3/39/AClashOfKings.jpg/300px-AClashOfKings.jpg",
        "http://awoiaf.westeros.org/images/thumb/2/24/AStormOfSwords.jpg/300px-AStormOfSwords.jpg",
        "http://awoiaf.westeros.org/images/thumb/a/a3/AFeastForCrows.jpg/300px-AFeastForCrows.jpg",
        "http://awoiaf.westeros.org/images/7/79/ADanceWithDragons.jpg"
    };
    private Image[] images;
    private EventDispatcher listeners = new EventDispatcher();

    public ImageList() {
        this.images = new EncodedImage[imageURLs.length];
    }

    public Image getItemAt(final int index) {
        if(images[index] == null) {
            images[index] = placeholder;
            Util.downloadUrlToStorageInBackground(imageURLs[index], "list" + index, (e) -> {
                    try {
                        images[index] = EncodedImage.create(Storage.getInstance().createInputStream("list" + index));
                        listeners.fireDataChangeEvent(index, DataChangedListener.CHANGED);
                    } catch(IOException err) {
                        err.printStackTrace();
                    }
            });
        }
        return images[index];
    }

    public int getSize() {
        return imageURLs.length;
    }

    public int getSelectedIndex() {
        return selection;
    }

    public void setSelectedIndex(int index) {
        selection = index;
    }

    public void addDataChangedListener(DataChangedListener l) {
        listeners.addListener(l);
    }

    public void removeDataChangedListener(DataChangedListener l) {
        listeners.removeListener(l);
    }

    public void addSelectionListener(SelectionListener l) {
    }

    public void removeSelectionListener(SelectionListener l) {
    }

    public void addItem(Image item) {
    }

    public void removeItem(int index) {
    }
};

ImageList imodel = new ImageList();

ImageViewer iv = new ImageViewer(imodel.getItemAt(0));
iv.setImageList(imodel);
hi.add(BorderLayout.CENTER, iv);

request.retry();

import com.codename1.components.SpanLabel;
import com.codename1.components.ToastBar;
import static com.codename1.ui.CN.*;
import com.codename1.ui.Display;
import com.codename1.ui.Form;
import com.codename1.ui.Dialog;
import com.codename1.ui.Label;
import com.codename1.ui.plaf.UIManager;
import com.codename1.ui.util.Resources;
import com.codename1.io.Log;
import com.codename1.ui.Toolbar;
import java.io.IOException;
import com.codename1.ui.layouts.BoxLayout;
import com.codename1.io.NetworkEvent;
import com.codename1.io.Storage;
import com.codename1.io.Util;
import java.util.Timer;
import java.util.TimerTask;

/**
 * This file was generated by [Codename One](https://www.codenameone.com/) for the purpose
 * of building native mobile applications using Java.
 */
public class MyApplication {

    private Form current;
    private Resources theme;

    public void init(Object context) {
        // use two network threads instead of one
        updateNetworkThreadCount(2);

        theme = UIManager.initFirstTheme("/theme");

        // Enable Toolbar on all Forms by default
        Toolbar.setGlobalToolbar(true);

        // Pro only feature
        Log.bindCrashProtection(true);

        // Manage both network errors (connectivity issues) and server errors (codes different from 2xx)
        addNetworkAndServerErrorListener();
    }

    public void start() {
        if(current != null){
            current.show();
            return;
        }

        String url = "https://www.informatica-libera.net/video/AVO_Cariati_Pasqua_2020.mp4"; // 38 MB

        Form form = new Form("Test Download 38MB", BoxLayout.y());
        Label infoLabel = new Label("Starting download...");
        form.add(infoLabel);

        try {
            Util.downloadUrlSafely(url, "myHeavyVideo.mp4", (percentage) -> {
                // percentage callback
                infoLabel.setText("Downloaded: " + percentage + "%");
                infoLabel.repaint();
            }, (filename) -> {
                // file saved callback
                infoLabel.setText("Downloaded completed");
                int fileSizeMB = Storage.getInstance().entrySize(filename) / 1048576;
                form.add("Checking files size: " + fileSizeMB + " MB");
                form.revalidate();
            });
        } catch (IOException ex) {
            Log.p("Error in downloading: " + url);
            Log.e(ex);
            form.add(new SpanLabel("Error in downloading:\n" + url));
            form.revalidate();
        }

        form.show();


    }

    public void stop() {
        current = getCurrentForm();
        if(current instanceof Dialog) {
            ((Dialog)current).dispose();
            current = getCurrentForm();
        }
    }

    public void destroy() {
    }

    private void addNetworkAndServerErrorListener() {
        // The following way to manage network errors is discussed here:
        // https://stackoverflow.com/questions/61993127/distinguish-between-server-side-errors-and-connection-problems
        addNetworkErrorListener(err -> {
            // prevents the event from propagating
            err.consume();

            if (err.getError() != null) {
                // this is the case of a network error,
                // like: java.io.IOException: Unreachable
                Log.p("Error connectiong to: " + err.getConnectionRequest().getUrl(), Log.ERROR);
                // maybe there are connectivity issues, let's try again
                ToastBar.showInfoMessage("Reconnect...");
                Timer timer = new Timer();
                timer.schedule(new TimerTask() {
@Override
                    public void run() {
                        err.getConnectionRequest().retry();
                    }
                }, 2000);
            } else {
                // this is the case of a server error
                // logs the error
                String errorLog = "REST ERROR\nURL:" + err.getConnectionRequest().getUrl()
                        + "\nMethod: " + err.getConnectionRequest().getHttpMethod()
                        + "\nResponse code: " + err.getConnectionRequest().getResponseCode();
                if (err.getConnectionRequest().getRequestBody() != null) {
                    errorLog += "\nRequest body: " + err.getConnectionRequest().getRequestBody();
                }
                if (err.getConnectionRequest().getResponseData() != null) {
                    errorLog += "\nResponse message: " + new String(err.getConnectionRequest().getResponseData());
                }
                if (err.getConnectionRequest().getResponseErrorMessage() != null) {
                    errorLog += "\nResponse error message: " + err.getConnectionRequest().getResponseErrorMessage();
                }
                Log.p(errorLog, Log.ERROR);

                Log.sendLogAsync();
                ToastBar.showErrorMessage("Server Error", 10000);
            }
        });
    }

}

Form hi = new Form("Test UIID", BoxLayout.y());
Button button = new Button("Generate 10 UIID");
hi.add(button);
hi.show();
button.addActionListener(l -> {
    String myId = "myUsername"; // do not exceed 12 characters
    Preferences.set("CustomDeviceId__$", Long.parseLong(myId, 36));
    hi.add(new SpanLabel("10 Random UUID"));
    for (int i = 0; i < 10; i++) {
        hi.add(new SpanLabel(Util.getUIID()));
    }
    hi.revalidate();
});