Android java: dealing with Trusted credentials on Android 7.1.1 below for letencrypt

Dealing with connection to https on old android may depend on Trusted credentials on the the device. 

Letsencrypt root certificate does not installed on Trusted credentials prior android 7.1.1.

Some application may throw:

java.security.cert.CertPathValidatorException: Trust anchor for certification path not found.


Solution 1 add user Trusted credentials 

Install Letsencrypt pem manually on old phone i.e android version 7.1.1 or older. You can download from https://letsencrypt.org/certs/isrgrootx1.pem?hl=en-US .

On your device (mine is evercoss gen pro x pro android 7.0). Go to setting -> Security.

You may find:

• Trusted Credentials 
• User Credentials
• Install from SD Card

Choose "Install from SD Card":

• Filed Name of Certification e.g ISGR ROOT X1 or Letsecrypt.
• Credentials Use select VPN and aps

Open your Android Studio project and create res/xml/network_security_config.xml.

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <base-config>
        <trust-anchors>
            <certificates src="system" />
            <certificates src="user" />
        </trust-anchors>
    </base-config>
</network-security-config>

Edit AndroidManifest.xml

...
   <application
    ... 
   android:networkSecurityConfig="@xml/network_security_config"
   ...
   >
...

If https server ever falls back to http (not https), you should add cleartextTrafficPermitted="true" to the <base-config> tag (Not Recommended except your application need to access http):

...
<base-config 
   ...
   cleartextTrafficPermitted="true"
   ...
>
...

if this XML fix doesn't work, it's not the certificate—it's the Android 7.0 Cipher bug. In that specific case, you will have to use Conscrypt library (Solution 2).

Solution 2 using Conscript Library

Add dependency into gradle.build app

dependencies {
    ...
    implementation 'org.conscrypt:conscrypt-android:2.5.2'
    ...
}

Initialize at application startup or foreground

...
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N_MR1) { 
    // Below Android 7.1.1
    Security.insertProviderAt(Conscrypt.newProvider(), 1);
}
...

Android java: input events processing (collection)

There 2 ways to handle input events from user input

1. Immediate: using listener
2. At process: at the end to process data, usually user fire "process" button 

Button

    @Override
    protected void onCreate(Bundle savedInstanceState) {
...
        // to process
        AppCompatButton buttonTest = findViewById(R.id.button_test); // change to your button id from layout
        buttonTest.setOnClickListener(myTest);
    }

    View.OnClickListener myButton = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // todo

        }
    };

TimePicker

1. Immediate 

...
        //on view created
        // date picker
        TimePicker myTimePicker = view.findViewById(R.id.my_time_picker);
        myTimePicker.setOnTimeChangedListener(timeChangeListener);
...
    // TimePicker Listeneer
    private final TimePicker.OnTimeChangedListener timeChangeListener =
            new TimePicker.OnTimeChangedListener() {
        @Override
        public void onTimeChanged(TimePicker view, int hourOfDay, int minute) {
            // TODO
        }
    };

2.  At process

    // Pull the values exactly as they are right now
    int hour = timePicker.getHour();
    int minute = timePicker.getMinute();

RadioGroup

1. Immediate

...
        //on view created
        // date picker
        RadioGroup radioSelectModeBackup = view.findViewById(R.id.radio_select_mode_backup);
        radioSelectModeBackup.setOnCheckedChangeListener(radioListener);
...
    // RadioGroup Listener
    RadioGroup.OnCheckedChangeListener radioListener = new RadioGroup.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(@NonNull RadioGroup radioGroup, int idSelected) {
            if (idSelected==R.id.radio_weekly) {
                // weekly
            } else if (idSelected==R.id.radio_moonthly) {
                // monthly
            }
        }
    };

2. At process 

    // Inside your "Save" or "Submit" button click listener
    int selectedId = radioSelectModeBackup.getCheckedRadioButtonId();

    if (selectedId == R.id.radio_weekly) {
        // Logic for weekly backup
    } else if (selectedId == R.id.radio_moonthly) {
        // Logic for monthly backup
    } else {
        // Nothing is selected (returns -1 if no default is set in XML)
    }

RecyclerView

RecyclerView layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="64dp"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="horizontal"
    android:background="#FFFFFF"
    android:gravity="center_vertical">

    <HorizontalScrollView
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:scrollbars="none"
        android:fillViewport="true">

        <TextView
            android:id="@+id/my_item_view"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center_vertical"
            android:paddingStart="12dp"
            android:paddingEnd="12dp"
            android:textSize="20sp"
            android:maxLines="1"
            android:textColor="#333333" />
    </HorizontalScrollView>

    <ImageButton
        android:id="@+id/btn_add_phrase"
        android:layout_width="64dp"
        android:layout_height="match_parent"
        android:src="@android:drawable/ic_input_add"
        android:background="?android:attr/selectableItemBackground"
        android:contentDescription="Add phrase"
        android:scaleType="centerInside"
        app:tint="#4CAF50" />

</LinearLayout>

RecyclerView Adapter and Holder

public class MyRecyclerView extends RecyclerView.Adapter<MyRecyclerView.ViewHolder> {

    String[] stringsTmp = {"Hello", "Test", "How are you?", "Help me write", "The quick brown fox jumps over the lazy dog\n The quick brown fox jumps over the lazy dog"};
    OnMyItemClickListener onMyItemClickListener;

    public MyRecyclerView(OnMyItemClickListener listener) {
        // Use the parameter 'listener', not the uninitialized global variable
        this.onMyItemClickListener = listener;
    }

    @NonNull
    @Override
    public MyRecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.layout_view_item, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MyRecyclerView.ViewHolder holder, int position) {
        // Get the string from your array and put it in the TextView
        String text = stringsTmp[position];
        holder.textView.setText(text);

        // Add a click listener for the item NOT WORKINGN HERE
        // Set the click here. It can see 'onMyItemClickListener' and 'text'
        holder.addButton.setOnClickListener(v -> {
            Log.e("dedetok", "onBindViewHolder Clicked : " + text);
            if (onMyItemClickListener != null) {
                onMyItemClickListener.getString(text);
            }
        });

    }

    @Override
    public int getItemCount() {
        return stringsTmp.length;
    }


    /*
     * View Holder
     */
    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView textView;
        public ImageButton addButton; // Changed from Button

        public ViewHolder(View view) {
            super(view);
            // Matches the ID in your item_phrase.xml
            textView = view.findViewById(R.id.my_item_view);
            addButton = view.findViewById(R.id.btn_add_phrase);

        }
    }

    public interface OnMyItemClickListener {
        void getString(String stringSelect);
    }
}

If you use action listener on item in holder, DO NOT add onItemSelected event into adapter or any else touch event. They will conflict with other event inside the items.

You need to implement interface  MyRecyclerView.OnMyItemClickListener on your activity or fragment.

You can remove all event on holder if you prefered to use onItemSelected event.

 

 

 

 

 

Debian 13: using systemd timesync to update ntp client time

Since Debain Jessie, Debian use systemd to synchronize ntp clinet

To list timezone:

# timedatectl list-timezones | grep Jakarta
Asia/Jakarta

To set timezone:

# timedatectl set-timezone Asia/Jakarta

To show

# timedatectl 
               Local time: Mon 2026-01-12 12:44:27 WIB
           Universal time: Mon 2026-01-12 05:44:27 UTC
                 RTC time: Mon 2026-01-12 05:44:27
                Time zone: Asia/Jakarta (WIB, +0700)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

Edit /etc/systemd/timesyncd.conf

...
[Time]
#NTP=
NTP=0.id.pool.ntp.org 1.id.pool.ntp.org 2.id.pool.ntp.org 2.id.pool.ntp.org 3.id.pool.ntp.org
#FallbackNTP=0.debian.pool.ntp.org 1.debian.pool.ntp.org 2.debian.pool.ntp.org 3.debian.pool.ntp.org
...

To restart service

# systemctl restart systemd-timesyncd

you can use old way using ntp client, but you need to remove this package

# timedatectl set-ntp false

Now you can install ntp and edit configuration /etc/ntp.conf.

 

 

Java: using build tool gradle wrapper to setup project and run

 

• java application openjdk 17
• gradle 8.7

install gradle 

# apt-get install gradle 


create folder project example

$ mkdir example
$ cd example

create init project

wrap gradle version for your project 

$ gradle wrapper --gradle-version 8.7
openjdk version "17.0.16" 2025-07-15
OpenJDK Runtime Environment (build 17.0.16+8-Debian-1deb12u1)
OpenJDK 64-Bit Server VM (build 17.0.16+8-Debian-1deb12u1, mixed mode, sharing)

init using gradle 8.7  debian 13 uses old 4.4 

$ ./gradlew init \
  --type java-application \
  --dsl groovy \
  --test-framework junit-jupiter \
  --package com.dedetok \
  --project-name example
openjdk version "17.0.16" 2025-07-15
OpenJDK Runtime Environment (build 17.0.16+8-Debian-1deb12u1)
OpenJDK 64-Bit Server VM (build 17.0.16+8-Debian-1deb12u1, mixed mode, sharing)
Downloading https://services.gradle.org/distributions/gradle-8.7-bin.zip
...............................................................................................................................
Unzipping ~/.gradle/wrapper/dists/gradle-8.7-bin/bhs2wmbdwecv87pi65oeuq5iu/gradle-8.7-bin.zip to ~/.gradle/wrapper/dists/gradle-8.7-bin/bhs2wmbdwecv87pi65oeuq5iu
Set executable permissions for: ~/.gradle/wrapper/dists/gradle-8.7-bin/bhs2wmbdwecv87pi65oeuq5iu/gradle-8.7/bin/gradle

Welcome to Gradle 8.7!

Here are the highlights of this release:
 - Compiling and testing with Java 22
 - Cacheable Groovy script compilation
 - New methods in lazy collection properties

For more details see https://docs.gradle.org/8.7/release-notes.html

Starting a Gradle Daemon, 1 incompatible Daemon could not be reused, use --status for details

Enter target Java version (min: 7, default: 21): 17

Select application structure:
  1: Single application project
  2: Application and library project
Enter selection (default: Single application project) [1..2] 1

Generate build using new APIs and behavior (some features may change in the next minor release)? (default: no) [yes, no] no


> Task :init
To learn more about Gradle by exploring our Samples at https://docs.gradle.org/8.7/samples/sample_building_java_applications_multi_project.html

BUILD SUCCESSFUL in 5m 12s
1 actionable task: 1 executed

./settings.gradle

plugins {
    // Apply the foojay-resolver plugin to allow automatic download of JDKs
    id 'org.gradle.toolchains.foojay-resolver-convention' version '0.8.0'
}

rootProject.name = 'example'
include('app')

./app/build.gradle

plugins {
    // Apply the application plugin to add support for building a CLI application in Java.
    id 'application'
}

repositories {
    // Use Maven Central for resolving dependencies.
    mavenCentral()
}

dependencies {
    // Use JUnit Jupiter for testing.
    testImplementation libs.junit.jupiter

    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'

    // This dependency is used by the application.
    implementation libs.guava
}

// Apply a specific Java toolchain to ease working on different environments.
java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(17)
    }
}

application {
    // Define the main class for the application.
    mainClass = 'com.dedetok.App'
}

tasks.named('test') {
    // Use JUnit Platform for unit tests.
    useJUnitPlatform()
}

./gradle/libs.versions.toml

[versions]
guava = "32.1.3-jre"
junit-jupiter = "5.10.1"

[libraries]
guava = { module = "com.google.guava:guava", version.ref = "guava" }
junit-jupiter = { module = "org.junit.jupiter:junit-jupiter", version.ref = "junit-jupiter" }

To show current gradle version

$ ./gradlew --version

------------------------------------------------------------
Gradle 8.7
------------------------------------------------------------

Build time:   2024-03-22 15:52:46 UTC
Revision:     650af14d7653aa949fce5e886e685efc9cf97c10

Kotlin:       1.9.22
Groovy:       3.0.17
Ant:          Apache Ant(TM) version 1.10.13 compiled on January 4 2023
JVM:          17.0.16 (Debian 17.0.16+8-Debian-1deb12u1)
OS:           Linux 6.12.57+deb13-amd64 amd64

Test run

$ ./gradlew run
Path for java installation '/usr/lib/jvm/openjdk-17' (Common Linux Locations) does not contain a java executable

> Task :app:run
Hello World!

BUILD SUCCESSFUL in 473ms
2 actionable tasks: 1 executed, 1 up-to-date

or you can run using style $ ./gradlew :app:run

Now add maridb jcoonect into project, using Traditional Groovy Approach. edit ./app/build.gradle

...
dependencies {
    // Use JUnit Jupiter for testing.
    testImplementation libs.junit.jupiter

    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'

    // This dependency is used by the application.
    implementation libs.guava

    // mariadb jconnector (single file no need change libs.versions.toml
    implementation 'org.mariadb.jdbc:mariadb-java-client:3.3.3'

    // using libs.versions.toml must editing this file 
    //implementation libs.mariadb.client

}
...

If you wish to useing Version Catalog Approach, use 2nd option for ./app/build.gradle and edit libs.version.toml

[versions]
guava = "32.1.3-jre"
junit-jupiter = "5.10.1"
mariadb = "3.3.3"

[libraries]
guava = { module = "com.google.guava:guava", version.ref = "guava" }
junit-jupiter = { module = "org.junit.jupiter:junit-jupiter", version.ref = "junit-jupiter" }
mariadb-client = { group = "org.mariadb.jdbc", name = "mariadb-java-client", version.ref = "mariadb" }


use Version Catalog Approach for complex project and involving multiple developers.

Edit ./app/src/main/java/com/dedetok/App.java

/*
 * This source file was generated by the Gradle 'init' task
 */
package com.dedetok;

import java.sql.*;

public class App {
    public String getGreeting() {
        return "Hello World!";
    }

    public static void main(String[] args) throws SQLException {
        System.out.println(new App().getGreeting());
        
        String dbUrl = "jdbc:mariadb://localhost:3306/mydatabase";
        String dbUName = "myuname";
        String dbPass = "mypass";
        
        Connection conn = DriverManager.getConnection(dbUrl, dbUName, dbPass);

    }
}

To generate single file jar for your project, edit  ./app/build.gradle

...
jar {
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE

    // change with yours
    manifest {
        attributes "Main-Class": "com.dedetok.App"
    }

    from {
        configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) }
    }
}
...

You can run directly using java command

$ ./gradlew build
...
$ java -jar ./app/build/libs/app.jar
Hello World!

Your jar file location is ./app/build/libs/

Now you can edit  ./app/src/main/java/com/dedetok/App.java finish your project. Use any text editor if you wish.

Debian 13: bash to clean up unused gradle in folder $HOME/.gradle

stop any gradle daemon (better run this after you start your Debian)

copy paste this bash and change permission to execute

#!/bin/bash

# Set the cutoff date yyyy-mm-dd
CUTOFF_DATE="2025-08-01"

# Gradle folder
GRADLE_DIR="$HOME/.gradle"

# List of folders to clean
FOLDERS=("android" "build-scan-data" "caches" "daemon" "kotilin-profile" "native" "notifications" "undefined-build" "wrapper" ".tmp")

# 1. Stop Gradle Daemons first so files aren't locked
if [ -f "$GRADLE_DIR/daemon" ]; then
    echo "Stopping Gradle daemons..."
    gradle --stop 2>/dev/null || ./gradlew --stop 2>/dev/null
fi

echo "Cleaning Gradle folders in $GRADLE_DIR modified before $CUTOFF_DATE..."

for folder in "${FOLDERS[@]}"; do
    TARGET="$GRADLE_DIR/$folder"
    if [ -d "$TARGET" ]; then
        echo "Processing $TARGET..."
        # Find and delete files modified before the cutoff date
        find "$TARGET" -type f ! -newermt "$CUTOFF_DATE" -print -delete
        # Remove empty directories
        find "$TARGET" -type d -empty -print -delete
    else
        echo "Folder $TARGET does not exist, skipping."
    fi
done

echo "Cleanup complete."

Note:

• change CUTOFF_DATE for any desire date
• add or remove FOLDERS depends on your folder structure