Revisions to Android APP FTP downloading file implementation in Java

Update build.gradle

Source Link

edited Feb 20 at 13:20

5.5k
2
10
40

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.46.1'
    implementation 'com.google.android.material:material:1.511.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.3'4'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.45.0'1'
}

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.4.1'
    implementation 'com.google.android.material:material:1.5.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.3'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.6.1'
    implementation 'com.google.android.material:material:1.11.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}

Tweeted twitter.com/StackCodeReview/status/1518107469926604801

occurred Apr 24, 2022 at 6:00

Update description

Source Link

edited Apr 24, 2022 at 1:53

JimmyHu

5.5k
2
10
40

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.34.1'
    implementation 'com.google.android.material:material:1.45.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'3'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.4.1'
    implementation 'com.google.android.material:material:1.5.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.3'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

Update description

Source Link

edited Oct 6, 2021 at 23:59

JimmyHu

5.5k
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Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.0'1'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.0'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

Project name: FTPDownloadFile

FTPconnection class implementation

package com.example.ftpdownloadfile;

import android.util.Log;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.SocketException;
import java.net.UnknownHostException;

public class FTPconnection {

    private native String getHostname();
    private native String getUsername();
    private native String getPassword();

    private static String FTPHostName = "";
    private static final int FTPPort = 21;
    private static String FTPUsername = "";
    private static String FTPPassword = "";

    public FTPconnection()
    {
        FTPHostName = getHostname();
        FTPUsername = getUsername();
        FTPPassword = getPassword();
    }

    //  Reference: https://stackoverflow.com/a/24605713/6667035
    public Boolean downloadAndSaveFile(String filename, File localFile)
            throws IOException {
        String LOG_TAG = "FTPconnection_download";
        FTPClient ftp = null;
        try {
            ftp = new FTPClient();
            ftp.connect(FTPHostName, FTPPort);
            Log.d(LOG_TAG, "Connected. Reply: " + ftp.getReplyString());

            ftp.login(FTPUsername, FTPPassword);
            Log.d(LOG_TAG, "Logged in");
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            Log.d(LOG_TAG, "Downloading");
            ftp.enterLocalPassiveMode();

            OutputStream outputStream = null;
            boolean success = false;
            try {
                outputStream = new BufferedOutputStream(new FileOutputStream(
                        localFile));
                success = ftp.retrieveFile(filename, outputStream);
            } finally {
                if (outputStream != null) {
                    outputStream.close();
                }
            }

            return success;
        } finally {
            if (ftp != null) {
                ftp.logout();
                ftp.disconnect();
            }
        }
    }
}

ftpdownloadfile.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getHostname(JNIEnv *env, jobject thiz) {
    std::string output = "Hostname";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getUsername(JNIEnv *env, jobject thiz) {
    std::string output = "Username";
    return env->NewStringUTF(output.c_str());
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_ftpdownloadfile_FTPconnection_getPassword(JNIEnv *env, jobject thiz) {
    std::string output = "Password";
    return env->NewStringUTF(output.c_str());
}

ExecutorService for new thread

ExecutorService executor = Executors.newSingleThreadExecutor();
      executor.submit(() -> {
          String threadName = Thread.currentThread().getName();
          showToast(threadName, Toast.LENGTH_SHORT);
          FTPconnection ftpConnect = new FTPconnection();
          final String LOG_TAG = "executor";
          try {
              String filename = "test.txt";
              Log.v(LOG_TAG,"Preparing to download " + filename);
              var result  = ftpConnect.downloadAndSaveFile(filename, Paths.get(getApplicationInfo().dataDir + "/" + filename).toFile());
              if (result == false) {
                  Log.v(LOG_TAG,"Fail to download " + filename + "!");
              } else {
                  Log.v(LOG_TAG,"Download " + filename + " successfully!");
              }
          } catch (Exception ex) {
              ex.printStackTrace();
          }
      });

User permission setting

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ftpdownloadfile">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FTPDownloadFile">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "com.example.ftpdownloadfile"
        minSdk 26
        targetSdk 31
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_11
        targetCompatibility JavaVersion.VERSION_11
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }
}

dependencies {

    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // https://mvnrepository.com/artifact/commons-net/commons-net
    implementation group: 'commons-net', name: 'commons-net', version: '20030805.205232'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

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