Category Archives: RDS

How to access an AWS RDS using JDBC in your Android app – Part II

In my last post, I described a quick way to set up an Amazon MySQL RDS (Relational Database Service).

In this post, I’m going to build an Android app which uses JDBC to search that database, and list results.

Caveat: As I mentioned in my previous post, this is a “quick and dirty” way of doing things, and it’s not recommended to do things exactly this way. However, this method is fine when you’re building a proof of concept or a demo and you need to get things done quickly. It took me an afternoon to throw together a working demo using this method!

To get started on your app, fire up Android Studio and create a “New Project” with an “Empty Activity”. Accept all the defaults, but make sure your app is for Java (unless you want to work with Kotlin).

We just want to add a few simple items for the user interface: a text input for searching on a term, a button to submit the search term, and a scrollview that can be used to display results. Let’s do that now.

When I created my empty activity, a new layout file was added called activity_main.xml. I opened that up in the design view, and added the widgets that I wanted. Eventually, I finished the layout by customizing it in the text view. Here’s the final layout:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <EditText
        android:id="@+id/editText"
        android:layout_width="357dp"
        android:layout_height="48dp"
        android:ems="10"
        android:hint="Enter Search term and hit button for results"
        android:inputType="text"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:layout_marginRight="8dp"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginLeft="8dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintHorizontal_bias="0.513"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"/>
    <Button
        android:id="@+id/btnSearch"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Search"
        android:layout_marginRight="8dp"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginLeft="8dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintTop_toBottomOf="@+id/editText"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginTop="8dp"/>

    <ScrollView
        android:id="@+id/scrollview"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_margin="8dp"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnSearch">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <TextView
                android:id="@+id/tvResults"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:text=""></TextView>
        </LinearLayout>
    </ScrollView>

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:text="Type in text, click a button to search"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

It looks like a lot, but it isn’t. Android layout files are quite verbose! One comment: notice that the ScrollView has a layout height of 0dp. It took me a few minutes of searching to figure out that this was necessary. Prior to doing that, the ScrollView results overlapped the search button and instructional text.

Notice that I’ve set Android @+ids for the parts that I need to access programmatically. I need to be able to click the search Button (@+id/btnSearch), get text from the input EditText (@+id/editText), and display text in the ScrollView‘s TextView (@+id/tvResults).

Next, I opened the MainActivity class, and added the methods needed to click the button, get results, and display them – like this:

package com.fullstackoasis.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.text.Editable;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements AsyncResponse {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button b = (Button)this.findViewById(R.id.btnSearch);
        b.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                searchByName();
            }
        });
    }

    protected void searchByName() {
        EditText et = (EditText)findViewById(R.id.editText);
        Editable editable = et.getText();
        String s = editable.toString();
        Log.d("MainActivity", "searchByName " + s);
        if (s.length() > 2) {
            MySQLAsyncTask mySQLAsyncTask = new MySQLAsyncTask();
            mySQLAsyncTask.setDelegate(this);
            mySQLAsyncTask.execute(s);
        } else {
            displayResults("Please type in at least 3 letters, for example 'Italian'");
        }
    }

    public void processFinish(String result) {
        if (result.length() > 502) {
            Log.d("MainActivity:", "processFinish " + result.substring(0, 500));
        } else {
            Log.d("MainActivity:", "processFinish " + result);
        }
        displayResults(result);
    }

    private void displayResults(String res) {
        TextView tvResults = (TextView)findViewById(R.id.tvResults);
        tvResults.setText(res);
    }
}

Now I only needed one more crucial bit, the Java class which contacts the Amazon RDS. I added a new Java class by clicking the menu item File > New > Java Class, and chose the name MySQLAsyncTask. I had it extend AsyncTask. The source for that class is shown next. If you copy this code for your own working demo, you will have to edit the url string to use your own RDS endpoint. Also, notice the big warnings about checking in files into source control if they contain hard-coded strings that would make your credentials publicly available! I’m not going to go into how to handle that here, but just don’t do it.

package com.fullstackoasis.myapplication;

import android.os.AsyncTask;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.PreparedStatement;

final class MySQLAsyncTask extends AsyncTask<String, Void, String> {
    private static final String url = "jdbc:mysql://healthdata-1.c84gpzpanfrn.us-east-1.rds.amazonaws.com:3306/food_inspections";
    private static final String user = "MY_WONDERFUL_USER_NAME"; // WARNING! DO NOT CHECK IN YOUR CREDENTIALS INTO PUBLIC SOURCE CONTROL
    private static final String pass = "MY_WONDERFUL_PASSWORD"; // WARNING! DO NOT CHECK IN YOUR CREDENTIALS INTO PUBLIC SOURCE CONTROL
    private static String res;
    private AsyncResponse delegate = null;

    void setDelegate(AsyncResponse d) {
        delegate = d;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }
    @Override
    protected String doInBackground(String... params) {
        try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            Connection con = DriverManager.getConnection(url, user, pass);
            System.out.println("Database Connection success "  + params);

            String result = "Database Connection Successful\n";
            // Let's search by dba_name and / or aka name.
            // Limit results by to top 10 results, and let user scroll

            PreparedStatement ps = con.prepareStatement("SELECT * FROM health_reports" +
                    " WHERE " +
                    "dba_name LIKE ? OR aka_name LIKE ? LIMIT 10");
            String searchPartial = params[0] + "%"; // LIKE 'Blah%'
            ps.setString(1, searchPartial);
            ps.setString(2, searchPartial);

            ResultSet rs = ps.executeQuery();
            ResultSetMetaData rsmd = rs.getMetaData();

            String sep = " | ";

            while (rs.next()) {
                result += rs.getInt(1) + sep + // id
                        rs.getInt(2) + sep + // inspection_id
                        rs.getString(3) + sep + // dba_name
                        rs.getString(4) + sep + // aka_name
                        rs.getInt(5) + sep + // license_num
                        rs.getString(6) + sep + // facility_type
                        rs.getString(7) + sep + // risk
                        rs.getString(8) + sep + // address
                        rs.getString(9) + sep + // city
                        rs.getString(10) + sep + // state
                        rs.getString(11) + sep; // zip
                try {
                    result += rs.getString(12).toString() + sep; // inspection_date
                } catch (Exception e) {
                    // e.printStackTrace();
                }
                result += rs.getString(13) + sep + // inspection_type
                        rs.getString(14) + sep + // results
                        rs.getString(15) + sep + // violations
                        rs.getString(16) + sep // location
                        ;
                result += System.lineSeparator();
                result += "------------";
                result += System.lineSeparator();
            }
            res = result;
            if (res.length() > 502) {
                Log.d("Task:", "Database Result success " + result.substring(0, 500));
            } else {
                Log.d("Task:", "Database Result success " + result);
            }
        } catch (Exception e) {
            e.printStackTrace();
            res = e.toString();
        }
        return res;
    }
    @Override
    protected void onPostExecute(String result) {
        Log.d("Task:", "onPostExecute");
        this.res = result;
        delegate.processFinish(result);
    }
}

This class uses the MySQL JDBC driver. You have to add the MySQL database connector as a module to your project. The instructions to do that are in StackOverflow – click that link and follow the instructions, which were pretty easy, at least with Android Studio 3.5.

For test purposes, I ran this demo in the Android Emulator. I typed in ‘Italian’ for the search term, and got back a bunch of results. It took a short while, because I never added any indexes to my database table, but that’s something to fine-tune later.

As a finishing touch, I built the Android APK, and loaded it onto my phone. Here’s a screenshot of the result:

Now, as mentioned earlier, you shouldn’t use a direct connection to the database in production code. A hacker might crack open your app, find the user name and password to your database, and do bad things! Ideally, you’ll want to connect to your database using some middleware which fields requests to the database, and makes sure that things like access permissions are enforced. That’s why this little Android app is just for demonstration purposes. The good part is that it can be built quickly, so you don’t have to waste time building middleware until you’re 100% sure you’re going to need it in a publicly available app!

Got comments? Send me an email at fullstackdev@fullstackoasis.com. Interested in more posts like this? Hit the subscribe button above. I write a new post about once a week.

How to access an AWS RDS using JDBC in your Android app – Part I

You’ve got a huge spreadsheet that has a lot of data in it, and you’ve built an Android app which works like a search engine on the data. Nice! But there’s a problem: when you build your app with all of that data in it, the APK is huge! You want to reduce the size of the app. And you also want to offload the search functionality onto a relational database, which is probably going to provide a more efficient search. How do you start?

This blog post explores one way to do it. It’s “quick and dirty”, and it’s not recommended to do things exactly this way. I’ll talk about why in Part II. But this method will give you a start.

Here’s a quick sketch of the idea: You put your data in the cloud using the Amazon Relational Database Service (RDS). Then you add JDBC calls to your app to access the cloud. It’s pretty quick. Here are the steps, using a simple example that I tried for myself.

Technical Details: My development environment runs Ubuntu 16.04, and I have a MySQL client and the MySQL database already installed on my local machine. I use Android Studio 3.5 IDE for building Android apps. Also, I have an Amazon AWS account set up already. You can follow this tutorial if you don’t have any of that, but then specific steps will differ for you.

Get Your Data Source Ready

For my data source, I downloaded some food inspection data from healthdata.gov in a csv (“comma-separated values”) format. I opened the csv file in a spreadsheet, selected some of the columns that I wanted, and exported them to another file, also in csv format. You can use the csv file that I generated by starting with this small, truncated version of the data. Later, you can use or create your own, very large data source for experiments.

Create an Amazon RDS MySQL Database

Visit the Amazon MySQL RDS page and click “Get Started”. If you don’t have an AWS account, you will need to sign up for one, first. Check out the pricing, if you are worried. There’s a free tier, great!

If you’re already signed in, another way to get started is to visit the AWS Management Console, search for “RDS”, and click the result for “Managed Relational Database Service”.

At this point, you’ll see a “Create Database” button. Choose “MySQL”, and click the “free tier”. Type in healthdata-1 for the name. Choose a username when requested. I’m using fullstackdev. Pick a secure password. The other parts of the form are straightforward. You can think about using IAM based authentication later. For this proof-of-concept piece of work, let’s keep it simple, and use password based authentication. For the rest, accept all defaults.

At this point, a page opens which says the database is being created.

AWS RDS creating database

Click the “modify” button. You’ll see that you can modify various things about the database later, if you want. Just be aware of this. For right now, you’ll need to “modify” the RDS so that it can be accessed from external sources – so choose “Public accessibility” and set it to Yes, and make sure to click the “Continue” button at the bottom of the page to save your changes. You need to do this so that you can create a database, load data into it, and access it via JDBC.

Now we’ve got an RDS in the cloud, and it’s accessible from our home environment. Next, we need to create a database.

Create Your Database and Manage Access

If you click the DB identifier in your RDS console, you will see an area called “Connectivity & security”. That area tells you what your endpoint is, and what your port is. The port defaults to 3306. Your endpoint will be something like healthdata-1.c84gpzpanfrn.us-east-1.rds.amazonaws.com. This is a URL you can use to access the database from another machine.

In the ‘Security’ pane, at the right, you will see your VPC (Virtual Private Cloud) security groups with a link to the default. Click that. It will take you to your Security Groups area. The default VPC security group should be preselected. Look at the bottom panel, where you should see the “Description”, “Inbound”, “Outbound”, and “Tags” tabs. Click “Inbound” and hit the “Edit” button. Click the “Add Rule” button, select MySQL/Aurora, make sure that the protocol is set to TCP/IP and the port to 3306, thne choose “MyIP” as the source. Your IP address will be set when doing this. Then hit the “Save” button.

Remember that you’ve added this rule just for your own IP address! You’re doing this for test purposes. Later, if you want, you can make different inbound rules, but this setup is good for a proof-of-concept.

Now the RDS is accessible. I am comfortable using the command line for MySQL client, so I used this to step into the cloud, and create my database. You can use whatever tool you want to do this.

First, I connected via this command:

mysql -u fullstackdev -P 3306 -p -h healthdata-1.c84gpzpanfrn.us-east-1.rds.amazonaws.com healthdata-1

The -p option tells the client to ask for a password interactively. I gave the password that I had set up earlier, and immediately, I was connected. This is what I saw:

Type: MySQL/Aurora,
Protocol: TCP
Port Range: 3306
Source: MyIP
Description: MySQL client

show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| innodb             |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.03 sec)

It’s the usual default MySQL database setup.

I had already designed a database around the food inspection data that I had decided to import. I created my own database like this:

CREATE DATABASE food_inspections;
USE food_inspections;
DROP TABLE health_reports;
CREATE TABLE health_reports (
    id INT AUTO_INCREMENT PRIMARY KEY,
	inspection_id INT,
	dba_name TEXT,
	aka_name TEXT,
	license_num INT,
	facility_type TEXT,
	risk TEXT, address TEXT,
	city TEXT, state TEXT,
	zip TEXT, inspection_date DATE,
	inspection_type TEXT, results TEXT,
	violations TEXT, location TEXT
);

I didn’t add any indexes for the columns other than the primary key. That can all be added later, when performance tuning.

Push Your Data to Amazon RDS MySQL Database

AWS provides instructions for pushing data to a MySQL RDS in the cloud. Since we have a new RDS which is already set up, we can skip straight to step 5, “Load the Data”.

They tell you to use the mysqlimport command, and you can do that if you want. There are other tools that can be used to import data, too. However, since I was already in the MySQL client, I used the LOAD DATA command, like so:

LOAD DATA LOCAL INFILE 'Food_Inspections_small.csv' INTO TABLE health_reports
	FIELDS TERMINATED BY ',' ENCLOSED BY '"'
    LINES TERMINATED BY '\n' (@inspection_id, @dba_name, @aka_name,
		@license_num, @facility_type, @risk, @address, @city, @state, @zip,
		@inspection_date, @inspection_type, @results, @violations, @location)
	SET inspection_id = @inspection_id, dba_name = @dba_name, aka_name = @aka_name,
		license_num = @license_num, facility_type = @facility_type, risk = @risk,
		address = @address, city = @city, state = @state, zip = @zip,
		inspection_date = @inspection_date, inspection_type = @inspection_type,
		results = @results, violations = @violations, location = @location;

Keep in mind that you may need to modify this command for your own purposes. I had launched the MySQL client from within the same directory where my Food_Inspections_small.csv was located, , so this command worked for me straightaway.

Now, my RDS is all set up, complete with data! That is half the battle. In my next blog post, I’ll cover how to access the RDS using an Android app.

Got comments? Send me an email at fullstackdev@fullstackoasis.com. Interested in more posts like this? Hit the subscribe button above. I write a new post about once a week.