Java

Secondary Develop Elastel Gateways by Java

Elastel gateways are built on an Open Linux system embedded computer, allowing users to create custom applications using Java. By installing the Java Development Kit (JDK) on the Elastel embedded computer, you can develop and run your own Java applications.

Typical use cases include:

• High-performance data processing and device control
• Serial, network, and protocol communication (e.g., Modbus RTU/TCP, MQTT, TCP/UDP)
• Real-time control and edge logic processing
• Integration with low-level device drivers or GPIO access

1. Supported Models and JDK Installation

Due to different Elastel model using various version of ARM processors, corresponding JDK version software packages need to be downloaded.

Product	ARM Processor	Supported JDK Version
EG500/EG410/ElastBox400/EG324L	ARM64	Latest Version (e.g., JDK24)
EG324	ARM32	Up to JDK11
EC212/EC211	ARM32	Not Supported (due to limited storage)

1.1. JDK Download and Configuration

1. EG500/EG410/ElastBox400/EG324L (ARM64)

   These models support the latest JDK versions, here using JDK24 as an example. Open https://www.oracle.com/java/technologies/downloads to download the ARM64 compressed package. On the Elastel embedded computer, download the file using the curl command and decompress it to the /usr/local/java directory:

   sudo mkdir -p /usr/local/java && curl -SL https://download.oracle.com/java/24/latest/jdk-24_linux-aarch64_bin.tar.gz | sudo tar -xz -C /usr/local/java

   Navigate to the decompressed JDK directory and set the system environment variables (different JDK versions require setting actual paths):

   cd /usr/local/java/jdk-24.0.1
   export JAVA_HOME=$(pwd)
   export PATH=$JAVA_HOME/bin:$PATH

   Verify the installation:

   java -version
   javac -version

   

2. EG324 (ARM32)

   EG324 runs Ubuntu 20.04 OS supporting up to JDK11, which can be installed via apt:

   sudo apt update
   sudo apt install openjdk-11-jdk -y

   Verify the installation:

   java -version
   javac -version

   

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2. Programming Example: LED Control (ledtest)

The following program controls the system LED blinking via /dev/led:

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class ledtest {

	public static void main(String[] args) {

		FileOutputStream led = null;
		
		try {
			led = new FileOutputStream("/dev/led");
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		}
		
		while(true) {
				try {
					led.write('1');	//led on
					Thread.sleep(500);
					led.write('0');	//led off
					Thread.sleep(500);
				} catch (IOException e) {
					e.printStackTrace();
				}
				catch (InterruptedException e) {
					e.printStackTrace();
				}		
		}
		//led.close();
	}
}

2.1. Compiling the Program (On the Elastel Gateway)

1. Create Java Source File Create a ledtest.java file and copy the code above into it, or upload it via SFTP.

2. Compile the Program

   javac ledtest.java

2.2. Running the Program (On the Elastel Gateway)

cd /home/admin
java ledtest

The LED will blink every 0.5 seconds, indicating successful control.

Note

This section only provide example of how to compile and run Java test programs on the Elastel ARM device. For Java program development on a PC, please refer to relevant documentation.

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3. Recommended Practices

• Deploy programs to persistent paths like /home/admin to avoid temporary directories.
• Use built-in interfaces (e.g., serial ports, GPIO, LED) for development.
• Configure /etc/init.d/rcS for startup services or use crontab for scheduled runs.

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4. Appendix Tables

EG324 Peripheral Resource	Device Interface Name
COM1	/dev/ttyAMA0
COM2	/dev/ttyAMA1
COM3	/dev/ttyAMA2
COM4	/dev/ttyAMA3
SYS LED Indicator	/dev/led
SYS2 LED Indicator	/dev/led2
Buzzer	/dev/buzzer
Ethernet Port 1	eth0
Ethernet Port 2	eth1

Note

For other models, please contact Elastel support or refer to models hardware manuals for Peripheral Interface tables.

• Official Website: https://www.elastel.com
• Support Email: support@elastel.com