SAP HANA IoT Part 4: Setting up Java Program to read serial port in Raspberry Pi

[Former Member]

Now we are going to perform:

Step 3 – Using Java in Raspberry Pi in order to read serial data of Arduino

This part is the most challenging part for someone who is new to Raspberry Pi, so we have decided to create the entire setup in the utmost simplistic way in 5 sub-steps:

Step 1: Install java in the Raspberry Pi.

Usually Raspbian comes with Java installed but you can still check it via the following command:

java -version

When you update your Raspbian, it will also update the Java library, if required.

sudo apt-get update

Step 2: The communication is in serial mode, between Arduino and Raspberry Pi, so we need a way to make our Java program to understand it. So Download the below files :

• libjawt.so from here
• librxtxSerial.so from here
• RXTXcomm.jar from here

and go to the download folder of the files and type below commands:

sudo cp libjawt.so /usr/lib/jvm/jdk-8-oracle-arm-vfp-hflt/lib/arm
sudo cp RXTXcomm.jar /usr/lib/jvm/jdk-8-oracle-arm-vfp-hflt/jre/lib
sudo cp librxtxSerial.so /usr/lib/jvm/jdk-8-oracle-arm-vfp-hflt/lib/arm
sudo cp librxtxSerial.so /usr/lib/jni/              

Now, we are assuming here that you have your jdk-8-oracle-arm-vfp-hflt inside your /usr/lib/jvm. If you don’t, then your Java won’t be updated to jdk-8 and you have to update the JDK and JRE .sudo apt-get install oracle-java8-installerStep 3: Now you can copy below Java code.

1. import java.io.BufferedReader;
2. import java.io.InputStreamReader;
3. import java.io.OutputStream;
4. import gnu.io.CommPortIdentifier;
5. import gnu.io.SerialPort;
6. import gnu.io.SerialPortEvent;
7. import gnu.io.SerialPortEventListener;
8. import java.util.Enumeration;
9. import java.net.HttpURLConnection;
10. import java.net.URL;
12. public class SerialTestGET implements SerialPortEventListener {
13. SerialPort serialPort;
14. static int sensorValue = 0;
15. /** The port we're normally going to use. */
16. private static final String PORT_NAMES[] = {
17. "/dev/tty.usbserial-A9007UX1", // Mac OS X
18. "/dev/ttyACM0", // Raspberry Pi
19. "/dev/ttyUSB0", // Linux
20. "COM3", // Windows
21. };
22. /**
23. * A BufferedReader which will be fed by a InputStreamReader
24. * converting the bytes into characters
25. * making the displayed results codepage independent
26. */
27. private BufferedReader input;
28. /** The output stream to the port */
29. private OutputStream output;
30. /** Milliseconds to block while waiting for port open */
31. private static final int TIME_OUT = 2000;
32. /** Default bits per second for COM port. */
33. private static final int DATA_RATE = 9600;
35. public void initialize() {
36. // the next line is for Raspberry Pi and
37. // gets us into the while loop and was suggested here was suggested http://www.raspberrypi.org/phpBB3/viewtopic.php?f=81&t=32186
38. System.setProperty("gnu.io.rxtx.SerialPorts", "/dev/ttyACM0");
40. CommPortIdentifier portId = null;
41. Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();
43. //First, Find an instance of serial port as set in PORT_NAMES.
44. while (portEnum.hasMoreElements()) {
45. CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
46. for (String portName : PORT_NAMES) {
47. if (currPortId.getName().equals(portName)) {
48. portId = currPortId;
49. break;
50. }
51. }
52. }
53. if (portId == null) {
54. System.out.println("Could not find COM port.");
55. return;
56. }
58. try {
59. // open serial port, and use class name for the appName.
60. serialPort = (SerialPort) portId.open(this.getClass().getName(),
61. TIME_OUT);
63. // set port parameters
64. serialPort.setSerialPortParams(DATA_RATE,
65. SerialPort.DATABITS_8,
66. SerialPort.STOPBITS_1,
67. SerialPort.PARITY_NONE);
69. // open the streams
70. input = new BufferedReader(new InputStreamReader(serialPort.getInputStream()));
71. output = serialPort.getOutputStream();
73. // add event listeners
74. serialPort.addEventListener(this);
75. serialPort.notifyOnDataAvailable(true);
76. } catch (Exception e) {
77. System.err.println(e.toString());
78. }
79. }
81. /**
82. * This should be called when you stop using the port.
83. * This will prevent port locking on platforms like Linux.
84. */
85. public synchronized void close() {
86. if (serialPort != null) {
87. serialPort.removeEventListener();
88. serialPort.close();
89. }
90. }
92. /**
93. * Handle an event on the serial port. Read the data and print it.
94. */
95. public synchronized void serialEvent(SerialPortEvent oEvent) {
96. if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
97. try {
98. String inputLine=input.readLine();
99. //System.out.println(inputLine);
100. sendGet(inputLine);
101. } catch (Exception e) {
102. System.err.println(e.toString());
103. serialPort.removeEventListener();
104. serialPort.close();
105. }
106. }
107. // Ignore all the other eventTypes, but you should consider the other ones.
108. }
110. // HTTP GET request
111. public void sendGet(String inputLine) throws Exception {
113. try{
114. //if difference is more than 3 then send data to SAP HANA
115. if(inputLine != null && inputLine .length() > 0 && Math.abs(sensorValue - Integer.parseInt(inputLine)) > 3 ){
117. sensorValue = Integer.parseInt(inputLine);
118. //Considering that A001 sensor is connection with this raspberry pie for now
119. //we can even pass this with command line but for simplicityhardcoding it
120. //Replace with your HANA server URL and port number
121. String url = "http:///demoApp/demo01/app01/services/putSensorReading.xsjs?id=A001&value=";
122. url = url + inputLine;
124. URL obj = new URL(url);
125. HttpURLConnection con = (HttpURLConnection) obj.openConnection();
127. // optional default is GET
128. con.setRequestMethod("GET");
130. //add request header
131. //con.setRequestProperty("User-Agent", USER_AGENT);
133. int responseCode = con.getResponseCode();
134. if(responseCode == 200){
135. System.out.println("OK value:"+inputLine);
136. }else{
137. System.out.println("Error: Response code "+responseCode);
138. }
140. }
141. System.out.println("OK value: Less than 3");
142. }catch (Exception e) {
143. System.err.println(e.toString());
144. serialPort.removeEventListener();
145. serialPort.close();
146. }
148. }
150. public static void main(String[] args) throws Exception {
151. SerialTestGET main = new SerialTestGET();
152. main.initialize();
154. Thread t=new Thread() {
155. public void run() {
156. //the following line will keep this app alive for 1000 seconds,
157. //waiting for events to occur and responding to them (printing incoming messages to console).
158. try {Thread.sleep(1000000);} catch (InterruptedException ie) {}
159. }
160. };
161. t.start();
162. System.out.println("Started");
163. }
164. }

Step 4: Compile it using below command:

javac -source 1.6 -target 1.6 -cp /usr/lib/jvm/jdk-8-oracle-arm-vfp-hflt/jre/lib/RXTXcomm.jar SerialTestGET.java

Step 5: If there is no error (warnings may come), then your setup is right and you can now read the Arduino data in your serial port of Raspberry Pi, with the step 4 Java compiled code.

You can change the Java code of Step 3 and recompile it, in order to fit your requirements as well.

In the part 5, we will see how to configure the SAP HANA system and SAPUI5 application.