Java Servlets and Raspberry Pi IO
Question
I'm trying to learn how to write simple servlets to use with a Raspberry Pi. I want to control the board I/O via web.I'm using the Pi4J library which is a wrapper for the WiringPi C library.It works when I use it to blink a led locally so I assume that I'm doing something wrong coding my servlet.
This is the code I wrote:
package com.luca.servlet;
import com.pi4j.io.gpio.GpioController;
import com.pi4j.io.gpio.GpioFactory;
import com.pi4j.io.gpio.GpioPinDigitalOutput;
import com.pi4j.io.gpio.RaspiPin;
import com.pi4j.io.gpio.PinState;
public class MyServlet extends javax.servlet.http.HttpServlet {
private GpioController gpio=GpioFactory.getInstance();
private GpioPinDigitalOutput redLed=gpio.provisionDigitalOutputPin(RaspiPin.GPIO_23,PinState.LOW);
private GpioPinDigitalOutput greenLed=gpio.provisionDigitalOutputPin(RaspiPin.GPIO_22,PinState.LOW);
private GpioPinDigitalOutput blueLed=gpio.provisionDigitalOutputPin(RaspiPin.GPIO_21,PinState.LOW);
private GpioPinDigitalOutput[] pins=new GpioPinDigitalOutput[]{redLed,greenLed,blueLed};
@Override
public void doGet(javax.servlet.http.HttpServletRequest request,javax.servlet.http.HttpServletResponse response) throws java.io.IOException {
java.io.PrintWriter print=response.getWriter();
print.write("<body>"+
"<p> Choose a color! </p>"+
"<form action=\"first\" method=\"POST\">"+
"<input type=\"submit\" name=\"button\" value=\"red\"/>"+
"</form>"+
"<form action=\"first\" method=\"POST\">"+
"<input type=\"submit\" name=\"button\" value=\"green\"/>"+
"</form>"+
"<form action=\"first\" method=\"POST\">"+
"<input type=\"submit\" name=\"button\" value=\"blue\"/>"+
"</form>"+
"</body>");
}
public void doPost(javax.servlet.http.HttpServletRequest request,javax.servlet.http.HttpServletResponse response) throws java.io.IOException {
java.io.PrintWriter pw=response.getWriter();
String act=request.getParameter("button");
switch(act) {
case "red":
togglePin();
redLed.high();
pw.write("<p>the led is red!</p>");
break;
case "green":
togglePin();
greenLed.high();
pw.write("<p>the led is green</p>");
break;
case "blue":
togglePin();
blueLed.high();
pw.write("<p>the led is blue!</p>");
break;
}
}
private void togglePin() {
for (GpioPinDigitalOutput pin : pins)
if (pin.isHigh()) pin.toggle();
}
it compiles fine and I manually deploy it inside tomcat,with the deployment descriptor and all. But when I connect it says to me that the resource is unavailable. If I remove the GPIO related code it works fine.
Can someone please help me out? Google searching doesn't seem to help
2 answers
solution1
0 2015-12-08 15:28:05
You need to set an Url Pattern in order to access to your servlet methods like POST and GET .
For example use:
@WebServlet("/raspberryServelt")
public class MyServlet extends javax.servlet.http.HttpServlet {
...
And then access to the servlet methods doing a POST or GET request...
For example doing a get to:
localhost:8080/yourWebAppName/raspberryServelt
Will work...
solution2
0 2017-04-01 21:10:48
您必须将pi4j库放在项目WEB-INF / lib中
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