Add GET endpoint for one-shot pv value reads

Author: rerpha

src/main/java/org/phoebus/pvws/EpicsWebSocketServerApplication.java

@@ -18,19 +18,28 @@
 
 package org.phoebus.pvws;
 
+import org.epics.vtype.VType;
 import org.phoebus.pv.PV;
 import org.phoebus.pv.PVPool;
 import org.phoebus.pv.RefCountMap;
+import org.phoebus.pvws.ws.Vtype2Json;
 import org.phoebus.pvws.ws.WebSocket;
+import org.phoebus.pvws.ws.WebSocketPV;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.builder.SpringApplicationBuilder;
 import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
 import org.springframework.context.ApplicationContext;
+import org.springframework.http.MediaType;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
 
 import java.util.List;
 
 @SpringBootApplication
+@RestController
 public class EpicsWebSocketServerApplication extends SpringBootServletInitializer {
 
     public static void main(String[] args) {
@@ -53,4 +62,32 @@ public static void main(String[] args) {
     protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
         return application.sources(EpicsWebSocketServerApplication.class);
     }
+
+    @GetMapping(value= "/pvget", produces = MediaType.APPLICATION_JSON_VALUE)
+    public String pvget(@RequestParam String name) {
+        final WebSocketPV pv = new WebSocketPV(name, null);
+        String ret;
+        try {
+
+            // TODO make these configurable?
+            int maxAttempts = 100;
+            int retryDelay = 50;
+
+            VType lastValue = null;
+
+            for (int i = 0; i< maxAttempts; i++) {
+                Thread.sleep(retryDelay);
+                lastValue = pv.get();
+                if (lastValue != null) break;
+                System.out.println("value is" + lastValue + "attempt no " + i);
+            }
+
+            System.out.println("value is" + lastValue);
+            ret = Vtype2Json.toJson(name, lastValue, null, true, true);
+        } catch (final Exception ex) {
+            ret = String.format("Unable to get PV value for %s - exception %s", name, ex);
+        }
+        pv.dispose();
+        return ret;
+    }
 }

src/main/java/org/phoebus/pvws/ws/WebSocketPV.java

@@ -11,8 +11,6 @@
 import org.epics.vtype.VType;
 import org.phoebus.pv.PV;
 import org.phoebus.pv.PVPool;
-import org.springframework.beans.factory.annotation.Value;
-import org.springframework.stereotype.Component;
 
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
@@ -171,6 +169,17 @@ public void write(Object new_value) throws Exception
             throw new Exception("PV_WRITE_SUPPORT is disabled");
     }
 
+    /**
+     * Get current value by calling read() on the PV
+     * @return the current value
+     * @throws Exception on error
+     */
+    public VType get() throws Exception
+    {
+        pv = PVPool.getPV(name);
+        return pv.read();
+    }
+
     /** Close PV */
     public void dispose()
     {