added a convenience method.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@20756 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/Node.java

@@ -29,6 +29,7 @@ import hudson.FileSystemProvisioner;
 import hudson.Launcher;
 import hudson.node_monitors.NodeMonitor;
 import hudson.remoting.VirtualChannel;
+import hudson.remoting.Channel;
 import hudson.security.ACL;
 import hudson.security.AccessControlled;
 import hudson.security.Permission;
@@ -140,6 +141,16 @@ public abstract class Node extends AbstractModelObject implements Describable<No
         return Hudson.getInstance().getComputer(this);
     }
 
+    /**
+     * Gets the current channel, if the node is connected and online, or null.
+     *
+     * This is just a convenience method for {@link Computer#getChannel()} with null check. 
+     */
+    public final VirtualChannel getChannel() {
+        Computer c = toComputer();
+        return c==null ? null : c.getChannel();
+    }
+
     /**
      * Creates a new {@link Computer} object that acts as the UI peer of this {@link Node}.
      * Nobody but {@link Hudson#updateComputerList()} should call this method.
@@ -202,9 +213,7 @@ public abstract class Node extends AbstractModelObject implements Describable<No
      * Gets the {@link FilePath} on this node.
      */
     public FilePath createPath(String absolutePath) {
-        Computer computer = toComputer();
-        if (computer==null) return null; // offline
-        VirtualChannel ch = computer.getChannel();
+        VirtualChannel ch = getChannel();
         if(ch==null)    return null;    // offline
         return new FilePath(ch,absolutePath);
     }

core/src/main/java/hudson/model/Slave.java

@@ -291,7 +291,7 @@ public abstract class Slave extends Node implements Serializable {
     }
 
     public ClockDifference getClockDifference() throws IOException, InterruptedException {
-        VirtualChannel channel = getComputer().getChannel();
+        VirtualChannel channel = getChannel();
         if(channel==null)
             throw new IOException(getNodeName()+" is offline");
 

core/src/main/java/hudson/tools/JDKInstaller.java

@@ -344,7 +344,7 @@ public class JDKInstaller extends ToolInstaller {
          * Determines the platform of the given node.
          */
         public static Platform of(Node n) throws IOException,InterruptedException,DetectionFailedException {
-            return n.toComputer().getChannel().call(new Callable<Platform,DetectionFailedException>() {
+            return n.getChannel().call(new Callable<Platform,DetectionFailedException>() {
                 public Platform call() throws DetectionFailedException {
                     return current();
                 }
@@ -396,7 +396,7 @@ public class JDKInstaller extends ToolInstaller {
          * Determines the CPU of the given node.
          */
         public static CPU of(Node n) throws IOException,InterruptedException, DetectionFailedException {
-            return n.toComputer().getChannel().call(new Callable<CPU,DetectionFailedException>() {
+            return n.getChannel().call(new Callable<CPU,DetectionFailedException>() {
                 public CPU call() throws DetectionFailedException {
                     return current();
                 }