improved error diagnosis.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@3982 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/maven/MavenBuild.java

@@ -292,8 +292,18 @@ public class MavenBuild extends AbstractBuild<MavenModule,MavenBuild> {
             Map<String, String> vars = getEnvVars();
             if(debug)
                 listener.getLogger().println("Using env variables: "+vars);
-            return launcher.launchChannel(buildMavenCmdLine(listener).toCommandArray(),
-                out, null, vars);
+            try {
+                return launcher.launchChannel(buildMavenCmdLine(listener).toCommandArray(),
+                    out, null, vars);
+            } catch (IOException e) {
+                if(e.getMessage().contains("java: not found")) {
+                    // diagnose issue #659
+                    JDK jdk = getParent().getParent().getJDK();
+                    if(jdk==null)
+                        throw new IOException2(getParent().getParent().getDisplayName()+" is not configured with a JDK, but your PATH doesn't include Java",e);
+                }
+                throw e;
+            }
         }
 
         /**

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

@@ -1625,6 +1625,30 @@ public final class Hudson extends View implements ItemGroup<TopLevelItem>, Node
         }.process();
     }
 
+    /**
+     * If the user chose the default JDK, make sure we got 'java' in PATH.
+     */
+    public void doDefaultJDKCheck( StaplerRequest req, StaplerResponse rsp ) throws IOException, ServletException {
+        new FormFieldValidator(req,rsp,true) {
+            public void check() throws IOException, ServletException {
+                String v = request.getParameter("value");
+                if(!v.equals("(Default)"))
+                    // assume the user configured named ones properly in system config ---
+                    // or else system config should have reported form field validation errors.
+                    ok();
+                else {
+                    // default JDK selected. Does such java really exist?
+                    if(JDK.isDefaultJDKValid(Hudson.this))
+                        ok();
+                    else
+                        errorWithMarkup(
+                            "java is not in your PATH. Maybe you need to" +
+                            "<a href='"+request.getContextPath()+"/configure'>configure JDKs</a>?");
+                }
+            }
+        }.process();
+    }
+
     /**
      * Checks if the top-level item with the given name exists.
      */

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

 package hudson.model;
 
+import hudson.util.StreamTaskListener;
+import hudson.util.NullStream;
+import hudson.Launcher;
+
 import java.io.File;
+import java.io.IOException;
 import java.util.Map;
 
 /**
@@ -68,4 +73,23 @@ public final class JDK {
         if(!env.containsKey("HUDSON_HOME"))
             env.put("HUDSON_HOME", Hudson.getInstance().getRootDir().getPath() );
     }
+
+    /**
+     * Checks if "java" is in PATH on the given node.
+     *
+     * <p>
+     * If it's not, then the user must specify a configured JDK,
+     * so this is often useful for form field validation.
+     */
+    public static boolean isDefaultJDKValid(Node n) {
+        try {
+            TaskListener listener = new StreamTaskListener(new NullStream());
+            Launcher launcher = n.createLauncher(listener);
+            return launcher.launch("java -fullversion",new String[0],listener.getLogger(),null).join()==0;
+        } catch (IOException e) {
+            return false;
+        } catch (InterruptedException e) {
+            return false;
+        }
+    }
 }

core/src/main/resources/hudson/model/AbstractItem/configure-common.jelly

@@ -5,17 +5,24 @@
   <p:config-disableBuild/>
 
   <j:set var="jdks" value="${app.JDKs}" />
-  <j:if test="${!empty(jdks)}">
-    <f:entry title="JDK"
-             description="JDK to be used for this project">
-      <select class="setting-input" name="jdk">
-        <option>(Default)</option>
-        <j:forEach var="inst" items="${jdks}">
-        	<f:option selected="${inst.name==it.JDK.name}">${inst.name}</f:option>
-        </j:forEach>
-      </select>
-    </f:entry>
-  </j:if>
+  <j:choose>
+    <j:when test="${!empty(jdks)}">
+      <f:entry title="JDK"
+               description="JDK to be used for this project">
+        <select class="setting-input validated" name="jdk" checkUrl="'${rootURL}/defaultJDKCheck?value='+this.value">
+          <option>(Default)</option>
+          <j:forEach var="inst" items="${jdks}">
+            <f:option selected="${inst.name==it.JDK.name}">${inst.name}</f:option>
+          </j:forEach>
+        </select>
+      </f:entry>
+    </j:when>
+    <j:otherwise>
+      <f:entry>
+        <input type="hidden" value="(Default)" class="validated" checkUrl="'${rootURL}/defaultJDKCheck?value='+this.value" />
+      </f:entry>
+    </j:otherwise>
+  </j:choose>
 
   <!-- master/slave -->
   <j:if test="${!empty(app.slaves)}">