From cae208a8f2509c7f701e1159893ac3e9b2644643 Mon Sep 17 00:00:00 2001
From: Mark Waite <mark.earl.waite@gmail.com>
Date: Fri, 16 Nov 2018 14:48:04 -0700
Subject: [PATCH 1/2] [JENKINS-52282] Add isJavaWebStartSupported to
 JNLPLauncher

Seems cleaner to use JNLPLauncher than to use Functions.  Narrows the
scope of the method so that callers know it is specific to
JNLPLauncher.
---
 .../main/java/hudson/slaves/JNLPLauncher.java  | 15 +++++++++++++++
 .../hudson/slaves/JNLPLauncher/main.jelly      | 18 ++++++++++--------
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/core/src/main/java/hudson/slaves/JNLPLauncher.java b/core/src/main/java/hudson/slaves/JNLPLauncher.java
index bed08613d814..808fdef1311c 100644
--- a/core/src/main/java/hudson/slaves/JNLPLauncher.java
+++ b/core/src/main/java/hudson/slaves/JNLPLauncher.java
@@ -221,4 +221,19 @@ public boolean filterType(@Nonnull Class<?> contextClass, @Nonnull Descriptor de
         }
     }
 
+    /**
+     * Returns true if Java Web Start button should be displayed.
+     * Java Web Start is only supported when the Jenkins server is
+     * running with Java 8.  Earlier Java versions are not supported by Jenkins.
+     * Later Java versions do not support Java Web Start.
+     *
+     * This flag is checked in {@code config.jelly} before displaying the
+     * Java Web Start button.
+     * @return {@code true} if Java Web Start button should be displayed.
+     * @since FIXME
+     */
+    @Restricted(NoExternalUse.class) // Jelly use
+    public boolean isJavaWebStartSupported() {
+        return System.getProperty("java.version", "1.8").startsWith("1.8");
+    }
 }
diff --git a/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly b/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly
index 606a52e932fe..8409784e851c 100644
--- a/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly
+++ b/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly
@@ -37,14 +37,16 @@ THE SOFTWARE.
           ${%Connect agent to Jenkins one of these ways:}
         </p>
         <ul>
-          <li>
-            <p>
-              <a href="slave-agent.jnlp" id="jnlp-link">
-                <img src="${imagesURL}/webstart.gif" alt="${%launch agent}" />
-              </a>
-              ${%Launch agent from browser}
-            </p>
-          </li>
+          <j:if test="${it.launcher.javaWebStartSupported}">
+            <li>
+              <p>
+                <a href="slave-agent.jnlp" id="jnlp-link">
+                  <img src="${imagesURL}/webstart.gif" alt="${%launch agent}" />
+                </a>
+                ${%Launch agent from browser}
+              </p>
+            </li>
+          </j:if>
           <j:choose>
             <j:when test="${it.ACL.hasPermission(app.ANONYMOUS, it.CONNECT)}">
               <li>

From f33e5f874c2e8c7791378822433a99b9d83792ac Mon Sep 17 00:00:00 2001
From: Mark Waite <mark.earl.waite@gmail.com>
Date: Fri, 23 Nov 2018 13:13:07 -0700
Subject: [PATCH 2/2] Include hyperlink to jenkins.io Java Web Start redirect
 page

---
 .../hudson/slaves/JNLPLauncher/main.jelly     | 31 +++++++++++++------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly b/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly
index 8409784e851c..29507de2f6da 100644
--- a/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly
+++ b/core/src/main/resources/hudson/slaves/JNLPLauncher/main.jelly
@@ -37,16 +37,27 @@ THE SOFTWARE.
           ${%Connect agent to Jenkins one of these ways:}
         </p>
         <ul>
-          <j:if test="${it.launcher.javaWebStartSupported}">
-            <li>
-              <p>
-                <a href="slave-agent.jnlp" id="jnlp-link">
-                  <img src="${imagesURL}/webstart.gif" alt="${%launch agent}" />
-                </a>
-                ${%Launch agent from browser}
-              </p>
-            </li>
-          </j:if>
+          <j:choose>
+            <j:when test="${it.launcher.javaWebStartSupported}">
+              <li>
+                <p>
+                  <a href="slave-agent.jnlp" id="jnlp-link">
+                    <img src="${imagesURL}/webstart.gif" alt="${%launch agent}" />
+                  </a>
+                  ${%Launch agent from browser}
+                </p>
+              </li>
+            </j:when>
+            <j:otherwise>
+              <li>
+                <p>
+                  <a href="https://jenkins.io/redirect/java11-java-web-start">
+                    ${%Java Web Start is not available for the JVM version running Jenkins}
+                  </a>
+                </p>
+              </li>
+            </j:otherwise>
+          </j:choose>
           <j:choose>
             <j:when test="${it.ACL.hasPermission(app.ANONYMOUS, it.CONNECT)}">
               <li>