WIP

I tried to get this working but no cigar, unfortunately I've run out of
time.

src/main/java/hudson/plugins/ec2/ssh/EC2UnixLauncher.java

@@ -37,11 +37,7 @@
 import hudson.slaves.CommandLauncher;
 import hudson.slaves.ComputerLauncher;
 
-import java.io.File;
-import java.io.FileOutputStream;
-import java.io.IOException;
-import java.io.OutputStreamWriter;
-import java.io.PrintStream;
+import java.io.*;
 import java.net.InetSocketAddress;
 import java.net.Proxy;
 import java.nio.charset.StandardCharsets;
@@ -234,11 +230,9 @@ protected void launchScript(EC2Computer computer, TaskListener listener) throws
                 sess.close();
             }
 
-            // TODO: parse the version number. maven-enforcer-plugin might help
             final String javaPath = node.javaPath;
-            executeRemote(computer, conn, javaPath + " -fullversion",
-                    "sudo amazon-linux-extras install java-openjdk11; "
-                    + "sudo yum install -y fontconfig java-11-openjdk", logger, listener);
+            checkJavaInstalled(computer, conn, javaPath, logger, listener);
+            java
             executeRemote(computer, conn, "which scp", "sudo yum install -y openssh-clients", logger, listener);
 
             // Always copy so we get the most recent remoting.jar
@@ -311,6 +305,24 @@ private boolean executeRemote(EC2Computer computer, Connection conn, String chec
         return true;
     }
 
+    private boolean checkJavaInstalled(EC2Computer computer, Connection conn, String javaPath, PrintStream logger, TaskListener listener)
+            throws IOException, InterruptedException {
+        String installCommand = "sudo amazon-linux-extras install java-openjdk11; "
+                + "sudo yum install -y fontconfig java-11-openjdk";
+
+        logInfo(computer, listener,"Verifying: " + javaPath);
+        if (conn.exec(javaPath + "-fullversion", logger) == 0 ) {
+            // If supported java version
+            return true;
+        }
+        logInfo(computer, listener, "Installing: java");
+        if (conn.exec(installCommand, logger) == 0) {
+            return true;
+        }
+        logWarning(computer, listener, "Failed to install: " + installCommand);
+        return false;
+    }
+
     private File createIdentityKeyFile(EC2Computer computer) throws IOException {
         EC2PrivateKey ec2PrivateKey = computer.getCloud().resolvePrivateKey();
         String privateKey = "";