Use applicationName as the first fallback for both imageName and installerName.

applicationName is intended to be the display name of the application, so it makes sense for this to be used by default.

Intended to fix beryx#127 but needs testing on macOS to be absolutely certain.

Author: hakanai

doc/user_guide.adoc

@@ -316,7 +316,7 @@ imageOutputDir:: the directory passed as argument to the `--output` option when
     _usage example_: `imageOutputDir = file("$buildDir/my-packaging-image")`
 
 imageName:: the argument passed to the `--name` option when running `jpackage` to create an application image. +
-    _defaultValue_: `_project.name_` +
+    _defaultValue_: the `applicationName` configured for the `application` plugin, then `_project.name_` +
     _usage example_: `imageName = "MyApp"`
 
 imageOptions:: list of additional options to be passed to the `jpackage` executable when creating the appliction image. +
@@ -340,7 +340,7 @@ installerOutputDir:: the directory passed as argument to the `--output` option w
     _usage example_: `installerOutputDir = file("$buildDir/my-packaging-installer")`
 
 installerName:: the argument passed to the `--name` option when running `jpackage` to create an application installer. +
-    _defaultValue_: `_project.name_` +
+    _defaultValue_: the `applicationName` configured for the `application` plugin, then `_project.name_` +
     _usage example_: `installerName = "MyApp"`
 
 jvmArgs:: list of JVM arguments to be passed to the virtual machine. +

src/main/groovy/org/beryx/runtime/data/JPackageData.groovy

@@ -16,6 +16,7 @@
 package org.beryx.runtime.data
 
 import org.beryx.runtime.util.Util
+import org.gradle.api.plugins.JavaApplication
 import org.gradle.api.tasks.Internal
 
 import static org.beryx.runtime.util.Util.EXEC_EXTENSION
@@ -106,14 +107,19 @@ class JPackageData {
     String getMainClassOrDefault() {
         this.@mainClass ?: Util.getMainClass(project)
     }
+
     @Input
     String getImageNameOrDefault() {
-        this.@imageName ?: project.name
+        this.@imageName
+                ?: project.extensions.getByType(JavaApplication).applicationName
+                ?: project.name
     }
 
     @Input
     String getInstallerNameOrDefault() {
-        this.@installerName ?: project.name
+        this.@installerName
+                ?: project.extensions.getByType(JavaApplication).applicationName
+                ?: project.name
     }
 
     @OutputDirectory