Gradle项目中ObservableValue.subscribe()调用示例及问题解决

问题背景 #

尝试在Gradle项目中调用JavaFX 21新增的ObservableValue.subscribe()方法时，编译报error: cannot find symbol错误，即使在build.gradle.kts中指定了JavaFX 24版本，仍怀疑Gradle加载了不包含该方法的旧版本。

原代码与配置 #

build.gradle.kts

repositories {
  mavenCentral()
}

plugins {
  java
  application
  id("org.openjfx.javafxplugin") version "0.1.0"
}

javafx {
  version = "24"
  modules("javafx.base")
}

application {
  mainClass = "Main"
}

src/main/java/Main.java

import java.util.function.Consumer;
import javafx.application.Application;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.value.ObservableValue;
import javafx.stage.Stage;

public class Main extends Application {
  public static void main(String[] args) { launch(args); }
  @Override public void start(Stage stage) {
    ObservableValue<Object> prop = new SimpleObjectProperty<Object>(null);
    prop.subscribe(new Consumer<Object>() { public void accept(Object t) {} });
  }
}

编译错误 #

执行./gradlew build后报错：

> Task :compileJava FAILED
/home/user/question/src/main/java/Main.java:11: error: cannot find symbol
    prop.subscribe(new Consumer<Object>() { public void accept(Object t) {} });
        ^
  symbol:   method subscribe(<anonymous Consumer<Object>>)
  location: variable prop of type ObservableValue<Object>
1 error
[Incubating] Problems report is available at: file:///home/user/question/build/reports/problems/problems-report.html

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler output below.
  /home/user/question/src/main/java/Main.java:11: error: cannot find symbol
      prop.subscribe(new Consumer<Object>() { public void accept(Object t) {} });
          ^
    symbol:   method subscribe(<anonymous Consumer<Object>>)
    location: variable prop of type ObservableValue<Object>
  1 error

* Try:
> Check your code and dependencies to fix the compilation error(s)
> Run with --scan to get full insights.

BUILD FAILED in 924ms
1 actionable task: 1 executed

后续测试 #

使用第三方提供的代码测试后发现：直接用gradle run可成功运行，但使用Gradle Wrapper的./gradlew run仍报错。

非Wrapper运行结果 #

$ tree -a
.
├── build.gradle.kts
├── settings.gradle.kts
└── src
    └── main
        └── java
            └── com
                └── example
                    └── Main.java

6 directories, 3 files

$ gradle -version

------------------------------------------------------------
Gradle 8.10.2
------------------------------------------------------------

Build time:    2024-09-23 21:28:39 UTC
Revision:      415adb9e06a516c44b391edff552fd42139443f7

Kotlin:        1.9.24
Groovy:        3.0.22
Ant:           Apache Ant(TM) version 1.10.14 compiled on August 16 2023
Launcher JVM:  21.0.5 (Oracle Corporation 21.0.5+1-nixos)
Daemon JVM:    /nix/store/f042x32jfm94d3cgaga8d6xl8vy6sg46-openjdk-21.0.5+11/lib/openjdk (no JDK specified, using current Java home)
OS:            Linux 6.6.69 amd64

$ gradle run

> Task :run
Property value = null
Property value = Hello, World!
Property value = Hi, mom!

BUILD SUCCESSFUL in 529ms
2 actionable tasks: 2 executed

Wrapper运行结果 #

$ tree -a
.
├── build.gradle.kts
├── settings.gradle.kts
└── src
    └── main
        └── java
            └── com
                └── example
                    └── Main.java

6 directories, 3 files

$ gradle wrapper

BUILD SUCCESSFUL in 449ms
1 actionable task: 1 executed

$ ./gradlew -version

------------------------------------------------------------
Gradle 8.10.2
------------------------------------------------------------

Build time:    2024-09-23 21:28:39 UTC
Revision:      415adb9e06a516c44b391edff552fd42139443f7

Kotlin:        1.9.24
Groovy:        3.0.22
Ant:           Apache Ant(TM) version 1.10.14 compiled on August 16 2023
Launcher JVM:  21.0.5 (Oracle Corporation 21.0.5+1-nixos)
Daemon JVM:    /nix/store/vc52hvhclai81s6yyg7mng0g0mfvnqim-openjdk-21.0.5+11/lib/openjdk (no JDK specified, using current Java home)
OS:            Linux 6.6.69 amd64

$ ./gradlew run

> Task :compileJava FAILED
/home/user/question/src/main/java/com/example/Main.java:16: error: cannot find symbol
    property.subscribe(value -> System.out.println("Property value = " + value));
            ^
  symbol:   method subscribe((value)->S[...]alue))
  location: variable property of type SimpleObjectProperty<Object>
1 error

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler error output for details.

* Try:
> Run with --info option to get more log output.
> Run with --scan to get full insights.

BUILD FAILED in 446ms
1 actionable task: 1 executed

问题解决 #

最终定位为Java安装配置问题：Gradle和Gradle Wrapper使用了不同的JAVA_HOME和Java安装环境。在NixOS的overlay中原本配置：

p.jdk.override {
  enableJavaFX = true;
  openjfx_jdk = p.openjfx.override { withWebKit = true; };
};

将p.openjfx.override改为p.openjfx23.override后问题解决。目前仍存在疑问：为何Gradle Wrapper会优先使用系统Java安装中的JavaFX，而非build.gradle.kts中指定的版本。

内容的提问来源于stack exchange，提问作者Michael D. Adams