如何获取使用以下代码启动的 JavaFX 应用程序的句柄？
CPUUsageChart.launch(CPUUsageChart.class);
CPUUsageChart 从 JavaFX 扩展了 Application，我从一个简单 Java 项目的 main 方法启动它。
我最终想要实现的是，我可以在简单的Java代码中启动App并使用它的方法，这样我就不必在Application扩展类的Constructor中进行调用了。我只想使用 JavaFX 的能力来绘制图表并将它们保存到 HDD 以供以后使用，但我不需要看到任何用 JavaFX 制作的 GUI。
【问题讨论】：
建议的解决方案
您可以only launch an application once，因此您的应用程序类将永远只有一个实例。
由于应用程序只有一个实例，因此可以在应用程序启动时将对该实例的引用存储在应用程序的静态变量中，并且可以根据需要从静态方法（一种单例模式）。
注意事项
必须注意确保：
示例解决方案
下面的示例代码使用一个锁和一个条件来确保应用程序实例在您尝试使用它之前可用。当不再需要 JavaFX 平台时，它还需要显式关闭。
感谢 StackOverflow 用户 James-D 对此代码的一些编辑帮助。
import javafx.application.Application;
import javafx.application.Platform;
import javafx.collections.ObservableList;
import javafx.embed.swing.SwingFXUtils;
import javafx.scene.Scene;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.XYChart;
import javafx.stage.Stage;
import javax.imageio.ImageIO;
import java.io.File;
import java.io.IOException;
import java.nio.file.Paths;
import java.time.LocalDateTime;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class CPUUsageChart extends Application {
private static CPUUsageChart appInstance;
private static final Lock lock = new ReentrantLock();
private static final Condition appStarted = lock.newCondition();
/**
* Starts the application and records the instance.
* Sets the JavaFX platform not to exit implicitly.
* (e.g. an explicit call to Platform.exit() is required
* to exit the JavaFX Platform).
*/
@Override
public void start(Stage primaryStage) {
lock.lock();
try {
Platform.setImplicitExit(false);
appInstance = this;
appStarted.signalAll();
} finally {
lock.unlock();
}
}
/**
* Get an instance of the application.
* If the application has not already been launched it will be launched.
* This method will block the calling thread until the
* start method of the application has been invoked and the instance set.
* @return application instance (will not return null).
*/
public static CPUUsageChart getInstance() throws InterruptedException {
lock.lock();
try {
if (appInstance == null) {
Thread launchThread = new Thread(
() -> launch(CPUUsageChart.class),
"chart-launcher"
);
launchThread.setDaemon(true);
launchThread.start();
appStarted.await();
}
} finally {
lock.unlock();
}
return appInstance;
}
/**
* Public method which can be called to perform the main operation
* for this application.
* (render a chart and store the chart image to disk).
* This method can safely be called from any thread.
* Once this method is invoked, the data list should not be modified
* off of the JavaFX application thread.
*/
public void renderChart(
ObservableList<XYChart.Data<Number, Number>> data
) {
// ensure chart is rendered on the JavaFX application thread.
if (!Platform.isFxApplicationThread()) {
Platform.runLater(() -> this.renderChartImpl(data));
} else {
this.renderChartImpl(data);
}
}
/**
* Private method which can be called to perform the main operation
* for this application.
* (render a chart and store the chart image to disk).
* This method must be invoked on the JavaFX application thread.
*/
private void renderChartImpl(
ObservableList<XYChart.Data<Number, Number>> data
) {
LineChart<Number, Number> chart = new LineChart<>(
new NumberAxis(),
new NumberAxis(0, 100, 10)
);
chart.setAnimated(false);
chart.getData().add(
new XYChart.Series<>("CPU Usage", data)
);
Scene scene = new Scene(chart);
try {
LocalDateTime now = LocalDateTime.now();
File file = Paths.get(
System.getProperty("user.dir"),
"cpu-usage-chart-" + now + ".png"
).toFile();
ImageIO.write(
SwingFXUtils.fromFXImage(
chart.snapshot(null, null),
null
),
"png",
file
);
System.out.println("Chart saved as: " + file);
} catch (IOException e) {
e.printStackTrace();
}
}
}
要使用它（从任何线程）：
try {
// get chartApp instance, blocking until it is available.
CPUUsageChart chartApp = CPUUsageChart.getInstance();
// call render chart as many times as you want
chartApp.renderChart(cpuUsageData);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} finally {
// note your program should only ever exit the platform once.
Platform.exit();
}
完整的示例应用程序，它创建五个 CPU 使用数据图表，每个图表中有十个样本，每个样本间隔 100 毫秒。当示例调用图表应用程序来渲染图表时，它将在当前 java 工作目录中创建图表 png 图像文件，并将文件名输出到系统控制台。不显示 JavaFX 阶段或窗口。
从How to get percentage of CPU usage of OS from java复制的 CPU 使用率示例代码
import javafx.application.Platform;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.chart.XYChart;
import javax.management.*;
import java.lang.management.ManagementFactory;
public class ChartTest {
public static void main(String[] args) {
try {
CPUUsageChart chart = CPUUsageChart.getInstance();
for (int i = 0; i < 5; i++) {
ObservableList<XYChart.Data<Number, Number>> cpuUsageData = FXCollections.observableArrayList();
for (int j = 0; j < 10; j++) {
cpuUsageData.add(
new XYChart.Data<>(
j / 10.0,
getSystemCpuLoad()
)
);
Thread.sleep(100);
}
chart.renderChart(cpuUsageData);
}
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} catch (MalformedObjectNameException | ReflectionException | InstanceNotFoundException e) {
e.printStackTrace();
} finally {
Platform.exit();
}
}
public static double getSystemCpuLoad() throws MalformedObjectNameException, ReflectionException, InstanceNotFoundException {
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
ObjectName name = ObjectName.getInstance("java.lang:type=OperatingSystem");
AttributeList list = mbs.getAttributes(name, new String[]{ "SystemCpuLoad" });
if (list.isEmpty()) return Double.NaN;
Attribute att = (Attribute)list.get(0);
Double value = (Double)att.getValue();
if (value == -1.0) return Double.NaN; // usually takes a couple of seconds before we get real values
return ((int)(value * 1000) / 10.0); // returns a percentage value with 1 decimal point precision
}
}
样本输出（Y 轴上的 CPU 使用率百分比，以及 X 轴上以十分之一秒的采样间隔为单位的时间）。
背景信息
替代实现
【讨论】：