Java并发编程与JavaFX场景嵌入技术解析

# Java并发编程与JavaFX场景嵌入技术解析 ## 1. Java并发编程中的Service抽象类 在Java并发编程中，`Task<V>`类定义的是一次性任务，执行一次后便不会再次运行。而`Service<V>`抽象类则是`Worker`接口的一种可复用实现。 ### 1.1 Service抽象类的特性 - **可重置状态**：`Service<V>`扩展了`Worker`的状态模型，允许将其状态重置为`Worker.State.READY`。 - **包含字段**：它包含一个`Task<V>`类型的字段和一个`java.util.concurrent.Executor`类型的字段。 - **额外属性**：除了`Worker`接口的九个只读属性外，`Service<V>`还有一个名为`executor`的`Executor`类型的读写属性。 ### 1.2 Service类的方法 | 方法 | 描述 | | --- | --- | | `protected abstract Task createTask()` | 扩展`Service<V>`的类必须重写此方法以生成一个新创建的`Task`。 | | `public void start()` | 仅当`Service<V>`对象处于`Worker.State.READY`状态时才能调用。它调用`createTask()`获取一个新的`Task`，并从`executor`属性获取一个`Executor`，若未设置则创建自己的`Executor`，然后将`Service<V>`对象的九个`Worker`属性绑定到`Task`的属性上，最后将`Task`转换到`Worker.State.SCHEDULED`状态并在`Executor`上执行。 | | `public void reset()` | 仅当`Service<V>`的状态不是`Worker.State.SCHEDULED`或`Worker.State.RUNNING`时才能调用。它解除`Service<V>`的九个属性与底层`Task`的绑定，并将其值重置为初始值。 | | `public void restart()` | 取消当前正在执行的`Task`（如果有），然后执行`reset()`，接着调用`start()`。 | | `public final boolean cancel()` | 取消当前正在执行的`Task`（如果有）；否则将`Service<V>`转换到`Worker.State.CANCELLED`状态。 | ### 1.3 ServiceExample示例代码 ```java import javafx.application.Application; import javafx.beans.binding.Bindings; import javafx.beans.binding.IntegerBinding; import javafx.beans.binding.StringBinding; import javafx.beans.property.IntegerProperty; import javafx.beans.property.ReadOnlyObjectProperty; import javafx.beans.property.SimpleIntegerProperty; import javafx.concurrent.Service; import javafx.concurrent.Task; import javafx.concurrent.Worker; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.geometry.HPos; import javafx.geometry.Insets; import javafx.geometry.Pos; import javafx.scene.Scene; import javafx.scene.SceneBuilder; import javafx.scene.control.Button; import javafx.scene.control.Label; import javafx.scene.control.ProgressBar; import javafx.scene.control.ProgressBarBuilder; import javafx.scene.control.TextField; import javafx.scene.control.TextFieldBuilder; import javafx.scene.layout.BorderPaneBuilder; import javafx.scene.layout.ColumnConstraintsBuilder; import javafx.scene.layout.GridPane; import javafx.scene.layout.GridPaneBuilder; import javafx.scene.layout.HBox; import javafx.scene.layout.HBoxBuilder; import javafx.stage.Stage; import java.util.concurrent.atomic.AtomicBoolean; public class ServiceExample extends Application { private Model model; private View view; public static void main(String[] args) { Application.launch(args); } public ServiceExample() { model = new Model(); } @Override public void start(Stage stage) throws Exception { view = new View(model); hookupEvents(); stage.setTitle("Service Example"); stage.setScene(view.scene); stage.show(); } private void hookupEvents() { view.startButton.setOnAction(new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent actionEvent) { model.shouldThrow.getAndSet(false); ((Service) model.worker).restart(); } }); view.cancelButton.setOnAction(new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent actionEvent) { model.worker.cancel(); } }); view.exceptionButton.setOnAction(new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent actionEvent) { model.shouldThrow.getAndSet(true); } }); } private static class Model { public Worker<String> worker; public AtomicBoolean shouldThrow = new AtomicBoolean(false); public IntegerProperty numberOfItems = new SimpleIntegerProperty(250); private Model() { worker = new Service<String>() { @Override protected Task createTask() { return new Task<String>() { @Override protected String call() throws Exception { updateTitle("Example Service"); updateMessage("Starting..."); final int total = numberOfItems.get(); updateProgress(0, total); for (int i = 1; i <= total; i++) { try { Thread.sleep(20); } catch (InterruptedException e) { return "Canceled at " + System.currentTimeMillis(); } if (shouldThrow.get()) { throw new RuntimeException("Exception thrown at " + System.currentTimeMillis()); } updateTitle("Example Service (" + i + ")"); updateMessage("Processed " + i + " of " + total + " items."); updateProgress(i, total); } return "Completed at " + System.currentTimeMillis(); } }; } }; } } private static class View { public ProgressBar progressBar; public Label title; public Label message; public Label running; public Label state; public Label totalWork; public Label workDone; public Label progress; public Label value; public Label exception; public TextField numberOfItems; public Button startButton; public Button cancelButton; public Button exceptionButton; public Scene scene; private View(final Model model) { progressBar = ProgressBarBuilder.create() .minWidth(250) .build(); title = new Label(); message = new Label(); running = new Label(); state = new Label(); totalWork = new Label(); workDone = new Label(); progress = new Label(); value = new Label(); exception = new Label(); numberOfItems = TextFieldBuilder.create() .maxWidth(40) .build(); startButton = new Button("Start"); cancelButton = new Button("Cancel"); exceptionButton = new Button("Exception"); final ReadOnlyObjectProperty<Worker.State> stateProperty = model.worker.stateProperty(); progressBar.progressProperty().bind(model.worker.progressProperty()); title.textProperty().bind( model.worker.titleProperty()); message.textProperty().bind( model.worker.messageProperty()); running.textProperty().bind( Bindings.format("%s", model.worker.runningProperty())); state.textProperty().bind( Bindings.format("%s", stateProperty)); totalWork.textProperty().bind( model.worker.totalWorkProperty().asString()); workDone.textProperty().bind( model.worker.workDoneProperty().asString()); progress.textProperty().bind( Bindings.format("%5.2f%%", model.worker.progressProperty().multiply(100))); value.textProperty().bind( model.worker.valueProperty()); exception.textProperty().bind(new StringBinding() { { super.bind(model.worker.exceptionProperty()); } @Override protected String computeValue() { final Throwable exception = model.worker.getException(); if (exception == null) return ""; return exception.getMessage(); } }); model.numberOfItems.bind(new IntegerBinding() { { super.bind(numberOfItems.textProperty()); } @Override protected int computeValue() { final String text = numberOfItems.getText(); int n = 250; try { n = Integer.parseInt(text); } catch (NumberFormatException e) { } return n; } }); startButton.disableProperty().bind( stateProperty.isEqualTo(Worker.State.RUNNING)); cancelButton.disableProperty().bind( stateProperty.isNotEqualTo(Worker.State.RUNNING)); exceptionButton.disableProperty().bind( stateProperty.isNotEqualTo(Worker.State.RUNNING)); final HBox topPane = HBoxBuilder.create() .padding(new Insets(10, 10, 10, 10)) .spacing(10) .alignment(Pos.CENTER) .children(progressBar) .build(); final GridPane centerPane = GridPaneBuilder.create() .hgap(10) .vgap(10) .padding(new Insets(10, 10, 10, 10)) .columnConstraints( ColumnConstraintsBuilder.create() .halignment(HPos.RIGHT) .minWidth(65) .build(), ColumnConstraintsBuilder.create() .halignment(HPos.LEFT) .minWidth(200) .build() ) .build(); centerPane.add(new Label("Title:"), 0, 0); centerPane.add(new Label("Message:"), 0, 1); centerPane.add(new Label("Running:"), 0, 2); centerPane.add(new Label("State:"), 0, 3); centerPane.add(new Label("Total Work:"), 0, 4); centerPane.add(new Label("Work Done:"), 0, 5); centerPane.add(new Label("Progress:"), 0, 6); centerPane.add(new Label("Value:"), 0, 7); centerPane.add(new Label("Exception:"), 0, 8); centerPane.add(title, 1, 0); centerPane.add(message, 1, 1); centerPane.add(running, 1, 2); centerPane.add(state, 1, 3); centerPane.add(totalWork, 1, 4); centerPane.add(workDone, 1, 5); centerPane.add(progress, 1, 6); centerPane.add(value, 1, 7); centerPane.add(exception, 1, 8); final HBox buttonPane = HBoxBuilder.create() .padding(new Insets(10, 10, 10, 10)) .spacing(10) .alignment(Pos.CENTER) .children(new Label("Process"), numberOfItems, new Labe ```