JavaFX:使用 REST 服务并在前端显示数据

JavaFX : Consuming REST service and displaying the data in front-end

我正在开发一个 JavaFX(在带有 SceneBuilder 的 JDK8 上)项目,它应该与基于 Spring-MVC 的服务器连接,我想从服务器访问一些对象并显示它。我已经对 Spring 服务器进行了编程以根据请求返回所需的对象,但我对 UI 编程和 JavaFX 的不熟悉使它有点困难。

在 FXML 文件中,我已经添加了一个网格窗格,我想在那里显示对象。我将不胜感激你们的任何帮助以开始使用。我只有基本代码,但我将其粘贴在下面:

Canvas.fxml :

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>

<GridPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/8">
  <columnConstraints>
    <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
    <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
  </columnConstraints>
  <rowConstraints>
    <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
    <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
    <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
  </rowConstraints>
</GridPane>

画布模型class:

public class Canvas {

    private int canvasid;

    private final StringProperty canvasName;

    private final StringProperty canvasTitle;

    private final StringProperty canvasImage;

    private byte[] canvasImageInBytes;


    public Canvas(String canvasName, String canvasTitle, String canvasImage){
        this.canvasName = new SimpleStringProperty(canvasName);
        this.canvasTitle = new SimpleStringProperty(canvasTitle);
        this.canvasImage = new SimpleStringProperty(canvasImage);
    }
//Getters and setters ommitted
}

主要 class :

public class Main extends Application {

    private Stage primaryStage;

    @Override
    public void start(Stage primaryStage) throws Exception{
       Parent root = FXMLLoader.load(getClass().getResource("../View/mainui.fxml"));

primaryStage.setTitle("CheckAPP");
       primaryStage.setScene(new Scene(root, 300, 600));
        primaryStage.setFullScreen(false);
        primaryStage.setMaximized(false);

        primaryStage.show();
    }
    public static void main(String[] args) {
        launch(args);
    }

    public Stage getPrimaryStage() {
        return this.primaryStage;
    }

}

现在向以下请求:

http://localhost:8080/canvaslist

它将 return 一个 java.util.List 我想显示在 GridPane 中。图片是字符串格式。我知道这不是一个常规问题,因为它不起作用,但我正在努力为 UI 编程,但我不知道还能转向哪里。非常感谢您的帮助。

只是加上我的几分钱来帮助你。

  1. 使用 background thread 从服务中获取数据,因为获取响应可能需要一些时间。在 JavaFX 应用程序线程上执行它可能会导致不良的用户体验。在这种情况下 Task 会帮助你。
  2. 收到响应后,从中构建一个必要的 object / collection of object,您将使用它来更新场景图上的元素。
  3. 由于 JavaFX Application Thread 是唯一可以访问 live scene graph 元素的线程,因此您不能直接在后台线程中使用它们(使用它们将导致 IllegalStateException)。您可以使用 Platform.runLater or calling the methods of the task which are guaranteed to update state on the FX Application Thread, like updateProgress(...), updateMessage(...), getValue(...)
  4. 更新 JavaFX 场景图上的数据
  5. 使用您在 Step-2 中构建的 object / collection of object 创建(或更新)FX 场景图形元素。
  6. 如果您有一个接受 ObservableList 作为其内容的控件(如 TableView 或 ListView),您可以 绑定 内容和 Task 的 属性,根据使用情况在执行期间/之后自动更新它们。
  7. 但在你的情况下,因为你有 GridPane,所以我们可能需要更进一步,编写逻辑来创建控件并将它们添加到 GridPane

例子

我创建了一个使用服务的示例,解析 JSON 数据并从中创建 GridPane。 JSON 有 list of few people on Whosebug 以及他们的名字、他们的喜好(根据我的说法)和 SO 上的个人资料照片。

它使用后台任务从服务加载 JSON 数据,使用任务的 setOnSucceeded(...) 处理程序将其传递给 createGridPane(onservableList),后者创建 GridPane.

GridPane 的其中一列包含相应人员的个人资料照片。由于下载这些图像可能需要一些时间,因此我为每个用户生成 multiple threadsload the image

您可以找到 source code here.

它使用 GSON 作为库将 JSON 转换为 POJO class。

import com.google.common.reflect.TypeToken;
import com.google.gson.Gson;
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.concurrent.Task;
import javafx.concurrent.WorkerStateEvent;
import javafx.event.EventHandler;
import javafx.geometry.HPos;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.geometry.VPos;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ScrollPane;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.*;
import javafx.stage.Stage;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;


public class ConsumeJSON extends Application {

    private ObservableList<PeopleOnSO> listOfPeople;
    private static final String JSON_URL = "https://api.myjson.com/bins/3jwmh";
    private static final String IMAGE_URL = "http://www.fontspring.com/presentation_20150512/images/ajax_loader_blue_512.gif";
    private final ExecutorService executorService = Executors.newCachedThreadPool();
    private Image loadImage;

    @Override
    public void start(Stage stage) throws Exception {

        loadImage = new Image(IMAGE_URL);
        VBox root = new VBox();
        root.setAlignment(Pos.TOP_CENTER);
        root.setPadding(new Insets(20));
        root.setSpacing(20);

        Button button = new Button("Fill GridPane");

        root.getChildren().addAll(button);


        button.setOnAction(e -> {
            // Display loading image
            ImageView loading = new ImageView(loadImage);
            loading.setFitWidth(60);
            loading.setFitHeight(60);
            root.getChildren().add(loading);
            executorService.submit(fetchList);
        });


        fetchList.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
            @Override
            public void handle(WorkerStateEvent t) {
                listOfPeople = FXCollections.observableArrayList(fetchList.getValue());
                GridPane gridPane = createGridPane(listOfPeople);
                //Remove Loading Image and add GridPane
                root.getChildren().remove(1);
                VBox.setVgrow(gridPane, Priority.ALWAYS);
                root.getChildren().add(gridPane);
                stage.sizeToScene();
            }
        });

        ScrollPane scrollPane = new ScrollPane(root);
        Scene scene = new Scene(scrollPane, 600, 500);
        stage.setScene(scene);
        stage.setTitle("Load Data from JSON");
        stage.show();

        stage.setOnCloseRequest(e -> {
            executorService.shutdown();
        });
    }

    public GridPane createGridPane(ObservableList<PeopleOnSO> listOfPeople){
        GridPane gridPane = new GridPane();
        gridPane.setAlignment(Pos.CENTER);
        gridPane.setGridLinesVisible(true);
        gridPane.setPadding(new Insets(20));
        gridPane.setMinHeight(500);
        gridPane.setMaxWidth(500);

        //Create headings
        Label nameHeading = new Label("Name");
        nameHeading.setStyle("-fx-font-weight: bold");
        Label likeHeading = new Label("Likes");
        likeHeading.setStyle("-fx-font-weight: bold");
        Label imageHeading = new Label("Image");
        imageHeading.setStyle("-fx-font-weight: bold");

        gridPane.add(nameHeading, 0, 0);
        gridPane.add(likeHeading, 1, 0);
        gridPane.add(imageHeading, 2, 0);

        // Aligning at center
        alignElements(nameHeading, likeHeading, imageHeading);

        // Setting Constraints
        for (int i = 0; i < 3; i++) {
            ColumnConstraints column = new ColumnConstraints(150);
            // column.setPercentWidth(80);
            gridPane.getColumnConstraints().add(column);
        }

        for (int i = 0; i < listOfPeople.size(); i++) {

            PeopleOnSO people = listOfPeople.get(i);
            Label nameLabel = new Label(people.getName());
            Label likeLabel = new Label(people.getLike());
            ImageView imageView = new ImageView(loadImage);
            imageView.setFitHeight(60);
            imageView.setFitWidth(60);

            //Thread for loading images later
            FetchImage fetchImage = new FetchImage(people.getImageUrl());
            fetchImage.setOnSucceeded(worker -> {
                imageView.setImage((Image) fetchImage.getValue());
            });

            executorService.submit(fetchImage);

            // Adding to GridPane and necessary configuration
            gridPane.add(nameLabel, 0, i + 1);
            gridPane.add(likeLabel, 1, i + 1);
            gridPane.add(imageView, 2, i + 1);

            //Aligning at center
            alignElements(nameLabel, likeLabel, imageView);

            gridPane.getRowConstraints().add(new RowConstraints(80));
        }
        return gridPane;
    }

    /**
     * Align elements at the center
     * @param nodes
     */
    private void alignElements(Node ... nodes ) {
        for(Node node : nodes) {
            GridPane.setHalignment(node, HPos.CENTER);
            GridPane.setValignment(node, VPos.CENTER);
        }
    }

    /**
     * Task to fetch details from JSONURL
     * @param <V>
     */
    private Task<List<PeopleOnSO>> fetchList = new Task() {
        @Override
        protected List<PeopleOnSO> call() throws Exception {
            List<PeopleOnSO> list = null;
            try {
                Gson gson = new Gson();
                list = new Gson().fromJson(readUrl(JSON_URL), new TypeToken<List<PeopleOnSO>>() {
                }.getType());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return list;
        }
    };

    /**
     * Task to fetch images for individual ImageViews
     * @param <V>
     */
    private class FetchImage<V> extends Task<Image> {

        private String imageUrl;

        public FetchImage(String imageUrl) {
            this.imageUrl = imageUrl;
        }

        @Override
        protected Image call() throws Exception {
            Image image = new Image(imageUrl);
            return image;
        }

    }

    /**
     * Read the URL and return the json data
     * @param urlString
     * @return
     * @throws Exception
     */
    private static String readUrl(String urlString) throws Exception {
        BufferedReader reader = null;
        try {
            URL url = new URL(urlString);
            reader = new BufferedReader(new InputStreamReader(url.openStream()));
            StringBuffer buffer = new StringBuffer();
            int read;
            char[] chars = new char[1024];
            while ((read = reader.read(chars)) != -1)
                buffer.append(chars, 0, read);

            return buffer.toString();
        } finally {
            if (reader != null)
                reader.close();
        }
    }

    private class PeopleOnSO {

        private final String name;
        private final String like;
        private final String imageUrl;

        public PeopleOnSO(String name, String like, String imageUrl){
            this.name = new String(name);
            this.like = new String(like);
            this.imageUrl = new String(imageUrl);
        }

        public String getName() {
            return name;
        }

        public String getLike() {
            return like;
        }

        public String getImageUrl() {
            return imageUrl;
        }
    }

    public static void main(String[] args) {
        launch(args);
    }
}