java - JLabel.setIcon() 无法按预期工作

Question

我正在为 Java Swing 编写这个 Google map 组件。我只需要使用谷歌静态 map 。我希望 map 根据读取用户输入的按钮操作进行更新，但包装在 JLabel 中的图像不会更新。

我将静态 map 缓存在 ma​​pCache.jpg 中，并在每次 ActionListener 触发时将 JLabel ma​​pContent 的图标设置为它。但它就是行不通。 mapCache.jpg 在我的系统上更新，但它只是在程序中不更新。我尝试从 JScrollPane 中删除 imageicon 或删除 mapContent，但这些都不起作用。我怀疑 JVM 缓存了图像文件。如果是这样，我该如何清除缓存？

这是我的类内容:

private static final long serialVersionUID = 2243575060653389810L;
private String latlong;
private int zoomLevel;
private JLabel mapContent;
private ImageIcon mapImage;

public MapComponent(float lat, float lon, int zoom){
    latlong = validateLatlong(lat,lon);
    zoomLevel = validateZoomLevel(zoom);
    queryMap();

    setLayout(new BorderLayout());
    mapImage = new ImageIcon("mapCache.jpg");
    mapContent = new JLabel(mapImage);
    JScrollPane sp = new JScrollPane(mapContent);
    add(sp, BorderLayout.CENTER);

    JPanel inputPane = new JPanel();
    JLabel latLabel = new JLabel("Latitude: ");
    final JTextField latText = new JTextField(""+lat);
    JLabel longLabel = new JLabel("Longitude: ");
    final JTextField longText = new JTextField(""+lon);
    JLabel zoomLabel = new JLabel("Zoom Level: ");
    final JTextField zoomText = new JTextField(""+zoomLevel);
    zoomText.setPreferredSize(new Dimension(20,15));
    JButton mapGo = new JButton("Go");
    mapGo.addActionListener(new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e) {
            try{
                queryMap(Float.parseFloat(latText.getText()), Float.parseFloat(longText.getText()), Integer.parseInt(zoomText.getText()));
                mapImage.setImage(new ImageIcon("mapCache.jpg").getImage());
                mapContent.setIcon(null);
                mapContent.setIcon(mapImage);  // Doesn't work!
            }
            catch(Exception ex){
                ex.printStackTrace();
            }
        }
    });
    inputPane.add(latLabel);
    inputPane.add(latText);
    inputPane.add(longLabel);
    inputPane.add(longText);
    inputPane.add(zoomLabel);
    inputPane.add(zoomText);
    inputPane.add(mapGo);
    add(inputPane, BorderLayout.PAGE_END);

    setVisible(true);
}

private void queryMap(){
    try {
        String imageUrl = "http://maps.google.com/staticmap?center="+latlong+"&zoom="+zoomLevel+
                "&size=1000x750&maptype=roadmap&markers="+latlong+
                "&key=ABQIAAAAgb5KEVTm54vkPcAkU9xOvBR30EG5jFWfUzfYJTWEkWk2p04CHxTGDNV791-cU95kOnweeZ0SsURYSA&format=jpg";
        System.out.println(imageUrl);
        String destinationFile = "mapCache.jpg";
        URL url = new URL(imageUrl);
        InputStream is = url.openStream();
        OutputStream os = new FileOutputStream(destinationFile);
        byte[] b = new byte[2048];
        int length;
        while ((length = is.read(b)) != -1) {
            os.write(b, 0, length);
        }
        is.close();
        os.flush();
        os.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

public void queryMap(float lat, float lon, int zoom){
    latlong = validateLatlong(lat,lon);
    zoomLevel = validateZoomLevel(zoom);
    queryMap();
}

private String validateLatlong(float lat, float lon){
    lat = Math.min(lat, 90);
    lat = Math.max(lat, -90);
    lon = Math.min(lon, 90);
    lon = Math.max(lon, -90);
    return lat+","+lon;
}

private int validateZoomLevel(int zoom){
    zoom = Math.min(zoom, 15);
    zoom = Math.max(zoom, 1);
    return zoom;
}

Answer 1

ImageIcon，使用Image作为其后备源，Image将其图像数据缓存在内存中。在尝试将图像数据重新应用到标签之前，您需要刷新图像数据

mapContent.setIcon(null);

mapImage.getImage().flush();
mapContent.setIcon(mapImage);  // Doesn't work! - Does now :)

我还建议您查看The try-with-resources Statement并更好地处理您的资源，例如......

try (InputStream is = url.openStream(); OutputStream os = new FileOutputStream(destinationFile)) {
    byte[] b = new byte[2048];
    int length;
    while ((length = is.read(b)) != -1) {
        os.write(b, 0, length);
    }
}