使用 JFileChooser 保存 BufferedImage 会引发一些问题

Question

我有一个相当简单的绘图程序，它使用 BufferedImage 作为画布。我有一个单独的类 (IOClass) 来处理保存图像和打开另一个图像。我在通过saveImage() 方法保存 BufferedImage 时遇到了一些麻烦。这是整个课程：

 package ui;

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JFileChooser;
import javax.swing.JFrame;

// class for Saving & Opening images (for the bufferedImage called 'background'
public class IOClass {
    static BufferedImage image;

    public IOClass(BufferedImage image) {
        this.image = image;
    }

    public static final JFileChooser fileChooser = new JFileChooser();
    public void saveImage() {
        int saveValue = fileChooser.showSaveDialog(null);
        if (saveValue == JFileChooser.APPROVE_OPTION) {
            try {
                ImageIO.write(image, "png", new File(fileChooser
                        .getSelectedFile().getAbsolutePath()
                        + fileChooser.getSelectedFile().getName()));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public BufferedImage openImage() {
        int open = fileChooser.showOpenDialog(null);

    }
}

所以，正如您通过阅读saveImage() 方法所看到的，这就是问题所在。程序打开，您绘制一张图片，您使用“另存为”菜单选项转到 JMenuBar，这会激活一个打开此类的 actionListener 并启动新的fileChooser，您可以在其中使用 JFileChooser 保存图像。图像拒绝保存，而是引发 IllegalArguementException。问题必须出在这个 Save 方法中，我假设它发生在 ImageIO.write(bla bla bla) 方法中。我该怎么做才能确保正确保存此图像，以及我到底做错了什么？我已经阅读了一点 JFileChooser API，我认为这是其中唯一真正重要的部分，但如果我应该回去添加一些东西，请告诉我。谢谢。

额外： JFileChooser 仅在用户按下主程序（未显示）的 JMenuBar 上的“另存为”按钮时出现。主程序使用“Nimbus”主题，使用代码段即可使用：

try {
            UIManager
                    .setLookAndFeel("javax.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (UnsupportedLookAndFeelException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

当我之前尝试某些东西时，打开 JFileChooser 时也会以 Nimbus 主题打开，但现在，它只会以正常、无聊、默认的 Swing 外观打开。我该怎么做才能恢复 Nimbus 主题（看起来好多了）。

编辑：根据要求，完整的堆栈跟踪：

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: image == null!
    at javax.imageio.ImageTypeSpecifier.createFromRenderedImage(Unknown Source)
    at javax.imageio.ImageIO.getWriter(Unknown Source)
    at javax.imageio.ImageIO.write(Unknown Source)
    at ui.IOClass.saveImage(IOClass.java:26)
    at ui.ProgramUI$saveAsListener.actionPerformed(ProgramUI.java:406)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.AbstractButton.doClick(Unknown Source)
    at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
    at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

线程“AWT-EventQueue-0”java.lang.IllegalArgumentException 中的异常：image == null！

异常指出它被抛出是因为您的图像为空，因此问题不在上面的代码中，而在调用上述代码的代码中：您传入的是空图像。

要以一种或另一种方式证明它，请对其进行测试：

    if (saveValue == JFileChooser.APPROVE_OPTION) {
      System.out.println("is image null? " + (image == null));
      try {
        // ....

同样，这些家伙：

static BufferedImage image;
public static final JFileChooser fileChooser = new JFileChooser();

不应该是静态的。同样，JFileChooser 可能会因此丢失 Nimbus L&F，因为它是在类加载时启动的，在您设置 L&F 之前，而不是在实例化 IOClass 的对象时启动。

---

编辑
顺便说一句，这不应该：

ImageIO.write(image, "png", new File(fileChooser
                    .getSelectedFile().getAbsolutePath()
                    + fileChooser.getSelectedFile().getName()));

是这个吗？：

ImageIO.write(image, "png", fileChooser.getSelectedFile());