Class.getResource（）返回null(Class.getResource() retu

我想显示在JPanel的照片，但我不断收到错误：

java.lang.IllegalArgumentException异常：输入== NULL！

我不明白发生了什么。

这里是我使用的代码：

public void actionPerformed(ActionEvent e) {
    try {
        Image image=ImageIO.read(getClass().getResource("img/" +num.getText()+".jpg"));

        Image resized = image.getScaledInstance(200, 200, 100);
        pictureFrame.setIcon(new ImageIcon(resized));
    } catch (Exception ex){
        ex.printStackTrace();
    }
}

这只是导致我得到的错误！

堆栈跟踪产生如下：

Java.lang.IllegalArgumentException: input == null!
    at javax.imageio.ImageIO.read(ImageIO.java:1362)
    at work.Item.actionPerformed(Item.java:96)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6297)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
    at java.awt.Component.processEvent(Component.java:6062)
    at java.awt.Container.processEvent(Container.java:2039)
    at java.awt.Component.dispatchEventImpl(Component.java:4660)
    at java.awt.Container.dispatchEventImpl(Container.java:2097)
    at java.awt.Component.dispatchEvent(Component.java:4488)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4575)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4236)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4166)
    at java.awt.Container.dispatchEventImpl(Container.java:2083)
    at java.awt.Window.dispatchEventImpl(Window.java:2489)
    at java.awt.Component.dispatchEvent(Component.java:4488)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:668)
    at java.awt.EventQueue.access$400(EventQueue.java:81)
    at java.awt.EventQueue$2.run(EventQueue.java:627)
    at java.awt.EventQueue$2.run(EventQueue.java:625)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
    at java.awt.EventQueue$3.run(EventQueue.java:641)
    at java.awt.EventQueue$3.run(EventQueue.java:639)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:638)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

我该如何解决这个问题？我已经检查了图像的位置，并从不同的位置都试过，总是得到同样的错误！

我使用NetBeans IDE中。

Answer 1:

假设getClass()返回com.foo.bar.MyActionListener ， getClass().getResource("img/foo.jpg")查找一个文件名为foo.jpg在包com.foo.bar.img 。如果图像是不是在这个包，或者如果它是在这个方案，但它的根目录不是在classpath中，该方法将返回null。

如果IMG文件夹是在classpath的根目录，你应该使用getClass().getResource("/img/foo.jpg")注意龙头/ ），或getClass().getClassLoader().getResource("img/foo.jpg")

Answer 2:

你应该给你的源文件的相对路径。对于为例，如果你有这样的：

src
 --img
 --classes

而你是在classes文件夹，你应该这样写：

getClass().getResource("../img/" +num.getText()+".jpg")