为什么我的小程序会抛出 AccessControlException？

Question

我正在尝试构建一个名为 game 的 Java 小程序，这是我以前从未做过的事情（我一直只是构建独立的应用程序）。我的小程序在 Eclipse 中测试时运行良好，但是当我尝试将其放在我的网站上时，我在控制台中收到以下错误：

java.lang.reflect.InvocationTargetException
    at com.sun.deploy.util.DeployAWTUtil.invokeAndWait(DeployAWTUtil.java:116)
    at sun.plugin2.applet.Plugin2Manager.runOnEDT(Plugin2Manager.java:3541)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Plugin2Manager.java:3072)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Plugin2Manager.java:1497)
    at java.lang.Thread.run(Thread.java:680)
Caused by: java.security.AccessControlException: access denied (java.util.PropertyPermission user.dir read)
    at java.security.AccessControlContext.checkPermission(AccessControlContext.java:374)
    at java.security.AccessController.checkPermission(AccessController.java:546)
    at java.lang.SecurityManager.checkPermission(SecurityManager.java:532)
    at java.lang.SecurityManager.checkPropertyAccess(SecurityManager.java:1285)
    at java.lang.System.getProperty(System.java:667)
    at java.io.UnixFileSystem.resolve(UnixFileSystem.java:118)
    at java.io.File.getAbsolutePath(File.java:501)
    at game.<init>(game.java:117)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at java.lang.Class.newInstance0(Class.java:355)
    at java.lang.Class.newInstance(Class.java:308)
    at sun.plugin2.applet.Plugin2Manager$13.run(Plugin2Manager.java:3060)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:199)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:682)
    at java.awt.EventQueue.access$000(EventQueue.java:85)
    at java.awt.EventQueue$1.run(EventQueue.java:643)
    at java.awt.EventQueue$1.run(EventQueue.java:641)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:652)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Exception: java.lang.reflect.InvocationTargetException

上面写着access denied (java.util.PropertyPermission user.dir read)，但我不知道它试图从用户的文件系统中读取内容的位置。

它还显示at game.<init>(game.java:117)，但我进入我的文件并在第 114 行向控制台输出了一条消息，但它从未被写入。然后我想它可能正在查看public game() 内的第 117 行，所以我寻找它，它是鼠标事件侦听器的开始。对我来说这是有道理的，这将是 Java 需要权限才能读取的内容，因此我删除了所有内容，然后删除了所有导入以更好地衡量。然后我清除了 Chrome 和 Java 的缓存并重试。同样的错误。

1. 这是什么意思，我解释错了吗？
2. 当它说第 117 行时，它是第 117 行的什么？
3. 为什么会发生这种情况？
4. 我该如何解决？
5. 以后如何预防？

供参考，这里是public game()的代码：

public game() throws MalformedURLException{

    JPanel board = new chessboard();
    board.setSize(320, 320);
    board.setLocation(0, 0);

    System.out.println("Got this far");

    Piece wp1 = new Piece(wpawn, a2);
...
    Piece bk = new Piece(bking, e8);


    board.add(wp1);
...
    board.add(bk);

    wp1.setLocation(wp1.square.getPoint());
...     
    bk.setLocation(bk.square.getPoint());

    add(board);
    repaint();

    addMouseListener(new MouseAdapter(){
        public void mousePressed(MouseEvent evt){

            for (int i = 0; i < 8; i++){
                for (int j = 0; j < 8; j++){
                    if (squares[i][j].piece != null)
                        System.out.println(squares[i][j].getPointString() + ": " + squares[i][j].piece.type);
                }
            }

            Point p = evt.getPoint();
            if (0 < p.x && p.x < 319 && 0 < p.y && p.y < 319){
                Square clicked = getSquare(p);
                System.out.println("up: " + clicked.getPointString());
                if (clicked.piece != null){
                    pickedUp = true;
                    pickedUpPiece = clicked.piece;
                }
            }
        }
        public void mouseReleased(MouseEvent evt){
            if (pickedUp){
                Point p = evt.getPoint();
                if (0 < p.x && p.x < 319 && 0 < p.y && p.y < 319){
                    System.out.println("down: " + getSquare(p).getPointString());
                    movePiece(pickedUpPiece, getSquare(p).getColumn(), getSquare(p).getRow());
                }
                pickedUp = false;
            }
            else System.out.println("Not picked up");
        }
    });
}

Answer 1

堆栈跟踪的关键输出是：

at java.io.File.getAbsolutePath(File.java:501)
at game.<init>(game.java:117)

这意味着您的 game.java 文件在第 117 行正在调用 getAbsolutePath()。嵌入在浏览器中的 Java 小程序不允许访问本地文件系统。