java - System.out 重定向到 JTextPane

Question

package htmlconsole;

import java.awt.BorderLayout;

public class HTMLConsole extends JFrame {

    private JPanel contentPane;
    private JTextPane textPane;

    public class Interceptor extends PrintStream
    {
        public Interceptor(OutputStream out)
        {
            super(out,true);
        }
        @Override
        public void print(String s)
        {
            super.print(s);
            textPane.setText(textPane.getText()+s);
        }

        @Override 
        public void println(String s)
        {
            super.println(s);
            textPane.setText(textPane.getText()+"\n<br>");
        }       
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    HTMLConsole frame = new HTMLConsole();
                    frame.setVisible(true);

                    System.out.println("Hello");

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public HTMLConsole() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        JTextPane textPane = new JTextPane();
        textPane.setEditable(false);
        textPane.setContentType("text/html");
        textPane.setText("");

        contentPane.add(textPane, BorderLayout.CENTER);

        //redirect stream
        PrintStream interceptor = new Interceptor(System.out);
        System.setOut(interceptor);
    }
}

输出:

Hellojava.lang.NullPointerException
    at console.Console$Interceptor.print(Console.java:29)
    at java.io.PrintStream.println(Unknown Source)
    at console.Console$Interceptor.println(Console.java:35)
    at console.Console$1.run(Console.java:47)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(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.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)

我该如何修正这个程序？非常令人困惑的是，在未使用的“打印”方法中抛出了异常!

更新:

将 JTextPane textPane textPane = new JTextPane(); 替换为 textPane = new JTextPane(); 后异常消失，但现在窗口内没有显示任何内容。

Answer 1

你的构造函数调用

JTextPane textPane = new JTextPane(); // local variable declaration and initialization

而不是调用

this.textPane = new JTextPane()

因此拦截器使用的 textPane 字段为空。

另请注意，如堆栈跟踪所示，super.println() 调用 print()。这将导致传递给 println() 的每个字符串都被附加到文本 Pane 两次。