java - 将 System.in 重定向到 swing 组件

Question

大家好，我正在使用 Swing 和 Apache Commons 制作一个终端应用程序。我能够轻松地将 System.out 和 System.err 重定向到 JTextArea 但我如何为 System.in 做到这一点 ？我需要覆盖 Inputstream 方法吗？我是否需要将 String 从 JTextArea 转换为字节数组，然后将其传递给 InputStream？代码示例会很好。

Answer 1

我最近尝试了同样的事情，这是我的代码:

class TexfFieldStreamer extends InputStream implements ActionListener {

    private JTextField tf;
    private String str = null;
    private int pos = 0;

    public TexfFieldStreamer(JTextField jtf) {
        tf = jtf;
    }

    //gets triggered everytime that "Enter" is pressed on the textfield
    @Override
    public void actionPerformed(ActionEvent e) {
        str = tf.getText() + "\n";
        pos = 0;
        tf.setText("");
        synchronized (this) {
            //maybe this should only notify() as multiple threads may
            //be waiting for input and they would now race for input
            this.notifyAll();
        }
    }

    @Override
    public int read() {
        //test if the available input has reached its end
        //and the EOS should be returned 
        if(str != null && pos == str.length()){
            str =null;
            //this is supposed to return -1 on "end of stream"
            //but I'm having a hard time locating the constant
            return java.io.StreamTokenizer.TT_EOF;
        }
        //no input available, block until more is available because that's
        //the behavior specified in the Javadocs
        while (str == null || pos >= str.length()) {
            try {
                //according to the docs read() should block until new input is available
                synchronized (this) {
                    this.wait();
                }
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
        //read an additional character, return it and increment the index
        return str.charAt(pos++);
    }
}

并像这样使用它:

    JTextField tf = new JTextField();
    TextFieldStreamer ts = new TextFieldStreamer(tf);
    //maybe this next line should be done in the TextFieldStreamer ctor
    //but that would cause a "leak a this from the ctor" warning
    tf.addActionListener(ts);

    System.setIn(ts);

我已经有一段时间没有编写 Java 代码了，所以我可能不是最新的模式。您可能还应该重载 int available() 但我的示例仅包含使其与 BufferedReader 的 readLine() 一起工作的最低限度功能。

编辑:要使其适用于 JTextField，您必须使用 implements KeyListener 而不是 implements ActionListener然后在您的 TextArea 上使用 addKeyListener(...)。您需要的函数而不是 actionPerformed(...) 是 public void keyPressed(KeyEvent e) 然后您必须测试 if (e.getKeyCode () == e.VK_ENTER) 而不是使用整个文本，您只需使用光标前最后一行的子字符串

//ignores the special case of an empty line
//so a test for \n before the Caret or the Caret still being at 0 is necessary
int endpos = tf.getCaret().getMark();
int startpos = tf.getText().substring(0, endpos-1).lastIndexOf('\n')+1;

用于输入字符串。因为否则每次按下 Enter 时您都会阅读整个 TextArea。