如何防止每次调用主机时都创建类的新实例? [英] How to prevent creating a new instance of the class every time the host is called?

问题描述

在我的Java程序中，每一个 Chrome扩展程序的主机(或本机应用程序)当我的Chrome扩展程序调用主机时，就会创建 Applet 类的新实例.

In my Java program which is a Chrome extension's host (or a native app), every time the host is called by my Chrome extension, then a new instance of my Applet class is created.

如何防止这种情况发生?我的意思是，所有主机扩展名-主机调用都需要有一个Applet对象，该如何实现?

How to prevent that from happening? I mean I need to have one single object of Applet for all host-extension-host calls, how to achieve that?

这是我的程序:

import javax.swing.JOptionPane;

public class Applet {

    static Applet myApplet;

    public Applet(){
        System.err.println("new instance created!");
    }

    public static void main(String[] args) {
        try {
            if (myApplet == null)
                myApplet = new Applet();
            myApplet.readMessage();
            myApplet.sendMessage("{\"data\": \"somee data\"}");
        } catch (Exception ex) {
            System.err.println("error");
            JOptionPane.showMessageDialog(null, ex.getMessage());
        }
    }

    public String readMessage() {
        String msg = "";
        try {
            int c, t = 0;
            for (int i = 0; i <= 3; i++) {
                t += Math.pow(256.0f, i) * System.in.read();
            }

            for (int i = 0; i < t; i++) {
                c = System.in.read();
                msg += (char) c;
            }
        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, "error in reading message from JS");
        }
        return msg;
    }

    public void sendMessage(String msgdata) {
        try {
            int dataLength = msgdata.length();
            System.out.write((byte) (dataLength & 0xFF));
            System.out.write((byte) ((dataLength >> 8) & 0xFF));
            System.out.write((byte) ((dataLength >> 16) & 0xFF));
            System.out.write((byte) ((dataLength >> 24) & 0xFF));

            // Writing the message itself
            System.out.write(msgdata.getBytes());
            System.out.flush();
        } catch (IOException e) {
            JOptionPane.showMessageDialog(null, "error in sending message to JS");
        }
    }
}

我相信不需要添加任何扩展名或background.js代码，但是如果您也需要查看这些代码，请告诉我.

I beleive there is no need for adding any extension or background.js code, but please let me know if you need to see those, too.

非常感谢您.

推荐答案

首先-使用 chrome.runtime.connectNative 而不是 chrome.runtime.sendNativeMessage (示例).

在您的本机应用程序(Java)中，使用无限循环来不断接收消息.目前，您只接收和发送一条消息.在那之后，什么都没有发生，因此您的应用程序可以退出. stdio本机消息传递协议非常简单:

In your native application (Java), use an infinite loop to keep receiving messages. At present, you're only receiving and sending a message. After that, nothing else happens, so your application understandably exits. The stdio native messaging protocol is very simple:

• 读取32位消息的长度(本机字节顺序).
• 读取JSON编码的消息(长度如前所述).
• 写入32位消息的长度(本机字节顺序).
• 写入JSON编码的消息(长度如前所述).
• 重复直到任一端断开端口.

您的程序应包含一个实现上述协议的(无限)循环.这是具有所需流程的程序结构:

Your program should contain an (infinite) loop that implements the above protocol. This is a program structure that has the desired flow:

class Applet {
    public static void main(String[] args) {
        new Applet(); // Initialize application.
    }

    Applet() {
        while (true) {
            readMessage();
            // ... and save the state for later processing if needed

            // Send the reply:
            sendMessage("{\"data\": \"somee data\"}");
        }
    }

    // TODO: Implement readMessage and sendMessage (see question).
}

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