Server-Sent Events (SSE)是一種基于HTTP協(xié)議的單向通訊技術(shù)狂秦，只能服務(wù)器向客戶端發(fā)送消息肉拓，如果客戶端需要向服務(wù)器發(fā)送消息葵硕，則需要一個新的 HTTP 請求罐监。SSE的實現(xiàn)方法可能參考阮一鋒老師的文章吴藻。
在Java中，并沒有像HTML5中SSE的封裝實現(xiàn)弓柱，但我們可以模擬一個沟堡，以下為Java與Node.js服務(wù)器后臺通訊的實現(xiàn):

import java.io.*;
import java.net.*;

public class Sse {

    public Sse() {
        try {
            URL url = new URL("http://localhost:3400");
            HttpURLConnection urlConnection = (HttpURLConnection)url.openConnection();
            urlConnection.setRequestMethod("POST");
            urlConnection.setDoOutput(true);
            urlConnection.setDoInput(true);
            urlConnection.setUseCaches(false);
            urlConnection.setRequestProperty("Connection", "Keep-Alive");
            urlConnection.setRequestProperty("Charset", "UTF-8");
            urlConnection.setRequestProperty("Content-Type", "text/plain; charset=UTF-8");
            this.output(urlConnection);
            InputStream is = new BufferedInputStream(urlConnection.getInputStream());
            this.readStream(is);
        } catch(Exception e) {
            System.out.println("Error:" + e.getMessage());
        }
    }
    
    public void output(HttpURLConnection conn) {
        String data = "HelloNode SSE.";
        try {
            byte[] dataBytes = data.getBytes();
            conn.setRequestProperty("Content-Length", String.valueOf(dataBytes.length));
            OutputStream os = conn.getOutputStream();
            os.write(dataBytes);
            os.flush();
            os.close();
        } catch(Exception e) {}
    }
    
    public void readStream(InputStream is) {
        BufferedReader reader = null;
        StringBuffer sb = new StringBuffer();
        try {
            reader = new BufferedReader(new InputStreamReader(is));
            String line = "";
            while((line = reader.readLine()) != null) {
                this.parseMessage(line);
            }
            reader.close();
        } catch(Exception e) {
            System.out.println("Error:" + e.getMessage());
        }
    }
    
    public void parseMessage(String msg) {
        //這里可以寫接收消息后的邏輯
    }

    public static void main(String[] args) {
        new Sse();
    }
}

而node.js服務(wù)器端的代碼則如下：

var http = require("http");

var server = http.createServer(function(req, res) {
    let chunks = [], len = 0;
    req.on("data", chunk => {
        chunks.push(chunk);
        len += chunk.length;
    }).on("end", () => {
        let buf = Buffer.concat(chunks, len);
        console.log("PostData:", buf.toString());
    });
    setInterval(function() {
        //這里可以根據(jù)用戶請求的操作進(jìn)行數(shù)據(jù)處理及返回
        res.write(Date.now() + "\r\n");
    }, 3000);
});

server.listen(3400);

以上為簡單實現(xiàn)， 其中省略了服務(wù)器端的error捕獲以及數(shù)據(jù)處理及返回的操作, 希望能對正在學(xué)習(xí)相關(guān)技術(shù)的人有一點點用處矢空。