Android中與服務器進行URL交互

Android中與服務器交互主流方式與Java後端服務器交互方式一樣，採用RESTful API +Json的交互方式，針對不同的數據形式以及不同的解析方法。
而下面例子代碼是簡單地通過URL與服務器交互（本質上向服務器發送請求，從服務器接收數據）。

JavaWeb的本質也是如此，前端的js代碼操作數據，發送數據給服務器，然後從服務器接收數據。

主流交互方式可看這篇文章

//Android與服務器通過URL交互
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;

class LoginService {
    static String loginByGet(String username, String password) {
        try {
            String path = "http://192.168.31.169:8080/AndroidClient_war_exploded/LoginServlet?username="
                    + URLEncoder.encode(username, "UTF-8")
                    + "&password="
                    + URLEncoder.encode(password, "UTF-8");
                    
            URL url = new URL(path);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setConnectTimeout(5000);
            connection.setRequestMethod("GET");
            int code = connection.getResponseCode();
            if (code == 200) {
                InputStream is = connection.getInputStream();
                return StreamTools.readInputStream(is);           //StreamToolsL是自己寫的類，將InputStream轉化成OutStream
            } else {
                return null;
            }
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

    static String loginByPost(String username, String password) {
        try {
            String path = "http://192.168.31.169:8080/AndroidClient_war_exploded/LoginServlet";
            
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5000);
            conn.setRequestMethod("POST");

            String data = "username=" + URLEncoder.encode(username, "UTF-8")
                    + "&password=" + URLEncoder.encode(password, "UTF-8");
                    
            conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            conn.setRequestProperty("Content-Length", data.length() + "");
            conn.setDoOutput(true);      //setDoOutput()默認是false，需要手動設置爲true

            OutputStream os = conn.getOutputStream();
            os.write(data.getBytes());
            int code = conn.getResponseCode();
            if (code == 200) {
                InputStream is = conn.getInputStream();
                return StreamTools.readInputStream(is);
            } else {
                return null;
            }
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }
}

HttpURLConnection的setDoOutput()默認是false，需要手動設置爲true，完了就可以調用getOutputStream()方法從服務器端獲得字節輸出流。