如何在MainActivity.java中创建简单的HTTP请求？(Android Studio)

Question

我正在使用Android Studio,我花了几个小时试图在我的MainActivity.java文件中做一个简单的HTTP请求,并尝试了多种方法,并看到了很多关于这个主题的网页,但却无法弄清楚.

当我尝试OkHttp时,我收到一条关于无法在主线程上执行此操作的错误.现在我试着这样做:

public static String getUrlContent(String sUrl) throws Exception {
    URL url = new URL(sUrl);
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("GET");
    connection.setDoOutput(true);
    connection.setConnectTimeout(5000);
    connection.setReadTimeout(5000);
    connection.connect();
    BufferedReader rd = new BufferedReader(new InputStreamReader(connection.getInputStream()));
    String content = "", line;
    while ((line = rd.readLine()) != null) {
        content += line + "\n";
    }
    return content;
}

我将该方法直接放在MainActivity.java中,我的click事件从MainActivity.java中的另一个方法执行它:

try {
    String str = getUrlContent("https://example.com/WAN_IP.php");
    displayMessage(str);
}
catch(Exception e){
    displayMessage(e.getMessage());
}

但是现在没有崩溃,我可以告诉该行抛出的异常是"BufferedReader",但是e.getMessage()是空白的.

我是Android Studio和Java的新手,所以请善待并帮助我解决这个非常基本的问题.最终我需要向服务器发送请求,看起来OkHttp是最好的方法,但我没有在网上随处可见的Android Studio中找到OkHttp的"Hello World".

Answer 1

您不应该在主线程上发出网络请求.延迟是不可预测的,它可能会冻结用户界面.

如果您使用HttpUrlConnection主线程中的对象,Android会通过抛出异常来强制执行此行为.

然后,您应该在后台发出网络请求,然后在主线程上更新UI.该AsyncTask班可用于该用途的情况下,非常方便!

private class GetUrlContentTask extends AsyncTask<String, Integer, String> {
     protected String doInBackground(String... urls) {
        URL url = new URL(urls[0]);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");
        connection.setDoOutput(true);
        connection.setConnectTimeout(5000);
        connection.setReadTimeout(5000);
        connection.connect();
        BufferedReader rd = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String content = "", line;
        while ((line = rd.readLine()) != null) {
            content += line + "\n";
        }
        return content;
     }

     protected void onProgressUpdate(Integer... progress) {
     }

     protected void onPostExecute(String result) {
         // this is executed on the main thread after the process is over
         // update your UI here
         displayMessage(result);
     }
 }

你以这种方式开始这个过程:

new GetUrlContentTask().execute(sUrl)