1. 使用HttpURLConnection发起GET请求并解析响应

HttpURLConnection GET 请求的核心链路

在 Android 中发起一次 GET 请求，本质上是把「权限声明 → 后台线程 → 建立连接 → 读取响应 → 更新 UI」串成一条完整链路。HttpURLConnection 本身是同步阻塞 API，因此必须放在工作线程中执行，否则会触发 NetworkOnMainThreadException。

关键实现代码

下面是一个完整可运行的 GET 请求方法，包含权限检查、线程切换、响应码判断和响应体读取：

// AndroidManifest.xml 中声明
// <uses-permission android:name="android.permission.INTERNET" />

public class HttpGetTask {

    private static final String TAG = "HttpGetTask";

    /**
     * 在后台线程发起 GET 请求，通过回调返回结果
     */
    public static void doGet(final String urlStr, final Callback callback) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection conn = null;
                try {
                    URL url = new URL(urlStr);
                    conn = (HttpURLConnection) url.openConnection();
                    conn.setRequestMethod("GET");
                    conn.setConnectTimeout(5000);
                    conn.setReadTimeout(5000);

                    int responseCode = conn.getResponseCode();
                    Log.d(TAG, "响应码: " + responseCode);

                    if (responseCode == HttpURLConnection.HTTP_OK) {
                        // 读取响应体
                        InputStream is = conn.getInputStream();
                        BufferedReader reader = new BufferedReader(
                                new InputStreamReader(is, "UTF-8"));
                        StringBuilder sb = new StringBuilder();
                        String line;
                        while ((line = reader.readLine()) != null) {
                            sb.append(line).append("\n");
                        }
                        reader.close();
                        is.close();

                        final String body = sb.toString().trim();
                        callback.onSuccess(responseCode, body);
                    } else {
                        callback.onError(responseCode, "HTTP " + responseCode);
                    }

                } catch (IOException e) {
                    Log.e(TAG, "请求失败", e);
                    callback.onError(-1, e.getMessage());
                } finally {
                    if (conn != null) {
                        conn.disconnect();
                    }
                }
            }
        }).start();
    }

    public interface Callback {
        void onSuccess(int code, String body);
        void onError(int code, String message);
    }
}

在 Activity 中调用并更新 UI

public class MainActivity extends AppCompatActivity {

    private TextView tvResult;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tvResult = findViewById(R.id.tv_result);

        HttpGetTask.doGet("https://httpbin.org/get", new HttpGetTask.Callback() {
            @Override
            public void onSuccess(final int code, final String body) {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tvResult.setText("响应码: " + code + "\n\n" + body);
                    }
                });
            }

            @Override
            public void onError(final int code, final String message) {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tvResult.setText("请求失败: " + message);
                    }
                });
            }
        });
    }
}

响应码与处理策略对照