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网络操作

Android平台下的原生网络操作可以分为以下几步：

1. 创建URL对象；
2. 通过URL对象获取HttpURLConnection对象；
3. 通过HttpURLConnection对象设置请求头键值对、网络连接超时时间等；
4. 通过HttpURLConnection对象的connect()方法建立网络连接；
5. 通过响应码判断请求是否成功，如果成功的话获取输入流，对返回的结果进行处理并显示；
   这里要注意的是，网络请求操作不能直接放在ui线程中，需要另外开启一个线程去处理网络请求，因为网络请求操作是一个耗时的操作。

布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MainActivity"android:orientation="vertical"><Buttonandroid:id="@+id/btn_sendget"android:layout_width="match_parent"android:layout_height="wrap_content"android:text="点击发送get请求"/><Buttonandroid:id="@+id/btn_sendpost"android:layout_width="match_parent"android:layout_height="wrap_content"android:text="点击发送post请求"/><TextViewandroid:id="@+id/tv"android:layout_width="match_parent"android:layout_height="wrap_content"android:scrollbars="vertical"android:fadeScrollbars="false"/></LinearLayout>

GET请求

这里说一下用到的方法的作用：
setConnectTimeout：设置请求超时时间；
setRequestMethod：设置请求方法；
setRequestProperty：设置请求属性；
connect()：建立网络连接；
getResponseCode()：获取响应码；

 try {new Thread(new Runnable() {@Overridepublic void run() {try {URL url = new URL("http://www.imooc.com/api/teacher?type=2&page=1");HttpURLConnection connection = (HttpURLConnection)url.openConnection();connection.setConnectTimeout(30*1000);connection.setRequestMethod("GET");connection.setRequestProperty("Content-Type","application/json");connection.setRequestProperty("Charset","UTF-8");connection.setRequestProperty("Accept-Charset","UTF-8");connection.connect();int responseCode = connection.getResponseCode();//如果请求成功if (responseCode == HttpURLConnection.HTTP_OK) {//获取输入流InputStream inputStream = connection.getInputStream();byte[] bytes = new byte[1024];StringBuffer result = new StringBuffer();int len = 0;while ((len = inputStream.read(bytes)) != -1) {result.append(new String(bytes,0,len));}//不能直接在其它线程更新ui线程，可以使用此方法或者使用handlerrunOnUiThread(new Runnable() {@Overridepublic void run() {tv.setText(result);}});Log.d(TAG, "onClick: " + result);}}catch (Exception e) {e.printStackTrace();}}}).start();} catch (Exception e) {e.printStackTrace();}

POST请求

 new Thread(new Runnable() {@Overridepublic void run() {try {URL url = new URL("http://www.imooc.com/api/teacher?type=2&page=1");HttpURLConnection connection = (HttpURLConnection) url.openConnection();connection.setConnectTimeout(30 * 1000);connection.setRequestProperty("Content-Type","application/json");connection.setRequestProperty("Charset","UTF-8");connection.setRequestProperty("Accept-Charset","UTF-8");connection.connect();int responseCode = connection.getResponseCode();if (responseCode == HttpURLConnection.HTTP_OK) {InputStream inputStream = connection.getInputStream();int  len = 0;byte[] bytes = new byte[1024];StringBuffer result = new StringBuffer();while ((len = inputStream.read(bytes)) != -1) {result.append(new String(bytes,0,len));}Log.d(TAG, "responseCode: " + responseCode);Log.d(TAG, "result: " + result);runOnUiThread(new Runnable() {@Overridepublic void run() {tv.setText(result);}});} else {Log.d(TAG, "responseCode: " + responseCode);}} catch (MalformedURLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}}).start();

解析返回的json数据

 public List<Lesson> JsonToArray(String str) {List<Lesson> lessonList = new ArrayList<>();try {JSONObject jsonObject = new JSONObject(str);JSONArray jsonArray = jsonObject.getJSONArray("data");for (int i = 0; i < jsonArray.length(); i++) {JSONObject lesson = (JSONObject) jsonArray.get(i);int id = lesson.getInt("id");int learner = lesson.getInt("learner");String name = lesson.getString("name");String picSmall = lesson.getString("picSmall");String picBig = lesson.getString("picBig");String description = lesson.getString("description");Lesson lesson1 = new Lesson();lesson1.setId(id);lesson1.setDescription(description);lesson1.setLearner(learner);lesson1.setPicBig(picBig);lesson1.setPicSmall(picSmall);lesson1.setName(name);lessonList.add(lesson1);}} catch (JSONException e) {e.printStackTrace();}return lessonList;}

注意事项

Android9.0以后，使用http访问网络需要添加配置文件；首先在res目录下新建一个xml资源目录，然后创建配置文件，配置文件的名称必须是neteork_security_config.xml；
内容：

<?xml version="1.0" encoding="utf-8"?>
<network-security-config><!--允许http请求的加载--><base-config cleartextTrafficPermitted = "true"/>
</network-security-config>