Android http 部分问题解决方案

前言

最近老板给了个小任务，要求写一个android功能模块，用于校友信息查询。

需要用到简单的 http post向后端请求数据。

踩了几个坑，查了许多博客，总算是写完了。

代码

Talk is cheap, show me the code.

AndroidManifest.xml 授予权限

<manifest --->
    ---
    <!-- 授予权限 -->
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    ---
</manifest>

布局文件 activity_main.xml 生成一个按钮

<LinearLayout>
    ---
    <Button
    	android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_search"
        android:onClick="searchName" />
    ---
</LinearLayout>

MainActivity.java

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView)findViewById(R.id.name_message);
    }
    
    /** Called when the user clicks the Search button */
    public void searchName(View view){
        // Get the message of name in response to button
        EditText editText = (EditText) findViewById(R.id.edit_name);
        final String name = editText.getText().toString();

        //check the available of internet
        ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        // fetch data
        //开发机（后端）ip 10.0.2.2
        Log.d("test","Internet connected.");
        post("http://10.0.2.2:8080/android/",name);//此处使用了http链接，则targetSdkVersion不能超过27，否则应改用https链接
    }
    
    /** Post the name to the server */
    public void post(final String ur, final String name){
        Log.d("test","Into the function named post.");
        final Handler handler = new Handler();
        new Thread() {//注意此处 在Android4.0以后，网络请求需要开子线程，否则报错
            @Override
            public void run(){
                Log.d("test","Thread running.");
                try {
                    URL url = new URL(ur);
                    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                    Log.d("test","Create http connection.");
                    connection.setConnectTimeout(3000);
                    connection.setRequestMethod("POST");
                    connection.setDoInput(true);
                    connection.setDoOutput(true);
                    connection.setUseCaches(false);
                    //添加header参数
                    connection.setRequestProperty("Accept-Charset","UTF-8");
                    connection.setRequestProperty("Content-Type","application/x-www-form-urlencoded");
                    Log.d("test", "connection setting over.");
                    connection.connect();
                    Log.d("test","HttpConnected.");
                    DataOutputStream outputStream = new DataOutputStream(connection.getOutputStream());
                    //添加body参数
                    //如有多个参数用&隔开
                    //如"name=" + name + "&age=" + age;
                    String content = "name=" + name;
                    outputStream.writeBytes(content);
                    outputStream.flush();
                    outputStream.close();

                    //接受数据
                    if(connection.getResponseCode()==HttpURLConnection.HTTP_OK){
                        // 获取来自网络的输入流
                        // 使用缓冲字符输入流
                        // 字节流转字符流
                        BufferedReader br = null;
                        br = new BufferedReader(new InputStreamReader(connection.getInputStream()));

                        json="";
                        // 使用缓冲流读取到的每一行数据
                        String line = "";

                        while ((line = br.readLine()) != null) {
                            json += line.trim();
                        }

                        Log.d("test","Receive " + json);

                        // json数据产生完毕，该解析了
						//由于子线程中不能安全的操作TextView
                        //故采用此法将服务器返回的数据显示于TextView
                        handler.post(runnableUi);
                    }
                } catch (MalformedURLException e) {
                    Log.d("test","url error.");
                    e.printStackTrace();
                } catch (IOException e) {
                    Log.d("test","io error.");
                    e.printStackTrace();
                }
            }
        }.start();
    }
    Runnable runnableUi = new Runnable(){
        @Override
        public void run() {
            //更新界面
            textView.setText(json);
        }
    };
}

坑

• 权限问题

  注意在AndroidManifest.xml中加入如下语句

  <uses-permission android:name="android.permission.INTERNET" />
  

• 线程问题

  Android4.0（sdk 14）以后，网络请求 需要开子线程，否则报错

• 明文链接问题

  sdk 28 以后，Android禁止使用明文链接（http）

  故而targetSdkVersion不得超过27 或 后端改用https