Android基础——网络编程

松仔log

已于 2025-03-01 00:52:48 修改

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分类专栏： # Android基础文章标签： android 网络 java android studio

于 2021-07-29 15:53:25 首次发布

本文链接：https://blog.youkuaiyun.com/qq_35258036/article/details/119182292

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网络编程

网络编程是什么?
WebView
HttpURLConnection访问网络
HttpURLConnection最佳用法

网络编程是什么?

网络编程指Android系统使用http协议和服务器交互，以传输或获取相关数据。

WebView

Web控件可以让我们在应用程序中嵌入浏览器，展示网页信息。

修改activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <WebView
        android:id="@+id/web_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>

声明权限：

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

修改MainActivity：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        WebView webView=findViewById(R.id.web_view);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.setWebViewClient(new WebViewClient());
        webView.loadUrl("https://www.baidu.com");

    }
}

HttpURLConnection访问网络

修改activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/send_request"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="send_request" />

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/response_text"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </ScrollView>

</LinearLayout>

声明权限：

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

修改MainActivity

通过地址创建URL调用openConnection()方法获取HttpURLConnection实例，设置相关参数
通过getInputStream()方法获取到返回的数据流并读取解析
finally调用disconnect()关闭连接

public class MainActivity extends AppCompatActivity {

    private TextView responseText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        responseText = findViewById(R.id.response_text);
        Button sendRequest = findViewById(R.id.send_request);
        sendRequest.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sendRequestWithHttpURLConnection();
            }
        });

    }

    private void sendRequestWithHttpURLConnection() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                BufferedReader reader = null;
                try {
                    URL url = new URL("https://www.baidu.com");
                    connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(8000);
                    connection.setReadTimeout(8000);
                    InputStream inputStream = connection.getInputStream();

                    reader = new BufferedReader(new InputStreamReader(inputStream));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        response.append(line);
                    }
                    showResponse(response.toString());
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (reader != null) {
                        try {
                            reader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (connection != null) {
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }

    private void showResponse(final String toString) {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                responseText.setText(toString);
            }
        });
    }
}

若要向服务器提交数据，则使用POST：

connection.setRequestMethod("POST");
DataOutputStream outputStream=new DataOutputStream(connection.getOutputStream());
outputStream.writeBytes("username=admin&password=123456");

Tips:

Android不允许在子线程中进行UI操作，需要调用runOnUiThread()方法将线程切换到主线程
Android28以后不允许明文访问网址，可在Mainfest的application设置android:usesCleartextTraffic=“true” 或设置networkSecurityConfig指定类似如下的配置文件

    <?xml version="1.0" encoding="utf-8"?>
    <network-security-config>
        <domain-config cleartextTrafficPermitted="false">
            <domain includeSubdomains="true">secure.example.com</domain>
        </domain-config>
    </network-security-config>

HttpURLConnection最佳用法

一个程序可能在很多地方都需要用到网络，而请求网络的代码是相同的，为避免重复书写代码，我们可以将这部分代码抽出来作为工具类HttpURLConnectionUtil，当需要访问网络时输入地址即可返回数据：

public class HttpURLConnectionUtil {
    public static String sendHttpRequest(String address) {
        HttpURLConnection connection = null;
        try {
            URL url = new URL(address);
            connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setConnectTimeout(8000);
            connection.setReadTimeout(8000);
            connection.setDoInput(true);
            connection.setDoOutput(true);
            InputStream inputStream = connection.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            StringBuilder response = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            return response.toString();
        } catch (Exception e) {
            e.printStackTrace();
            return e.getMessage();
        } finally {
            if (connection != null) {
                connection.disconnect();
            }
        }
    }
}

但存在以下问题:

网络属于耗时操作，但sendHttpRequest()方法内并没有开启线程，这样有可能被主线程阻塞
但如果在sendHttpRequest()方法内开启线程，可能在服务器还没来得及响应，方法就已经结束了，导致数据无法返回
子线程无法通过return返回数据

解决办法是利用回调机制，定义接口：

public interface HttpURLConnectionCallback {
    void onFinish(String response);
    void onError(Exception e);
}

修改HttpURLConnectionUtil，加入HttpURLConnectionCallback作为参数：

public class HttpURLConnectionUtil {
    public static void sendHttpRequest(final String address, final HttpURLConnectionCallback callback) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                try {
                    URL url = new URL(address);
                    connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(8000);
                    connection.setReadTimeout(8000);
                    connection.setDoInput(true);
                    connection.setDoOutput(true);
                    InputStream inputStream = connection.getInputStream();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        response.append(line);
                    }
                    if (callback != null) {
                        callback.onFinish(response.toString());
                    }
                } catch (Exception e) {
                    if (callback != null) {
                        callback.onError(e);
                    }
                } finally {
                    if (connection != null) {
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }
}

当使用时，通过onFinish()方法返回数据，onError()方法处理异常：

HttpURLConnectionUtil.sendHttpRequest("https://www.baidu.com", new HttpURLConnectionCallback() {
            @Override
            public void onFinish(String response) {
                
            }

            @Override
            public void onError(Exception e) {

            }
        });

此外，还可以使用开源库OkHttp访问网络.