Android网络编程难题解析及解决策略

Android网络编程问题

一、Android网络编程基础

在Android中，网络编程主要依赖于HTTP协议进行数据的读写，为了简化网络请求的过程，Android提供了多种方法，如HttpURLConnection和第三方库如Retrofit、OkHttp等。

1. HttpURLConnection简介

HttpURLConnection是Java提供的一个用于发送HTTP请求的类，它支持GET和POST请求，可以用来与RESTful API进行交互。

2. 实现GET请求

以下是一个使用HttpURLConnection实现GET请求的示例：

权限配置：需要在AndroidManifest.xml中添加互联网权限。

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

创建请求：创建一个类来处理网络请求。

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
public class NetworkUtils {
    public static String getJsonData(String urlString) {
        StringBuilder result = new StringBuilder();
        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setConnectTimeout(5000);
            connection.setReadTimeout(5000);
            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String line;
                while ((line = reader.readLine()) != null) {
                    result.append(line);
                }
                reader.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result.toString();
    }
}

使用请求：可以在Activity中使用上面的方法来获取数据。

import android.os.Bundle;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView textView = findViewById(R.id.textView);
        new Thread(() -> {
            String jsonData = NetworkUtils.getJsonData("https://api.example.com/data");
            runOnUiThread(() -> textView.setText(jsonData));
        }).start();
    }
}

3. 实现POST请求

除了GET请求，我们同样可以使用HttpURLConnection进行POST请求，下面是一个简化的POST请求示例。

创建POST请求：

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
public class NetworkUtils {
    public static String postJsonData(String urlString, String jsonInputString) {
        StringBuilder result = new StringBuilder();
        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("POST");
            connection.setConnectTimeout(5000);
            connection.setReadTimeout(5000);
            connection.setDoOutput(true);
            connection.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
            OutputStream os = connection.getOutputStream();
            os.write(jsonInputString.getBytes("UTF-8"));
            os.close();
            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String line;
                while ((line = reader.readLine()) != null) {
                    result.append(line);
                }
                reader.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result.toString();
    }
}

二、使用网络框架连接后台数据并在APP中展示数据结果

在Android中，常用的网络框架有OkHttp和Retrofit，以下是使用OkHttp进行网络请求的示例。

安装网络框架环境：需要在项目的build.gradle文件中的dependencies代码块中添加OkHttp的依赖。

implementation 'com.squareup.okhttp3:okhttp:4.9.0'

使用网络框架连接后台数据并在APP中展示数据结果：在onCreate方法中，初始化有关变量，并定义按钮的点击事件监听函数及定义Handler对象重写其用来接受子线程消息的handleMessage方法，及主线程UI修改主界面的方法。

private EditText et_url;
private TextView tv_source;
private Context mContext;
private Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        String result = (String)msg.obj;
        tv_source.setText(result);
    }
};
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mContext = this;
    et_url = (EditText) findViewById(R.id.et_url);
    Button bt_looksource = (Button) findViewById(R.id.bt_looksource);
    tv_source = (TextView) findViewById(R.id.tv_source);
    bt_looksource.setOnClickListener(this);
}
@Override
public void onClick(View view) {
    final String url_str = et_url.getText().toString().trim();
    if(TextUtils.isEmpty(url_str)){
        Toast.makeText(mContext,"url不能为空",Toast.LENGTH_SHORT).show();
        return ;
    }
    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                OkHttpClient client = new OkHttpClient();
                Request request = new Request.Builder()
                        .url(url_str)
                        .build();
                Response response = client.newCall(request).execute();
                if (response.isSuccessful()) {
                    String str = response.body().string();
                    Message msg = new Message();
                    msg.obj = str;
                    handler.sendMessage(msg);
                } else {
                    Message msg = new Message();
                    msg.obj = "请求失败";
                    handler.sendMessage(msg);
                }
            } catch (IOException e) {
                e.printStackTrace();
            ]