Android 下载服务器上的文件

申请权限

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

API大于6.0时主动申请权限

public static void ApplyPermission(Context context) {         ActivityCompat.requestPermissions((Activity) context, new String[]{                 Manifest.permission.CAMERA,            Manifest.permission.READ_EXTERNAL_STORAGE,            Manifest.permission.WRITE_EXTERNAL_STORAGE,            Manifest.permission.INTERNET    }, 1);}

添加okhttp依赖

implementation 'com.squareup.okhttp3:okhttp:3.10.0'

下载文件工具类

public class DownloadUtil {         private static DownloadUtil downloadUtil;    private final OkHttpClient okHttpClient;    public static DownloadUtil get() {             if (downloadUtil == null) {                 downloadUtil = new DownloadUtil();        }        return downloadUtil;    }    public DownloadUtil() {             okHttpClient = new OkHttpClient();    }    /**     * @param url          下载连接     * @param destFileDir  下载的文件储存目录     * @param destFileName 下载文件名称     * @param listener     下载监听     */    public void download(final String url, final String destFileDir, final String destFileName, final OnDownloadListener listener) {             Request request = new Request.Builder()                .url(url)                .build();        OkHttpClient client = new OkHttpClient();        try {                 Response response = client.newCall(request).execute();        } catch (IOException e) {                 e.printStackTrace();        }        //异步请求        okHttpClient.newCall(request).enqueue(new Callback() {                 @Override            public void onFailure(Call call, IOException e) {                     // 下载失败监听回调                listener.onDownloadFailed(e);            }            @Override            public void onResponse(Call call, Response response) throws IOException {                     InputStream is = null;                byte[] buf = new byte[2048];                int len = 0;                FileOutputStream fos = null;                //储存下载文件的目录                File dir = new File(destFileDir);                if (!dir.exists()) {                         dir.mkdirs();                }                File file = new File(dir, destFileName);                try {                         is = response.body().byteStream();                    long total = response.body().contentLength();                    fos = new FileOutputStream(file);                    long sum = 0;                    while ((len = is.read(buf)) != -1) {                             fos.write(buf, 0, len);                        sum += len;                        int progress = (int) (sum * 1.0f / total * 100);                        //下载中更新进度条                        listener.onDownloading(progress);                    }                    fos.flush();                    //下载完成                    listener.onDownloadSuccess(file);                } catch (Exception e) {                         listener.onDownloadFailed(e);                }finally {                         try {                             if (is != null) {                                 is.close();                        }                        if (fos != null) {                                 fos.close();                        }                    } catch (IOException e) {                         }                }            }        });    }    public interface OnDownloadListener{             //下载成功之后的文件        void onDownloadSuccess(File file);        //下载进度        void onDownloading(int progress);        //下载异常信息        void onDownloadFailed(Exception e);    }}

使用

DownloadUtil.get().download("http://47.112.96.171:8081/in/test.html", "/mnt/sdcard/", "test.html",        new  DownloadUtil.OnDownloadListener() {                 @Override            public void onDownloadSuccess(File file) {                     Log.e("---------", "onDownloadSuccess");            }            @Override            public void onDownloading(int progress) {                     Log.e("---------", "onDownloading");            }            @Override            public void onDownloadFailed(Exception e) {                     Log.e("---------", "onDownloadFailed" + e.getMessage());            }        });

NetworkOnMainThreadException异常
解决：网络耗时请求要放在子线程中

Handler handler = new Handler() {         @Override    public void handleMessage(Message msg) {             super.handleMessage(msg);        Bundle data = msg.getData();        String val = data.getString("value");        Log.i("mylog", "请求结果为-->" + val);        // TODO        // UI界面的更新等相关操作    }};/** * 网络操作相关的子线程 */Runnable networkTask = new Runnable() {         @Override    public void run() {             // TODO        // 在这里进行 http request.网络请求相关操作        DownloadUtil.get().download("http://47.112.96.171:8081/in/test.html", "/mnt/sdcard/", "test.html",                new  DownloadUtil.OnDownloadListener() {                         @Override                    public void onDownloadSuccess(File file) {                             Log.e("---------", "onDownloadSuccess");                    }                    @Override                    public void onDownloading(int progress) {                             Log.e("---------", "onDownloading");                    }                    @Override                    public void onDownloadFailed(Exception e) {                             Log.e("---------", "onDownloadFailed" + e.getMessage());                    }                });    }};//调用new Thread(networkTask).start();

communication to … not permitted by network security policy异常
网络安全策略不允许与 www…com之间进行明文通信
原因：Android P以后限制了非加密的流量请求

解决方案：

在res目录下创建xml文件夹，新建文件network_security_config.xml
在文件中输入以下内容：

<?xml version="1.0" encoding="utf-8"?><network-security-config>    <base-config cleartextTrafficPermitted="true" /></network-security-config>

在AndroidManifest中的application里添加你新建的 xml文件

<application        ****        android:networkSecurityConfig="@xml/network_security_config"        **** >

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