android 下载文件，file的读写应用

朴灿烈づ我的快乐病毒、 2022-07-14 12:37 175阅读 0赞

先看代码：

public class MainActivity extends AppCompatActivity {
    
        String TAG = MainActivity.class.getCanonicalName();
        private ImageView imageview;
        private Button load;
    
        String path = "http://img06.tooopen.com/images/20161120/tooopen_sl_187242346264.jpg";
    
        private Bitmap bitmap;
        private File picfile;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            imageview = (ImageView) findViewById(R.id.imageview);
            load = (Button) findViewById(R.id.btn_load);
            load.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    File file = createPicfile();
                    if (null != file){
    
                        String absolutePath = file.getAbsolutePath();
                        Log.e(TAG, "onClick: "+absolutePath );
                        String filepath = absolutePath+getFilePath(path);
                        Log.e(TAG, "onClick: "+filepath );
                        picfile = new File(filepath);
                        if (picfile.exists()){
                            Log.e(TAG, "onClick: "+"文件存在" );
    
                            bitmap = BitmapFactory.decodeFile(picfile.getAbsolutePath());
                            if (null != bitmap){
                                Message msg = Message.obtain();
                                msg.what =2;
                                handler.sendMessage(msg);
                            }else {
                                Log.e(TAG, "onClick: "+"文件下载错误" );
                            }
    
                        }else {
                            Log.e(TAG, "onClick: "+"文件不存在" );
                            try {
                                picfile.createNewFile();
                                new Thread(new Runnable() {
                                    @Override
                                    public void run() {
                                        loadpicture(picfile,path);
                                    }
                                }).start();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
    
                        }
    
                    }else {
                        Log.e(TAG, "createPicfile: "+"没有sd卡" );
                    }
    
                }
            });
        }
    
        private void loadpicture(File picfile, String path) {
            try {
                FileOutputStream fos = new FileOutputStream(picfile);
                URL url = new URL(path);
                HttpURLConnection httpconn = (HttpURLConnection) url.openConnection();
                httpconn.setConnectTimeout(5000);
                httpconn.setRequestMethod("GET");
                int code = httpconn.getResponseCode();
                if (HttpURLConnection.HTTP_OK == code){
                    Log.e(TAG, "loadpicture: "+"正在下载、、、、" );
                    Log.e(TAG, "loadpicture: "+"下载文件大小:"+ httpconn.getContentLength());
                    InputStream is = httpconn.getInputStream();
                    byte[] buff = new byte[512];
                    int len ;
    
                    while((len = (is.read(buff))) != -1){          //刚开始时把while写成if，只会运行一次
                        fos.write(buff,0,len);
    
                    }
                    is.close();
                    fos.flush();
                    fos.close();
                    Log.e(TAG, "loadpicture: "+"下载完成、、" );
    
                    bitmap = BitmapFactory.decodeFile(picfile.getAbsolutePath());
                    if (null != bitmap) {
                        Message msg = Message.obtain();
                        msg.what = 1;
                        handler.sendMessage(msg);
                    }
                }
    
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    
        private String getFilePath(String path) {
            if (null != path){
                StringBuilder builder = new StringBuilder(path.trim());
    
                int i = builder.lastIndexOf("/");
                String filepath = builder.substring(i);
                return filepath;
            }else {
                return null;
            }
        }
    
        private File createPicfile() {
            if (Environment.getExternalStorageState().equals(Environment.getExternalStorageState())){
                String s = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Picture";
                File file = new File(s);
                if (!file.exists()){
                    file.mkdir();
                }
                return file;
            }else {
                Log.e(TAG, "createPicfile: "+"没有sd卡" );
            }
            return null;
        }
    
        Handler handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
    
                if (msg.what == 1){
                    imageview.setImageBitmap(bitmap);
                    Log.e(TAG, "handleMessage: "+"网络下载图片显示 ");
                }
                if (msg.what == 2){
                    imageview.setImageBitmap(bitmap);
                    Log.e(TAG, "handleMessage: "+"本地获取图片显示" );
                }
    
            }
        };
    }
    
    记得加权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <uses-permission android:name="android.permission.INTERNET"/>
    
    demo下载地址：https://github.com/renjiemei1225/LoadImageAndSave