Android实现下载图片并保存到SD卡中

我会带着你远行 2022-06-18 07:49 256阅读 0赞

1.java代码，下载图片的主程序

先实现显示图片，然后点击下载图片按钮，执行下载功能。

从网络上取得的图片，生成Bitmap时有两种方法，一种是先转换为byte\[\]，再生成bitmap；一种是直接用InputStream生成bitmap。

（1）ICS4.0及更高版本中的实现

4.0中不允许在主线程，即UI线程中操作网络，所以必须新开一个线程，在子线程中执行网络连接；然后在主线程中显示图片。

public class IcsTestActivity extends Activity { 
    
        private final static String TAG = "IcsTestActivity";
        private final static String ALBUM_PATH
                = Environment.getExternalStorageDirectory() + "/download_test/";
        private ImageView mImageView;
        private Button mBtnSave;
        private ProgressDialog mSaveDialog = null;
        private Bitmap mBitmap;
        private String mFileName;
        private String mSaveMessage;
    
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
    
            mImageView = (ImageView)findViewById(R.id.imgSource);
            mBtnSave = (Button)findViewById(R.id.btnSave);
    
            new Thread(connectNet).start();
    
            // 下载图片
            mBtnSave.setOnClickListener(new Button.OnClickListener(){
                public void onClick(View v) {
                    mSaveDialog = ProgressDialog.show(IcsTestActivity.this, "保存图片", "图片正在保存中，请稍等...", true);
                    new Thread(saveFileRunnable).start();
            }
            });
        }
    
        /** * Get image from newwork * @param path The path of image * @return byte[] * @throws Exception */
        public byte[] getImage(String path) throws Exception{
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5 * 1000);
            conn.setRequestMethod("GET");
            InputStream inStream = conn.getInputStream();
            if(conn.getResponseCode() == HttpURLConnection.HTTP_OK){
                return readStream(inStream);
            }
            return null;
        }
    
        /** * Get image from newwork * @param path The path of image * @return InputStream * @throws Exception */
        public InputStream getImageStream(String path) throws Exception{
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5 * 1000);
            conn.setRequestMethod("GET");
            if(conn.getResponseCode() == HttpURLConnection.HTTP_OK){
                return conn.getInputStream();
            }
            return null;
        }
        /** * Get data from stream * @param inStream * @return byte[] * @throws Exception */
        public static byte[] readStream(InputStream inStream) throws Exception{
            ByteArrayOutputStream outStream = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int len = 0;
            while( (len=inStream.read(buffer)) != -1){
                outStream.write(buffer, 0, len);
            }
            outStream.close();
            inStream.close();
            return outStream.toByteArray();
        }
    
        /** * 保存文件 * @param bm * @param fileName * @throws IOException */
        public void saveFile(Bitmap bm, String fileName) throws IOException {
            File dirFile = new File(ALBUM_PATH);
            if(!dirFile.exists()){
                dirFile.mkdir();
            }
            File myCaptureFile = new File(ALBUM_PATH + fileName);
            BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(myCaptureFile));
            bm.compress(Bitmap.CompressFormat.JPEG, 80, bos);
            bos.flush();
            bos.close();
        }
    
        private Runnable saveFileRunnable = new Runnable(){
            @Override
            public void run() {
                try {
                    saveFile(mBitmap, mFileName);
                    mSaveMessage = "图片保存成功！";
                } catch (IOException e) {
                    mSaveMessage = "图片保存失败！";
                    e.printStackTrace();
                }
                messageHandler.sendMessage(messageHandler.obtainMessage());
            }
    
        };
    
        private Handler messageHandler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                mSaveDialog.dismiss();
                Log.d(TAG, mSaveMessage);
                Toast.makeText(IcsTestActivity.this, mSaveMessage, Toast.LENGTH_SHORT).show();
            }
        };
    
        /* * 连接网络 * 由于在4.0中不允许在主线程中访问网络，所以需要在子线程中访问 */
        private Runnable connectNet = new Runnable(){
            @Override
            public void run() {
                try {
                    String filePath = "https://img-my.csdn.net/uploads/201211/21/1353511891_4579.jpg";
                    mFileName = "test.jpg";
    
                    //以下是取得图片的两种方法
                    方法1：取得的是byte数组, 从byte数组生成bitmap
                    byte[] data = getImage(filePath);
                    if(data!=null){
                        mBitmap = BitmapFactory.decodeByteArray(data, 0, data.length);// bitmap
                    }else{
                        Toast.makeText(IcsTestActivity.this, "Image error!", 1).show();
                    }
                    
    
                    //******** 方法2：取得的是InputStream，直接从InputStream生成bitmap ***********/
                    mBitmap = BitmapFactory.decodeStream(getImageStream(filePath));
                    //********************************************************************/
    
                    // 发送消息，通知handler在主线程中更新UI
                    connectHanlder.sendEmptyMessage(0);
                    Log.d(TAG, "set image ...");
                } catch (Exception e) {
                    Toast.makeText(IcsTestActivity.this,"无法链接网络！", 1).show();
                    e.printStackTrace();
                }
    
            }
    
        };
    
        private Handler connectHanlder = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                Log.d(TAG, "display image");
                // 更新UI，显示图片
                if (mBitmap != null) {
                    mImageView.setImageBitmap(mBitmap);// display image
                }
            }
        };
    
    }

main.xml文件，只有一个button和一个ImageView

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" >
        <Button android:id="@+id/btnSave" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="保存图片" />
        <ImageView android:id="@+id/imgSource" android:layout_width="wrap_content" android:layout_height="wrap_content" android:adjustViewBounds="true" />
    </LinearLayout>

3.在mainfest文件中增加互联网权限和写sd卡的权限

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