Android实现下载图片并保存到SD卡中

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 = "http://img.my.csdn.net/uploads/201402/24/1393242467_3999.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            }        }    };}

（2）2.3以及以下版本可以在主线程中操作网络连接，但最好不要这样做，因为连接网络是阻塞的，如果5秒钟还没有连接上，就会引起ANR。

public class AndroidTest2_3_3 extends Activity {private final static String TAG = "AndroidTest2_3_3"; private final static String ALBUM_PATH = Environment.getExternalStorageDirectory() + "/download_test/"; private ImageView imageView; private Button btnSave; private ProgressDialog myDialog = null; private Bitmap bitmap; private String fileName; private String message; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); imageView = (ImageView)findViewById(R.id.imgSource); btnSave = (Button)findViewById(R.id.btnSave); String filePath = "http://hi.csdn.net/attachment/201105/21/134671_13059532779c5u.jpg"; fileName = "test.jpg"; try { //////////////// 取得的是byte数组, 从byte数组生成bitmap byte[] data = getImage(filePath); if(data!=null){ bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);// bitmap imageView.setImageBitmap(bitmap);// display image }else{ Toast.makeText(AndroidTest2_3_3.this, "Image error!", 1).show(); } //////////////////////////////////////////////////////// //******** 取得的是InputStream，直接从InputStream生成bitmap ***********/ bitmap = BitmapFactory.decodeStream(getImageStream(filePath)); if (bitmap != null) { imageView.setImageBitmap(bitmap);// display image } //********************************************************************/ Log.d(TAG, "set image ..."); } catch (Exception e) { Toast.makeText(AndroidTest2_3_3.this,"Newwork error!", 1).show(); e.printStackTrace(); } // 下载图片 btnSave.setOnClickListener(new Button.OnClickListener(){ public void onClick(View v) { myDialog = ProgressDialog.show(AndroidTest2_3_3.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(bitmap, fileName); message = "图片保存成功！"; } catch (IOException e) { message = "图片保存失败！"; e.printStackTrace(); } messageHandler.sendMessage(messageHandler.obtainMessage()); } }; private Handler messageHandler = new Handler() { @Override public void handleMessage(Message msg) { myDialog.dismiss(); Log.d(TAG, message); Toast.makeText(AndroidTest2_3_3.this, message, Toast.LENGTH_SHORT).show(); } };}

 

下载进度条的可以参考我的另外一个帖子：Android更新下载进度条

 

2.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" > <Buttonandroid:id="@+id/btnSave" android:layout_width="wrap_content" android:layout_height="wrap_content"android:text="保存图片" /><ImageViewandroid: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"/>

4.预览图：

注：本实例图片是本人拍摄的位于东京西郊美军横田基地的一个大门。

横田基地的图片已经删除，所以无法加载。更新了我空间相册的另外一张图，此图较小，所以保存时很快，“图片正在保存中，请稍等...”的画面会一闪而过。

在4.2.1魅族mx3真机上验证如下：