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 = "//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
            }
        }
    };

}

（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"
    >
    <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"/>

4.预览图：

转：http://blog.csdn.net/ameyume/article/details/6528205