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 = "";
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 = "";
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();
}
};
}
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：
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：
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