我正在尝试使用Google Example Page从网址下载图片。当我在BitmapFactory.decodeStream方法中使用InputStream时，我read，我不能使用两次。我试图这样做，但它不起作用'因为它在解码图像中返回null，我不知道我能做什么。
这是我的代码：
这部分是AsyncTask类中的doInBackground方法
Bitmap bitmapImage;
URL imageUrl = null;
try {
imageUrl = new URL(url[0]);
HttpGet httpRequest = null;
httpRequest = new HttpGet(imageUrl.toURI());
HttpClient httpclient = new DefaultHttpClient();
HttpResponse response = (HttpResponse) httpclient.execute(httpRequest);
HttpEntity entity = response.getEntity();
BufferedHttpEntity bufHttpEntity = new BufferedHttpEntity(entity);
InputStream instream = bufHttpEntity.getContent();
bitmapImage = CommonMethods.decodeSampledBitmapFromResource(instream, thumb_width, thumb_width);
instream.close();
return bitmapImage;
} catch (URISyntaxException e) {
e.printStackTrace();
return null;
} catch (MalformedURLException e) {
e.printStackTrace();
return null;
} catch (IOException e) {
e.printStackTrace();
return null;
}
public static Bitmap decodeSampledBitmapFromResource(InputStream instream,
int reqWidth, int reqHeight) throws IOException {
//Copy instream for decode twice
ByteArrayOutputStream out = new ByteArrayOutputStream();
copy(instream,out);
ByteArrayInputStream instream2 = new ByteArrayInputStream(out.toByteArray());
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(instream, null, options);
instream2.close();
options.inJustDecodeBounds = false;
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
return BitmapFactory.decodeStream(instream, null, options);
}
public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float) height / (float) reqHeight);
} else {
inSampleSize = Math.round((float) width / (float) reqWidth);
}
}
return inSampleSize;
}
//Copy instream method
public static void copy(InputStream input, OutputStream output) throws IOException{
byte[] buffer = new byte[Constants.IO_BUFFER_SIZE];
int n = 0;
while (-1 != (n = input.read(buffer))) {
output.write(buffer, 0, n);
}
}
答案 0 :(得分：5)
BitmapFactory.decodeStream返回null，因为输入流被使用了两次，我没有尝试过你的代码，但它接缝正常，或者我错了。 无论如何，我有一个更好的解决方案。只需使用BufferedInputStream包装inputStream，在第二次读取之前，调用＆＃34; reset＆＃34;第一。注意普通的inputStreams不支持＆＃34; reset＆＃34;，你可以调用它但不会发生任何事情。 我的代码：
public static Bitmap decodeSampledBitmapFromStream(InputStream inputStream,
int reqWidth, int reqHeight)
throws IOException {
if (!widthHeightCheck(reqWidth, reqHeight))
return BitmapFactory.decodeStream(inputStream);
// First decode with inJustDecodeBounds=true to check dimensions
if (!(inputStream instanceof BufferedInputStream)) {
inputStream = new BufferedInputStream(inputStream);
}
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
Rect rect = new Rect(-1, -1, -1, -1);
BitmapFactory.decodeStream(inputStream, rect, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
inputStream.reset();
return BitmapFactory.decodeStream(inputStream, rect, options);
}
答案 1 :(得分：1)
我认为您可以通过在自定义WrappedStream中包装从httpEntity获取的流来实现此目的。此WrappedStream将在读取原始流时提供第二个输入流。 （这是用PipedStream完成的）
使用此代码获取图像大小后：
options.inJustDecodeBounds = true;
WrappedStream wrappedStream = new WrappedStream(instream);
BitmapFactory.decodeStream(wrappedStream, null, options);
你可以打电话
InputStream reReadStream = wrappedStream.getReReadStream();
options.inJustDecodeBounds = false;
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
return BitmapFactory.decodeStream(reReadStream, null, options);
最后，这里是WrappedStream的实现（它只是将所有调用委托给包装的inputStream，并在pipedOutputStream中写入所有读取（或跳过）的字节）
import java.io.IOException;
import java.io.InputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
/** Simple class wrapping an InputStream and feeding a secondary InputStream
* to re-read the data that was originally available in the inputStream.
**/
public class WrappedStream extends InputStream {
private InputStream urlStream;
private PipedOutputStream pipedStream;
public WrappedStream(InputStream urlStream) {
this.urlStream = urlStream;
this.pipedStream = new PipedOutputStream();
}
/**
* return a fresh InputStream to re-read the data
*/
public InputStream getReReadStream() throws IOException {
return new PipedInputStream(pipedStream);
}
@Override
public int available() throws IOException {
return urlStream.available();
}
@Override
public void close() throws IOException {
urlStream.close();
}
@Override
public void mark(int readlimit) {
urlStream.mark(readlimit);
}
@Override
public boolean markSupported() {
return urlStream.markSupported();
}
@Override
public int read() throws IOException {
int b = urlStream.read();
pipedStream.write(b);
return b;
}
@Override
public int read(byte[] buffer) throws IOException {
int l = urlStream.read(buffer);
pipedStream.write(buffer);
return l;
}
@Override
public int read(byte[] buffer, int offset, int length) throws IOException {
int l = urlStream.read(buffer, offset, length);
pipedStream.write(buffer, offset, length);
return l;
}
@Override
public void reset() throws IOException {
urlStream.reset();
}
@Override
//bytes skipped must available on the re-read stream so we read and write them.
public long skip(long byteCount) throws IOException {
long bytesToSkip = byteCount;
long skippedBytes = 0;
//ugly trick required to not loosing bytes if we ever skip more than Integer.MAX_VALUE bytes
while(bytesToSkip>Integer.MAX_VALUE){
_skip(Integer.MAX_VALUE);
bytesToSkip -=Integer.MAX_VALUE;
skippedBytes +=Integer.MAX_VALUE;
}
byte[] b = new byte[(int)bytesToSkip];
skippedBytes += read(b);
return skippedBytes;
}
private int _skip(int byteCount) throws IOException {
byte[] b = new byte[(int)byteCount];
return read(b);
}
}
请注意，我没有测试此代码。这只是为了给你一些如何解决问题的想法。
另一点：即使此代码永远不会创建一个巨大的位图，整个流将保留在内存中，直到构建缩放的位图。
答案 2 :(得分：0)
这是从服务器下载位图的方法，只需更少的代码即可满足您的要求
Bitmap downloadBitmap(String url)
{
Bitmap image = null;
InputStream in = null;
try
{
in = new java.net.URL(url).openStream();
BitmapFactory.Options opts = new BitmapFactory.Options();
opts.inSampleSize = 2;
image = BitmapFactory.decodeStream(new FlushedInputStream(in),null,opts);
in.close();
}
catch (MalformedURLException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
return image;
}
在上面的代码中我们使用 opts.inSampleSize = 2; 这意味着位图将缩小到原始大小的一半，以避免内存异常，如果我们要加载大量图像，我们必须这样做
其中使用的其他一些课程
static class FlushedInputStream extends FilterInputStream
{
public FlushedInputStream( InputStream inputStream )
{
super(inputStream);
}
@Override
public long skip(long n) throws IOException
{
long totalBytesSkipped = 0L;
while (totalBytesSkipped < n)
{
long bytesSkipped = in.skip(n - totalBytesSkipped);
if (bytesSkipped == 0L)
{
int byte1 = read();
if (byte1 < 0)
{
break; // we reached EOF
}
else
{
bytesSkipped = 1; // we read one byte
}
}
totalBytesSkipped += bytesSkipped;
}
return totalBytesSkipped;
}
}
答案 3 :(得分：0)
找到适合你的代码
final HttpEntity entity = response.getEntity();
if (entity != null) {
InputStream inputStream = null;
try {
inputStream = entity.getContent();
BitmapFactory.Options options = new BitmapFactory.Options();
//options.inSampleSize = 2;
final Bitmap bitmap = BitmapFactory
.decodeStream(inputStream, null, options);
return bitmap;
} catch (Exception e) {
e.printStackTrace();
} finally {
if (inputStream != null) {
inputStream.close();
}
entity.consumeContent();
}
}
请替换正确的变量，如果您想缩放图像，可以在获取位图后缩放图像。
答案 4 :(得分：0)
请使用以下代码下载并将图像显示到imageview。
public class image extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Bitmap bitmap = DownloadImage("http://www.gophoto.it/view.php?i=http://1.bp.blogspot.com/-2LTvCCufBKc/T3L3KgcTj2I/AAAAAAAABbQ/Ki60e1LU9sE/s1600/Sachin%2BTendulkar.png");
ImageView img = (ImageView) findViewById(R.id.img);
img.setImageBitmap(bitmap);
}
private InputStream OpenHttpConnection(String urlString) throws IOException {
InputStream in = null;
int response = -1;
URL url = new URL(urlString);
URLConnection conn = url.openConnection();
if (!(conn instanceof HttpURLConnection))
throw new IOException("Not an HTTP connection");
try {
HttpURLConnection httpConn = (HttpURLConnection) conn;
httpConn.setAllowUserInteraction(false);
httpConn.setInstanceFollowRedirects(true);
httpConn.setRequestMethod("GET");
httpConn.connect();
response = httpConn.getResponseCode();
if (response == HttpURLConnection.HTTP_OK) {
in = httpConn.getInputStream();
}
} catch (Exception ex) {
throw new IOException("Error connecting");
}
return in;
}
private Bitmap DownloadImage(String URL) {
Bitmap bitmap = null;
InputStream in = null;
try {
in = OpenHttpConnection(URL);
bitmap = BitmapFactory.decodeStream(in);
in.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
return bitmap;
}
}